5-HT2A and D2 receptor blockade increases cortical DA release via 5-HT1A receptor activation: a possible mechanism of atypical antipsychotic-induced cortical dopamine release

Journal of Neurochemistry, 2001, 76, 1521±1531

5-HT2A and D2 receptor blockade increases cortical DA release via 5-HT1A receptor activation: a possible mechanism of atypical antipsychotic-induced cortical dopamine release Junji Ichikawa, Hideo Ishii, Stefania Bonaccorso, Wiley L. Fowler, Ian A. O'Laughlin and Herbert Y. Meltzer Division of Psychopharmacology, Departments of Psychiatry & Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA

Abstract Atypical antipsychotic drugs (APDs), all of which are relatively more potent as serotonin (5-HT)2A than dopamine D2 antagonists, may improve negative symptoms and cognitive dysfunction in schizophrenia, in part, via increasing cortical dopamine release. 5-HT1A agonism has been also suggested to contribute to the ability to increase cortical dopamine release. The present study tested the hypothesis that clozapine, olanzapine, risperidone, and perhaps other atypical APDs, increase dopamine release in rat medial prefrontal cortex (mPFC) via 5-HT1A receptor activation, as a result of the blockade of 5-HT2A and D2 receptors. M100907 (0.1 mg/ kg), a 5-HT2A antagonist, signi®cantly increased the ability of both S(±)-sulpiride (10 mg/kg), a D2 antagonist devoid of 5-HT1A af®nity, and R(1)-8-OH-DPAT (0.05 mg/kg), a 5-HT1A agonist, to increase mPFC dopamine release. These effects of M100907 were abolished by WAY100635 (0.05 mg/kg), a

5-HT1A antagonist, which by itself has no effect on mPFC dopamine release. WAY100635 (0.2 mg/kg) also reversed the ability of clozapine (20 mg/kg), olanzapine (1 mg/kg), risperidone (1 mg/kg), and the R(1)-8-OH-DPAT (0.2 mg/kg) to increase mPFC dopamine release. Clozapine is a direct acting 5-HT1A partial agonist, whereas olanzapine and risperidone are not. These results suggest that the atypical APDs via 5-HT2A and D2 receptor blockade, regardless of intrinsic 5-HT1A af®nity, may promote the ability of 5-HT1A receptor stimulation to increase mPFC DA release, and provide additional evidence that coadministration of 5-HT2A antagonists and typical APDs, which are D2 antagonists, may facilitate 5-HT1A agonist activity. Keywords: atypical antipsychotic drugs, D2 receptor, dopamine release, 5-HT2A receptor, 5-HT1A receptor, rat medial prefrontal cortex. J. Neurochem. (2001) 76, 1521±1531.

The atypical antipsychotic drugs (APDs) clozapine, and olanzapine at high doses, but not the typical APDs haloperidol or S(±)-sulpiride, produce greater increases in dopamine (DA) release in rat medial prefrontal cortex (mPFC) compared with the nucleus accumbens (NAC) or striatum (STR) (Moghaddam and Bunney 1990; Volonte et al. 1997; Li et al. 1998; Kuroki et al. 1999). However, low dose olanzapine and another atypical APD, risperidone, increase DA release, to a similar extent, in the mPFC and NAC (Kuroki et al. 1999). The increased DA release in the mPFC has been hypothesized to contribute to the ability to improve negative symptoms and some domains of cognition in schizophrenia (Moghaddam and Bunney 1990; Kuroki et al. 1999; Meltzer and McGurk 1999). The ability to increase DA release in the mPFC has been shown to inversely correlate with the ratio of the af®nity of atypical

APDs for serotonin (5-HT)2A and D2 receptors (Kuroki et al. 1999). Atypical APDs have been shown to have higher af®nity for 5-HT2A than D2 receptors in vitro (Meltzer et al. 1989) and in vivo (Stockmeier et al. 1993; Zhang and Bymaster 1999). Therefore, it was of interest to study the mechanism by which 5-HT2A and D2 receptor blockade Received August 23, 2000; accepted November 3, 2000. Address correspondence and reprint requests to J. Ichikawa, 1601 23rd Avenue South, The First Floor Laboratory Rm-1117, The Psychiatric Hospital at Vanderbilt, Nashville, TN 37212, USA. E-mail: [email protected] Abbreviations used: APDs, antipsychotic drugs; AUC, area under the curve; DA, dopamine; 5,7-DHT, 5,7-di-hydroxytryptamine; DRN, dorsal raphe nucleus; 5-HT, serotonin; mPFC, medial prefrontal cortex; NAC, nucleus accumbens; STR, striatum; VTA, ventral tegmental area.

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

1521

1522 J. Ichikawa et al.

facilitate DA release in the mPFC. However, atypical APDs have variable and often potent af®nity for other monoamine receptors (Schotte et al. 1996). Thus, direct and/or indirect effects of these agents on receptors other than 5-HT2A and D2 receptors could modulate DA release in the mPFC. In particular, opposite effects of 5-HT2A and 5-HT1A receptor stimulation are well-known (Millan et al. 1992). Selective 5-HT1A receptor agonists, e.g. R(1)-8-OHDPAT, increase DA release in the mPFC (Tanda et al. 1994; Kuroki et al. 1996; Gobert et al. 1998; Rollema et al. 2000; Sakaue et al. 2000), suggesting this is a potential basis for the action of at least some of the atypical APDs. 5-HT1A receptor activation may be one of the mechanisms which in¯uence clozapine-induced DA release in the mPFC. Clozapine has been reported to be a 5-HT1A receptor partial agonist (Newman-Tancredi et al. 1998) and its ability to increase DA release in the mPFC is inhibited by WAY100635, a 5-HT1A receptor antagonist (Rollema et al. 1997). Ziprasidone and quetiapine are also 5-HT1A receptor partial agonists, while olanzapine, risperidone, sertindole and haloperidol have low af®nity for 5-HT1A receptors (Newman-Tancredi et al. 1998). 5-HT2A receptor antagonists, e.g. M100907, do not increase DA release in the mPFC (Gobert and Millan 1999; Rollema et al. 2000). As examples of 5-HT1A/5±HT2A interactions, ritanserin, a 5-HT2A/2C, or ketanserin, a 5-HT2A receptor antagonist, increases the 5±HT1A behavioral syndrome (Backus et al. 1990), whereas 8-OH-DPAT, a 5-HT1A receptor agonist, attenuated, and WAY100635 potentiated, the head twitch response in rats given DOI, a 5-HT2A/2C receptor agonist, directly into the mPFC (Willins and Meltzer 1997). Electrophysiological studies have demonstrated that both 5-HT1A receptor activation and 5-HT2A receptor blockade produce membrane hyperpolarization in the mPFC that inhibits neuronal activity (Araneda and Andrade 1991). There is also evidence that 8-OH-DPAT, ritanserin, and M100907, a selective 5-HT2A receptor antagonist, potentiate the effect of raclopride, a D2/3 receptor antagonist, to suppress conditioned avoidance response (Wadenberg et al. 1996, 1998), a model for antipsychotic activity. Furthermore, ritanserin potentiated raclopride-induced DA release in the mPFC (Andersson et al. 1995), while R(1)-8-OHDPAT potentiated the ability of S(±)-sulpiride, another D2/3 receptor antagonist, to increase DA release in the mPFC, an effect reversed by WAY100635 (Ichikawa and Meltzer 1999a). These results indicate that either 5-HT1A receptor activation or 5-HT2A receptor blockade can interact with D2 receptor antagonism to increase DA release in the mPFC. However, it should be noted that ritanserin has appreciable af®nity (Ki values, nM) for D2 (36), a1-adrenergic (35), and a2-adrenergic (54) receptors (Leysen et al. 1993), and could potentiate raclopride-induced DA release in the mPFC via a2-adrenoceptor blockade, as has been shown by idazoxan, an a2-adrenoceptor antagonist (Hertel et al.

1999). Thus, selective 5-HT2A receptor antagonists, e.g. M100907, are needed to determine the effect of 5-HT2A and D2 receptor blockade on DA release. The present study was designed to test the hypothesis, by using selective agonists and antagonists, that: (1) 5-HT1A receptor activation, but not 5-HT2A receptor blockade, increases DA release; (2) 5-HT2A receptor blockade and 5-HT1A receptor activation have synergistic effects on DA release; (3) 5-HT1A receptor activation, 5-HT2A receptor blockade, or the combination, potentiate the ability of D2 receptor blockade to increase DA release; and that (4) 5-HT1A receptor blockade attenuates the ability of the atypical APDs clozapine, olanzapine and risperidone, to increase DA release in the mPFC. Materials and methods Animals Male Sprague-Dawley albino rats (Zivic-Miller Laboratories, Porterville, PA, USA) weighing 250±350 g were housed two to three per cage and maintained in a controlled 12 : 12-h light±dark cycle and under constant temperature at 228C, with free access to food and water. Surgery and microdialysis Rats were anesthetized with a combination (i.p.) of xylazine (13 mg/kg, Rompun; Shawnee Mission, KS, USA) and ketamine hydrochloride (87 mg/kg, Ketaset; Fort Dodge Laboratories, Fort Dodge, IA, USA) and mounted in a stereotaxic frame (Stoetling, Wood Dale, IL, USA). Two stainless 21 G guide cannula with a dummy probe were placed and ®xed by cranioplastic cement (Plastic One, Roanoke, VA, USA) onto the cortex dorsal to the mPFC. Stereotaxic coordinate of probe, when implanted, is A 1 3.2, L-0.8, V-5.5 mm, relative to bregma; incision bar level: 2 3.0 mm, according to the atlas of Paxinos and Watson (1986). Concentric-shaped dialysis probes were constructed as follows. A silica-glass capillary tube (150 mm o.d., 75 mm i.d., Polymicro Technologies, Phoenix, AZ, USA) was inserted through the inner bore of a 25 G stainless tube. The stainless tube was inserted into a 28 G Te¯on tubing and then the Te¯on tubing was inserted into the inner bore of a 18 G stainless-tube. The hollow ®ber dialysis membrane (polyacrylonitrile/sodium methalylsulfonate polymer, 310 mm o.d., 220 mm i.d., molecular weight cut-off 40 000, AN69 HF, Hospal) was ®tted over the glass capillary and into the end of the 25 G stainless tube. This junction (0.5 mm) was glued with epoxy (5-Minute Epoxy; Devkon, Danverse, MA, USA) after the length of the hollow dialysis ®ber was cut to 3.0 mm and the tip of the membrane (0.5 mm) plugged with epoxy. Thus, the length of exposed non-glued surface for dialyzing was 2 mm. Three to ®ve days following cannulation, a dialysis probe was implanted into the mPFC under slight anesthesia with methoxy¯urane (Metofane; Pitman-Moore, Mundelein, IL, USA). For systemic administration of drugs or vehicle, a catheter constructed from microbore Tygon tubing (TGY-010, 0.03' o.d., 0.01' i.d.; Small Parts Inc., Miami Lakes, FL, USA) was implanted subcutaneously in the intrascapular space of the rats. Rats were then housed individually overnight in a dialysis cage. After the

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

Atypical antipsychotics and 5-HT1A activation 1523

overnight perfusion (0.4 mL/min) of the probe (approximately 15 h), dialysate samples (12 mL) were collected every 30 min. The perfusion medium was Dulbecco's phosphate-buffered saline solution (Sigma, St Louis, MO, USA) including Ca21 (138 mm NaCl, 8.1 mm Na2HPO4, 2.7 mm KCl, 1.5 mm KH2PO4, 0.5 mm MgCl, 1.2 mm CaCl2, pH ˆ 7.4). After stable baseline values in the dialysates were obtained, each drug or vehicle was administered to the rats. The location of the dialysis probes were veri®ed at the end of each experiment by manual brain dissection and with 100-mm brain slices (OTS-4000; FHC, Bowdoinham, ME, USA). The procedures applied in these experiments were approved by the Institutional Animal Care and Use Committee of Vanderbilt University in Nashville, TN, USA.

USA) were dissolved in deionized water. Clozapine hydrochloride (Sandoz, Basel, Switzerland), risperidone (RBI, Natick, MA, USA), S(±)-sulpiride (RBI, Natick, MA, USA) and M100907 (Marion Merrell Dow, OH, USA) were dissolved in 0.1 m tartaric acid

Biochemical assay Dialysate samples (12 mL/30 min) were directly applied onto a HPLC with electrochemical detection with a 10-mL sample loop and analyzed for DA with a Millennium chromatogram manager (Waters, Milford, MA, USA). DA was separated on a stainless steel, reversed phase column (BDS Hypersil 3 mm C18, 1.0  100 mm; Keystone Scienti®c, Bellefonte, PA, USA) at 358C maintained by column oven (831 Temperature Controller; Gilson, Middleton, WI, USA) or by column heater (LC-22C Temperature Controller; BAS, West Lafayette, PA, USA). The mobile phase consisted of 48 mm anhydrous citric acid and 24 mm sodium acetate trihydrate containing 0.5 mm EDTA-Na2, 10 mm NaCl, 2 mm dodecyl sulfate sodium salt (Acros, Pittsburgh, PA, USA) and 17% (v/v) acetonitrile, adjusted to pH 4.8 with concentrated NaOH, and was pumped at the ¯ow rate of 0.05 mL/min by LC-10AD (Shimadzu, Kyoto, Japan). DA was detected by a 3-mm glassy carbon unijet working electrode (MF-1003, BAS) set at 1 0.58 V (LC-4C, BAS) vs. an Ag/AgCl reference electrode. Reagents used were analytical or HPLC grade. Drugs R(1)-8-OH-DPAT (RBI, Natick, MA, USA), WAY100635 (Sandoz, Basel, Switzerland) and (1/±)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (RBI, Natick, MA,

Fig. 1 The effect of R(1)-8-OH-DPAT, a selective 5-HT1A receptor agonist, and WAY100635, a selective 5-HT1A receptor antagonist, on DA release in the mPFC. (a) R(1)-8-OH-DPAT (II) signi®cantly increased DA release at 0.1 mg/kg (X; F1,9 ˆ 40.38, p , 0.001), 0.2 mg/kg (L F1,9 ˆ 176.70, p , 0.001) and 0.5 mg/kg (P; F1,9 ˆ 39.07, p , 0.001), but not 0.05 mg/kg (W; F1,9 ˆ 3.61, p ˆ 0.09), compared with vehicle controls (A). One-way ANOVA showed that the effect of R(1)-8-OH-DPAT (0.05 mg/kg) on DA release at 30 min following injection, was signi®cantly different from that of vehicle controls at the corresponding time (F1,9 ˆ 24.93, p , 0.001). (b) WAY100635 (I) had no effect on DA release at 0.05 (W), 0.1 (X), 0.2 (L) or 0.5 mg/kg (P), compared with vehicle controls (A). (c) The ability of R(1)-8-OH-DPAT (0.2 mg/kg) (II) to increase DA release was abolished by WAY100635 (0.2 mg/kg) (I), given 30 min prior to R(1)-8-OH-DPAT (X; F1,9 ˆ 43.40, p ˆ 0.001), compared with the effect of R(1)-8 OH-DPAT alone (W). R(1)-8-OH-DPAT-induced DA release abolished by WAY100635 (X; F1,10 ˆ 4.27, p ˆ 0.07) was not signi®cantly different from vehicle controls (A). n ˆ 4±6.

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

1524 J. Ichikawa et al.

Fig. 2 The effect of M100907, a selective 5-HT2A receptor antagonist, on the ability of R(1)-8-OH DPAT, a selective 5-HT1A receptor agonist, to increase DA release in the mPFC. (a) The ability of R(1)-8-OH-DPAT (0.05 mg/kg) (II) to increase DA release was signi®cantly increased by M100907 (I), given 30 min prior to R(1)-8OH-DPAT, at 0.03 mg/kg (X; F1,9 ˆ 23.60, p , 0.001), 0.1 mg/kg (L F1,9 ˆ 13.14, p ˆ 0.006) and 1 mg/kg (P; F1,9 ˆ 21.42, p ˆ 0.001), respectively, compared with the effect of R(1)-8-OHDPAT alone which had no signi®cant effect on DA release (W). (b) M100907 (0.1 mg/kg) (I), given 30 min prior to R(1)-8-OH-DPAT (II), signi®cantly increased the ability of R(1)-8-OH-DPAT at 0.1

(X; F1,9 ˆ 7.77, p ˆ 0.021), but not 0.2 mg/kg (P; F1,9 ˆ 0.02, p ˆ 0.89), to increase DA release, compared with the effect of R(1)-8-OH-DPAT alone at 0.1 (W) or 0.2 mg/kg (L), respectively. (c) WAY100635 (0.05 mg/kg) (WAY), given 5 min prior to M100907 (I), abolished R(1)-8-OH-DPAT (0.05 mg/kg) (II)-induced DA release enhanced by M100907 (0.1 mg/kg) (L F1,10 ˆ 13.42, p ˆ 0.004), compared with the effect of a combination of M100907 and R(1)-8OH-DPAT (X). (d) M100907 alone (I) had no signi®cant effect on DA release at 0.03 (W), 0.1 (X) or 1.0 mg/kg (L), compared with vehicle controls (A).

solution and was adjusted to pH 6±7 with NaOH. Vehicle or drugs were administered through the indwelling subcutaneous catheter.

(StatView 4.5 for the Macintosh). A p , 0.05 was considered signi®cant in this study. All results are given as means ^ SE.

Data analysis Only results derived from healthy rats with correctly positioned dialysis probes were included in the data analysis. Mean predrug baseline levels (time 2 60, time 2 30 and time 0) were designated as 100%. Repeated measure anova followed by Fisher's protected least signi®cant difference posthoc pairwise comparison procedure and one-way anova were used to determine group differences

Results Basal DA levels in the dialysates from the mPFC were 1.91 ^ 0.09 (fmol/10 mL/30 min, not corrected by percentage recovery of a dialysis probe) (n ˆ 104). There were no signi®cant differences in basal extracellular DA levels in the

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

Atypical antipsychotics and 5-HT1A activation 1525

Fig. 3 The effect of R(1)-8-OH-DPAT, a selective 5-HT1A receptor agonist, and M100907, a selective 5 HT2A receptor antagonist, on the ability of S(±)-sulpiride, a selective D2/3 receptor antagonist, to increase DA release in the mPFC. (a) S(±)-sulpiride (10 mg/kg) (II) signi®cantly increased DA release (L F1,10 ˆ 17.21, p ˆ 0.002), compared with vehicle controls (A). R(1)-8-OH-DPAT (0.05 mg/kg) (I),given 30 min prior to S(±)-sulpiride (II), signi®cantly increased the ability of S(±)-sulpiride (10 mg/kg) to increase DA release (W; F1,10 ˆ 8.98, p ˆ 0.013), compared with the effect of S(±)-sulpiride alone. (b) M100907 (0.1 mg/kg) (I), given 30 min prior to S(±)-sulpiride (II), signi®cantly increased the ability of S(±)-sulpiride (10 mg/kg) to increase DA release (W; F1,10 ˆ 18.27, p ˆ 0.0021), compared

with the effect of S(±)-sulpiride alone (L). (c) The combination (I) of M100907 (0.1 mg/kg), given 5 min prior to R(1)-8-OH-DPAT, and R(1)-8-OH-DPAT (0.05 mg/kg), given 30 min prior to S(±)-sulpiride (II), signi®cantly increased the ability of S(±)-sulpiride (10 mg/kg) to increase DA release (X; F1,10 ˆ 8.96, p ˆ 0.0112), compared with the effect of S(±)-sulpiride alone (W), but not signi®cantly different (F1,12 ˆ 0.02, p ˆ 0.89) from the effect of combination alone (L). (d) WAY100635 (WAY, 0.05 mg/kg), a selective 5-HT1A receptor antagonist, given 5 min prior to M100907 (I), abolished S(±)-sulpiride (10 mg/kg) (II)-induced DA release enhanced by M100907 (0.1 mg/kg) (X; F1,10 ˆ 39.95, p , 0.0001), compared with the effect of a combination of M100907 and S(±)-sulpiride (W). n ˆ 6±8.

mPFC between treatment groups. The injection of either 0.1 m tartaric acid neutralized with NaOH or deionized water through an indwelling subcutaneous catheter had no signi®cant effect on extracellular levels of DA in the mPFC. Therefore, the data for the effects of either 0.1 m tartaric acid neutralized with NaOH or deionized water on extracellular DA levels were combined and used as the vehicle controls for statistical analysis and graphical presentation.

R(1)-8-OH-DPAT (0.1, 0.2 and 0.5, but not 0.05, mg/kg) produced an inverted U-shape increase in DA release in the mPFC with the maximum increase at 0.2 mg/kg (Fig. 1a); this increase was completely reversed by WAY100635 (0.2 mg/kg) (Fig. 1c). R(1)-8-OH-DPAT (0.05 mg/kg) produced a signi®cant increase in DA release only at 30 min following injection. WAY100635 (0.05, 0.1, 0.2 or 0.5 mg/kg) by itself had no signi®cant effect on DA release in the mPFC (Fig. 1b).

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

1526 J. Ichikawa et al.

Fig. 4 The effect of WAY100635, a selective 5-HT1A receptor antagonist on the ability of clozapine, risperidone and olanzapine, atypical antipsychotic drugs which are 5 HT2A/D2 antagonist and 5-HT1A receptor partial agonist (clozapine), to increase DA release in the mPFC. WAY100635 (0.2 mg/kg) (I), given 30 min prior to clozapine (20 mg/kg, a), risperidone (1 mg/kg, b) and olanzapine (1 mg/kg, c) (II), signi®cantly attenuated their ability to increase DA release (clozapine: X; F1,10 ˆ 11.58, p ˆ 0.007) (risperidone: X; F1,11 ˆ 11.16, p ˆ 0.007), and (olanzapine: X; F1,10 ˆ 13.92, p ˆ 0.004), respectively, compared with each effect of themselves

(W). The DA release (X) attenuated by WAY100635 (clozapine 20 mg/kg: F1,10 ˆ 13.26, p ˆ 0.005; risperidone 1 mg/kg: F1,10 ˆ 20.11, p ˆ 0.001; olanzapine 1 mg/kg: F1,10 ˆ 83.86, p , 0.001) was signi®cantly different from vehicle controls (A). (d) WAY100635 (0.2 mg/kg) (I), given 30 min prior to high dose olanzapine (10 mg/kg) (II), had no signi®cant effect on the ability to increase DA release (X; F1,10 ˆ 1.80, p ˆ 0.21), compared with olanzapine alone (W). WAY100653 (L; 0.2 mg/kg) alone had no effect on DA release. n ˆ 5±8.

M100907 (0.03, 0.1 and 1 mg/kg) signi®cantly potentiated R(1)-8-OH-DPAT (0.05 and 0.1 mg/kg)-induced DA release in the mPFC (Fig. 2a). M100907 (0.1 mg/kg) also signi®cantly potentiated R(1)-8-OH-DPAT (0.1, but not 0.2, mg/kg)-induced DA release in the mPFC (Fig. 2b). The potentiation by M100907 (0.1 mg/kg) of R(1)-8-OH-DPAT (0.0.5 mg/kg) was completely reversed by WAY100635 (0.05 mg/kg) (Fig. 2c). M100907 (0.03, 0.1 and 1 mg/kg) by itself had no signi®cant effect on DA release in the mPFC.

S(±)-sulpiride (10 mg/kg) alone slightly but signi®cantly increased DA release in the mPFC (Fig. 3a). This effect was further increased by R(1)-8-OH-DPAT (0.05 mg/kg) as well as M100907 (0.1 mg/kg) (Figs 3a and b, respectively). The combination of R(1)-8-OH-DPAT (0.05 mg/kg), M100907 (0.1 mg/kg), and S(±)-sulpiride (10 mg/kg) also signi®cantly increased DA release in the mPFC (Fig. 3c). However, this increase was comparable to that produced by the combination of R(1)-8-OH-DPAT (0.05 mg/kg) and M100907 (0.1 mg/kg) without S(±)-sulpiride (Fig. 3c), and

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

Atypical antipsychotics and 5-HT1A activation 1527

was not signi®cantly different from the increase produced by the combination of R(1)-8 OH-DPAT (0.05 mg/kg) and S(±)-sulpiride (10 mg/kg) (Fig. 3a), or the combination of M100907 (0.1 mg/kg) and S(±)-sulpiride (10 mg/kg) (Fig. 3b), respectively. Most importantly, WAY100635 (0.05 mg/kg) completely abolished the effect of the combination of M100907 (0.1 mg/kg) and S(±)-sulpiride (10 mg/kg) on DA release in the mPFC (Fig. 3d). Clozapine (20 mg/kg), risperidone (1 mg/kg) and olanzapine (1 mg/kg) markedly increased DA release in the mPFC; these increases were signi®cantly attenuated by WAY100635 (0.2 mg/kg) (Figs 4a±c), respectively. Interestingly, however, the ability of high dose olanzapine (10 mg/kg) to increase DA release in the mPFC was not signi®cantly affected by WAY100635 (0.2 mg/kg) (Fig. 4d). Discussion The present results demonstrate that in the mPFC: (1) activation of 5-HT1A receptors by R(1)-8 OH-DPAT increases DA release; (2) 5-HT2A receptor blockade by M100907 potentiates the effect of 5-HT1A receptor activation by R(1)-8-OH-DPAT on DA release; (3) D2 receptor blockade by S(±)-sulpiride potentiates the effect of 5-HT1A receptor activation by R(1)-8-OH-DPAT on DA release; (4) combined blockade of 5-HT2A and D2 receptors by M100907 and S(±)-sulpiride, respectively, produces a greater increase in DA release than that by each alone; (5) 5-HT1A receptor blockade by WAY100635 abolishes the effect of the combination of M100907 and S(±)-sulpiride on DA release; and (6) WAY100635 attenuated the ability of clozapine, risperidone and olanzapine to increase DA release. Role of 5-HT1A receptors Stimulation of 5-HT1A receptors by R(1)-8-OH-DPAT increased DA release in the mPFC, consistent with previous reports (Tanda et al. 1994; Kuroki et al. 1996; Gobert et al. 1998; Rollema et al. 2000). These increases were abolished by WAY100635 (Fig. 1). Sakaue et al. (2000) have recently reported that: (1) local application of 8-OH-DPAT in the perfusion medium signi®cantly increased DA release in the mPFC; (2) systemic administration and local application of MKC-242, a selective 5-HT1A receptor agonist (Matsuda et al. 1995), increased DA release in the mPFC, and that this increase was antagonized by coperfusion of WAY100635; and (3) pretreatment of rats with 5,7-DHT (di-hydroxytryptamine), which has toxic effects on 5-HT neurons and destroys 5-HT neuron terminals, had no signi®cant effect on the ability of MKC-242 to increase DA release in the mPFC. The results of Sakaue et al. (2000) suggest that activation of postsynaptic 5-HT1A receptors in the mPFC may increase DA release in that region. Electrophysiological studies

Table 1 Receptor binding af®nity (Ki, nM) of antipsychotic drugs

Clozapine Risperidone Olanzapine Ziprasidone Haloperidol

5-HT1A

5-HT2A

D2

a1

a2

180 250 2720a 37c 3080

3Š.3 0Š.16 1Š.9 0Š.25c 25

150 3Š.3 17 2Š.8c 1Š.4

7b 2a,b 19b 12c 46b

8b 3b 230b . 1000c 360b

The Ki values in rats are from Schotte et al. (1996). aCloned human receptors; bfrom Bymaster et al. (1996); cfrom Arnt and Skarsfeldt (1998).

demonstrated that systemic administration of R(1)-8-OHDPAT (Arborelius et al. 1993) and 8-OH-DPAT (Prisco et al. 1994) increases the burst ®ring rate of DA neurons in the ventral tegmental area (VTA), possibly via stimulation of 5-HT1A autoreceptors in the dorsal raphe nucleus (DRN). This increase in the ®ring rate could result in an increase in DA release in the mPFC. However, this seems to be unlikely, since R(1)-8-OH-DPAT has been reported to increase the DA neuron ®ring in the VTA, only at a much higher dose range (0.01±0.1 mg/kg, i.v.), compared with the dose (, 0.001 mg/kg, i.v.) which completely shut down the ®ring of 5-HT neurons in the DRN (Lejeune et al. 1997). The results of Lejeune et al. (1997) suggested that reduction of 5-HT activity in the DRN via stimulation of 5-HT1A autoreceptors is not related to increased DA neuron ®ring in the VTA. There is also a dissociation between the VTA DA neuron activity and the release of DA from the VTA DA terminals, since ritanserin, a 5-HT2A/2C receptor antagonist, which increases DA neuron ®ring in the VTA (Ugedo et al. 1989), did not increase DA release in the mPFC (Andersson et al. 1995; Hertel et al. 1996). Therefore, it is more likely that stimulation of 5-HT1A receptors located in the mPFC (Pompeiano et al. 1992; Khawaja et al. 1995) increases DA release in that region. The present ®nding that R(1)-8-OHDPAT produced an inverted U-shape increase in DA release in the mPFC is of interest in this regard. This effect may be due to increased stimulation of postsynaptic 5-HT1A receptors or nonselective effects in the mPFC at higher dose of R(1)-8-OH-DPAT, although the precise mechanism remains unknown. Interaction of 5-HT1A and 5-HT2A receptors WAY100635 completely abolished the effect of M100907 to potentiate R(1)-8-OH-DPAT-induced DA release in the mPFC (Fig. 2). This indicates that 5-HT2A receptor blockade increases the effect of 5-HT1A receptor activation on DA release in the mPFC. This hypothesis is consistent with electrophysiological studies which demonstrated that systemic M100907 potentiates the ability of 8-OH-DPAT to suppress the basal ®ring rate of spontaneously active cells in

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

1528 J. Ichikawa et al.

the mPFC whereas 8-OH-DPAT attenuates the ability of DOI, a 5-HT2A/2C receptor agonist, to potentiate the l-glutamate-induced excitation of quiescent cells in the mPFC (Ashby et al. 1994). 5-HT1A and 5-HT2A receptors in the mPFC (Pazos et al. 1985; Pompeiano et al. 1992) are co-localized on the same cell and may mediate hyperpolarization and depolarization, respectively (Araneda and Andrade 1991). M100907 (0.1 mg/kg) had no effect on the ability of R(1)-8-OH-DPAT (0.2 mg/kg) to produce maximal increase in DA release, possibly because the effect of 5-HT1A receptor stimulation on DA release was already maximal. M100907, 0.03 mg/kg, may also provide maximal blockade of 5-HT2A receptors with regard to potentiating the effect of 5-HT1A receptor activation, because the effects of M100907 (0.03, 0.1 and 1 mg/kg) on R(1)-8-OH-DPAT (0.05 mg/kg)-induced DA release in the mPFC were virtually identical. These results suggest that 5-HT2A receptor blockade does not lead to excessive 5-HT1A receptor activation, which might be expected to diminish the effect of 5-HT1A receptor activation on DA release in the mPFC. M100907 by itself had no signi®cant effect on DA release in the mPFC (Fig. 2d); these results are consistent with the report of Gobert and Millan (1999) and Rollema et al. (2000). 5-HT1A receptor activation by simultaneous blockade of 5-HT2A and D2 receptors S(±)-sulpiride has not been reported to have appreciable af®nity for 5-HT1A, 5-HT2A, a1-adrenergic, and a2adrenergic receptors, and appears to be selective for D2 and D3 receptors. The effect of S(±)-sulpiride on DA release is most likely due to blockade of D2 autoreceptors (Santiago and Westerink 1991a, 1991b). R(1)-8-OH-DPAT and M100907, respectively, potentiated S(±)-sulpiride (10 mg/ kg)-induced DA release in the mPFC (Figs 3a±b), an effect reversed by WAY100635 (Ichikawa and Meltzer 1999a; Fig. 3d, respectively). We have extended these ®ndings to the combination of M100907 and haloperidol, a D2 receptor antagonist, and found that M100907 also potentiates haloperidol-induced DA release in the mPFC (LieÂgeois et al. 2000). R(1)-8-OH-DPAT had no additional effect on the ability of the combination of M100907 and S(±)sulpiride to increase DA release in the mPFC (Fig. 3c), indicating that this combination may not produce excessive 5-HT1A receptor activation with respect to the effect on DA release in the mPFC. Thus, it is hypothesized that simultaneous blockade of 5-HT2A and D2 receptors increases DA release in the mPFC by enhancing the effect of 5-HT1A receptor stimulation by endogenous 5-HT. 5-HT1A receptor activation by atypical APDs We reported that the ability of clozapine, olanzapine, risperidone, amperozide, haloperidol and S(±)-sulpiride to preferentially increase DA release in the mPFC compared with the NAC was inversely correlated with the difference

in af®nity for 5-HT2A and D2 receptors (Kuroki et al. 1999), i.e. potent blockade of 5-HT2A receptors relative to weak D2 receptor blockade (Ichikawa and Meltzer 1999b; Meltzer et al. 1989). Ziprasidone, a 5-HT2A/D2 antagonist and 5-HT1A receptor partial agonist (Seeger et al. 1997), also has greater effects on DA release in the mPFC, compared with the NAC (Ichikawa and Meltzer 1997) or the STR (Rollema et al. 2000). Attenuation by WAY100635 of the ability of clozapine, risperidone and low dose olanzapine (1 mg/kg) to increase DA release in the mPFC (Figs 4a±c) suggests that clozapine, risperidone and low dose olanzapine increase DA release in the mPFC, in part, via 5-HT1A receptor activation. The lack of an effect of WAY100635 on the ability of high dose olanzapine (10 mg/kg) to increase DA release in the mPFC (Fig. 4d) suggests that factors other than 5-HT1A receptor activation may contribute to the DA release induced by 10 mg/kg olanzapine. Similar results have also been reported by Rollema et al. (2000) that WAY100635 (0.1 mg/kg, s.c.) attenuated the ability of clozapine (3.2 mg/ kg, p.o.) and ziprasidone (10 mg/kg, p.o.) to increase DA release in the mPFC, whereas WAY100635 had no signi®cant effect on olanzapine (10 mg/kg, p.o.)-induced DA release in that region. These authors (Rollema et al. 2000) suggested that clozapine and ziprasidone, but not olanzapine (see Table 1), increase DA release in the mPFC via direct activation of 5-HT1A receptors. However, the present data demonstrate that the ability of olanzapine, at a low dose (1 mg/kg), but not at 10 mg/kg, to increase DA release in the mPFC, may result from 5-HT1A receptor activation. The dose-dependent and preferential increase in DA release in the mPFC produced by high dose olanzapine compared with the NAC (Kuroki et al. 1999) may be related to other mechanisms, e.g. noradrenergic system (Hertel et al. 1999). We have recently reported that M100907 potentiated the ability of haloperidol at a low to moderate dose (0.01±0.1 mg/kg), but not higher dose (0.3±1 mg/kg), to increase DA release in the mPFC (LieÂgeois et al. 2000). This potentiation by M100907 was also reversed by WAY100635 (Ichikawa et al. unpublished data). These results suggest that functional 5-HT1A receptor activation, leading to an increase in cortical DA release, may be resulted from an appropriate combination of potent 5-HT2A and relatively weak D2 receptor blockade. The mechanism by which atypical APDs increase DA release in the mPFC may be due to: (1) direct 5-HT1A receptor activation (e.g. clozapine and ziprasidone); (2) 5-HT1A receptor activation secondary to combined blockade of 5-HT2A and D2 receptors (e.g. olanzapine and risperidone); or (3) both of the above (e.g. clozapine and ziprasidone). Risperidone, 1 mg/kg, is unlikely to directly activate 5-HT1A receptors, because of its modest af®nity for 5-HT1A receptors (Ki ˆ 250 nm), relative to that for D2 and 5-HT2A receptors (Ki ˆ 3.3 and 0.16 nm, respectively, Table 1). It may do so indirectly since risperidone

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

Atypical antipsychotics and 5-HT1A activation 1529

(1 mg/kg) increased 5-HT release in the mPFC (Hertel et al. 1996; Ichikawa et al. 1998), and has been reported to inhibit 5-HT neuronal activity in the dorsal raphe nucleus by increased 5-HT release in that region (Hertel et al. 1997). It should be noted that WAY100635 partially attenuated the ability of clozapine, olanzapine and risperidone to increase DA release at a dose which completely abolished the maximum effect of R(1)-8-OH-DPAT on DA release in the mPFC. The partial attenuation indicates that some other mechanisms, e.g. a2-adrenoceptor blockade, may also contribute to the ability of clozapine (Ki ˆ 8 nm; see the Table 1) and risperidone (3 nm) to increase DA release in the mPFC since idazoxan, an a2-adrenoceptor antagonist, potentiated the ability of raclopride, a D2 receptor antagonist, to increase DA release in the mPFC (Hertel et al. 1999). It is also possible that the clozapine-induced increase in extracellular glutamate in the mPFC (Daly and Moghaddam 1993; Cartmell et al. 2000) contributes to the ability of clozapine to increase DA release in the mPFC, since the clozapine-induced DA release was blocked by LY341495, a selective metabolic glutamate mGlu2/3 receptor antagonist (Cartmell et al. 2000). However, it is unlikely that this explains the inhibitory effect of WAY100635 since 5-HT1A receptor blockade by NAN-190 has been reported to increase extracellular glutamate, an effect antagonized by 8-OH-DPAT (Matsuyama et al. 1996). Clinical signi®cance Many, but not all, of the current generation of atypical APDs have been developed on the basis of the model of weak D2 and potent 5-HT2A receptor blockade (Meltzer et al. 1989). It was subsequently noted that some of these APDs were also 5-HT1A receptor partial agonists:, e.g. clozapine, quetiapine and ziprasidone (Seeger et al. 1997; NewmanTancredi et al. 1998). The results reported here suggest that atypical APDs, which are all 5-HT2A/D2 receptor antagonist, have the ability to act via 5-HT1A receptor stimulation, at least with respect to the ability to preferentially increase cortical DA release, regardless of whether they are direct acting 5-HT1A receptor agonists or partial agonists. 5-HT1A receptor activation by atypical APDs may also contribute to their effects as antipsychotics by diminishing APD-induced DA release in the NAC since R(1)-8-OH-DPAT inhibits the ability of clozapine and risperidone to increase DA release in the NAC (Ichikawa and Meltzer 2000). We have also reported that R(1)-8-OH-DPAT potentiated high dose S(±)-sulpiride (25 mg/kg)-induced DA release in the mPFC, but not NAC (Ichikawa and Meltzer 1999a). Based on these consideration, 5-HT1A partial agonists/D2 receptor antagonists, which lack 5-HT2A receptor antagonist ef®cacy, e.g. buspirone (pKi ˆ 7.8 for 5-HT1A and 7.8 for D2 receptors; Glennon et al. 1992), NAN-190 (8.9 and 8.0, respectively; Glennon et al. 1992), and LY165163 (8.7 and 7.0, respectively; Millan et al. 1995) may be of some use as

adjunctive treatments for schizophrenia. However, clinical effects of buspirone in schizophrenia are controversial. A pilot study of buspirone added to typical APDs demonstrated no improvement in positive and negative symptoms in patients with schizophrenia (Brody et al. 1990), whereas an open trial of buspirone added to haloperidol in schizophrenic patients showed signi®cant decrease in positive symptoms with no change in negative symptoms (Goff et al. 1991). Concomitant use of tandospirone, a 5 HT1A receptor agonist and weak D2 receptor antagonist (Shimizu et al. 1988), with haloperidol has been reported to improve some elements of memory functions in schizophrenic patients, and did not reduce psychotic symptoms (Sumiyoshi et al. 2000). Doses and treatment period may be critical factors (e.g. buspirone, 10±60 mg/kg/day for up to 4 weeks; Brody et al. 1990). Additional controlled studies are needed to determine the therapeutic effects of buspirone and tandospirone. In conclusion, the combination of 5-HT2A and D2 receptor blockade increases DA release in the mPFC, via activation of 5-HT1A receptors. Clozapine, olanzapine, and risperidone may increase DA release in the mPFC, in part, via 5-HT1A receptor activation, which is produced by simultaneous blockade of 5-HT2A/D2 receptors and the 5-HT1A receptor agonist property of clozapine itself, but not olanzapine or risperidone. Acknowledgements The present study was supported, in part, by Warren Medical Institute foundation. We are grateful to Ms Anna R. Alboszta for an excellent technical assistance.

References Andersson J. L., Nomikos G. G., Marcus M., Hertel P., Mathe J. M. and Svensson T. H. (1995) Ritanserin potentiates the stimulatory effects of raclopride on neuronal activity and dopamine release selectively in the mesolimbic dopaminergic system. NaunynSchmiedeberg's Arch. Pharmacol. 352, 374±385. Araneda R. and Andrade R. (1991) 5-Hydroxytryptamine2 and 5-hydroxytryptamine1A receptors mediate opposing responses on membrane excitability in rat association cortex. Neuroscience 40, 399±412. Arborelius L., Chergui K., Murase S., Nomikos G. G., Hook B. B., Chouvert G., Hacksell U. and Svensson T. H. (1993) The 5-HT1A receptor selective ligands, R (1)-8-OH-DPAT and (S)-UH 301, differentially affect the activity of midbrain dopamine neurons. Naunyn-Schmiedeberg's Arch. Pharmacol. 347, 353±362. Arnt J. and Skarsfeldt T. (1998) Do novel antipsychotics have similar pharmacological characteristics? A review of the evidence. Neuropsychopharmacology 18, 63±101. Ashby C. R., Edwards E. and Wang R. Y. (1994) Electrophysiological evidence for a functional interaction between 5-HT1a and 5-HT2a receptors in the rat medial prefrontal cortex: an iontophoretic study. Synapse 17, 173±181. Backus L. I., Sharp T. and Grahame-Smith D. G. (1990) Behavioural evidence for a functional interaction between central 5-HT2 and 5-HT1A receptors. Br. J. Pharmacol. 100, 793±799.

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

1530 J. Ichikawa et al.

Brody D., Adler L. A., Kim T., Angrist B. and Rotrosen J. (1990) Effects of buspirone in seven schizophrenic subjects. J. Clin. Psychopharmacol. 10, 68±69. Bymaster F. P., Calligaro D. O., Falcone J. F., Marsh R. D., Moore N. A., Tye N. C., Seeman P. and Wong D. T. (1996) Radioreceptor binding pro®le of the atypical antipsychotic olanzapine. Neuropsychopharmacology 14, 87±96. Cartmell J., Perry K. W., Salhoff C. R., Monn J. A. and Schoepp D. D. (2000) The potent, selective mGlu2/3 receptor agonist LY379268 increases extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, and 5-hydroxyindole-3-acetic acid in the medial prefrontal cortex of the freely moving rat. J. Neurochem. 75, 1147±1154. Daly D. A. and Moghaddam B. (1993) Actions of clozapine and haloperidol on the extracellular levels of excitatory amino acids in the prefrontal cortex and striatum of conscious rats. Neurosci. Lett. 152, 61±64. Glennon R. A., Raghupathi R., Bartyzel P., Teitler M. and Leonhardt S. (1992) Binding of phebylalkylamine derivatives at 5-HT1C and 5-HT2 serotonin receptors: evidence for a lack of selectivity. J. Med. Chem. 35, 734±740. Gobert A. and Millan M. J. (1999) Serotonin (5-HT) 2A receptor activation enhances dialysis levels of dopamine and noradrenaline, but not 5-HT, in the frontal cortex of freely-moving rats. Neuropharmacology 38, 315±317. Gobert A., Rivet J. M., Audinot C., Newman-Tancredi A. N., Cistarelli L. and Millan M. J. (1998) Simultaneous quanti®cation of serotonin, dopamine and noradrenaline levels in single frontal cortex dialysates of freely-moving rats reveals a complex pattern of reciprocal auto- and heteroreceptor-mediated control of release. Neuroscience 84, 413±429. Goff D. C., Midha K. K., Brotman A. W., McCormick S., Waites M. and Amico E. T. (1991) An open trial of buspirone added to neuroleptics in schizophrenic patients. J. Clin. Psychopharmacol. 11, 193±197. Hertel P., Nomikos G. G., Iurlo M. and Svensson T. H. (1996) Risperidone: regional effects in vivo on release and metabolism of dopamine and serotonin in the rat brain. Psychopharmacology 124, 74±86. Hertel P., Nomikos G. G. and Svensson T. H. (1997) risperidone inhibits 5-hydroxytryptaminergic neuronal activity in the dorsal raphe nucleus by local release of 5-hydroxytryptamine. Br. J. Pharmacol. 122, 1639±1646. Hertel P., Fagerquist M. V. and Svensson T. H. (1999) Enhanced cortical dopamine output and antipsychotic-like effects of raclopride by a2 adrenoceptor blockade. Science 286, 105±107. Ichikawa J. and Meltzer H. Y. (1997) Ziprasidone, a new antipsychotic, produces a preferential increase in extracellular dopamine (DA) utilization in the medial prefrontal cortex (mPFC). Soc. Neurosci. Abstract. 23, 161.7. Ichikawa J. and Meltzer H. Y. (1999a) R (1)-8-OH-DPAT, a serotonin1A receptor agonist, potentiated S (-)-sulpiride-induced dopamine release in rat medial prefrontal cortex and nucleus accumbens but not striatum. J. Pharmacol. Exp. Ther. 291, 1227±1232. Ichikawa J. and Meltzer H. Y. (1999b) Relationship between dopaminergic and serotonergic neuronal activity in the frontal cortex and the action of typical and atypical antipsychotic drugs. Eur. Arch. Psychiat. &. Clin. Neurosci. 249, S90±S98. Ichikawa J. and Meltzer H. Y. (2000) The effect of serotonin1A receptors on antipsychotic drug-induced dopamine release in rat striatum and nucleus accumbens. Brain Res. 858, 252±263. Ichikawa J., Kuroki T., Dai J. and Meltzer H. Y. (1998) Effect of antipsychotic drugs on extracellular serotonin levels in rat medial

prefrontal cortex and nucleus accumbens. Eur. J. Pharmacol. 351, 171. Khawaja X., Evans N., Reilly Y., Ennis C. and Minchin M. C. W. (1995) Characterization of the binding of [3H]WAY-100635, a novel 5-hydroxytryptamine1A receptor antagonist, to rat brain. J. Neurochem. 64, 2716±2726. Kuroki T., Ichikawa J., Dai J. and Meltzer H. Y. (1996) R (1)-8-OHDPAT, a 5-HT1A receptor agonist, inhibits amphetamine-induced serotonin and dopamine release in rat medial prefrontal cortex. Brain Res. 743, 357±361. Kuroki T., Meltzer H. Y. and Ichikawa J. (1999) Effect of antipsychotic drugs on extracellular dopamine levels in rat medial prefrontal cortex and nucleus accumbens. J. Pharmacol. Exp. Ther. 288, 774±781. Lejeune F., Newman-Tancredi A., Audinot V. and Millan M. J. (1997) Interactions of (1)- and (-)-8- and 7-hydroxy-2-(di-n-propylamino) tetralin at human (h) D3, hD2 and h serotonin1A receptors and their modulation of the activity of serotonergic and dopaminergic neurons in rats. J. Pharmacol. Exp. Ther. 280, 1241±1249. Li X.-M., Perry K. W., Wong D. T. and Bymaster F. P. (1998) Olanzapine increases in vivo dopamine and norepinephrine release in rat prefrontal cortex, nucleus accumbens and striatum. Psychopharmacology 136, 153±161. LieÂgeois J. F., Ichikawa J., Bonaccorso S. and Meltzer H. Y. (2000) M100907, a 5-HT2A receptor antagonist, potentiates haloperidolinduced dopamine (DA) release in the medial prefrontal cortex (mPFC), but inhibits that in the nucleus accumbens (NAC). Soc. Neurosci. Abst. 26, 143.15. Leysen J. E., Janssen P. M. F., Schotte A., Luyten W. H. M. L. and Megens A. A. H. P. (1993) Interaction of antipsychotic drugs with neurotransmitter receptor sites in vitro and in vivo in relation to pharmacological and clinical effects: role of 5HT2 receptors. Psychopharmacol. 112, S40±S54. Matsuda T., Yoshikawa T., Suzuki M., Asano S., Somboonthum P., Takuma K., Nakano Y., Morita T., Nakasu Y., Kim H. S., Egawa M., Tobe A. and Baba A. (1995) Novel benzodioxan derivative, 5-(3-[(2S)-1,4-benzodioxan-2- ylmethyl) amino]propoxy)-1,3benzodioxole HCl (MKC-242), with a highly potent and selective agonist activity at rat central serotonin1A receptors. Jpn. J. Pharmacol. 69, 357±366. Matsuyama S., Nei K. and Tanaka C. (1996) Regulation of glutamate release via NMDA and 5-HT1A receptors in guinea pig dentate gyrus. Brain Res. 728, 175±180. Meltzer H. Y. and McGurk S. R. (1999) The effects of clozapine, risperidone, and olanzapine on cognitive function in schizophrenia. Schizophr. Bull. 25, 233±255. Meltzer H. Y., Matsubara S. and Lee J.-C. (1989) Classi®cation of typical and atypical antipsychotic drugs on the basis of D-1, D-2, and serotonin2 pKi values. J. Pharmacol. Exp. Ther. 251, 238±246. Millan M. J., Canton H. and Lavielle G. (1992) Targeting multiple serotonin receptors: mixed 5-HT1A agonists/5-HT1C/2 antagonists as therapeutic agents. Drug News Perspective 5, 397±406. Millan M. J., Rivet J.-M., Audinot V., Gobert A., Lejeune F., Brocco M., Newman-Tancredi A., Maurel-Remy S. and Bervoets K. (1995) Antagonist properties of LY 165,163 at pre- and postsynaptic dopamine D2, D3 and D1 receptors: modulation of agonist actions at 5-HT1A receptors in vivo. J. Pharmacol. Exp. Ther. 273, 1418±1427. Moghaddam B. and Bunney B. S. (1990) Acute effects of typical and atypical antipsychotic drugs on the release of dopamine from prefrontal cortex, nucleus accumbens, and striatum of the rat: an in vivo microdialysis study. J. Neurochem. 54, 1755±1760.

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531

Atypical antipsychotics and 5-HT1A activation 1531

Newman-Tancredi A., Gavaudan S., Conte C., Chaput C., Touzard M., Verriele L., Audinot V. and Millan M. J. (1998) Agonist and antagonist actions of antipsychotic agents at 5-HT1A receptors: a [35S]GTPgS binding study. Eur. J. Pharmacol. 355, 245±256. Paxinos G. and Watson C. (1986) The Rat Brain in Stereotaxic Coordinates. Academic Press, New York. Pazos A., Cortes R. and Palacios J. M. (1985) Quantitative autoradiographic mapping of serotonin receptors in the rat brain. II. Serotonin-2 receptors. Brain Res. 346, 231±249. Pompeiano M., Palacios J. M. and Mengod G. (1992) Distribution and cellular localization of mRNA coding for 5-HT1A receptor in the rat brain: correlation with receptor binding. J. Neurosci. 12, 440±453. Prisco S., Pagannone S. and Esposito E. (1994) Classi®cation of typical and atypical antipsychotic drugs on the basis of D-1, D-2, and serotonin2 pKi values. J. Pharmacol. Exp. Ther. 271, 83±90. Rollema H., Lu Y., Schmidt A. W. and Zorn S. H. (1997) Clozapine increases dopamine release in prefrontal cortex by 5-HT1A receptor activation. Eur. J. Pharmacol. 338, R3±R5. Rollema H., Lu Y., Schmidt A. W., Sprouse J. and Zorn S. H. (2000) 5-HT1A receptor activation contributes to ziprasidone-induced dopamine release in rat prefrontal cortex. Biol. Psychiatry 48, 229±237. Sakaue M., Somboonthum P., Nishihara B., Koyama Y., Hashimoto H., Baba A. and Matsuda T. (2000) Postsynaptic 5-hydroxytryptamine1A receptor activation increases in vivo dopamine release in rat prefrontal cortex. Br. J. Pharmacol. 129, 1028±1034. Santiago M. and Westerink B. H. C. (1991a) The regulation of dopamine release from nigrostriatal neurons in conscious rats: The role of somatodendritic autoreceptors. Eur. J. Pharmacol. 204, 79±85. Santiago M. and Westerink B. H. C. (1991b) Characterization and pharmacological responsiveness of dopamine release recorded by microdialysis in the substantia nigra of conscious rats. J. Neurochem. 57, 738±747. Schotte A., Janssen P. F. M., Gommeren W., Luyten W. H. M. L., Van Gompel P., De Lesage A. S., Loore K. and Leysen J. E. (1996) Risperidone compared with new and reference antipsychotic drugs: in vitro and in vivo receptor binding. Psychopharmacology 124, 57±73. Seeger T. F., Seymour P. A., Schmidt A. W., Zorn S. H., Schulz D. W., Lebel L. A., McLean S., Guanowsky V., Howard H. R., Lowe J. A.

and Heym J. (1997) Ziprasidone (CP-88,059): a new antipsychotic with combined dopamine and serotonin receptor antagonist activity. J. Pharmacol. Exp. Ther. 275, 113. Shimizu H., Karai N., Hirose A., Tatsuno T., Tanaka H., Kumasaka Y. and Nakamura M. (1988) Interaction of SM-3997 with serotonin receptors in rat brain. Jpn. J. Pharmacol. 46, 311±314. Stockmeier C. A., DiCarlo J. J., Zhang Y., Thompson P. and Meltzer H. Y. (1993) Characterization of typical and atypical antipsychotic drugs based on in vivo occupancy of serotonin2 and dopamine2 receptors. J. Pharmacol. Exp. Ther. 266, 1374±1384. Sumiyoshi T., Matsui M., Yamashita I., Nohara S., Uehara T., Kurachi M. and Meltzer H. Y. (2000) Effect of adjunctive treatment with serotonin-1A agonist tandospirone on memory functions in schizophrenia. J. Clin. Psychopharmacol. 20, 386±388. Tanda G., Caroni E., Frau R. and Di Chiara G. (1994) Increase of extracellular dopamine in the prefrontal cortex: a trait of drugs with antidepressant potential? Psychopharmacology 115, 288. Ugedo L., Grenhoff J. and Svensson T. H. (1989) Ritanserin, a 5-HT2 receptor antagonist, activates midbrain dopamine neurons by blocking serotonergic inhibition. Psychopharmacology 98, 45±50. Volonte M., Monferini E., Cerutti M., Fodritto F. and Borsini F. (1997) BIMG 80, a novel potential antipsychotic drug: evidence for multireceptor actions and preferential release of dopamine in prefrontal cortex. J. Neurochem. 69, 182±190. Wadenberg M. L., Salmi P., Jimenez P., Svensson T. and Ahlenius S. (1996) Enhancement of antipsychotic-like properties of the dopamine D2 receptor antagonist, raclopride, by the additional treatment with the 5-HT2 receptor blocking agent, ritanserin, in the rat. Eur. J. Neuropsychopharmacol. 6, 305±310. Wadenberg M. L., Hicks P. B., Richter J. T. and Young K. A. (1998) Enhancement of antipsychotic-like properties of raclopride in rats using the selective serotonin2a receptor antagonist MDL 100,907. Biol. Psychiatry 44, 508±515. Willins D. L. and Meltzer H. Y. (1997) Direct injection of 5-HT2A receptor agonists into the medial prefrontal cortex produces a head-twitch response in rats. J. Pharmacol. Exp. Ther. 282, 699±706. Zhang W. and Bymaster F. P. (1999) The in vivo effects of olanzapine and other antipsychotic agents on receptor occupancy and antagonism of dopamine D1, D2, D3, 5HT2A and muscarinic receptors. Psychopharmacol. 141, 267±278.

q 2001 International Society for Neurochemistry, Journal of Neurochemistry, 76, 1521±1531