M100907 and Clozapine, but not Haloperidol or Raclopride, Prevent Phencyclidine-Induced Blockade of NMDA Responses in Pyramidal Neurons of the Rat Medial Prefrontal Cortical Slice Rex Y. Wang, Ph.D., and Xiaofu Liang, M.D. In the present study, we demonstrate that, in a results suggest that the prototype (clozapine) and a concentration-dependent manner, M100907 (formerly candidate (M100907) atypical APDs might be effective in MDL 100907, a highly selective 5-HT2A receptor antagonist ameliorating schizophrenic symptoms including cognitive and a purported atypical antipsychotic drug [APD]), but and neuropsychological deficits, which are induced in not its much less active stereoisomer M100009, completely humans who abuse PCP. We hypothesize that the ability of prevents or markedly reverses the phencyclidine (PCP)- M100907 and clozapine to prevent or reverse the PCP- induced blockade of N-methyl-D-aspartate (NMDA) induced blockade of the NMDA receptor channel is responses in pyramidal neurons of the medial prefrontal attributed to their 5-HT2A receptors antagonizing property. cortex (mPFC). Furthermore, the atypical APD clozapine, Therefore, with further systematic studies, the ability of but not the typical APD haloperidol or raclopride (a compounds to prevent or reverse PCP’s blockade of NMDA selective dopamine D2,3 receptor antagonist), mimicked the responses may prove to be an effective electrophysiological action of M100907, preventing the PCP-induced effect. model for screening potential atypical APDs and predicting These results suggest that M100907 might be an antidote their therapeutic efficacy in cognitive deficits. for treating the PCP-induced psychotomimetic state that [Neuropsychopharmacology 19:74–85, 1998] closely resembles schizophrenia; they could also account for © 1998 American College of Neuropsychopharmacology. the antipsychotic potential of M100907. Furthermore, our Published by Elsevier Science Inc. KEY WORDS: Antipsychotic drugs; Phencyclidine; 5-HT2A The psychotomimetic state induced by the noncompeti- receptors; NMDA receptors; Pyramidal cells; Medial tive N-methl-D-aspartate (NMDA) receptor channel prefrontal cortex blockers, such as PCP and ketamine, in normal human subjects is thought to be a better model for schizophre- nia than that produced by amphetamine. In humans, not only does PCP cause hallucinations and delusions, From the Department of Psychiatry and Behavioral Science, SUNY at Stony Brook, Stony Brook, New York, USA. but it also causes an associated apathetic state and a Address correspondence to: Dr. R. Y. Wang, Department of Psy- type of formal thought disorder that are more distinc- chiatry and Behavioral Science, SUNY at Stony Brook, Putnam Hall, tive features of schizophrenia (Allen and Young 1978; South Campus, Stony Brook, NY 11794-8790, USA. Received 7 October 1997; revised 9 December 1997; accepted 27 Javitt and Zukin 1991; Kristensen et al. 1992; Krystal et December 1997. al. 1994; Malhotra et al. 1996, 1997a,b; Pearlson 1981). NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 1 © 1998 American College of Neuropsychopharmacology Published by Elsevier Science Inc. 0893-133X/98/$19.00 655 Avenue of the Americas, New York, NY 10010 PII S0893-133X(98)00003-7 NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 1 Antipsychotic Drugs and PCP-Induced Effect 75 Furthermore, in schizophrenics, NMDA receptor antag- nisms by which the aforementioned APDs reverse the onists produce an exacerbation of psychotic symptoms PCP/ketamine-induced effect are not clear. and cognitive impairment (Javitt and Zukin 1991; Lahti We have previously demonstrated that both cloza- et al. 1995; Malhotra et al. 1996, 1997a,b). Cognitive deficits pine and M100907 [R-(1)-a-(2,3-dimethoxyphenil)-1-[4- have also been observed in PCP- or ketamine-treated fluorophenylethyl)]-4-piperidinemethanol (Kehne et al. rats (Alessandri et al. 1989; Danysz et al. 1988; Jentsch et 1996; Sorensen et al. 1993); but not raclopride, markedly al. 1997a; Verma and Moghaddam 1996) and monkeys potentiate NMDA receptor-mediated neurotransmis- (Boyce et al. 1991; Jentsch et al. 1997b). In addition, un- sion in pyramidal cells of the mPFC and this effect is an- like normal subjects, both schizophrenics (Ingvar and tagonized by the selective NMDA receptor antagonist Franzen 1974; Weinberger et al. 1986, 1988; Weinberger D(2)-2-amino-5-phosphonopentanoic acid (d-AP5) (Ar- and Berman 1996) and PCP-abusing humans (Hertz- vanov and Wang 1998; Arvanov et al. 1997). Haloperi- man et al. 1990; Wu et al. 1991) failed to activate frontal dol was less effective than clozapine and M100907 in cortical regions during performance of frontal-depen- potentiating NMDA responses. Furthermore, M100907 dent tasks. These observations form the foundation for and clozapine markedly potentiate; whereas, haloperi- the glutamate hypothesis of schizophrenia in which it is dol depresses, glutamate neurotransmission elicited by postulated that an aberrant glutamatergic neurotrans- electrical stimulation of the forceps minor (white mat- mission, particularly NMDA receptor hypofunction, re- ter) in the mPFC. The latter finding might be related to sults in both the cognitive and the psychiatric manifes- the fact that haloperidol, but not M100907 or clozapine, tation of the disorder (Carlsson and Carlsson 1990; depresses the (6)-a-amino-3-hydroxy-5-methylisoxazole- Deutsch et al. 1989; Kim et al. 1980; Moghaddam 1994; 4-propionic acid (AMPA)-induced response in a con- Olney and Farber 1995; Wachtel and Turski 1990). centration dependent manner (Arvanov and Wang 1998; Although typical APDs, which not only alleviate Arvanov et al. 1997). M100907 enhances the release of schizophrenic symptoms but also cause extrapyramidal excitatory amino acids (EAAs) induced by NMDA or side effects (EPS), are in general not very effective in electrical stimulation of the forceps minor; EAAs, in treating PCP-induced psychoses (Allen and Young turn, activate both NMDA and non-NMDA receptors, 1978; Pearlson 1981), evidence has been accumulating depolarize membrane potential, and remove the Mg21 in animal studies to suggest that some APDs, particu- block of the NMDA receptor–ionophore complex, and larly those atypical ones (which possess antipsychotic thereby dramatically increasing NMDA-induced in- activity but lack EPS), are capable of reversing the PCP- ward current by 350 to 550% in pyramidal cells (Ar- induced effect. For example, the potency of a series of vanov and Wang 1998). neuroleptics in blocking PCP-induced hyperlocomotion Based on our findings, we predict that M100907 is ca- in rodents correlated with their affinity for 5-hydroxy- pable of preventing or reversing PCP-induced blockade tryptamine2A (5-HT2A) receptors (Gleason and Shannon of NMDA receptor–ionophore complex because: (1) the 1997; Maurel-Remy et al. 1995). Moreover, the atypical block of NMDA-induced inward current by ketamine/ APDs clozapine and olanzapine have been shown to re- PCP is highly voltage-dependent; and (2) the onset/off- verse noncompetitive NMDA antagonist-induced social set of ketamine/PCP’s blockade of the NMDA receptor withdrawal in rats (Corbett et al. 1995) and prevent channel is a function of repeated presentations of the MK-801 neurotoxicity (Farber et al. 1996). Clozapine agonist (Honey et al. 1985; MacDonald et al. 1987). also ameliorated a long-lasting cognitive deficit induced Therefore, experiments were designed to examine this by repeated administration of PCP in monkeys (Jentsch possibility. For comparison, the ability of clozapine, ha- et al. 1997b). In addition, clozapine, but not haloperidol, loperidol, raclopride, and M100009 to prevent/reverse has been shown to improve PCP-induced impairment PCP’s effect was also investigated. of performance in a water maze (Okuyama et al. 1997). Similarly, it has been demonstrated that clozapine and seroquel, but not haloperidol or risperidone, antagonize MATERIALS AND METHODS PCP-induced deficits in sensorimotor gating of the star- Preparation of mPFC Slices tle response (Bakshi et al. 1994; Keith et al. 1991; Swerd- low et al. 1996). In contrast, it has been reported that ha- The techniques and procedures for preparation of rat loperidol reduces significantly both MK-801-induced mPFC slices and for standard intracellular recording of popping and hyperactivity in mice (Rosse et al. 1995); presumed pyramidal neurons have been described pre- haloperidol and raclopride, but not SCH 23390, reverse viously (Arvanov and Wang 1998; Arvanov et al. 1997). the disruptive effect of ketamine on spatial delayed al- Briefly, male Sprague–Dawley rats were decapitated ternation performance (Verma and Moghaddam 1996); under halothane anesthesia, and their brains were re- both haloperidol and clozapine reverse PCP-induced moved and cooled in ice-cold artificial cerebrospinal increases in striatal neuron firing in free-moving rats fluid (ACSF). The coronal (transverse) slices of mPFC (White et al. 1995). At present, the underlying mecha- (450-mm thick) were cut in ice-cold ACSF containing (in 76 R.Y. Wang and X. Liang NEUROPSYCHOPHARMACOLOGY 1998–VOL. 19, NO. 1 mM: NaCl 117, KCl 4.7, CaCl2 2.5, MgCl2 1.2, NaHCO3 terval of approximately 15 min produced a consistent 25, NaH2PO4 1.2 and D-glucose 11, aerated with 95% inward current, although the baseline current caused O2/5% CO2 (pH 7.4) and kept submerged at room tem- by NMDA varied from cell to cell (30–200 pA). Typi- perature for at least 1 h to allow for recovery. A single slice cally, two or three stable consecutive control responses