Clozapine and cocaine effects on dopamine and serotonin release in nucleus accumbens during psychostimulant behavior and withdrawal

Abstract

There is an increasing awareness that a psychosis, similar to that of schizophrenic psychosis, can be derived from cocaine addiction. Thus, the prototypical atypical antipsychotic medication, clozapine, a 5-HT 2/DA 2 antagonist, was studied for its effects on cocaine-induced dopamine (DA) and serotonin (5-HT) release in nucleus accumbens (NAcc) of behaving male Sprague–Dawley laboratory rats with In Vivo Microvoltammetry, while animals' locomotor (forward ambulations), an A 10 behavior, was monitored at the same time with infrared photobeams. Release mechanisms for monoamines were determined by using a depolarization blocker, gamma-butyrolactone (γBL). BRODERICK PROBE® microelectrodes selectively detected release of DA and 5-HT within seconds and sequentially in A 10 nerve terminals, NAcc. Acute and subacute studies were performed for each treatment group. Acute studies are defined as single injection of drug(s) after a stable baseline of each monoamine and locomotor behavior has been achieved. Subacute studies are defined as 24-h follow-up studies on each monoamine and locomotor behavior, in the same animal at which time, no further drug was administered. Results showed that (1) acute administration of cocaine (10 mg/kg ip) ( n=5) significantly increased both DA and 5-HT release above baseline ( P<.001) while locomotion was also significantly increased above baseline ( P<.001). In subacute studies, DA release decreased significantly below baseline ( P<.001) and significant decreases in 5-HT release occurred at the 15-min mark and at each time point during the second part of the hour ( P<.05); the maximum decrease in 5-HT was 40% below baseline. Locomotor behavior, on the other hand, increased significantly above baseline ( P<.05). (2) Acute administration of clozapine/cocaine (20 and 10 mg/kg ip, respectively; n=6) produced a significant block of the cocaine-induced increase in DA ( P<.001) and 5-HT release ( P<.001). Cocaine-induced locomotion was blocked simultaneously with each monoamine by clozapine as well ( P<.001). In subacute studies, DA release continued to be blocked presumably via clozapine by exhibiting a statistically significant decrease ( P<.001), but 5-HT release increased significantly ( P<.001), while cocaine-induced locomotor activity also continued to be antagonized by clozapine, i.e., locomotor activity exhibited no difference from baseline ( P>.05). In summary, acute studies (a) support previous data from this laboratory and others that cocaine acts as a stimulant on the monoamines, DA and 5-HT and on locomotor behavior as well and (b) show that clozapine, 5-HT 2/DA 2 antagonist, blocked enhanced DA, 5-HT and psychomotor stimulant behavior induced by cocaine. Subacute studies (a) suggest that withdrawal responses occurred in the cocaine group, based on recorded deficiencies in monoamine neurotransmitters (b) show that withdrawal effects in the cocaine group likely presynaptic, were distinguished from locomotor behavior, classically known to be mediated postsynaptically, and finally, (c) suggest that clozapine, with longer lived pharmacokinetic properties, reversed 5-HT cocaine-related withdrawal effects, but was unable to reverse DA cocaine-related withdrawal responses. Taken together with data from this laboratory, in which the 5-HT 2A/2C antagonist, ketanserin, affected cocaine neurochemistry in much the same way as did clozapine, a mediation by either separate or combined 5-HT 2A/2C receptors for these clozapine/cocaine interactions, is suggested. Further studies, designed to tease out the responses of selective 5-HT 2A and 5-HT 2C receptor compounds to cocaine and clozapine/cocaine, are underway.