Haloperidol treatment differentially regulates [ 3H]DTG and [ 3H](+)-3-PPP labeled σ binding sites

Abstract

The effect of repeated haloperidol administration on σ binding sites in brain membranes was assessed using [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine ((+)-3-PPP) and [ 3H]1,3-di-o-tolylguanidine (DTG). Administration of haloperidol (1 mg/kg, i.p.) to guinea pigs for 14 consecutive days followed by a 4 day drug-free period prior to sacrifice resulted in 75% and 6% decreases in the specific binding of [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [ 3H]1,3-di-o-tolylguanidine, respectively, when measured using a single concentration (2 nM) of radioligand. Scatchard analysis revealed a reduction in both the maximum number of [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding sites and the affinity of these sites for the radioligand; the potency of 1,3-di-o-tolylguanidine to inhibit [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding was also reduced. In parallel studies, the potency of 1,3-di-o-tolylguanidine to inhibit [ 3H]1,3-di-o-tolylguanidine binding was unaffected by haloperidol treatment, but the potency of (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine against [ 3H]1,3-di-o-tolylguanidine was reduced 3-fold. Phenytoin, which increased (10-fold) the potency of dextromethorphan to inhibit [ 3H]1,3-di-o-tolylguanidine binding in control membranes, had no effect in membranes obtained from haloperidol-treated animals. The reduction in [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding was dependent upon the duration of the drug-free period and amounted to 73% and 25% in brain membranes prepared from animals sacrificed 14 days and 28 days, respectively, following cessation of drug treatment. Repeated administration of other antipsychotic and σ agents including DTG, dextromethorphan, spiperone, chlorpromazine and clozapine had no effect on [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine or [ 3H]1,3-di-o-tolylguanidine binding. These findings suggest that repeated haloperidol administration selectively regulates [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine binding in guinea pig brain membranes. However, the observations that repeated drug treatment resulted in (1) reduced affinity of (+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine for [ 3H]1,3-di-o-tolylguanidine binding sites, and (2) a loss of the ability of phenytoin to increase dextromethorphan's potency against [ 3H]1,3-di-o-tolylguanidine, suggest that [ 3H](+)-3-(3-hydroxyphenyl)-N-(1-propyl)piperidine and [ 3H]1,3-di-o-tolylguanidine binding sites are distinct but functionally coupled.