Developments in the drug treatment of schizophrenia

Subcortical excitatory amino acid levels after acute and subchronic administration of typical and atypical neuroleptics

The effects of three atypical neuroleptic compounds, clozapine, sulpiride, and (-)-3-(3-hydroxyphenyl)-N-n-propyl-piperidine ((-)-3-PPP) were compared to the effects of haloperidol and saline on excitatory amino acid levels in the rodent nucleus accumbens and corpus striatum after acute (1 day) and subchronic (28 days) treatment. Equivalent doses of each drug were determined by assessing their in vivo displacement of [3H]spiperone binding in the nucleus accumbens and corpus striatum. After acute treatment, all three atypical neuroleptics, but not haloperidol, produced a significant decrease in nucleus accumbens glutamate concentrations. Acute haloperidol treatment significantly elevated glutamate concentrations in the corpus striatum when compared to all three atypical drugs. After subchronic treatment, (-)-3-PPP significantly increased glutamate concentrations in the nucleus accumbens when compared to the effects of haloperidol and clozapine. There were no major between-group differences in glutamate levels after subchronic treatment in the corpus striatum. The effects of acute and subchronic neuroleptic administration on aspartate levels in the nucleus accumbens and corpus striatum were highly variable. These findings indicate that atypical and typical neuroleptics may alter subcortical excitatory amino acid levels in a site-specific manner.

Haloperidol prevents induction of the hsp70 heat shock gene in neurons injured by phencyclidine (PCP), MK801, and ketamine

The non-competitive NMDA receptor antagonists, PCP (phencyclidine), MK801, and ketamine produce psychosis in humans and abnormal vacuoles in posterior cingulate and retrosplenial rat cortical neurons. We show that PCP (> or = 5 mg/kg), MK801 (> or = 0.1 mg/kg), and ketamine (> 20 mg/kg) induce hsp70 mRNA and HSP70 heat shock protein in these vacuolated, injured neurons, and PCP also induces hsp70 in injured neocortical, piriform, and amygdala neurons. The PCP, MK801, and ketamine drug induced injury occurs in 30 day and older rats, but not in 0-20 day old rats, and is prevented by prior administration of the antipsychotic drugs haloperidol and rimcazole. Since haloperidol and rimcazole block dopamine and sigma receptors, and since M1 muscarinic cholinergic receptor antagonists also prevent the injury produced by PCP, MK801, and ketamine, future studies will be needed to determine whether dopamine, sigma, M1, or other receptors mediate the injury.

Clozapine has sub-micromolar affinity for 5-HT1A receptors in human brain tissue

The affinities of a range of antipsychotic drugs at human hippocampal 5-HT1A receptors, defined by specific [3H]8-OH-DPAT binding, were determined. Clozapine demonstrated the highest affinity; all other antipsychotics studied demonstrated pK(i) values below 6.0 5-HT1A receptors are found on cortical glutamatergic neurons, a dysfunction of which may occur in schizophrenia. Binding at this site indicates a possible mechanism contributing to the unique efficacy of clozapine in the treatment of some schizophrenic patients.

Neuropsychiatric disorders: investigation of schizophrenia and substance abuse

Because neuropsychiatric disorders involve functional and neurochemical cerebral abnormalities, positron emission tomography (PET) is ideally suited for their investigation. The use of tracers to measure regional brain glucose metabolism and/or blood flow has allowed the evaluation of brain function in psychiatric patients. The use of radioligands to assess receptor concentration has enabled an evaluation of the extent to which specific neurotransmitter systems are involved in the pathogenesis of mental illness. This article reviews the application of PET technology to the understanding of schizophrenic disorders and substance abuse.