Effect of co administration of haloperidol and large neutral amino acids (tryptophan and valine) on rats striatal dopamine, serotonin and their metabolism.

Haloperidol is a high potency typical neuroleptic used in the treatment of schizophrenia. Administration of haloperidol produces muscles related side effects commonly known as extrapyramidal effects (EPS). These effects are not produced following the administration of atypical neuroleptics such as clozapine. A severe side effect of clozapine treatment is however, agranulocytosis. Development of antipsychotics with little/no EPS and/or other side effects is one of the exploring fields of drug research. This involves investigation on the mechanism by which a typical neuroleptic acting via serotonergic mechanism tends to produce less or no EPS. The present study is, therefore, designed to determine the effect of serotonin precursor tryptophan and a large neutral amino acid (valine) other than tryptophan on the modulation of neurochemical changes in the striatum. Neurochemical estimation were done by HPLC-EC. Present study showed that administration of tryptophan increased tryptophan, 5HT, 5HIAA and DA concentration in the striatum. DOPAC and HVA were not effected. Administration of valine increased DOPAC concentration in the striatum and did not alter tryptophan, 5HT, 5HIAA, DA and HVA concentration. Administration of the haloperidol increased HVA, 5HT and 5HIAA concentration. No effect was produced on tryptophan, DOPAC and DA levels. Valine administration followed by haloperidol injection did not alter striatal tryptophan, 5HT, DA, DOPAC and HVA concentration but decreased 5HIAA concentration. Administration of tryptophan followed by haloperidol injection increased tryptophan and 5HT concentrations and decreased DA levels. No effect was produced on 5HIAA, DOPAC and HVA concentrations. Administration of TRP increased plasma and brain concentration as well as DA levels in the striatum. Administration of valine did not decrease striatal TRP concentration while Haloperidol increased striatal 5-HT and 5-HIAA concentrations and no change in DA levels after haloperidol administration. whereas prior injection of TRP that increased 5HT concentration did not alter haloperidol-induced DA turnover in the brain.