Effect of Parachlorophenylalanine, an Inhibitor of the Serotonin Synthesis Enzyme, on the Brain Dopamine System of Cataleptic Mice

This study examined the effects of administration of parachlorophenylalanine (PCPA), an inhibitor of the key serotonin synthesis enzyme, on the freezing reaction and dopamine brain system in CBA/Lac mice with a hereditary predisposition to catalepsy. Administration of PCPA (300 mg/kg/day, 3 days) did not affect the duration of cataleptic freezing. At the same time, dopamine content decreased in the hypothalamus and midbrain and increased in the striatum and nucleus accumbens of mice after PCPA treatment. The administration of the drug did not affect the levels of DOPAC and HVA (dopamine metabolites) in all studied brain structures. In addition, a PCPA-induced increase in the mRNA level of DRD2 receptor gene in the midbrain and Comt (catechol-O-methyltransferase) gene in the hypothalamus and midbrain were found. However, no effect of PCPA on the expression of DRD1 receptor gene and Th (tyrosine hydroxylase, key dopamine synthesis enzyme) gene in the brain was found. Thus, inhibition of the key enzyme of 5-HT synthesis had a significant effect on the brain DA system of CBA/Lac mice, with the greatest changes found in the midbrain and hypothalamus.