Tyrosine hydroxylase and cholecystokinin mRNA levels in the substantia nigra, ventral tegmental area, and locus ceruleus are unaffected by acute and chronic haloperidol administration.

1. The studies described herein were designed to test the hypothesis that a neuroleptic, haloperidol, may alter the level of expression of the tyrosine hydroxylase and cholecystokinin genes in discrete brain regions. 2. In situ hybridization was employed to quantitate changes in concentration of mRNA for tyrosine hydroxylase and cholecystokinin in the ventral tegmental area, substantia nigra, and locus ceruleus after acute or chronic treatment with haloperidol or vehicle. 3. Haloperidol had no effect on the level of tyrosine hydroxylase or cholecystokinin mRNAs, in the ventral tegmentum, substantia nigra, or locus ceruleus, at either 3 or 19 days of drug administration. 4. These data suggest that haloperidol administration does not alter the level of tyrosine hydroxylase or cholecystokinin mRNAs in midbrain dopamine neurons of the rat.