Increase of proenkephalin mRNA and enkephalin content of rat striatum after daily injection of haloperidol for 2 to 3 weeks.

Proenkephalin mRNA has been detected in striatum, hypothalamus, cortex, cerebellum, hippocampus, midbrain, and brain stem of rat by RNA ("Northern") blot analysis using a 918-base-pair DNA hybridization probe complementary to proenkephalin mRNA [Comb, M., Seeburg, P. H., Adelman, J., Eiden, L. & Herbert, E. (1982) Nature (London) 295, 663-666]. The size of the mRNA species in all brain regions is approximately 1,400 bases, and it was found to be comparable with that of bovine adrenal medulla and human pheochromocytoma. The data were quantified by densitometric scanning of the autoradiograms: the area under the peak is proportional to the amount of standard proenkephalin mRNA from bovine adrenal medulla. The relative content of proenkephalin mRNA in the various brain regions correlates generally with the content of [Met5]enkephalin-like immunoactivity of these regions. Rats receiving daily intraperitoneal injection of haloperidol (1 or 2 mg/kg) show a fourfold increase of proenkephalin mRNA content in striatum but not other brain regions. In agreement with previous reports, [Met5]enkephalin-like immunoactivity increased twofold in striatum.