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

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Abstract
Proenkephalin mRNA was detected in striatum, hypothalamus, cortex, cerebellum, hippocampus, midbrain, and brain stem of the rat by RNA (Northern) blot analysis using a 918 base-pair DNA hybridization probe complementary to proenkephalin mRNA. The size of the mRNA species in all brain regions is .apprx. 1400 bases, and it was comparable to 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 generally correlates with the content of [Met5]enkephalin-like immunoactivity of these regions. Rats receiving daily injection of haloperidol (1 or 2 mg/kg) show a 4-fold increase of proenkephalin mRNA content in striatum but not other brain regions. In agreement with previous reports, [Met5]enkephalin-like immunoactivity increased 2-fold in striatum.