QUANTITATION OF PREPROENKEPHALIN MESSENGER-RNA LEVELS IN BRAIN-REGIONS FROM MALE FISCHER RATS FOLLOWING CHRONIC COCAINE TREATMENT USING A RECENTLY DEVELOPED SOLUTION HYBRIDIZATION ASSAY

Quantitative solution hybridization assays were used to determine the picogram amounts of preproenkephalin mRNA (PPenk mRNA) and the microgram quantities of total rat RNA in extracts of eight brain regions from rats which had received three daily intraperitoneal injections of cocaine (10 or 30 mg/kg/day) or saline for 14 days. The young adult male Fischer rats were sacrificed 30 min after the final injection. The highest density of PPenk mRNA (pg PPenk mRNA/mu-g total cellular RNA) was found in extracts of striatum (34.08 +/- 1.79 pg/mu-g for 11 saline-treated rats), followed by extracts of nucleus accumbens (10.08 +/- 0.81 pg/mu-g), and extracts of hypothalamus (2.99 +/- 0.31 pg/mu-g). Extracts of frontal cortex (1.78 +/- 0.24 pg/mu-g), pituitary (1.39 +/- 0.08 pg/mu-g), central grey (1.31 +/- 0.16 pg/mu-g), and cerebellum (1.24 +/- 0.09 pg/mu-g) had intermediate values. Extracts of hippocampus (0.53 +/- 0.03 pg/mu-g) had the lowest density. No significant differences were found among the treatment groups in any brain area investigated. Therefore, chronic cocaine treatment as administered in this protocol did not alter expression of the gene encoding proenkephalin.