Reduced expression of gamma-aminobutyric acid type A/benzodiazepine receptor gamma 2 and alpha 5 subunit mRNAs in brain regions of flurazepam-treated rats.

Previous studies showed that chronic benzodiazepine administration in rats affected the gamma-aminobutyric acid (GABA)A/benzodiazepine receptor. The present experiment investigated the effects of chronic flurazepam treatment on the mRNA levels for alpha 1, alpha 5, gamma 2, and gamma 2L (an alternatively spliced product of the gamma 2 gene) subunits of the GABAA/benzodiazepine receptor in rat cerebral cortex, cerebellum, and hippocampus. Rats were treated with flurazepam for 2 or 4 weeks, and the mRNA levels were measured while rats were still receiving drug or 48 hr after 4-week flurazepam treatment had been stopped. The level of alpha 5 mRNA was also measured in other rats 4 hr after a single injection of flurazepam or diazepam. The levels of mRNAs were analyzed by Northern blotting using digoxigenin-labeled oligonucleotide probes. Compared with the pair-handled controls, the levels of gamma 2 subunit mRNA in cortex and hippocampus were not changed after flurazepam treatment for 2 weeks. However, with rats treated with flurazepam for 4 weeks the levels of gamma 2 subunit mRNA were significantly reduced in cortex (31%) and hippocampus (39%) but not in cerebellum. The values returned to control levels by 48 hr after termination of the treatment. The regional distribution and time course of reduced gamma 2 levels matched the decrease in benzodiazepine binding produced by the same chronic flurazepam treatment. The amounts of alpha 5 mRNA were reduced in cortex (23%) and hippocampus (18%) 4 hr after a single dose of flurazepam but not diazepam. The levels of alpha 5 mRNA remained reduced in cerebral cortex and hippocampus (about 50%) after 2 weeks but returned to control after 4 weeks of chronic treatment with flurazepam. No change in alpha 1 or gamma 2L subunit mRNAs was observed in any of the three brain regions examined after 4 weeks of flurazepam treatment. These results suggest that benzodiazepine receptor down-regulation after chronic benzodiazepine treatment may be related to the reduced expression of gamma 2 subunit mRNA, and they also suggest differential temporal and regional regulation of alpha 5 and gamma 2 subunit mRNAs in rat brain.