DEXAMETHASONE, BUT NOT STRESS, INDUCE MEASURABLE CHANGES OF MITOCHONDRIAL BENZODIAZEPINE RECEPTOR MESSENGER-RNA LEVELS IN RATS

The expression of the mitochondrial benzodiazepine receptor gene was a ssayed by a semi-quantitative non-radioactive reverse transcriptase po lymerase chain reaction (RT-PCR) assay. The level of amplified mitocho ndrial benzodiazepine receptor mRNA was expressed as a ratio of either glyceraldehyde-3-phosphate dehydrogenase (GAPDH) or beta-actin mRNA c o-amplified in the same RT-PCR assay. The relative amounts of mitochon drial benzodiazepine receptor RNA in several rat tissues were found to be similar to the previously reported relative amount of mitochondria l benzodiazepine receptor binding sites. The level of these binding si tes has also been reported to be altered by stress stimuli, In this st udy we specifically measured the effect of stress on the mRNA levels o f the mitochondrial benzodiazepine receptor as an alternative method t o the binding assay in an attempt to understand the mechanism by which stress alters binding, Sprague-Dawley male rats were either forced to swim for 15 min in 18 degrees C water or restrained in a plastic cyli nder for 45 min either once, or twice daily for 7 days. Neither the sw im stress, nor acute or chronic restraint stress, caused a measurable statistically significant relative change in mitochondrial benzodiazep ine receptor mRNA in the adrenal gland, kidney, testis and olfactory b ulb. However, daily treatment of rats for 7 days with 4 mg/kg of dexam ethasone caused a significant decrease in mitochondrial benzodiazepine receptor gene expression in adrenal glands. This finding and the meas urement of the relative levels of mitochondrial benzodiazepine recepto r mRNA in the various tissues indicate that mitochondrial benzodiazepi ne receptor density is regulated to some extent at the gene expression level. However, the lack of detectable stress-induced changes in mRNA levels for this receptor seem to indicate that either mRNA changes we re below detectable levels or that other mechanisms may be involved in the previously reported stress-induced changes of mitochondrial benzo diazepine receptor density. Because the focus of this work was on the regulation of mitochondrial benzodiazepine receptor gene expression, l igand binding studies to determine changes in receptor densities were not performed. (C) 1997 Elsevier Science B.V.