Corticosterone effects on rat calretinin mRNA in discrete brain nuclei and the testes

Calretinin is an EF-hand calcium binding protein found predominantly in discrete sets of neurons in the central system, and in the sex hormone producing cells of the gonads. Calretinin mRNA levels were measured in discrete brain areas from vehicle and corticosterone treated rats (subcutaneous injections of 0, 0.1, 1, or 10 mg, 7 days) using a micropunch ribonuclease protection assay. Treatment with high dose corticosterone (10 mg) caused a 93% decrease in calretinin mRNA levels in the hypothalamic paraventricular nucleus compared to controls. Two other brain regions, the medial amygdaloid nucleus and the nucleus reuniens, demonstrated an approximately 40% decrease in calretinin mRNA following high dose corticosterone. In separate experiments, adrenalectomy and diurnal corticosterone variations had no effect on calretinin mRNA in the brain areas examined. In the testes, corticosterone treatment decreased calretinin protein in a dose dependent fashion (to 81%, 68%, and 39% of controls at doses of 10, 1, and 0.1 mg/day, respectively). Low dose corticosterone treatments decreased testicular but not neuronal calretinin mRNA, whereas high dose corticosterone reduced calretinin mRNA in testes and several discrete brain areas. This suggests that corticosterone's effects on brain calretinin may be due to its pathological effects, e.g. energy depletion of brain cells or interference with the normal support functions of glia.