Expression of mRNA coding for the serotonin transporter in aged vs young rat brain: Differential effects of glucocorticoids

Serotonin transporter mRNA expression in midbrain of young and aged rats was measured after long-term infusion of dexamethasone (0.01 and 0.05 mg/kg/day). Aging alone had no effect. Dexamethasone significantly decreased expression in both young and old rats but the effect was greater in the aged group. Adrenocortical dysregulation is common in elderly depression; our results suggest that glucocorticoids interact with aging to exacerbate abnormalities of serotonergic function, contributing to reduced antidepressant effectiveness.