Metyrapone and fluoxetine suppress behavioural but not cardiac effects of sub‐chronic stress in rats

Abstract

To determine whether repetitive aversive episodes have enduring effects on cardiac autonomic control, male Sprague-Dawley rats (n=35) instrumented for telemetric recording of heart rate (HR) and locomotor activity (LOC) were subjected to footshock sessions on five consecutive days. During post-stress week, HR was reduced in the active (ΔHR=-23±3 bpm) and the inactive (ΔHR=−20±3 bpm) phases of the light/dark cycle, and LOC was reduced in the active phase (Δ= −0.9±0.1 cpm). Bradycardic effect was not related to reduced LOC, and persisted after sympathetic blockade with atenolol. Vagal blockade (scopomamine) was performed before and after the stress period; in both instances HR increased to the same level suggesting that stress-induced bradycardia was vagally-mediated. In different groups (n=7 each), SSRI Fluoxetine and inhibitor of corticosterone synthesis Metyrapone did not affect stress-induced cardiac changes but prevented reduction in LOC. We conclude that: i) behavioural effects (LOC) of chronic stress are mediated by stress-induced rises of corticosterone whereas cardiac effects are not; and ii) these locomotor could be prevented by SSRI treatment. Supported by NHMRC.