© 2017, Springer-Verlag GmbH Germany. Rationale: We recently reported that simultaneous exposure to amphetamine and various stressors resulted in reduced hypothalamic-pituitary-adrenal (HPA) and glycemic responses to the stressors. Since this is a new and relevant phenomenon, we wanted to further explore this interaction. Objectives: This study aims (i) to characterize the effect of various doses of amphetamine on the physiological response to a predominantly emotional stressor (forced swim) when the drug was given immediately before stress; (ii) to study if an interaction appears when the drug was given 30 min or 7 days before swim; and (iii) to know whether cocaine causes similar effects when given just before stress. Adult male rats were used and plasma levels of ACTH, corticosterone, and glucose were the outcomes. Results: Amphetamine caused a dose-dependent activation of the HPA axis, but all doses reduced HPA and glycemic responses to swim when given just before the stressor. Importantly, during the post-swim period, the stressor potently inhibited the ACTH response to amphetamine, demonstrating mutual inhibition between the two stimuli. The highest dose of amphetamine also reduced the response to swim when given 30 min before stress, whereas it caused HPA sensitization when given 7 days before. Cocaine also reduced stress-induced HPA activation when given just before swim. Conclusions: The present results demonstrate a negative synergy between psychostimulants (amphetamine and cocaine) and stress regarding HPA and glucose responses when rats were exposed simultaneously to both stimuli. The inhibitory effect of amphetamine is also observed when given shortly before stress, but not some days before.
- Negative synergy