Acute foot-shock stress decreased seizure susceptibility against pentylenetetrazole-induced seizures in mice: Interaction between endogenous opioids and cannabinoids.

ABSTRACT

BACKGROUND: Stressful conditions affect the brain's neurotransmission and neural pathways that are involved in seizure susceptibility. Stress alters the intensity and/or frequency of seizures. Although evidence indicates that chronic stress exerts proconvulsant effects and acute stress has anticonvulsant properties, the underlying mechanisms which mediate these effects are not well understood. In the present study, we assessed the role of endogenous opioids, endocannabinoids, as well as functional interaction between opioid and cannabinoid systems in the anticonvulsant effects of acute foot-shock stress (FSS) against pentylenetetrazole (PTZ)-induced seizures in mice. METHODS: Prolonged intermittent FSS was chosen as an acute stress model. Seizure threshold was determined after 30 min of stress induction in male Naval Medical Research Institute (NMRI) mice (20-30 g). Opioid and cannabinoid receptor antagonists were administered before animal placement in the FSS apparatus. RESULTS: Acute FSS significantly decreased seizure susceptibility in animals. The administration of the cannabinoid receptor 1 (CB1) antagonist, AM251, completely blocked the anticonvulsant effect of acute FSS at the doses of 1 pg/kg-100 µg/kg but not at 1 fg/kg. Pretreatment with the nonspecific opioid receptor antagonist, naltrexone (NTX), significantly inhibited the anticonvulsant effects of acute FSS at 1 and 2 mg/kg but not at 0.3 mg/kg. However, coadministration of the subeffective doses of AM251 (1 fg/kg) and NTX (0.3 mg/kg) reversed the anticonvulsant effects of acute FSS. CONCLUSIONS: Opioid and cannabinoid systems are involved in the anticonvulsant effects of acute FSS, and these neurotransmission systems interact functionally in response to acute FSS.