Diurnal variations in electroconvulsive shock-induced seizures: involvement of endogenous opioids

Electroconvulsive shock (ECS)-induced seizures present a clear cut diurnal rhythmicity when BALB/c mice are subjected to a light-dark (L/D) schedule. On the contrary, in the absence of external synchronizers no evident fluctuations in epileptic behaviour were evident. Naloxone decreased the threshold of ECS-induced convulsions, thus confirming an involvement of opioids in this type of behaviour. These findings indicate that opioids present a diurnal (L/D) but not circadian (L/L) rhythmicity in BALB/c mice.