Effects of Swimming Stress on the Development of Pentylene-Tetrazole Kindling in Rat: Role of Glucocorticoid and Opioids

Stress causes glucocorticoids (GCs) and endogenous opioids release. Some steroids have inhibitory effects but others are preconvulsant. Endogenous opioid mechanisms may probably aggrevate stress-induced seizures. Swimming at 20 degree C for 3 min (swim stress, SS) delays the onset of convulsions induced by pentylenetetrazol (PTZ) and aggravats electroshock-induced seizures. In this study we considered effect of repeated swimming stress on repeated injection of PTZ for induction of chemical kindling. 56wistar rats were housed in 7 groups of eight. Animals were kindled by PTZ injections (45mg/kg) given intraperitoneally every 48h. For considering of the effect of GCs and endogenous opioids we administrated metyrapone, an inhibitor of GCs Synthesis and naloxone as an opioid receptor antagonist. Metyrapone and naloxone applied 30 min before each PTZ injection. Process of kindling was aggravated by SS. Mean necessary days for inducing fifth stage of chemical kindling in SS group decreased to 3.3 days after PTZ injection in comparison to PTZ group (4.9 days). Kindling was prevented by treatment of metyrapone prior to each PTZ injection. Mean values of the seizure stages in different days in this group were significantly decreased comparing to PTZ group (except in the second and sixth days). Naloxone pretreatment delayed the process of kindling. In this group mean day inducing kindling increased to the ninth day and 50% of animals became kindled. Application of stress 30 min after naloxone aggravated the process of kindling and in this group all of animals became kindled. The results have been shown that swimming stress probably through releasing GCs and endogenous opioids increases the development of PTZ-induced kindling and mu opioid receptors may have a important role in the expression of opioid effects.