Naloxone improves impairment of spatial performance induced by pentylenetetrazol kindling in rats

The role of endogenous opioid peptides in impairment of spatial performance due to epileptogenesis was examined. Animals were kindled by repeated injections of pentylenetetrazol (PTZ) (40 mg/kg, i.p.) in the presence or absence of the opioid receptor antagonist naloxone. Naloxone in different doses (1, 5 and 10 mg/kg, i.p.) was applied 30 min before each PTZ injection. Behavioral testing was assessed 24 h and 10 days after the last injection in separate groups of animals using Morris water maze. Our results showed that PTZ-induced kindling produced a significant impairment of spatial learning and memory as compared with controls and this effect was not due to the aftereffect of repeated seizures. Naloxone pretreatment in the course of kindling had no effect on seizures development, however it caused an improvement of spatial learning and memory performance in kindled rats. It is likely that the long-lasting changes in neuronal responsiveness associated with kindling led to a defect in the processing of spatial information. These data suggest that endogenous opioid peptides released in the hippocampus during kindling are at least in part responsible for impairment of spatial performance in kindled animals.