ACTIVATION OF THE ENDOGENOUS OPIOID SYSTEM WITH METRAZOL SUBCONVULSIVANT DOSES

For the present study, the changes induced on opioid peptide system in the rat brain by a subconvulsant amount of metrazol (PTZ) (30 mg/lkg i.p.) were investigated. Using a microdialysis procedure we found a si gnificant opioid peptide release in hippocampus and amygdala, during t he early 60 min, following administration. Thereafter, the values retu rned to basal conditions. By autoradiagraphy experiments, we observed a significant decrease of mu receptor binding in different brain areas . Ligand binding analysis in membranes showed decreased number of rece ptors without changes in their affinity. Randall-Sellito test indicate d increased threshold to nociceptive stimulus, during the early 30 min after PTZ administration. Finally, in situ hibridization procedure re vealed increased levels of proenkephalin expression 24 h following PTZ . Our results suggest that a subconvulsant amount of PTZ is able to ac tivate opioid peptide system. These changes are relevant for the under standing the epileptogenesis process and mechanisms associated.