Opioid neurotransmission in the post-ictal analgesia: Involvement of mu(1)-opioid receptor

Pentylenetetrazol (PTZ), a non-competitive antagonist that blocks GABA-medi ated Cl- flux, was used in the present work to induce seizures in animals. The aim of this work is to study the neurochemical basis of the antinocicep tion induced by convulsions elicited by peripheral administration of PTZ (6 4 mg/kg). The analgesia was measured by the tail-flick test, in eight rats per group. Convulsions were followed by significative increase in the tail- flick latencies (TFL), for at least 120 min of the post-ictal period, perip heral administration of naltrexone (5 mg/kg, 10 mg/kg and 20 mg/kg) caused a significant decrease in the TFL in seizing animals, as compared to contro ls. These data were corroborated with peripheral administration of naloxona zine ( 10 mg/kg and 20 mg/kg), a mu (1)-opioid blocker, in the same doses u sed for non-specific antagonist. These results indicate that endogenous opi oids may be involved in the post-ictal analgesia. The involvement of mu (1) -opioid receptor was also considered. (C) 2001 Elsevier Science B.V. All ri ghts reserved.