Post-ictal analgesia: involvement of opioid, serotoninergic and cholinergic mechanisms

The neural mechanisms involved in post-ictal analgesia remain to be elucida ted. Pentylenetetrazol (PTZ) is used experimentally to induce seizure in an imal subjects. This non-competitive antagonist blocks GABA-mediated Cl- flu x. The aim of this work is to study the neurochemical basis of the antinoci ception induced by convulsions elicited by peripheral administration of PTZ (64 mg/kg). The analgesia was measured by the tail-flick test, in eight ra ts per group. Convulsions were followed by significant increase in the tail -flick latencies (TFL), at least for 30 min of the post-ictal period. Perip heral administration of naloxone (5 mg/kg and 10 mg/kg), atropine (1 mg/kg and 5 mg/kg), methysergide (1 mg/kg and 5 mg/kg) and ketanserine(1 mg/kg an d 2 mg/kg) caused a significant decrease in the TFL in seizing animals, as compared to controls. However, while naloxone antagonized analgesia 15 and 25 min post convulsions, the other drugs caused a blockade of the post-icta l analgesia in a relatively greater period of time. These results indicate that endogenous opioids, serotonin and acetylcholine may be involved in pos t-ictal analgesia. (C) 2001 Elsevier Science B.V. All rights reserved.