Post-ictal analgesia: involvement of opioid, serotoninergic and cholinergic mechanisms.
The neural mechanisms involved in post-ictal analgesia remain to be elucidated. Pentylenetetrazol (PTZ) is used experimentally to induce seizure in animal subjects. This non-competitive antagonist blocks GABA-mediated Cl(-) flux. The aim of this work is to study the neurochemical basis of the antinociception induced by convulsions elicited by peripheral administration of PTZ (64 mg/kg). The analgesia was measured by the tail-flick test, in eight rats per group. Convulsions were followed by significant increase in the tail-flick latencies (TFL), at least for 30 min of the post-ictal period. Peripheral 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 and 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-ictal analgesia in a relatively greater period of time. These results indicate that endogenous opioids, serotonin and acetylcholine may be involved in post-ictal analgesia.
Coimbra
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NC
Laboratório de Neuroanatomia e Neuropsicobiologia, Departamento de Farmacologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo (USP), 14049-900, (SP), Ribeirão Preto, Brazil. nccoimbr@fmrp.usp.br
Castro-Souza
C
C
Segato
E N
EN
Nora
J E
JE
Herrero
C F
CF
Tedeschi-Filho
W
W
Garcia-Cairasco
N
N
D000698:Analgesia; D000818:Animals; D001285:Atropine / Q000008:administration & dosage; D003292:Convulsants; D004195:Disease Models, Animal; D007274:Injections, Intraperitoneal; D007650:Ketanserin / Q000008:administration & dosage; D008784:Methysergide / Q000008:administration & dosage; D009043:Motor Activity / Q000187:drug effects; D018727:Muscarinic Antagonists / Q000008:administration & dosage*; D009270:Naloxone / Q000008:administration & dosage; D009292:Narcotic Antagonists / Q000008:administration & dosage*; D010147:Pain Measurement / Q000187:drug effects; D010433:Pentylenetetrazole; D051381:Rats; D017208:Rats, Wistar; D011930:Reaction Time / Q000187:drug effects; D012018:Reflex / Q000187:drug effects; D012640:Seizures / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D012702:Serotonin Antagonists / Q000008:administration & dosage*
D003292:Convulsants; D018727:Muscarinic Antagonists; D009292:Narcotic Antagonists; D012702:Serotonin Antagonists; D009270:Naloxone; D001285:Atropine; D007650:Ketanserin; D010433:Pentylenetetrazole; D008784:Methysergide