title: Endogenous opioid peptide-mediated neurotransmission in central and pericentral nuclei of the inferior colliculus recruits μ1-opioid receptor to modulate post-ictal antinociception.
abstract: BACKGROUND
  The aim of the present work was to investigate the involvement of the μ1-endogenous opioid peptide receptor-mediated system in post-ictal antinociception.
  
  
  METHODS
  Antinociceptive responses were determined by the tail-flick test after pre-treatment with the selective μ1-opioid receptor antagonist naloxonazine, peripherally or centrally administered at different doses.
  
  
  RESULTS
  Peripheral subchronic (24 h) pre-treatment with naloxonazine antagonised the antinociception elicited by tonic-clonic seizures. Acute (10 min) pre-treatment, however, did not have the same effect. In addition, microinjections of naloxonazine into the central, dorsal cortical and external cortical nuclei of the inferior colliculus antagonised tonic-clonic seizure-induced antinociception. Neither acute (10-min) peripheral pre-treatment with naloxonazine nor subchronic intramesencephalic blockade of μ1-opioid receptors resulted in consistent statistically significant differences in the severity of tonic-clonic seizures shown by Racine's index (1972), although the intracollicular specific antagonism of μ1-opioid receptor decreased the duration of seizures.
  
  
  CONCLUSIONS
  μ1-Opioid receptors and the inferior colliculus have been implicated in several endogenous opioid peptide-mediated responses such as antinociception and convulsion. The present findings suggest the involvement of μ1-opiate receptors of central and pericentral nuclei of the inferior colliculus in the modulation of tonic-clonic seizures and in the organisation of post-ictal antinociception.
authors: Laboratory of Neuroanatomy and Neuropsychobiology, Department of Pharmacology, School of Medicine of Ribeirão Preto of the University of São Paulo (FMRP-USP), Av. dos Bandeirantes, 3900, Ribeirão Preto, SP 14049-900, Brazil.
authors: Tatiana Tocchini
authors: TT
authors: Felippotti
authors: Renato Leonardo
authors: RL
authors: de Freitas
authors: Norberto Cysne
authors: NC
authors: Coimbra
mesh_terms: D000818:Animals; D007245:Inferior Colliculi / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D009270:Naloxone / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D018847:Opioid Peptides / Q000378:metabolism*; D010433:Pentylenetetrazole / Q000008:administration & dosage* / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017450:Receptors, Opioid, mu / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012640:Seizures / Q000139:chemically induced; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology
chemical_list: D018847:Opioid Peptides; C485765:Oprm1 protein, rat; D017450:Receptors, Opioid, mu; D009270:Naloxone; C034643:naloxonazine; D010433:Pentylenetetrazole