Endogenous opioid peptide-mediated neurotransmission in central and pericentral nuclei of the inferior colliculus recruits mu(1)-opioid receptor to modulate post-ictal antinociception

Background: The aim of the present work was to investigate the involvement of the mu(1)-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 mu(1)-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 mu(1)-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 mu(1)-opioid receptor decreased the duration of seizures. Conclusion: mu(1)-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 mu(1)-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. (C) 2011 Elsevier Ltd. All rights reserved.

FAPESP [proc. 1996/8574-9, 2009/00668-6, proc. 03/09129-4, proc. 01/03752-6, proc. 03/05256-1, proc. 2009/17258-5, TT-2, proc. 02/01497-1]

CNPq [474425/2008-8, proc. 301905/2010-0, proc. 501858/2005-9, proc. 372654/2006-1, proc. 372810/2008-0, proc. 372877/2010-9]

CAPES [AUX-PE-PNPD 2400/2009, proc. 23038.027801/2009-37]

FAEPA [proc. 537/1995, 70/2002]

CNPq in the Department of Physiology, Anatomy and Genetics [200629/2005-0]

FMRIB Centre of the Clinical Neurology Department of the University of Oxford, Oxford, England, UK