title: Antinociceptive effects of intracerebroventricular administration of guanine-based purines in mice: evidences for the mechanism of action.
abstract: It is well known that adenine-based purines exert multiple effects on pain transmission. However, less attention has been given to the potential effects of guanine-based purines (GBPs) on pain transmission. The aim of this study was to investigate the effects of intracerebroventricular (i.c.v.) guanosine and GMP on mice pain models. Mice received an i.c.v. injection of vehicle (saline or 10 muM NaOH), guanosine (5 to 400 nmol), or GMP (240 to 960 nmol). Additional groups were also pre-treated with i.c.v. injection of the A(1)/A(2A) antagonist caffeine (15 nmol), the non-selective opioid antagonist naloxone (12.5 nmol), or the 5'-nucleotidase inhibitor AOPCP (1 nmol). Measurements of CSF purine levels and cortical glutamate uptake were performed after treatments. Guanosine and GMP produced dose-dependent antinociceptive effects. Neither caffeine nor naloxone affected guanosine antinociception. Pre-treatment with AOPCP completely prevented GMP antinociception, indicating that conversion of GMP to guanosine is required for its antinociceptive effects. Intracerebroventricular administration of guanosine and GMP induced, respectively, a 180- and 1800-fold increase on CSF guanosine levels. Guanosine was able to prevent the decrease on cortical glutamate uptake induced by intraplantar capsaicin. This study provides new evidence on the mechanism of action of GBPs, with guanosine and GMP presenting antinociceptive effects in mice. This effect seems to be independent of adenosine and opioid receptors; it is, however, at least partially associated with modulation of the glutamatergic system by guanosine.
authors: Department of Biochemistry, ICBS, Federal University of Rio Grande do Sul, Porto Alegre, RS, Brazil. aschmidt@ufrgs.br
authors: André P
authors: AP
authors: Schmidt
authors: Ana Elisa
authors: AE
authors: Böhmer
authors: Renata
authors: R
authors: Leke
authors: Cristhine
authors: C
authors: Schallenberger
authors: Catiele
authors: C
authors: Antunes
authors: Mery Stéfani L
authors: MS
authors: Pereira
authors: Susana T
authors: ST
authors: Wofchuk
authors: Elaine
authors: E
authors: Elisabetsky
authors: Diogo O
authors: DO
authors: Souza
mesh_terms: D000700:Analgesics; D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D002211:Capsaicin; D002851:Chromatography, High Pressure Liquid; D018698:Glutamic Acid / Q000378:metabolism; D006151:Guanosine / Q000008:administration & dosage / Q000134:cerebrospinal fluid / Q000494:pharmacology*; D006157:Guanosine Monophosphate / Q000008:administration & dosage / Q000134:cerebrospinal fluid / Q000494:pharmacology*; D006358:Hot Temperature; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D009043:Motor Activity / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D010147:Pain Measurement / Q000187:drug effects; D004856:Postural Balance / Q000187:drug effects; D011597:Psychomotor Performance / Q000187:drug effects; D011930:Reaction Time / Q000187:drug effects
chemical_list: D000700:Analgesics; D009292:Narcotic Antagonists; D006151:Guanosine; D009270:Naloxone; D018698:Glutamic Acid; D006157:Guanosine Monophosphate; D002211:Capsaicin