Behavioural tolerance to morphine analgesia is supraspinally mediated: a quantitative analysis of dose-response relationships.
Brain Res
; 491(2): 316-27, 1989 Jul 10.
Article
em En
| MEDLINE
| ID: mdl-2765889
Repeated exposure of a rat to a nociceptive testing environment ('habituation') enhances its sensitivity to noxious thermal stimuli20 and reduces the antinociceptive effect of a subsequent acute dose of morphine ('behavioural tolerance'). The present study quantitatively characterises the effects of habituation upon morphine antinociception using hot-plate (50 and 55 degrees C) and reflex withdrawal tests (dipping the tail and hindpaws into water at 49 degrees C). Dose-response relationships were modeled with the empirical function; E = Eo + (EMAX*DN)/(ED50N + DN) where E is the time-integrated response, EMAX is the response attributable to morphine, Eo is the baseline response, D is the dose and N is a steepness parameter. Habituation reduced EMAX in both hot-plate tests and also reduced Eo on the 50 degrees C hot-plate. In both reflex tests, habituation reduced Eo to that of spinal animals and EMAX to a value intermediate between that of intact and spinal animals. Neither the ED50 nor the value of N was altered by habituation. Acute spinal novice and habituated animals had similar dose-response curves and parameters. Sham spinalisation had no significant effect on any of the parameters. It is concluded that habituation to the nociceptive testing environment substantially reduces the bulbospinal contribution to morphine analgesia but has no effect upon the spinal component.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Dor
/
Comportamento Animal
/
Encéfalo
/
Habituação Psicofisiológica
/
Analgesia
/
Morfina
Limite:
Animals
Idioma:
En
Revista:
Brain Res
Ano de publicação:
1989
Tipo de documento:
Article
País de afiliação:
Nova Zelândia