ISSN:
1432-2072
Keywords:
Conditioned place preference
;
Aversions
;
Naloxone
;
Morphine
;
U50-488
;
β-endorphin
;
Dynorphin
;
Arcuate nucleus
;
Rat
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Abstract The present study examines the influence of destruction of the medio-basal arcuate hypothalamus (MBH), the primary site of synthesis of central pools of β-endorphin (β-EP), upon the aversive properties of naloxone in a conditioned place preference paradigm. Bilateral radiofrequency lesions of the MBH resulted in a pronounced fall in levels of immunoreactive β-EP in the brain. Lesioned rats, in contrast to non-operated animals, showed a clear reduction in the conditioned place aversion produced by naloxone. However, they showed no loss of the conditioned preference produced by the mu-selective opioid receptor agonist, morphine, or the conditioned aversion produced by the kappaselective agonist, U50-488. In contrast to the effect of the lesions, suppression of circulating β-EP by dexamethasone treatment failed to influence conditioning produced by naloxone. Thus, the data indicate that the aversive properties of naloxone are attenuated by disruption of central (but not peripheral) β-EP activity. We suggest that these properties of naloxone reflect an antagonism of β-EP activity in the brain. In addition, the data indicate that differing mechanisms underlie the aversive actions of naloxone as compared to U50-488.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00432214
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