Differential effects of naloxone on approach and escape responses induced by electrical stimulation of the lateral hypothalamus or the mesencephalic central gray area in mice.
BALB/c mice implanted with a bipolar electrode were trained in a shuttle-box to initiate and to terminate a continuous electrical stimulation applied in the lateral hypothalamus (LH) or in the mesencephalic central gray area (CG). Following stabilization of the baseline response latencies, the subjects were subcutaneously injected with isotonic NaCl or with naloxone HCl (0.5, 2 or 10 mg/kg) 15 min or 45 min before a test session. In LH-stimulated animals no modification of the behavioral responses was observed after injection of 0.5 mg/kg of naloxone. The 2 mg/kg dose increased the value of escape latency (ON time) but had no effect on approach latency (OFF time). The 10 mg/kg dose also increased ON time. At this dose, an increase of OFF time was simultaneously observed but only 15 min after the injection. In CG-stimulated mice an increase of OFF time and a reduction of ON time were recorded 15 min after the injection of 0.5 mg/kg. Only the reduction of ON time was detected for the 45-min delay. The 2 mg and 10 mg/kg doses simultaneously increased OFF time and reduced ON time for the two delays. These results demonstrate 1) that the effects of naloxone on self-stimulation varied as a function of the structure considered 2) that the predominant characteristic of the considered structure (essentially "rewarding" as the LH or "aversive" as the CG) governs the modulations induced by naloxone.
Cazala
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Laboratoire de Psychophysiologie, URA CNRS 339, Université de Bordeaux I, UFR de Biologie, Talence, France.
David
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D000818:Animals; D004558:Electric Stimulation; D004924:Escape Reaction / Q000187:drug effects / Q000502:physiology*; D007026:Hypothalamic Area, Lateral / Q000502:physiology*; D007552:Isotonic Solutions; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009270:Naloxone / Q000494:pharmacology*; D010487:Periaqueductal Gray / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology
D007552:Isotonic Solutions; D009270:Naloxone; D012965:Sodium Chloride