Differential effects of intracerebral microinjection of morphine on approach and escape responses induced by lateral hypothalamic stimulation in the mouse.
BALB/c mice were implanted with a combined guide-cannula and bipolar stimulation electrode. The tip of the guide-cannula was positioned 1.0 mm above the electrode tip which was located in the lateral hypothalamus (LH). Mice were trained in a shuttle-box to initiate and terminate a continuous electrical stimulation of the LH. Following stabilization of the baseline response latencies two experiments were performed. In the first experiment, isotonic NaCl or morphine sulphate (0.5, 1.0 or 2.0 micrograms dissolved in NaCl) were injected into the LH (volume of the injection 0.5 mu 1). The lowest dose (0.5 microgram) of morphine rapidly decreased approach latency for LH stimulation over a period of two hours. The same result was observed with both 1.0 and 2.0 micrograms but with greater magnitude and a longer time course. In some animals, an increase in escape latency appeared but only at the dose of 1.0 microgram. In the second experiment, it was observed that intraperitoneal injection of naloxone (2.0 mg/kg) suppressed the shortening of latency of approach responses induced by the microinjection of 2.0 micrograms of morphine. These results suggest the involvement of opiate mechanisms in the regulation of LH self-stimulation.
Bendani
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T
Laboratoire de Psychophysiologie, UA CNRS 339, Université de Bordeaux I, Talence, France.
Cazala
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P
D000818:Animals; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004924:Escape Reaction / Q000187:drug effects*; D007031:Hypothalamus / Q000187:drug effects* / Q000502:physiology; D007276:Injections, Intraventricular; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009020:Morphine / Q000494:pharmacology*; D012653:Self Stimulation / Q000187:drug effects
D009020:Morphine