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Inhibitory effect of microinjection of morphine into the ventral medulla on ventricular extrasystoles induced by hypothalamic stimulation in the rabbit

Guo Xueqin, Liu Ningai, Li Peng

Department of Physiology, Shanghai Medical University. Shanghai, China

Abstract

Experiments were carried out on 63 rabbits anesthetized with chloralosc and
urethane. The animals were immobilized with gallamine triethiodide and maintained by artifical ventilation. Bilateral microinjection of morphine (5 fig in 0.5-1#mu#l)into the ventral medulla decreased the number of hypothalamic stimulationinduced ventricular extrasystoles (HVE).Electrical stimulation of the caudal raphe nuclei or microinjection of L-sodium glutamate (50m mol/L,0.5-1#mu#l) into the same area caused a decrease in the number of HVE. However, these effects were diminished following bilateral microinjection of naloxone into the ventral medulla. Inhibition of HVE by electrical stimulation of the deep peroneal nerve (DPN) was less obvious or even abolished by bilateral microinjection of naloxone (2#mu#g in 0.5-1#mu#l) into the ventral medulla. These results suggest that activation of the opiate receptors in the ventral medulla may inhibit HVE, and that the inhibitory effect of DPN stimulation on HVE may be mediated by activation of the opiate receptors in the ventral medulla via activation of the caudal raphe nuclei.

Key words: Ventral medulla;Morphine;Naloxone;Ventricular extrasystoles;Caudal raphenuclei

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Citing This Article：

Guo Xueqin, Liu Ningai, Li Peng. Inhibitory effect of microinjection of morphine into the ventral medulla on ventricular extrasystoles induced by hypothalamic stimulation in the rabbit. Acta Physiol Sin 1987; 39 (2): (in Chinese with English abstract).