[The role of midbrain periaqueductal grey in the inhibition of central cardiac ischemia by somatic nerve and its mechanism in rabbits].

UNLABELLED

Experiments were performed on vagotomized male rabbits weighing 1.8-2.2 kg. Urethane and chloralose were administered intravenously, and were paralyzed by flaxedil. After a cannula was inserted into femoral artery to measure blood pressure, the epicardial electrogram (EECG) was recorded. Then we inserted a bipolar electrode into caudal dorsolateral subdivision of periaqueductal grey (CDL), or dorsomedial hypothalamic nucleus (DMH). In some animals, a microinjecting tube was inserted into CDL for microinjection of enkephalin antibodies. In 12 animals, stimulation of CDL could elicit pressor response and elevation of EECG-ST segment. When stimulating deep peroneal nerve, these two responses were inhibited. In 14 animals, with brainstem transected in P5 level, the stimulation of DPN could not inhibit the presser response induced by CDL, but still inhibited the EECG-ST segment changes. After enkephalin antibodies were injected into CDL, DPN could not inhibited EECG-ST changes. In 4 animals, instead of enkephalin antibodies, rabbit serum had no effects. The unit discharges of 96 neurons in CDL were recorded by glass microelectrodes, among them, 15 neurons could be excited by DMH stimulation. We called these neurons the defence reaction related neurons. Stimulation of DPN or median nerve could inhibit the spontaneous discharge and DMH evoked discharge of these defence reaction related neurons.

CONCLUSIONS

1. DPN stimulation can inhibit the pressor response and cardiac ischemia induced by defence reaction centre in CDL of PAG. The inhibitory effect on cardiac ischemia is still eminently remained after the brainstem is cut in P5 level to eliminate the influence of hypothalamic arcuate nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)