RESPONSES OF THE DURAL CIRCULATION TO ELECTRICAL-STIMULATION OF TEE TRIGEMINAL GANGLION IN THE CAT

1. In cats anaesthetized with alpha-chloralose, electrical stimulation (ES) of the trigeminal ganglion produced a fall in blood pressure, a predominantly ipsilateral dilatation in the common carotid vascular be d and bilateral dilatation of the middle meningeal vascular bed, Secti on of the trigeminal root abolished these responses, 2, Dilatation in the middle meningeal artery was not affected by section of the cervica l sympathetic trunk nor by the section of the seventh cranial nerve tr unk, The dilator response was abolished by section of the spinal cord at the C3 level and by intravenous administration of bretylium (10 mg/ kg) or phentolamine (5 mg/kg), The response was significantly reduced by the prior administration of papaverine (10 mg/kg), 3, Functional ad renalectomy by means of a snare placed around the nerves and blood ves sels supplying the adrenal glands significantly reduced the response, Electrical stimulation of the trigeminal ganglion was accompanied by a fall in circulating levels of noradrenaline and serotonin, 4, We conc lude that ES of the trigeminal ganglion produces dilatation in the mid dle meningeal artery partly by autoregulation during the trigeminal de pressor response and partly by a reduction in the circulating levels o f noradrenaline. It differs from the dilatation seen in the general ca rotid circulation and the cortical microcirculation, which is mediated by parasympathetic nerves, There is no evidence that antidromic relea se of neuropeptides from sensory nerve endings in the dura plays a par t in the dilatation.