The Influence of the Fear Induced Procedure on the Concentration of Brain Catecholamines.

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Effects of stimulation of the hypothalamus that is thought to control emotional and behavioral patterns, eg fear, on the trigemino-autonomic reflex were studied in chloralose-anesthetized cats. The exact place of stimulation was the hypothalamic defense area, stimulation of which induced aggressive responses called defense reaction, such as mydriasis, increased blood pressure and tachycardia. The reflex discharges were recorded from the cervical vagel nerve, and the cardiac branch of the vagal nerve in response to electrical stimulation of the inferior alveolar nerve. The discharge in the cardiac branch of the vagal nerve evoked by the inferior alveolar nerve stimulation was completely abolished by transection of the cervical spinal cord, while it was not affected by section of the cervical vagal nerve. Thus the trigemino-autonomic reflex in the cardiac branch of the vagal nerve wholly consisted of the sympathetic nerve discharge (trigemino-sympathetic reflex), in contrast to that recorded form the cervical vagal nerve(trigemino-vagal reflex). The following results were obtained.1) The trigemino-vagal reflex was depressed by repetitive stimulation of the hypothalamic defense area. The threshold was below that for inducing cardiovascular changes. Short train pulse applied to the hypothalamic defense area suppressed the trigemino-vagal reflex for about 200ms with a peak at about 40ms. It is suggested that the hypothalamic effect on the trigemino-vagal reflex was centrally induced and not the secondary effect of cardiovascular changes.2) The trigemino-sympathetic reflex showed no definite changes in response to repetitive stimulation of the hypethalamic defense area.These results support the notion that the trigemino-autonomic reflex is centrally intergraded to suit the cardiovascular system to the needs of the organism in defense reaction.