Modification of the reflex response to stimulation of carotid sinus baroreceptors during and following stimulation of the hypothalamic defence area in the cat

Abstract

3. During hypothalamic stimulation the reflex fall in blood pressure resulting from a rise in sinus pressure was found to be undiminished whether sinus pressure was raised at the onset or at the 10th sec of hypothalamic stimulation.4. By contrast, in at least half the cats in which a reflex bradyeardia could be evoked from the sinus, this bradycardia was largely if not completely suppressed during hypothalamic stimulation. This suppression of reflex bradycardia occurred when sinus pressure was raised at the onset as well as at the 10th sec of stimulation.5. During the first 5 sec after hypothalamic stimulation the hypotensive response to an increase in carotid sinus pressure was much reduced; on the other hand the reduction in heart rate was exaggerated, sometimes to a very marked degree.6. The results suggest that stimulation of the hypothalamic defence area can modify baroreceptor reflexes and that this modification can include selective alterations in the various components of the reflex response.

Central neural mechanisms of the cerebral ischemic response. Characterization, effect of brainstem and cranial nerve transections, and simulation by electrical stimulation of restricted regions of medulla oblongata in rabbit.

“…This interaction between the primary cardiovascular response to cerebral ischemia and baroreceptor reflexes contrasts with that occurring in another centrally organized cardiovascular response, the defense reaction (Djojosugito et al, 1970;Gebber and Snyder, 1970;Humphreys et al, 1971) in which the cardiac component of the baroreceptor reflex is suppressed. These observations reinforce the view that the cardiac and vasomotor components of the baroreceptor reflex can be dissociated, and each separately controlled by other regions of the brain (Djojosugito et aL, 1970;Gebber and Synder, 1970;Humphreys et aL, 1971).…”

Mechanism of Hypothalamic Control of Cardiac Component of Sinus Nerve Reflex

“…Electrical stimulation of the carotid sinus nerve, which activates both receptor pathways, produces the same result. Stimulation of a particular area in the hypothalamus, usually called the defence area, has been repeatedly shown to inhibit the bradycardia produced by baroreceptor stimulation [Hilton, 1963;Humphreys, Joels and McAllen, 1971], by chemoreceptor stimulation [Thomas and Calaresu, 1973] or by sinus nerve stimulation [Hilton, 1963;Gebber and Snyder, 1970].…”

The vasomotor component of the carotid sinus baroreceptor reflex in the cat during stimulation of the hypothalamic defence area

“…59 P. W. HUMPHREYS AND N. JOELS Stimulion of the hypothclamus. Identification and stimulation of the defence area was carried out as described by Humphreys et al (1971). The stimulating electrode was a ground and electrolytically thinned stainless-steel needle insulated with Araldite 985E (C.I.B.A.)…”

“…During such stimulation the bradycardia normally induced by a rise in carotid sinus pressure is suppressed (Hilton, 1963(Hilton, , 1965Djojosugito, Folkow, Kylstra, Lisander & Tuttle, 1970;Gebber & Snyder, 1970;Humphreys, Joels & McAllen, 1971), but there is less unanimity about the response of the blood pressure. Hilton (1963Hilton ( , 1965 claimed that the reflex fall in pressure also was suppressed, Djojosugito et al (1970) observed suppression only at high intensities of hypothalamic stimulation, while Gebber & Snyder (1970) and Humphreys et al (1971) found that the fall in pressure was unaltered.…”

“…During such stimulation the bradycardia normally induced by a rise in carotid sinus pressure is suppressed (Hilton, 1963(Hilton, , 1965Djojosugito, Folkow, Kylstra, Lisander & Tuttle, 1970;Gebber & Snyder, 1970;Humphreys, Joels & McAllen, 1971), but there is less unanimity about the response of the blood pressure. Hilton (1963Hilton ( , 1965 claimed that the reflex fall in pressure also was suppressed, Djojosugito et al (1970) observed suppression only at high intensities of hypothalamic stimulation, while Gebber & Snyder (1970) and Humphreys et al (1971) found that the fall in pressure was unaltered. However, as Humphreys et al (1971) point out, 'the observation that a given increase in carotid sinus pressure evoked a similar fall in blood pressure whether or not the hypothalamic defence area was being stimulated simultaneously, does not necessarily imply that the hypothalamus was without effect on this component of the reflex response to baroreceptor stimulation'.…”