[Changes in arterial blood pressure and hypothalamic neural activity in response to caloric stimulation in guinea...

We investigated the effects of caloric stimulation on arterial blood pressure (AP) and neural activity in the hypothalamic paraventricular nucleus (PVN) in anesthetized guinea pigs. Hot water stimulation of the labyrinth produced a decrease in AP in 56 of 73 cases tested, and AP decrease followed by increase in 12 cases. In the cases where AP initially decreased and then increased, 92% of PVN neurons responded as excitatory or inhibitory to caloric stimulation. When the AP change was a decrease alone, the responsive rate of the PVN neurons was 63%, and no change in PVN neural activity was seen in the group which showed no AP change after caloric stimulation. The ratio of the PVN neurons showing inhibition in the group that showed AP decrease-increase sequence was significantly higher than that in the group showing AP decrease alone. AP changes following caloric stimulation were greatly reduced after electric destruction of the anterior and middle parts of the hypothalamus. This indicates that the activation of the hypothalamic neurons by the vestibular input is important to produce the vestibulovasomotor response and its pattern. When the same amount of stimulus was applied periodically to the labyrinth, the AP increment component was increased with time. It is suggested that the pattern of AP changes is greatly influenced by level of consciousness. It is suggested that the basal activity level of the autonomic nervous system, and the variety and magnitude of the vestibular stimuli should be synthetically evaluated when the autonomic nerve function test is applied to patients suffering dizziness.