Central nervous system mechanisms underlying the defense and vigilance reactions in rabbits

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Ray Winters, Committee Chair


The behavioral characteristics, cardiovascular responses, and neurophysiological substrates of two types of affective behavior, the defense reaction (DR) and the vigilance reaction (VR), were studied in rabbits. Electrical stimulation of the hypothalamic defense area (HDA), which evokes tachycardia, a pressor response and hyperventilation in anesthetized rabbits, was found to elicit an increase in hindlimb blood flow and a decrease in visceral blood flow, coupled with increases in plasma norepinephrine. The increase in hindlimb blood flow was mediated, in part, by an atropine-sensitive cholinergic muscle vasodilation system. Electrical stimulation of the HDA in conscious rabbits elicited agitated running, suggesting escape behavior. The cardiorespiratory components of the DR could also be elicited by stimulation of the paraventricular nucleus of the hypothalamus. The cardiomotor component of the baroreceptor reflex (BRR) is inhibited during the DR.Electrical stimulation of the hypothalamic vigilance area (HVA), which leads to a pressor response, bradycardia and inspiratory apnea, was found to elicit a decrease in hindlimb and visceral blood flow in anesthetized rabbits and alert immobility in conscious rabbits. The cardiomotor component of the BRR appears to be enhanced during the VR. Although the VR can also be elicited by electrical stimulation of the ventrolateral PAG (vlPAG), transection studies provided evidence that the VR elicited by stimulation of the HVA was not dependent upon the integrity of the vlPAG. Single cell recording studies indicated that the HDA and HVA modulate the neuronal activity of the solitary complex in the medulla.Taken together the results of these experiments are consistent with the view that the defense reaction and vigilance reaction are mediated by separate but coextensive populations of neurons whose parallel pathways from the hypothalamus interact at neurons in the solitary complex in the medulla and perhaps within the hypothalamus. The findings regarding involvement of the PVN in the DR suggest new lines of research in regards to the neural substrates of the DR.


Biology, Anatomy; Biology, Neuroscience; Psychology, Physiological

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