Three major areas of investigation are proposed. The first area is concerned with the intrinsic organization of brain stem networks involved in generating the basal discharges in sympathetic nerves (and, thus, the neurogenic component for the support of blood pressure). This research is predicated on previous work from our laboratory which indicates that the cardiac-related 2-6 c/s rhythm is sympathetic nerve dischage (SND) is representative of the fundamental organization of the brain stem sympathetic generator.
Our specific aims i n this area are to: 1) identify those brain stem regions which contain neurons with naturally occurring discharges locked to the 2-6 c/s rhythm in SND, 2) categorize the types (excitatory, inhibitory, phase switching) of brain stem neurons with sympathetic nerve-related activity in each region, and 3) define the synaptic connections between the various types of brain stem sympathetic neurons. In addition, we will test the hypothesis that networks of hypothalamic and spinal sympathetic neurons can act as subsidiary generators of 2-6 c/s activity in SND. These experiments will rely heavily on the techniques of post-event interval analysis and crosscorrelation (unit greater than sympathetic nerve and unit greater than unit). The experimental animal is the cat. The second area of investigation is concerned with information processing in the afferent limb of the baroreceptor reflex arc. Rather than exhibiting the unimodal pulse synchronous discharge pattern characteristic of baroreceptor afferents, a significant proportion of the interneurons in the medullary nucleus of baroreceptor fiber termination (i.e., nucleus of tractus solitarius; NTS) exhibit a polymodal distribution of firing occurrences in relation to the cardiac cycle. The purpose of our research in this area is to define the factors involved in creating the complex firing patterns of baroreceptor interneurons in NTS. The third area of investigation concerns the circuitry which links baroreceptor afferents to cardiac vagal preganglionic neurons. It appears from recent work that baroreceptor-induced activation of cardiac vagal preganaglionic neurons in the region of Nucleus Ambiguus is not mediated over a simple disynaptic pathway as once was presumed. We will test the hypothesis that a major route involves the brain stem sympathetic network. Specifically, we are interested in determining whether the cardiac-related rhythm in the discharges of brain stem sympathetic neurons is imposed (180 degrees out of phase) onto cardiac vagal neurons via direct coupling of the two systems.
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