The lateral reticular formation of the medulla (LRF) is a region of the brainstem that is known to have a role in controlling sympathetic outflow to the spinal cord, as well as participating in central pathways of the baroreflex arc. However, other inputs to the LRF have only begun to be examined, and the interaction of these inputs with each other has yet to be studied. The overall hypothesis of this proposal is that in the neurons in the LRF receive, and integrate, sympathetic and vagal afferent information. In addition, some of these neurons will receive somatosensory input and auditory or visual input, and will integrate this information with baroreceptor input. Finally, different nuclear groups in the midline raphe nuclei will have functional connections with LRF neurons. Electrophysiological techniques will be used, to determine response characteristics of individual LRF neurons to stimulation of cardiopulmonary response sympathetic characteristics well as vagal afferents. Different frequencies and intensities sites of stimulation will be used, and the conditioning-test technique will be used to examine interactions between these inputs. In addition, responses of neurons to natural as well as electrical stimulation of somatic afferents from the hindlimb will be determined, and the interaction of this input with sympathetic and vagal afferent input studied. All neurons will be tested for auditory and visual input, as well as baroreceptor input. For neurons with the latter input, blood pressure will be altered to change the amount of baroreceptor information reaching the neurons, and neuronal responses to sympathetic and vagal afferent re-tested under these different conditions. Finally, LRF neurons will be tested for input from midline raphe nuclei using electrical stimulation as well as glutamate injections to determine how this information alters neuronal responses to sympathetic, vagal, or somatosensory input. Thus, these experiments will examine how a variety of cardiovascular and somatosensory inputs to the brainstem are integrated at the level of individual neurons in LRF. The data will provide new information about central sympathetic vagal interactions, and may have implications regarding autonomic imbalances that could result in cardiac arrhythmias.
