application): The long-term goal of the research is to define the physiological significance of the rapid rhythmic components (cardiac-related and 10-Hz) in sympathetic nerve discharge (SND). Work from the principal investigator's (PI's) laboratory indicates that these rhythms arise from different systems of coupled neural oscillators in the brain stem. Each of the oscillators in each system preferentially or selectively controls a different portion of the spinal sympathetic outflow and thus a different cardiovascular target. The central hypothesis is that these rhythms reflect the ability of the brain to coordinate the discharges of sympathetic nerves to different targets. The specific hypotheses to be tested are 1) Highly differentiated patterns of spinal sympathetic outflow and the resulting cardiovascular responses, such as that occurring during the defense reaction, are emergent properties of the systems of coupled brainstem oscillators responsible for the 10-Hz and cardiac-related rhythms in SND. 2) Single brainstem neurons with activity correlated to the 10 Hz and/or cardiac-related rhythms in SND can be distinguished on the basis of the postganglionic nerves that they control. 3) Nonlinear frequency-locking of the generators of the cardiac-related and 10 Hz rhythms is an important mechanism for regulating the balance between those two components of SND and thus the pattern of spinal sympathetic outflow. 4) A newly-discovered 4 Hz noncardiac-related rhythm in SND is generated by forebrain circuits that control cardiovascular function. 5) Functionally distinct subsets of preganglionic neurons are linked by intraspinal connections. This would allow highly differentiated patterns of spinal sympathetic outflow generated in the brainstem to be reinforced or fine-tuned by use of these intraspinal connections. Experiments will be performed in vivo on urethane-anesthetized cats. Extracellular recordings of brainstem unit activity and local field potentials will be made concurrently with recordings of the discharges of postganglionic sympathetic nerves with diverse cardiovascular targets. The above listed hypotheses will be tested by examining the interrelations of these signals using computational methods including spike-triggered averaging, phase plane, ordinary and partial coherence and bicoherence analyses.
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