CARDIOVASCULAR REGULATION--SPINAL SYMPATHETIC MECHANISMS

Blood pressure is regulated to a significant degree by the level of
sympathetic nerve activity to the blood vessels. Vasoconstrictor
sympathetic preganglionic neurons (SPNs), the source of this activity
within the spinal cord, are located within a functionally heterogeneous
population of SPNs whose discharge is determined primarily by descending
inputs from a few discrete medullary regions. The long-term goal of the
proposed research is an understanding of the spinal processing of
information in these descending sympathetic pathways to SPNS,
particularly with regard to those inputs to SPNs regulating
vasoconstriction. Complementary electrophysiological, pharmacologic and
electron microscopic studies are planned which examine the functional
and structural relationships between splanchnic SPNs and their inputs
from the rosaw ventral medulla and the caudal mphe nuclei.
Specifically, criteria will be developed to distinguish splanchnic SPNs
in the rat which regulate adrenal medullary secretion, visceral
vasoconstriction, and gastrointestinal motility. Differences in the
responses of these functional classes of SPNs to medullary stimulation
will be examined to test the hypothesis that functional specificity
exists within descending pathways to splanchnic SPNS. Iontophoretic
application of transmitter agonists and antagonists will be used to
determine the role of excitatory amino acid transmission in the
brainstem stimulus-evoked excitations of SPNs and the potential
modulatory functions of medullary catecholaminergic and serotonergic
inputs to SPNS. Electron microscopic studies of the inputs to SPNs will
combine Phaseolus anterograde labeling of the axon terminals of
medullospinal pathways with immunocytochemical detection of transmitter
markers to obtain information on the ultrastructural basis of the
interactions between neurons in the medulla and those in the
intermediolateral nucleus, including SPNs. This integrated approach
will provide new information on the functioning of critical
cardiovascular regulatory pathways to the spinal cord and may suggest
new pharmacologic approaches to controlling arterial pressure.