Journal of Neuroscience, Vol 8, 1684-1693, Copyright © 1988 by Society for Neuroscience
Cardiovascular function is altered by picomole injections of glutamate into rat medulla
DO Nelson, HL Cohen, JL Feldman and DR McCrimmon
Department of Physiology, Northwestern University Medical School, Chicago, Illinois 60611.
Local neural circuitry in the nucleus tractus solitarius (NTS) involved in
cardiovascular control was studied by injecting nanoliter volumes of
excitatory amino acids into the structure. Experiments were performed on
urethane-anesthetized, artificially ventilated rats. Multibarrel
micropipettes were used for pressure ejection of drugs or a dye for marking
ejection sites. Ejected volumes, ranging from 200 pl to 25 nl, were
directly monitored for every injection. Injections of as little as 200 fmol
of L-glutamate in 200 pl into the medial and lateral NTS region rostral to
the obex elicited marked, site-specific decreases in arterial pressure and
heart rate. The majority of these responses were eliminated by blockade of
parasympathetic and sympathetic neural outflow. At sites caudal to obex, in
the commissural region of the NTS, L-glutamate injections produced marked
elevations in heart rate and arterial pressure which were sympathetically
mediated. Responses to L- glutamate were attenuated by concurrent injection
of glutamic acid diethyl ester and DL-2-amino-4-phosphonobutyrate, or
lidocaine. These results indicate a heterogeneity in the spatial
organization of brain- stem circuitry underlying cardiovascular control
that has not been previously described.
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