Journal of Neuroscience, Vol 6, 2384-2392, Copyright © 1986 by Society for Neuroscience
Respiratory motoneuronal activity is altered by injections of picomoles of glutamate into cat brain stem
DR McCrimmon, JL Feldman and DF Speck
The local neural circuitry underlying the control of breathing was studied
by injecting nanoliter volumes of excitatory amino acids into discrete
regions of cat brain stem. Experiments were performed on
chloralose-urethane anesthetized, vagotomized, paralyzed, and artificially
ventilated cats. Phrenic, intercostal, and recurrent laryngeal nerve
discharges were recorded. Multibarrel pipettes were used for recording and
pressure ejection of drugs or a dye for marking recording and ejection
sites. Ejected volumes were directly monitored for every injection.
Injections, proximal to neurons discharging with a respiratory periodicity,
of as little of 200 fmol of L-glutamate in 200 pl of saline elicited
marked, site-specific increases or decreases in respiratory motoneuronal
discharge. N-Methyl-D-aspartic acid and homocysteic acid elicited similar
site-specific alterations in respiratory motor output, although some
details of the response could differ qualitatively. Responses to all the
excitatory agents used were attenuated by concurrent injection of kynurenic
acid, DL-2-amino-4- phosphonobutyric acid, or glutamic acid diethyl ester.
There was no change in spontaneous phrenic nerve discharge in response to
injections of equivalent or larger volumes of saline or lidocaine. These
results indicate a heterogeneity in the spatial organization of the
brain-stem neural circuitry underlying respiratory control, which has not
been described previously. This injection technique may provide a mechanism
for probing the neural circuitry underlying other behaviors.
Previous Article | Next Article
