Journal of Applied Physiology, Vol 73, Issue 6 2333-2342, Copyright © 1992 by American Physiological Society

ARTICLES

Evidence that glycine and GABA mediate postsynaptic inhibition of bulbar respiratory neurons in the cat

A. Haji, R. Takeda and J. E. Remmers
Respiratory Research Group, Faculty of Medicine, University of Calgary Health Science Centre, Alberta, Canada.

Experiments were carried out on decerebrate cats to identify transsynaptic mediators of spontaneous postsynaptic inhibition of bulbar inspiratory and postinspiratory neurons. Somatic membrane potentials were recorded through the central micropipette of a coaxial multibarreled electrode. Blockers of type A gamma-aminobutyric acid (GABA-A) and glycine receptors were iontophoresed extracellularly from peripheral micropipettes surrounding the central pipette. Effective antagonism was demonstrated by iontophoresis of agonists with antagonists; application of strychnine antagonized the action of glycine but not GABA, and application of bicuculline antagonized the action of GABA but not glycine. In both types of neurons, iontophoresis of either antagonist depolarized the somatic membrane and increased input resistance throughout the respiratory cycle. Bicuculline preferentially depolarized the somatic membrane in both types of neurons during inactive phases. Strychnine increased the firing rate of inspiratory neurons during inspiration despite maintenance of somatic membrane potential at preiontophoresis levels. Tetrodotoxin reduced the effects of iontophoresed bicuculline and strychnine, suggesting that the action of the antagonists required presynaptic axonal conduction. The present results suggest that presynaptic release of both GABA and glycine contributes to tonic postsynaptic inhibition of bulbar respiratory neurons. GABA-A receptors appear to contribute to inhibition during inactive phases in inspiratory and postinspiratory neurons, whereas glycinergic mechanisms appear to contribute to inspiratory inhibition in inspiratory neurons.

This article has been cited by other articles:

				K. Ezure, I. Tanaka, and M. Kondo Glycine Is Used as a Transmitter by Decrementing Expiratory Neurons of the Ventrolateral Medulla in the Rat J. Neurosci., October 1, 2003; 23(26): 8941 - 8948. [Abstract] [Full Text] [PDF]

				A. Haji, M. Okazaki, H. Yamazaki, and R. Takeda Physiological Properties of Late Inspiratory Neurons and Their Possible Involvement in Inspiratory Off-Switching in Cats J Neurophysiol, February 1, 2002; 87(2): 1057 - 1067. [Abstract] [Full Text] [PDF]

				M. Krolo, E. A. Stuth, M. Tonkovic-Capin, F. A. Hopp, D. R. McCrimmon, and E. J. Zuperku Relative magnitude of tonic and phasic synaptic excitation of medullary inspiratory neurons in dogs Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2000; 279(2): R639 - R649. [Abstract] [Full Text] [PDF]

				Z. Dogas, M. Krolo, E. A. Stuth, M. Tonkovic-Capin, F. A. Hopp, D. R. McCrimmon, and E. J. Zuperku Differential Effects of GABAA Receptor Antagonists in the Control of Respiratory Neuronal Discharge Patterns J Neurophysiol, November 1, 1998; 80(5): 2368 - 2377. [Abstract] [Full Text] [PDF]

				X. M. Shao and J. L. Feldman Respiratory Rhythm Generation and Synaptic Inhibition of Expiratory Neurons in Pre-Botzinger Complex: Differential Roles of Glycinergic and GABAergic Neural Transmission J Neurophysiol, April 1, 1997; 77(4): 1853 - 1860. [Abstract] [Full Text] [PDF]