AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 6 1295-R1300, Copyright © 1995 by American Physiological Society
Effects on breathing of medullary bicuculline microinjections in immature opossums
J. P. Farber
Department of Physiology, University of Oklahoma Health Sciences Center, Oklahoma City 73190, USA.
The role of medullary gamma-aminobutyric acid A (GABAA)-receptor activation
in the expression of breathing was studied in suckling opossums (Didelphis
virginiana) from 4 to 8 wk of age. Animals were anesthetized with a
thiobarbiturate, and the ventral medulla was exposed so that drugs could be
microinjected into the medulla with a two-barrel glass micropipette. The
GABAA antagonist bicuculline at approximately 1-3 pmol total dose was
injected in volumes < 1 nl; injections of saline with pontamine sky blue
dye were used as controls and to mark location. Breathing pattern was
assessed using diaphragm electromyography (EMG). Effective sites for
bicuculline microinjection were obtained in the ventrolateral medulla, with
both lateral reticular and inferior olive nuclei present as rostrocaudal
markers. Responses among 18 tested animals included increased duration of
breaths (Ttot) and duration of inspiration (Ti). Peak amplitude of the
diaphragm EMG and peak amplitude of the diaphragm/Ti were not consistently
affected. Transient apnea, lasting at least 8 s, occurred in five of the
animals. Control solutions did not elicit respiratory responses. These
results suggest that neural circuitry in the medulla, using the
neurotransmitter GABA, can have an early role in the modulation of
breathing pattern.
