Effects on breathing of medullary bicuculline microinjections in
immature opossums.
Farber, Jay P.
Department of Physiology, University of Oklahoma Health Sciences
Center, P. O. Box 26901, Oklahoma City, OK 73190
APStracts 2:0165R, 1995.
The role of medullary GABAA receptor activation in the expression of
breathing was studied in suckling opossums (Didelphis virginiana)
from 4-8 weeks of age. Animals were anesthetized with a
thiobarbiturate, and the ventral medulla was exposed so that drugs
could be microinjected into the medulla using a 2 barrel glass
micropipette. The GABAA antagonist, bicuculline (bic), at approx. 1-3
pmole total dose, was injected in volumes less than 1 nL; injections
of saline with pontamine sky blue dye were used as controls and to
mark location. Breathing pattern was assessed using diaphragm EMG.
Effective sites for bic 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 (Pk diaph) and
Pk diaph/Ti were not consistently affected. Transient apnea lasting
at least 8 sec occurred in 5 of the above animals. Control solutions
did not elicit respiratory responses. These results suggest that
neural circuitry in the medulla, utilizing the neurotransmitter GABA,
can have an early role in the modulation of breathing pattern.
Received 21 December 1994; accepted in final form 19 June 1995.
APS Manuscript Number R723-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 July 1995.