Two conductances mediate thyrotropin releasing hormone-induced depolarization of neonatal rat spinal preganglionic and lateral horn neurons Miloslav Kolaj, Susan J. Shefchyk1 and Leo P. Renaud Neuroscience, Loeb Research Institute, Ottawa Civic Hospital and University of Ottawa, Ottawa, Ontario, CANADA K1Y 4E9, 1Department of Physiology, University of Manitoba, Winnipeg, Manitoba, CANADA R3E 3J7
APStracts 4:0089N, 1997.
ABSTRACT
Thyrotropin releasing hormone (TRH) has been recognized as a neuromodulator in several CNS regions, including the thoracolumbar spinal cord where an influence on cardiovascular autonomic function has been proposed. To identify the cellular mechanisms involved in the latter, whole-cell patch-clamp recordings were obtained from 52 thoracolumbar lateral horn cells, including 17 sympathetic preganglionic neurons (SPNs), in spinal cord slices from neonatal rat (11-21 days). Under current-clamp, bath applications of TRH (1- 20M) induced a slowly rising and prolonged membrane depolarization in 8 / 9 cells tested. Under voltage clamp (VH 65mV), 33/37 tested cells displayed a TRH-induced, tetrodotoxin-resistant inward current that was associated with either a reduction or an increase in membrane ion conductances. I-V relationships in 28 cells suggested two conductances: in 9 cells the current reversed 107mV; in 10 cells the I-V lines remained parallel, while in 9 cells the current reversed 40mV. In 3/3 cells, addition of 2mM barium was associated with an inward current, and the TRH-induced inward current was also suppressed, suggesting the presence of a resting barium- and TRH-sensitive potassium conductance. A residual barium- insensitive conductance was seen to reverse near 40mV. Intracellular dialysis with GTP- -S significantly enhanced the duration of the TRH effect, indicating that G-protein activation participates in the TRH response. These observations not only reveal a direct, G-protein mediated depolarizing action of TRH on neonatal rat SPN and lateral horn cells, but also imply that two separate conductances may be involved in the TRH responses in some neurons. 

Received 12 May 1997; accepted in final form 12 June 1997.
APS Manuscript Number J394-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 July 1997