Differences in activation of the motoneurone inhibitory receptors in a frog Rana ridibunda by GABA and glycine and their interaction
Kalinina, N.I.; Kurchavyĭ, G.G.; Amakhin, D.V.; Veselkin, N.P.
Rossiiskii Fiziologicheskii Zhurnal Imeni I.M. Sechenova 94(9): 1005-1016
2008
ISSN/ISBN: 0869-8139 PMID: 18953991 Document Number: 616149
The membrane potential responses evoked by GABA and glycine bath applications were studied intracellularly in the motoneurons of the isolated frog spinal cord. The amplitude of glycine-evoked responses was 1.5-2.0 larger than that of GABA-evoked response at the same concentration. EC50 were 0.75 mM and 1.57 mM for glycine and GABA, respectively. The amplitude of responses induced by the simultaneous applications of both agonists were 79.1 +/- 2.4% (n = 19) of the sum of individual responses and 130.1 +/- 1.5% (n = 19) of individual glycine-induced responses (partial occlusion). GABA-evoked responses were decreased by 85.3 +/- 0.2% (n = 10) as a result of glycine preliminary application while preapplication of GABA reduced glycine-evoked responses only by 52.9 +/- 0.3% (n = 11). Glycine- and GABA-evoked responses were selectively suppressed by strychnine and bicuculline, respectively. These results suggest that amphibian spinal motoneurones express (less specifically than those of mammals) both glycine (predominantly) and GABAA receptors, with asymmetric cross-inhibition possibly taking place in them.