Directionality and Inhibition in Crayfish Tangential Cells.
Raymon M. Glantz.
Department of Biochemistry and Cell Biology, Rice University, Houston
Texas, 77251.
APStracts 4:343N, 1997.
ABSTRACT
1. The purpose of this study was to characterize the inhibitory mechanism(s)
associated with directionally selective motion detection (DS) in nonspiking
tangential cells of crayfish optic lobe. The experiments employed
intracellular recording of synaptic potentials elicited with sinewave gratings
and pharmacological techniques. 2. Previous studies established that
tangential cells are subject to bicuculline-sensitive GABA-mediated
inhibition. In this study DS was reduced by 90% by bicuculline. The reduction
in DS was accompanied by a substantial increase in the response to null-
direction motion. 3. Bicuculline also altered the response to pulses of
illumination. The magnitude and time course of inhibition were derived from
the time varying difference between the control light response and that
elicited during bicuculline perfusion. Both the inhibitory delay (relative to
excitation) and the inhibitory amplitude are close to the expectations of a
linear model of DS. The inhibition is not prolonged with respect to excitation
but its risetime is about 2.5 times longer. The result implies a longer time
constant in the inhibitory pathway relative to that in the excitatory pathway.
4. The velocity-dependence of DS is related to the time course of inhibition.
The stimulus drift velocity eliciting maximum directionality is inversely
proportional to the inhibitory delay. 5. Bicuculline did not influence
orientation selectivity. 6. It is concluded that the quantitative features of
bicuculline-sensitive, GABA-mediated inhibition are consistent with a linear
model of DS.
Received 16 July 1997; accepted in final form 25 November 1997.
APS Manuscript Number J594-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 12 December 1997