Directionality and Inhibition in Crayfish Tangential Cells.
Raymon M. Glantz.
Department of Biochemistry and Cell Biology, Rice University, Houston
Texas, 77251.
APStracts 4:346N, 1997.
ABSTRACT
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. 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. 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 and
places limits on the frequency response of inhibition and DS.
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. Bicuculline did not influence
orientation selectivity. 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 3 December 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