Jh. Yang et al., POSTSYNAPTIC RESPONSES OF HORIZONTAL CELLS IN THE TIGER SALAMANDER RETINA ARE MEDIATED BY AMPA-PREFERRING RECEPTORS, Brain research, 797(1), 1998, pp. 125-134
The postsynaptic responses of sign-preserving second-order retinal neu
rons (horizontal cells (HCs) and off-bipolar cells) are mediated by CN
QX-sensitive AMPA/KA glutamate receptors. In this study we used recept
or-specific allosteric regulators of desensitization and selected anta
gonists to determine the glutamate receptor subtypes in tiger salamand
er horizontal cells. Two approaches were employed in this study. The f
irst was to measure postsynaptic currents induced by exogenously appli
ed glutamate under voltage clamp conditions in living retinal slices;
and the second was to record voltage responses controlled by endogenou
s glutamate released from photoreceptors in whole retinas. Application
of 100 mu M cyclothiazide (a specific AMPA receptor desensitization b
locker) enhanced the glutamate-induced current by about 5 fold. In con
trast, 300 mu gml(-1) ConA (a specific kainate receptor desensitizatio
n blocker), had no effect. GYKI 52466 (a specific AMPA receptor antago
nist) at 30 mu M almost completely suppressed the glutamate-induced in
ward current in HCs. Cyclothiazide at 100 mu M depolarized the HC dark
membrane potential by about 5 mV and reduced the amplitudes of the vo
ltage responses to dim Lights, but enhanced the voltage responses to b
right lights. Cyclothiazide had no effect on either the dark potential
or the light responses of rods and cones. Con A at 300 mu gml(-1) had
no effect on either the dark potential or the light responses of the
HC. GYKI 52466 (30 mu M) hyperpolarized the HC dark membrane potential
by about 55 mV and almost completely suppressed the light responses.
We conclude from these results that the postsynaptic glutamate- and Li
ght-induced responses in the tiger salamander retinal horizontal cells
are mediated by AMPA-preferring, and not kainate-preferring glutamate
receptors. The functional roles of AMPA receptors and their desensiti
zation kinetics in visual information processing are discussed. (C) 19
98 Elsevier Science B.V. All rights reserved.