Functional development of intrinsic properties in ganglion cells of the
mammalian retina.
GUO-YONG WANG , G-M RATTO , SILVIA BISTI & LEO M. CHALUPA.
Section of Neurobiology, Physiology & Behavior and the Center for
Neuroscience, University of California, Davis U.S.A.; Instituto di
Neurofisiologia, CNR Pisa Italy.
APStracts 4:168N, 1997.
ABSTRACT
Sensory neurons manifest pronounced changes in excitability during maturation,
but the factors contributing to this ubiquitous developmental phenomenon are
not well understood. To assess the contribution of intrinsic membrane
properties to such changes in excitability, in the present study whole-cell
patch-clamp recordings were made from developing ganglion cells in the intact
retina of postnatal rats. During a relatively brief developmental period (P7-
P27) ganglion cells exhibited pronounced changes in the discharge patterns
generated by depolarizing current injections. The youngest cells (P7-P17)
typically responded to maintained depolarizations with only a single spike or
a rapidly adapting discharge pattern. In contrast, the predominant response
mode of more mature cells (P21-P27) was a series of repetitive discharges that
lasted for the duration of the depolarization period, and by P25 all cells
responded in this manner. These functional changes characterized all three
morphologically defined cell classes identified by intracellular labeling with
Lucifer yellow. To determine if expression of the IA conductance and the
kinetics of the Na channel related to the increased excitability of developing
ganglion cells, described above, current- and voltage-clamp recordings were
made from individual neurons. The different firing patterns manifested by
developing retinal ganglion cells did not reflect the presence or absence of
the IA conductance, although cells expressing IA tended to generate spikes of
shorter duration. With maturation the speed of recovery from inactivation of
the Na current increased markedly, and this related to the increased
excitability of developing ganglion cells. Neurons yielding only a single
spike to maintained depolarization were characterized by the slowest speed of
recovery; cells with rapidly adapting discharges showed a faster recovery,
while those capable of repetitive firing recovered fastest from Na channel
inactivation. It is suggested that these changes in intrinsic membrane
properties may relate to the different functional roles subserved by ganglion
cells during development.
Received 20 February 1997; accepted in final form 24 July 1997.
APS Manuscript Number J152-7.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 28 August 1997