Journal of Neuroscience, Vol 11, 1810-1821, Copyright © 1991 by Society for Neuroscience
Control of retinal information coding by GABAB receptors
ZH Pan and MM Slaughter
Department of Biophysical Sciences, SUNY, School of Medicine, Buffalo 14214.
The directional selectivity of amacrine and ganglion cells was studied
using conventional intracellular recording techniques and drug application
in the superfused retina-eyecup preparation of the tiger salamander.
Baclofen, a GABAB receptor agonist, enhanced normal directional responses
in some directionally selective third-order neurons. In about 30% of the
cells that were not normally directional, baclofen induced
direction-selective responses. This effect was particularly marked when
2-amino-4-phosphonobutyrate (APB) was used to isolate the OFF pathway.
Comparisons of the effects of APB and baclofen on induced directional cells
indicate that directional information in the ON and OFF channels is often
handled separately and frequently is not aligned. This tends to obscure the
observation of directionality as seen from the soma. Application of
picrotoxin blocked both normal directional selectivity and baclofen-induced
directional selectivity in some cells. Superfusion of picrotoxin and
strychnine together blocked directionality in almost all cells. In both
normal and induced directionality, the null direction response varied from
cell to cell between a small depolarization, no voltage response, or a
hyperpolarization. Injection of positive current often revealed "silent"
inhibition. Some induced direction-selective cells did not show any
evidence of inhibition in the null direction. The similarities in the
response to baclofen, the influence of GABA and glycine antagonists, and
the characteristics of the null-direction responses suggest that both
normal and induced directionality originate from the same sources or
mechanisms. Baclofen also induced orientation selectivity, but this was
rarely observed.
Previous Article | Next Article
