Journal of Neuroscience, Vol 10, 394-402, Copyright © 1990 by Society for Neuroscience
The physiology of substance P in the rabbit retina
RA Zalutsky and RF Miller
Washington University School of Medicine, Department of Ophthalmology, St. Louis, Missouri 63110.
The neuropeptide substance P (SP) has been localized to amacrine and
ganglion cells in the rabbit retina. We have examined the effects of SP and
related peptides on rabbit retinal neurons using bath application and
intra- and extra-cellular electrophysiological methods in an in vitro
retina eyecup preparation. Substance P, at concentrations as low as 25 nM,
moderately excited most brisk ganglion cells. SP excited some ganglion
cells directly during cobalt block of synaptic transmission. Intracellular
recordings from amacrine cells demonstrated that some, but not all, were
depolarized by SP; pharmacological evidence suggested GABAergic amacrines
were probably among those sensitive to SP. SP did not affect horizontal
cells or the ERG, suggesting that the effects of this peptide are confined
to the inner retina. The effects of SP were strongly potentiated by
peptidase inhibitors, raising the possibility that endogenously released SP
may act quite locally in the rabbit retina. The relative potencies of SP
and the related peptides substance K and eledoisin on different cells
suggest that more than one tachykinin receptor subtype is present in the
rabbit retina. The responses of ganglion cells to SP desensitized with
repeated or prolonged applications. Comparison of a cell's light responses
before and after the receptors were desensitized revealed no qualitative
changes in receptive field characteristics, but quantitative changes in
excitability were apparent. SP antagonist analogs, although not potent,
specifically blocked the effects of SP on some ganglion cells. The effects
of these antagonists on light responses reinforced the inferences from
desensitization paradigms regarding the role of endogenous SP.(ABSTRACT
TRUNCATED AT 250 WORDS)