Journal of Neuroscience, Vol 8, 2269-2278, Copyright © 1988 by Society for Neuroscience
Modulation of cone horizontal cell activity in the teleost fish retina. II. Role of interplexiform cells and dopamine in regulating light responsiveness
XL Yang, K Tornqvist and JE Dowling
Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138.
Following the destruction of the terminals of the dopaminergic
interplexiform cells by intraocular injections of 6-hydroxydopamine (6-
OHDA), cone horizontal cells exhibited high light responsiveness in
prolonged darkness and their responses to moderate and bright full- field
flashes were as large as 60 mV. Furthermore, the light responsiveness of
these cells in the 6-OHDA-treated retinas was not enhanced by background
illumination. The application of dopamine (50 microM) by superfusion to
6-OHDA-treated retinas resulted in a decrease in light responsiveness and
changes in response waveform of the cone horizontal cells. Twenty minutes
following dopamine application the responses of the cone horizontal cells
closely resembled the response of cells recorded in prolonged dark-adapted
retinas. Dopamine caused similar changes in cone horizontal cells recorded
in light-exposed retinas, but had no obvious effects on rod horizontal
cells. The selective dopamine D1 receptor antagonist, Sch 23390, enhanced
cone horizontal cell responsiveness when applied to prolonged dark-adapted
retinas, mimicking background illumination. The light responsiveness of
cone horizontal cells recorded after application of Sch 23390 was less than
that for cells in retinas that had been exposed to background lights, but
light responsiveness could not be further enhanced by background
illumination. Another dopamine antagonist, (+)-butaclamol, was found to
have effects similar to Sch 23390 on cone horizontal cells, but
(-)-butaclamol, the inactive enantiomer, did not enhance the light
responsiveness of these cells. The results suggest that the dopaminergic
interplexiform cells play a crucial role in the regulation of cone
horizontal cell responsiveness by prolonged darkness and background
illumination. These cells may release dopamine tonically in the dark, which
suppresses cone horizontal cell responsiveness. Background illumination may
decrease dopamine release and liberate cone horizontal cells from the
suppression.