Slow light and dark adaptation of horizontal cells in the Xenopus retina: a role for endogenous dopamine.
A role for endogenous dopamine in the control of rod and cone contributions to a second-order retinal neuron, the horizontal cell (HC) was studied in the Xenopus retina. Relative rod and cone contributions were estimated from HC responses to scotopically balanced 491- and 650-nm flashes. In eyecups prepared in light then placed in darkness, cone input to the HC slowed and diminished on a time scale of hours. The decline in cone input was balanced by a slow growth of rod input to the HC. Administration of D-amphetamine, a dopamine releasing agent, restored the light-adapted waveform. The kinetics of slow light adaptation were examined by recording HC responses from eyecups that had been dark-adapted previously for 11-14 h. When test flashes fell on a dark field, cone input to the HC grew for 2-4 h, reached a plateau, and later declined. If, however, flashes were superimposed on a weak background field, cone input to the HC continued to increase monotonically at about 10%/h. This increase was abolished by superfusion with a nonspecific dopamine receptor blocker, cis-flupenthixol (50 microM), resulting in the complete suppression of cone-to-horizontal cell synaptic transfer and the enhancement of rod-to-horizontal cell communication. Subcutaneous injection of reserpine, a drug that depletes dopamine stores (2 mg/kg on 1-4 successive days), or intraocular injection of the dopamine neurotoxin, 6-hydroxydopamine (10-30 micrograms) slowed and reduced the amplitude of cone input to the HC, even in completely light-adapted eyes.(ABSTRACT TRUNCATED AT 250 WORDS)
Witkovsky
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Daniel B. Kirby Eye Institute, Department of Ophthalmology, New York University Medical Center, NY 10016.
Shi
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XP
D000818:Animals; D003623:Dark Adaptation / Q000502:physiology*; D003913:Dextroamphetamine; D004298:Dopamine / Q000378:metabolism / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D005475:Flupenthixol; D006892:Hydroxydopamines; D008027:Light; D008297:Male; D016627:Oxidopamine; D010786:Photoreceptor Cells / Q000502:physiology; D011954:Receptors, Dopamine / Q000378:metabolism; D012110:Reserpine; D012160:Retina / Q000166:cytology / Q000502:physiology*; D014981:Xenopus
D006892:Hydroxydopamines; D011954:Receptors, Dopamine; D012110:Reserpine; D016627:Oxidopamine; D005475:Flupenthixol; D003913:Dextroamphetamine; D004298:Dopamine