. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEUROBIOLOGY 265 Reference: Biol. Bull. 201: 265-267. (October :illll I Endogenous Zinc as a Neuromodulator in Vertebrate Retina: Evidence From the Retinal Slice Richaid L. Chappell {Hunter College, CUNY, 695 Park Ave., New York. New York 10021) iinil Stephen Reclenti1 Studies of the transretinal electroretinogram (ERG) of the skate (Raja erinacia) eyecup have provided evidence that endogenous zinc plays a role as a neuromodulator in vertebrate retina (1). With GABA receptor activity blocked by 200 /j,/W picrotoxin, superfu-
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. NEUROBIOLOGY 265 Reference: Biol. Bull. 201: 265-267. (October :illll I Endogenous Zinc as a Neuromodulator in Vertebrate Retina: Evidence From the Retinal Slice Richaid L. Chappell {Hunter College, CUNY, 695 Park Ave., New York. New York 10021) iinil Stephen Reclenti1 Studies of the transretinal electroretinogram (ERG) of the skate (Raja erinacia) eyecup have provided evidence that endogenous zinc plays a role as a neuromodulator in vertebrate retina (1). With GABA receptor activity blocked by 200 /j,/W picrotoxin, superfu- sinn of the zinc chelating agent histidine (100 /tA/) increased by about 2-fold the ON (b-wave) and OFF (d-wave) components of the ERG. In addition, as shown first in the salamander retina (2) and more recently in mammalian retinas (3, 4), an accumulation of zinc has been localized to the base of the photoreceptors in skate (5). These observations support the suggestion that zinc, co-re- leased with glutamate from photoreceptor terminals, may serve as ' Program in Biology. The Graduate School and University Cen- ter. CUNY. 365 Fifth Ave., New York, NY 10016. a neuromodulator in the outer plexiform layer of the vertebrate retina. By acting on the receptor terminal to reduce calcium entry, zinc could serve as a feedback signal to modulate transmitter release (2). If this is the case, one would expect to observe an effect of histidine application on the conductance of second-order cells in the retina of the skate. We have tested this hypothesis by the use of whole-cell, patch- clamp recordings from horizontal cells in the skate retinal slice preparation. The slices (-200 /^im thick) from the all-rod retina of the skate were positioned on a glass slide and visualized using a fixed-stage microscope equipped with a water-immersion objec- tive and Nomarski differential interference contrast optics. Whole- cell patch recordings were obtained under conditions of steady ambient il
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