New discoveries in the retina have provided a unique view of how dopamine (DA) operates as a neurotransmitter. In certain fish retinae, DA, acting through D-1 receptors linked to adenylate cyclase, serves to uncouple electrical synapses between horizontal cells. In other fish species, DA induces the physical retraction of cones and the elongation of rods by an action on D-2 receptors localized to the photoreceptor membrane. These novel actions of DA provide important clues for investigating the physiological role of DA elsewhere in the nervous system.
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