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Spano PF, Govoni S, Hofmann M, Kumakura K, Trabucchi M. 
“Physiological and Pharmacological Influences on Dopaminergic Receptors in the Retina”. 
Advances in Biochemical Psychopharmacology. 1977;16:307-310.
The retina is a functional, histological and embryological part of the central nervous system (CNS) and contains almost all the putative neurotransmitters so far identified in the brain. Dopamine (DA) in the retina is the predominant amine in terms of amount present based on chemical (7,16) and histochemical evidence. Autoradiographic studies have shown that retinal DA occurs in a population of amacrine-like cells, the so-called dopaminergic junctional cells. These cells are located at the junction of the inner nuclear and inner plexiform layers, make multiple synaptic connections with a variety of cell types, and may have small vertical fibers oriented toward the horizontal cells (11). The physiologic role of DA in the retina is largely unknown. However, it has been shown that dopaminergic junctional cells in the retina are capable of accumulating and storing DA. At the same time, these cells may release DA as a consequence of stimulation of the retina with light (10). Moreover electrophysiological experiments with exagenously applied DA indicate that this amine may function as an inhibitory transmitter (1), as it has been shown in other areas of the CNS innervated by DA, such as caudate nucleus (2). On the other hand, an adenylate cyclase, which is preferentially stimulated by DA, has been described in homogenates of rat caudate nucleus (9), rat n. accumbens and the olfactorium (8), and rat cerebral cortex (18), as well as in homogenate of retinas from several mammalian species (rat, rabbit, cat, calf, and monkey)'(3,15,18). These findings have led to the suggestion that in these areas the DA-stimulated adenylate cyclase and the DA receptor may be related, and that the physiological effects of DA could be mediated by cyclic adenosine monophosphate (cAMP). The following experiments were designed to test this hypothesis and to investigate conditions and drugs which influence adenylate cyclase activity in the retina. Male Charles River rats (110-130 g), New Zealand rabbits (2.5-3.0 kg), and cats from our colony (3 - kg) were used in our experiments. Adenylate cyclase activity was measured in homogenates of the retinas according to the method of Kebabian and others (9) with minor modifications. The cyclic AMP was assayed using the activation of a purified cAMP dependent protein kinase described by Kuo and Greengard (12). Protein was measured
Notes # : Nonstriatal Dopaminergic Neurons. Publ.: Costa E, Gessa GL
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