Evidence for dopaminergic innervation on kitten retinal ganglion cells

Effects of iontophoretically applied dopamine and its receptor antagonists on physiologically identified retinal ganglion cells were studied in the optically intact eye of pentobarbitone anaesthetised kittens (7-9 weeks of age) and the results were compared with the effects obtained from adult cats (18-22 weeks of age). In both the adult and the kitten, dopamine had an inhibitory effect on visually evoked and spontaneous activity of the retinal ganglion cells, irrespective of cell type. However, unlike in the adult, the effects of dopamine in kittens were variable and not dependent on retinal eccentricity. In adult cells, only L-sulpiride (a potent D2 receptor antagonist) reduced the inhibitory effect of exogenous dopamine, whereas in kitten cells, both alpha-flupenthixol (a potent D1 receptor antagonist) and L-sulpiride did so. When applied alone, neither alpha-flupenthixol nor affected the activity of ganglion cells in adults, but in kittens both antagonists produced an excitatory effect in some cells. Physiologically active dopaminergic innervation seemed, therefore, to be present on the immature ganglion cells, but was subsequently 'eliminated' during the course of postnatal development. Furthermore, in immature cells, both D1 and D2 type receptors are present but only D2 receptors remain in adult. Therefore, there is a mismatch between dopamine receptors and dopamine in the adult retina and this mismatch may be the consequence of a developmental event.