Tyrosine hydroxylase immunoreactivity in the retina of the diabetic sand rat Psammomys obesus.

The pattern of tyrosine hydroxylase (TH)-immunoreactivity, which labels dopamine neurons in the retina, is described in a diurnal sand rat Psammomys obesus. As in other rodent species, dopamine innervation is composed of large neurons located in the amacrine cell layer and sending processes mainly to sublamina 1 of the inner plexiform layer, where they form ring-like structures around unlabeled cell bodies. Thin varicose axon-like processes running to sublamina 3 are also present in significant number like in other diurnal animals. A few interplexiform cells are observed. Psammomys obesus rapidly develops hyperglycemia when held in captivity and fed normal synthetic laboratory rat diet, providing a model for the study of diabetes related impairment of dopamine metabolism in the retina. The pathomorphological analysis of TH-immunoreactivity was achieved in a population of diabetic Psammomys and compared with the normal. It indicates that moderate hyperglycemia induces a decrease of TH-immunoreactivity in dopamine dendrites only, while severe hyperglycemia can provoke dopamine neuron degeneration.