DOPAMINERGIC INTERPLEXIFORM CELLS IN THE RETINA OF PIGMENTED AND HYPOPIGMENTED QUAILS (COTURNIX-COTURNIX-JAPONICA)

Interplexiform cells (IPCs) have not been previously described as a co mponent of the population of tyrosine hydroxylase (TH) immunoreactive (presumably dopaminergic) cells in the avian retina. In this study, ca rried out in both pigmented and imperfect albino mutant quails (Coturn ix coturnix japonica), we initially describe TH immunoreactive cells i n the inner nuclear layer whose internal dendritic arborization extend s into strata 1, 3 and 4/5 of the inner plexiform layer. Then, we desc ribe ascending processes arising from the somata or proximal dendrites of these cells. These sclerally directed processes (100-1,000 mu m lo ng) run across the inner nuclear layer to terminate within the outer p lexiform layer, sometimes even reaching the outer nuclear layer. Hence , the cells bearing such processes correspond well with the definition of IPCs. The number of scleral processes is higher in mutant (48 +/- 19/retina) than in normal(12 +/- 10/retina) quails and are distributed throughout the retina except the area surrounding the pecten. Compari son of biochemical assays for dopamine in the two strains reveals a si gnificantly higher dopamine content in the mutant quails which could b e related to its increased number of dopaminergic IPC processes.