Density distribution of dopaminergic neurons in the retina of a marine teleost, Thamnoconus (Navodon) modestus

By means of tyrosine hydroxylase immnocytochemical detection, regional densities of dopaminergic (DAergic) neurons were measured in 6 whole-mounted retinas of a marine teleost, Thamnoconus (Navodon) modestus. Isodensity lines of DAergic cells in the right retina were drawn to make a contour map. Depending upon the range of cell densities, the retinal field was divided into 3 regions: zone A, containing more than 300 per mm square; zone B, from 200 to 299; and zone C, below 200. Zone A was located in the small temporal (A 1) and nasal (A 2) areas as well as in the peripheral margin (A 3). Zone B formed a horizontal streak-like band between regions A 1 and A 2. Low density areas (C) were located dorsally or ventrally to zone B. Where the densities were higher, soma sizes appeared to be smaller. DAergic neurons in the peripheral zone A 3 were bipolar and the dendrites ran parallel to the retinal margin, while DAergic neurons in the other zones were multipolar and the dendrites ran in various directions. The presence of the small temporal (A 1) and nasal areas (A 2) with high densities of DAergic neurons, as well as the streak-like area (B) with a relatively high density, may correspond to similar areas in the isodensity contour map of ganglion cells.