MORPHOMETRY AND DISTRIBUTION OF DISPLACED DOPAMINERGIC CELLS IN RAT RETINA

The majority of dopaminergic (DA) cells, labeled by tyrosine hydroxyla se (TH) immunohistochemistry, are located in the amacrine cell layer ( i.e., the innermost sublayer of the inner nuclear layer) in the rat re tina. We describe a small population of DA cells, observed in retinal wholemounts, that are displaced to either the inner plexiform layer (D AIcs) or the ganglion cell layer (DAGcs). Contrary to some other speci es, such cells are few in number in the rat retina. Their systematic s tudy was made in young and adult retinas by retinal mapping, camera lu cida drawing, and computer-aided three-dimensional reconstruction. Loc ated predominantly in the superior temporal quadrant, they are observe d as soon as the second postnatal day. Most of the morphometric parame ters studied were not significantly different between the two types of displaced DA cells, despite the characteristic appearance of intersti tial cells. Two hypotheses are proposed for the origin of their displa cement: either it is accidental or programmed. Our results favor the f ormer possibility.