Regional specialization of the rat retina: catecholamine-containing amacrine cell characterization and distribution.

The distribution of catecholaminergic amacrine cells has been investigated in rats by means of immunohistochemical labelling of wholemounted retinas. Two groups of catecholamine-containing cells could be distinguished on the basis of their catecholamine and biosynthetic enzyme content. Both groups could be stained with an anti-tyrosine hydroxylase (TH) antiserum. The first group was composed of large, strongly TH-immunoreactive stellate amacrine cells, located principally in the innermost row of the inner nuclear layer (INL) and sending processes to the outermost sublamina of the inner plexiform layer (IPL). Some were displaced in the IPL or in the ganglion cell layer (GCL). This first group of cells can be regarded as dopaminergic since they were also stained by an anti-dopamine (DA) antiserum. The second group was composed of small, weakly TH-positive cell bodies, located slightly more sclerad within the INL. Their processes were usually not labelled with anti-TH. Identical cells could be better visualized with an anti-phenylethanolamine-N-methyltransferase (PNMT) antiserum. Their processes were observed in the middle sublamina of the IPL. A great number of these cells were displaced in the GCL. They could be regarded as epinephrine cells. Concerning the density and distribution throughout the retina a striking difference was observed between the superior and inferior halves of the retina, whereas a lower difference was observed between the nasal and temporal regions. Almost all the PNMT-immunoreactive cells were located throughout the upper retina, whereas the DA-cells were especially concentrated in the upper temporal quadrant. The distribution of the DA cells parallels that of the ganglion cells whose density is also maximal in the upper temporal retina.