Population magnitudes and distribution of the major modal classes of cat retinal ganglion cell as estimated from HRP filling and a systematic survey of the soma diameter spectra for classical neurones.

A survey of diameter spectra in presented for classic neurones of the cat retinal ganglion cell layer. From these, with the aid of retrograde HRP filling for central retina, a set of density distribution maps has been prepared for each of the major modes of the neuronal diameter spectrum. The total population of classical neurones, the presumed ganglion cells of Hughes ('75), confirms published values with a minimum of some 207,000 comprised 5,600 cells in the alpha mode, 80,700 cells in the beta mode, and 120,700 cells in the gamma mode. A proportion of classical neurones in the gamma mode do not fill by retrograde transport of HRP from either optic nerve or superior colliculus. Their morphology is characteristic and includes a conspicuous basophilic nuclear bar or fold; they remain subsequent to ganglion cell retrograde degeneration and resemble some profiles of the amacrine layer. It is presumed that they represent a class of displaced amacrine cells. Estimates based on ganglion cell identification by HRP filling indicate populations of about 80,000 cells in both the gamma and the beta modes and a total count of about 170,000 ganglion cells; a good agreement with Hughes and Wässle's ('76) optic nerve fibre count, but lower than the classic neurone count. It is concluded that the distribution maps for ganglion cells in each of the three modes of the soma diameter spectra are similar in form and resemble that of the total neurone density map. The ganglion cell population of the gamma mode in the visual streak is not found to increase in proportion relative to that of the beta mode, as has been reported elsewhere.