Morphological identification of on- and off-centre brisk transient (Y) cells in the cat retina.

Brisk transient (Y) cells were recorded extracellularly in the cat retina. The position and shape of their receptive field centres were plotted on a tangent screen, together with retinal landmarks, such as blood vessels adjacent to the recording area. After recording the retina was processed as a whole mount and stained with a reduced-silver method (see appendix). This technique stains the entire alpha cell population including the dendritic trees. Alpha cells are the morphological correlate of the brisk transient cells (Boycott & Wässle 1974; Cleland et al. 1975). Maps of the screen plot and the histological preparation could be accurately superimposed by means of the retinal landmarks and each recorded brisk transient unit could unequivocally be attributed to a particular alpha cell. Alpha cell dendritic trees are unistratified in either of two laminae within the inner plexiform layer: (1) close to the inner nuclear layer border, 'outer alpha cells', or (2) about 10 micrometers further towards the ganglion cell layer, 'inner alpha cells'. This stratification difference can be observed in whole mounts for large populations of cells (Wässle et al. 1981). Of the recorded brisk transient cells, all on-centre units were inner alphas and all off-centre units outer alphas.