The inner plexiform layer in the retina of the cat: electron microscopic observations

Neural connections of cells ramifying in the inner plexiform layer of the cat retina have been studied by serial section electron microscopy. Flat cone bipolars and invaginating cone bipolars segregate their axon terminals to different sublaminae of the IPL (sublamina a and sublamina b, respectively) where they relate to different subtypes of the same class of ganglion cell (a and b types respectively). Rod bipolar axon terminals end solely in sublamina b and synapse with amacrine cells (AI and AII). AI provides reciprocal synapses to clusters of rod bipolar axon terminals. The AII amacrine provides rod input to a type ganglion cells by means of chemical synapses and to b type ganglion cells through gap junctions with invaginating cone bipolar terminals. Amacrine cells exist which interconnect rod and cone bipolars, but some amacrines appear to be related specifically to neurons branching in particular sublaminae. Both large- and small-bodied ganglion cells have amacrine-dominated input while the medium-bodied ganglion cells with small dendritic trees have cone bipolar-dominated input.