Identification of amacrine and ganglion cells in the carp retina.

1. Amacrine and ganglion cells in the carp retina were identified from such criteria as photoresponses, intracellular dye staining, responses to optic nerve stimulation and behaviour to a synapse blocking agent. 2. Responses of ganglion cells were accompanied by spike discharges., either facilitated or suppressed by photic stimulation. The cells were also invaded by antidromic impulses, which survived after chemical synapses had been blocked by application of atomized CoCl2 solution. In subsequent histology of the Procion-stained neurones, the cell bodies were found in the ganglion cell layer and the axons were often traced. 3. Amacrine cells were subdivided into two types. The first type gave rise to transient depolarizations at both on- and offsets of spot and annulus illuminations, usually being associated with spike discharges of which the amplitudes varied in different cells. In histology, the cell bodies of this type were situated in the inner nuclear layer and dendrites ramified in two or more discrete sublayers of the inner plexiform layer (the stratified amacrine cell of Cajal). 4. The second type of amacrine cells produced sustained responses during illumination, being associated with no spike but with small oscillatory wavelets. The cell bodies were situated in the inner nuclear layer and the dendrites ramified in a single sublayer of the inner plexiform layer (the monolayered amacrine cell). 5. An attempt was made to see the effect of activation of centrifugal fibres on amacrine cells, but almost all of about 200 cells examined did not respond to optic nerve stimulation. Only two cells produced, with long latency, a small post-synaptic depolarization which disappeared after chemical synapses in the retina had been blocked. It is considered that the physiological role of the centrifugal system is insignificant in the carp retina.