Synapses from bipolar cells onto dopaminergic amacrine cells in cat and rabbit retinas.

Dopaminergic amacrine cells in the vertebrate retina have long been characterized as 'interamacrine' as they were only found to be pre- and postsynaptic to other amacrine cells. Immunohistochemistry with antibodies directed against tyrosine hydroxylase (TH) revealed synapses from bipolar cell axon terminals to TH-containing neuronal processes at ribbon synapses in the rhesus monkey retina. This finding challenged the notion of the dopaminergic amacrine cell phenotype as 'interamacrine'. In order to determine if the finding of synapses from bipolar cells to dopaminergic amacrine cells could be generalized to other species, we studied the synaptic organization of dopaminergic amacrine cells in the retinas of cats and rabbits with electron microscopy of TH immunoreactivity. In both species, TH-immunoreactive processes were found to be postsynaptic to bipolar axon terminals at ribbon synapses demonstrating that the original finding in the primate may be a significant feature in the retinas of many other vertebrates as well.