Chemically specific retinal ganglion cells collateralize to the pars ventralis of the lateral geniculate nucleus and optic tectum in the pigeon (Columba livia).

Immunohistochemical and retrograde tracing techniques were combined to study the retinal ganglion cells which project to the pars ventralis of the lateral geniculate nucleus (GLv) in the pigeon. Using two different fluorescent tracers, two histochemically-distinct populations of ganglion cells were found to project to both the GLv and the optic tectum. The first population of ganglion cells exhibited tyrosine hydroxylase-like immunoreactivity and represented about 20% of all ganglion cells which were retrogradely labeled from the GLv. The second population of ganglion cells showed substance P-like immunoreactivity and represented about 13% of all ganglion cells projecting to the GLv. These results confirm earlier suggestions that the retinal axons projecting to the GLv also project elsewhere and demonstrate that heterogeneity of retinal ganglion cells transmitters is evident even within a single retino-recipient nucleus such as the GLv.