Bilateral ganglion cell branches in the normal rat: a demonstration with electrophysiological collision and cobalt tracing methods

The application of microelectrode recording and anatomical tracing methods to the subcortical optic projections of the normal rat shows that the uncrossed pathway from the retina of this mammal is substantially composed of branches of crossed axons. In the recording experiments, paired stimuli to the optic tracts produces an attenuated antidromic response in the optic nerve which is best explained by the collision of impulses which travel in branches of the same parent axon. Cobalt injection of one optic tract results in retrograde filling of axons in the entire contralateral optic nerve and filling of axons in restricted regions of the ipsilateral optic nerve. This procedure also results in the filling of axons in the opposite optic tract. The locations of the filled axons in the opposite tract correspond to the positions of crossed and uncrossed projections from the temporal retinae: ventrolateral and dorsomedial, respectively. The position of the temporal retinal projections in both optic tracts was determined by applying silver degeneration methods after small lesions of the retina.