Aberrant retinotectal projections in the frog

Cell death in the retinal ganglion cell layer during optic nerve regeneration for the frog Rana pipiens

Cell number in the retinal ganglion cell layer of adult Rana pipiens was estimated from cresyl stained wholemounts. Values for normal animals ranged from 466,000 to 643,000 but differences between sides of individual animals varied by 9% or less. During optic nerve regeneration, following unilateral extracranial optic nerve crush, cell numbers in experimental retinae fell compared to their unoperated partners with the majority of the loss taking place between 56 and 84 days; by 200 day only half the cell complement remained. Since retrograde transport of horseradish peroxidase labelled 87% of cells in the normal ganglion cell layer, most of the loss during regeneration must have been from the ganglion cell population.

Removal of retinal input fails to elicit isthmo-tectal sprouting in the frog

The retina and nucleus isthmi both project in laminar fashion to the superficial layers of the frog's tectum. In order to determine whether isthmo-tectal axons show collateral sprouting after retinotectal input is removed, we injected [3H] proline into the nucleus isthmi and measured the volume of the crossed isthmo-tectal projection. We found no evidence of collateral sprouting.