SEVERITY OF GANGLION-CELL DEATH DURING EARLY POSTNATAL-DEVELOPMENT ISMODULATED BY BOTH NEURONAL-ACTIVITY AND BINOCULAR COMPETITION

The influence of postnatal neuronal activity on the magnitude of retin al ganglion cell death has been studied in cats. A constant blockade o f activity in one eye starting just after birth does not change the se verity of naturally occurring ganglion cell death, and as in normal an imals, the ganglion cell population declines from 250,000 to 160,000 o ver a 4- to 6-week period. However, the population of retinal ganglion cells in the active untreated eye of monocularly deprived cats is inc reased 12% above normal (180,000 vs. 160,000 in each of four cases). T his increase of 20,000 cells is permanent, and presumably reflects the competitive advantage in their target nuclei that the still active ax ons have over their silenced companions from the treated eye. Surprisi ngly, in one animal treated successfully for long duration with TTX in both eyes, the population of ganglion cells was elevated in both eyes (200,000 and 208,000 ganglion cells). This increase matches that achi eved by early unilateral enucleation (Williams et al., 1983). Our resu lts demonstrate that the complete blockade of activity reduces the sev erity of naturally occurring cell death in a population of CNS sensory neurons. The effects of unilateral blockade emphasize that the activi ty-dependent modulation of neuron death only occurs under conditions t hat do not place the inactive population of neurons at a competitive d isadvantage.