Severity of ganglion cell death during early postnatal development is modulated by both neuronal activity and...

The influence of postnatal neuronal activity on the magnitude of retinal ganglion cell death has been studied in cats. A constant blockade of activity in one eye starting just after birth does not change the severity of naturally occurring ganglion cell death, and as in normal animals, the ganglion cell population declines from 250,000 to 160,000 over a 4- to 6-week period. However, the population of retinal ganglion cells in the active untreated eye of monocularly deprived cats is increased 12% above normal (180,000 vs. 160,000 in each of four cases). This increase of 20,000 cells is permanent, and presumably reflects the competitive advantage in their target nuclei that the still active axons have over their silenced companions from the treated eye. Surprisingly, in one animal treated successfully for long duration with TTX in both from the population of ganglion cells was elevated in both eyes (200,000 and 208,000 ganglion cells). This increase matches that achieved by early unilateral enucleation (Williams et al., 1983). Our results demonstrate that the complete blockade of activity reduces the severity of naturally occurring cell death in a population of CNS sensory neurons. The effects of unilateral blockade emphasize that the activity-dependent modulation of neuron death only occurs under conditions that do not place the inactive population of neurons at a competitive disadvantage.