Delay of ganglion cell death by tetrodotoxin during retinal development in chick embryos

Neuronal activity plays an important role in the formation of topographic projection in the nervous system. In order to examine the role of neuronal activity on the retinotectal projection system, tetrodotoxin (TTX) was injected into one eye ball of the chick embryo once between day 9 and 14 of incubation and the number of dying retinal ganglion cells (RGCs) stained with Nile blue in the whole-mounted retinae were counted. In the control retinae, dying RGCs first appeared at stage 36 and disappeared after stage 43. The peak of RGC death was at stage 38 in the temporal and the central parts and at stage 39 in the nasal part. The total amount of dying RGCs in the temporal part was less than that in the central and the nasal parts. After injection of TTX into one eye ball, the peak of RGC death was at stage 40, which was 2 days later than that in the control retinae. TTX treatment did not affect the total amount of dying RGCs in the treated eye, but resulted in their decrease in the vehicle-treated eye which was contralateral to TTX treatment. These findings indicate that inhibition of neuronal activity of RGCs by TTX treatment delays the timing of RGC death.