The present study has examined the emergence of cholinergic
stratification within the developing inner plexiform layer (IPL),
and the effect of ablating the cholinergic amacrine cells on
the formation of other stratifications within the IPL. The
population of cholinergic amacrine cells in the ferret's
retina was identified as early as the day of birth, but their
processes did not form discrete strata until the end of the
first postnatal week. As development proceeded over the next
five postnatal weeks, so the positioning of the cholinergic
strata shifted within the IPL toward the outer border, indicative
of the greater ingrowth and elaboration of processes within
the innermost parts of the IPL. To examine whether these
cholinergic strata play an instructive role upon the development
of other stratifications which form within the IPL, one-week-old
ferrets were treated with l-glutamate in an attempt
to ablate the population of cholinergic amacrine cells. Such
treatment was shown to be successful, eliminating all of the
cholinergic amacrine cells as well as the alpha retinal ganglion
cells in the central retina. The remaining ganglion cell classes
as well as a few other retinal cell types were partially reduced,
while other cell types were not affected, and neither retinal
histology nor areal growth was compromised in these ferrets.
Despite this early loss of the cholinergic amacrine cells, which
are eliminated within 24 h, other stratifications within the
IPL formed normally, as they do following early elimination
of the entire ganglion cell population. While these cholinergic
amacrine cells are present well before other cell types have
differentiated, apparently neither they, nor the ganglion cells,
play a role in determining the depth of stratification for other
retinal cell types.
A connectomics approach to understanding a retinal disease