During recent years a key
role as morphogen has been postulated for the
neurotransmitter acetylcholine in the developing
Central Nervous System.
Acetylcholine released from growing
axons regulates
growth, differentiation and plasticity. The
acetylcholine distribution is frequently defined by
acetylcholinesterase and
choline acetyltransferase expression patterns. The
cholinergic/cholinoceptive system in the
adult zebrafish retina has been described. Nevertheless, there are no data regarding the developing
retina. The
acetylcholinesterase and
choline acetyltransferase distribution patterns during
zebrafish retinal development are very
similar. In both cases the first positive
elements appear in the plexiform layers and in later stages reactive
amacrine cells have been observed in the
ganglion cell layer and inner nuclear layer. In the
adult retina a
cholinergic and cholinoceptive
neuropile band is observed in the inner plexiform layer. Displaced
amacrine cells and
amacrine cells positive to both markers have been observed.
Transient expressions of
choline acetyltransferase in the
optic nerve and outer plexiform layer and of
acetylcholinesterase in
amacrine cells and displaced
amacrine cells are observed during
retinal development coinciding with the arrangement of the pioneering
retinal projections into the
optic tectum. The mature distribution pattern of the
cholinergic/ cholinoceptive system in the
adult retina is conserved along the phylogenetic scale, thus it seems to be a primary feature acquired relatively early during the evolution of
vertebrates (AU)