Researchers at the Scripps Research Institute in California, US, focused on amacrine
and horizontal cells in mice two types of neuron involved in the visual signalling pathway.
Close relationships have been observed between 5-HT and GABA in vertebrates, such as the rabbit (Osborne & Beaton 1986) and the cat (Wassle & Chun 1988), with double-labeling studies demonstrating the coexistence of these 2 neurotransmitters in amacrine cells of the retina.
Dual expression of GABA or serotonin and dopamine in Xenopus amacrine cells is transient and may be regulated by laminar cues.
The list includes cells called amacrine
and horizontal interneurons, retinal progenitor cells and photoreceptors.
Retinogenesis proceeds in two distinct yet overlapping histogenetic periods, characterized by the development of early-born cells (ganglion, horizontal, cone, and amacrine
cells) mostly during embryogenesis and late-born cells [rods, bipolar cells (BCs), and MGCs] during early postnatal development (Livesey and Cepko 2001; Martins and Pearson 2008; Young 1985b).
However, all those studies had failed to detect any regenerated inner retina nerve cells, except when the Muller glia cells were genetically modified with genes that specifically promote the formation of amacrine
cells, which act as intermediaries in transmitting nerve signals.
In the normal retina (Figure 6(a)), anti-GABA antibody labels the inner plexiform layer (IPL), the amacrine
cells located on the inner lamina of the INL, and the horizontal cells located on the outer lamina of the INL.
There are six basic classes of retinal neurons: the photoreceptor, horizontal, bipolar, amacrine
, interplexiform and ganglion cells.
Instead of the the eye's bipolar, horizontal and amacrine
cells, which process the information gathered by the rods and cones, the electronic retina has "signal transfer gates, memories, logic gates and driver circuits,' each on its own silicon layer.
Looking closer, he found that the neurons only needed to be in direct contact with one type of retinal cells, called amacrine
cells, to permanently lose the ability to grow axons quickly.
After two weeks, the team found no effect on blood vessels of the inner retina, but did find a significant increase in the number of dying cells of the inner and outer nuclear layers which include amacrine
cells that participate in transmitting the visual signal; Muller cells that also participate in the visual signal and support the photoreceptors; and, photoreceptors, which are responsible for color and night vision.
Targeting of amacrine
cell neurites to appropriate synaptic laminae in the developing zebrafish retina.