Abstract
Purpose: :
To investigate the development of cholinergic and GABAergic synapses between starburst amacrine cells (SACs) and ganglion cell types, with a focus on the spatial organization and physiological properties of such transmissions between SACs and direction selective ganglion cells (DSGCs).
Methods: :
Simultaneous (double and triple) patch-clamp recordings were made from ganglion cells and their neighboring displaced SACs in the flat-mount rabbit retina. Synaptic transmission was studied as a function of animal age.
Results: :
Two kinds of cholinergic synapses were found among SACs and ganglion cells in the postnatal rabbit retina. The first type was a slow, asynchronous synaptic transmission mediated by non-alpha7 nicotinic receptors. This type of transmission was detected among SACs and between SACs and ganglion cells, including DSGCs, alpha ganglion cells and several other ganglion cell types. Such cholinergic transmission was prominent at early postnatal ages and declined with development as stage II retinal waves diminished. The second type was a fast synchronous transmission, mediated largely by alpha7 nicotinic receptors and detected between SACs and DSGCs. This type was present at birth and persisted throughout postnatal development.GABAergic transmission was detected between SACs and DSGCs at birth. The postsynaptic responses were mediated by GABA-A receptors and showed a transient peak. The responses became more robust and attained a delayed component with development. Triple patch recordings were made from On-Off DSGCs and two of their neighboring SACs from anterior and posterior (or dorsal and ventral) directions. Statistical analysis suggested that spatial asymmetry in GABAergic input from SACs began as early as birth. Recordings from a DSGC and four neighbor SACs from all four orthogonal directions also suggested an early presence of spatial asymmetry in GABAergic, but not cholinergic, input from SACs to DSGCs.
Conclusions: :
A slow type of nicotinic transmission was used to mediate stage II retinal waves during development and seemed to be associated with extra- or peri-synaptic transmission. A fast type of nicotinic transmission is used for synaptic transmission between SACs and DSGCs. This fast form was distinct (and not developed) from the early slow form of transmission. The GABAergic, but not the cholinergic, transmission from SACs to DSGCs seemed to have attained a spatial asymmetry long before eye opening. GABAregic transmission in prenatal rabbits is under investigation.
Keywords: acetylcholine • amacrine cells • ganglion cells