Amacrine cells constitute a unique class of axonless neurons whose pre- and postsynaptic contacts subserve visual processing in the inner retina. Although the amacrine cells have been the subject of numerous morphological and pharmacological studies, there have been surprisingly few studies which directly examined their physiology. As a result, the full range of amacrine cell response properties has yet to be determined and much of our knowledge of amacrine cell function has been attained indirectly, from physiological work directed at the ganglion cells. A multidisciplinary approach is proposed to study the physiology, morphology, and pharmacological interactions of amacrine cells in the rabbit retina. The long-term goal of this research is to elucidate how amacrine cells influence bipolar to ganglion cell transmission, and how these interactions contribute to the formation of ganglion cell responses in the mammalian retina. Three major specific aims are proposed.
The first aim i s to determine the different light-evoked response and receptive field properties displayed by rabbit amacrine cells. This will be accomplished by obtaining intracellular recordings from amacrine cells in the rabbit retina-eyecup during presentation of various photic stimuli. Amacrine cell receptive fields will be described utilizing the same criteria used in prior studies to characterize ganglion cells, including complex response properties. My preliminary data indicate that rabbit amacrine cells exhibit some of the complex receptive field properties formerly thought to be limited to ganglion cells, such as direction and orientation selectivity.
The second aim i s to determine the morphology of amacrine cells and correlate this with their response properties. Physiologically-characterized amacrine cells will be labelled with horseradish peroxidase (HRP) to visualize their dendritic architectures. The neuronal profiles obtained will then be compared to amacrine cells described in Golgi and histochemical studies whose synaptic connections and/or neurotransmitters are known.
The third aim i s to examine the actions of the putative amacrine cell transmitter, GABA and acetylcholine, on amacrine cell responses. This work will elucidate the extent and specifically of the interconnections between amacrine cells subserved by these transmitters. Comparison of these results with those of prior pharmacological studies of rabbit ganglion cells will be made to localize more precisely the sites of specific transmittter effects, and to provide insights into which ganglion cell response properties are dependent on amacrine cell input.
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