I. Dopamine desensitizes the retina for light adaptation, while cannabinoids may enhance photosensitivity. In goldfish, dopamine D1- and cannabinoid CB1 receptors are on the pre-synaptic membrane of cones and Mb bipolar cells and, in bipolar cells, D1 and CB1 ligands have opposing actions on membrane currents. Hypothesis: Dopamine and cannabinoids are opposing neuromodulators that affect neural adaptation in the retina.
Specific Aim 1. For bipolar cells, determine the interaction of dopamine and cannabinoid ligands for control and dopamine-depleted retinas by using whole-cell recording in a retinal slice and calcium imaging with Fura-2 in isolated cells. Attention also will be paid to sequestering of G-proteins by CB1 receptors.
Specific Aim 2. For cones, continue studies on dopamine and CBl-mediated effects on membrane currents, effects of dopamine depletion, and the subcellular distribution of GABAA receptor subunits. This will be investigated by whole-cell recording from cones in the retinal slice, measurement of calcium flux with Fura-2 in isolated cells. Attention will be paid to drug interactions and G-protein sequestering. GABAA receptor subunits ((1, (1, (3, and () will be localized by electron microscopy immunocytochemistry (EM-ICC) vis a vis CB1 receptors and in response to dopamine depletion. II. The vanilloid receptor 1 (VR1), a member of the Drosophila TRP family, and caveolin-1, a constituent membrane in caveolae, appear restricted to photoreceptor ribbons. Both proteins may be associated with membrane channels. In frog cones, caffeine-sensitive Ca2+ stores are present, and calcium has been localized to the ribbons. As smooth endoplasmic reticulum is not plentiful in goldfish spherules or pedicles, we propose to determine:
Specific Aim 3, if photoreceptor synaptic ribbons contain Ca2+ and the morphological substrates to serve as a reservoir for calcium uptake and subsequent release, and if this reservoir can be modulated pharmacologically.
This aim will be accomplished by EM-ICC, calcium imaging with Fura-2 and soft scanning X-ray microcopy to visualize concentrations of intracellular calcium. These studies will provide insight on two novel ideas: 1. cannabinoids and dopamine interact to modulate retinal adaptation in cones and bipolar cells, and 2. synaptic ribbons serve as a calcium store for transmitter release. As Parkinson's is a disease of CNS dopamine, insight also will be obtained on the function of dopamine-compromised retinas. ? ?
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