The goals of the research proposal include an investigation of the interaction of glutamate and glutamate-like agonists at the glutamate receptor on horizontal cells isolated from the catfish retina. Experments will be carried out to examine the nature of the desensitization that occurs at the glutamate receptor in the presence of high (greater than 100 MuM) concentrations glutamate and the relationship of Mg on the desensitization process. In addition, the glutamate-like analogs kainate and quisqualate will be investigated with regards to this desensitization process. Standard low resistance single electrode voltage clamp methods will be used to record the agonist activated currents in the presence and absence of Mg. It is proposed to examine the changes in filter characteristics of isolated horizontal cells by measuring the impedance of the cell using white noise current injection. These experiments will be done to better characterize the effect of the voltage sensitive conductances on cell impedance properties. In addition, this same method will be used to investigate the changes in electrontonic coupling initiated by dopamine at electrotonic synapses made between horizontal cells. These experiments will be carried out on samll groups (2-5) of isolated but coupled horizontal cells as well as horizontal cells in the intact retina. The role of cAMP in the dopamine initiated uncoupling process will be investigated by using cAMP agonists and antagonists. In conjunction with these experiments, we plan to examine the structure of the electrontonic coupling using the electron microscope.

National Institute of Health (NIH)
National Eye Institute (NEI)
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Visual Sciences A Study Section (VISA)
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University of Texas Medical Br Galveston
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Micci, M A; Christensen, B N (1996) Distribution of the inositol trisphosphate receptor in the catfish retina. Brain Res 720:139-47
Linn, C P; Christensen, B N (1992) Excitatory amino acid regulation of intracellular Ca2+ in isolated catfish cone horizontal cells measured under voltage- and concentration-clamp conditions. J Neurosci 12:2156-64
O'Dell, T J; Christensen, B N (1989) A voltage-clamp study of isolated stingray horizontal cell non-NMDA excitatory amino acid receptors. J Neurophysiol 61:162-72
O'Dell, T J; Christensen, B N (1989) Horizontal cells isolated from catfish retina contain two types of excitatory amino acid receptors. J Neurophysiol 61:1097-109
O'Dell, T J; Christensen, B N (1988) Mecamylamine is a selective non-competitive antagonist of N-methyl-D-aspartate- and aspartate-induced currents in horizontal cells dissociated from the catfish retina. Neurosci Lett 94:93-8
Sakuranaga, M; Ando, Y; Naka, K (1987) Dynamics of the ganglion cell response in the catfish and frog retinas. J Gen Physiol 90:229-59
Hals, G; Christensen, B N; O'Dell, T et al. (1986) Voltage-clamp analysis of currents produced by glutamate and some glutamate analogues on horizontal cells isolated from the catfish retina. J Neurophysiol 56:19-31
Hidaka, S; Christensen, B N; Naka, K (1986) The synaptic ultrastructure in the outer plexiform layer of the catfish retina: a three-dimensional study with HVEM and conventional EM of Golgi-impregnated bipolar and horizontal cells. J Comp Neurol 247:181-99
O'Dell, T; Christensen, B N (1986) N-methyl-D-aspartate receptors coexist with kainate and quisqualate receptors on single isolated catfish horizontal cells. Brain Res 381:359-62
Sakuranaga, M; Sato, S; Hida, E et al. (1986) Nonlinear analysis: mathematical theory and biological applications. Crit Rev Biomed Eng 14:127-84

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