Neural organization and neural interactions in mammalian retinas are investigated using intracellular electrophysiology, electron microscopy, and pharmacological manipulations. The relation between dendritic and receptive field sizes has been investigated in OFF-alpha and OFF-beta ganglion cells in cat retina. Receptive fields were mapped with slit stimuli and position-amplitude functions fit with Gaussian curves. Center radii (rc) were compared to dendritic-field diameters as revealed by intracellular marking with horseradish peroxidase. For alpha cells, little correlation between dendritic and receptive fields was observed, suggesting that neural factors in addition to dendritic geometries influence receptive field size. A computational model of ON-alpha ganglion cells shows that synaptic input signals must be quantal and dispersed across the dendritic arbor to achieve linear summation. Under these conditions, which occur with near-threshold stimulation, the receptive field is equal to the linear weighted sum of presynaptic receptive fields. The influence of selective D1 and D2 agonists on horizontal cell responses has been observed in cat and rabbit retinas. The D2 agonist LY171555 selectively enhances rod signal components at low stimulus intensities while leaving unaffected cone signal components seen at high intensities. The Dl agonist SKF38393 also enhances rod signals at low concentrations, but at higher concentrations, suppresses cone signals in addition. These effects point to multifaceted regulation of outer plexiform layer circuitry by dopamine receptors. The influence of GABAergic substances on responses of cat retinal horizontal cells has also been studied. Of particular note, dAVA, a putative GABA-A agonist and GABA-B antagonist attenuates and delays light responses, while bicuculline (but not its methyl halide) induces exaggerated depolarizing events at stimulus OFF. Bicuculline does not antagonize dAVA, however, suggestive of multiple sites of action for these nonclassical effects.
| Connaughton, V P; Graham, D; Nelson, R (2004) Identification and morphological classification of horizontal, bipolar, and amacrine cells within the zebrafish retina. J Comp Neurol 477:371-85 |
| Kolb, H; Nelson, R; Ahnelt, P et al. (2001) Cellular organization of the vertebrate retina. Prog Brain Res 131:3-26 |
| Nelson, R; Janis, A T; Behar, T N et al. (2001) Physiological responses associated with kainate receptor immunoreactivity in dissociated zebrafish retinal neurons: a voltage probe study. Prog Brain Res 131:255-65 |
| Connaughton, V P; Nelson, R (2000) Axonal stratification patterns and glutamate-gated conductance mechanisms in zebrafish retinal bipolar cells. J Physiol 524 Pt 1:135-46 |
| Nelson, R; Schaffner, A E; Li, Y X et al. (1999) Distribution of GABA(C)-like responses among acutely dissociated rat retinal neurons. Vis Neurosci 16:179-90 |
