Neural organization and neural interactions in mammalian retinas are investigated using intracellular recording and staining techniques, electron-microscopic (EM) and pharmacological approaches. In the inner plexiform layer of cat retina amacrine cells with depolarizing responses to both onset ant offset of photic stimuli (ON-OFF cells) are filled with horseradish peroxidase and identified as wide-field, monostratified types (Al9). In addition to a medium-field dendritic arbor surrounding the soma, A19 amacrine cells have multiple axon-like processes extending from dendritic tips. Impulses of variable height accompany depolarizations, and also occur spontaneously. Current clamp reveals that depolarizations result from a conductance increase. In the EM A19 cells synapse on alpha ganglion cells (GC's), and may energize their nonlinear subunits. OFF-beta cat retinal GC's reveal about equal numbers of amacrine and bipolar cell inputs whereas OFF-alpha GC's receive mainly amacrine input, as seen in serial EM reconstructions. OFF-alpha cells receive input from only one type of bipolar cell whereas OFF-beta cells receive input from two types. OFF-depolarizations arise from a conductance increase. Investigations of ON-alpha GC's reveal about 2000 chemical synapses distributed in dome-like fashion across the dendritic field. This dome-shaped synaptic weighting, as convolved with dendritic, and electrotonic factors, contributes to the Gaussian profile of alpha-GC receptive-field sensitivity. In the outer plexiform levers of cat and rabbit retinas, the dopaminergic agonist apomorphine depolarizes horizontal cells and both suppresses and delays cone-flicker signals. The effect is mimicked by SKF38393 and may be D1-like. The potentiating effects on cone signals of rod-desensitizing backgrounds is modelled by a feedback circuit in which dark-adapted, depolarized horizontal cells, release a substance that antagonizes cone feed-forward synaptic transmission.
| 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 |
