<p>The mechanisms underlying light-adaptation in goldfish retinal horizontal cells were investigated. The receptive-field size of horizontal cells was reduced by background illumination, but by a mechanism not mediated by dopamine, the only known modulator of horizontal cell receptive-field size. Light-induced changes in receptive-field size were shown to vary depending on which of two adaptation states the retina was in prior to background illumination. Presentation of background illumination to a dark-adapted retina resulted in a light-sensitized retina in which horizontal cell receptive-field size and responsiveness was increased. Application of background illumination to light-sensitized retinas lead to light-adapted retinas, in which horizontal cell receptive-field size was decreased.</p> <p>Two new putative adrenergic neurons were identified immunohistochemically in the goldfish retina. These cells, in particular a new type of interplexiform cell that could provide direct synaptic input to horizontal cells, raised the possibility that the light-dependent reduction in horizontal cell receptive-field size might be due to the release of an adrenergic transmitter. However, studies showed that the effects of adrenergic transmitters on horizontal cells were more consistent with an action at dopamine receptors than at adrenoreceptors. Because it was previously shown that the light-dependent reduction in horizontal cell receptive-field size did not depend on the action of dopamine, it was concluded that the adrenergic neurons are unlikely to be involved in this change.</p> <p>Studies on the effects of nitric oxide suggest that this free radical gas may be involved in the background illumination-induced reduction of horizontal cell receptive-field size. This was demonstrated by showing that horizontal cells are immunoreactive for nitric oxide synthase and that two inhibitors of nitric oxide synthase reduced the effects of background illumination on horizontal cell receptive-field size.</p> / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/7498 |
| Date | 10 1900 |
| Creators | Baldridge, Harold William |
| Contributors | Ball, Alexander K., Medical Sciences |
| Source Sets | McMaster University |
| Detected Language | English |
| Type | thesis |
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