The Journal of comparative neurology
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Light- or dark-adapted goldfish (Carassius auratus) retinas were treated with dopamine, which is believed to uncouple horizontal cells via D1 receptors, or with the dopamine antagonist haloperidol. Aldehyde-fixed retinas were freeze-fractured and the replicas examined by electron microscopy to identify horizontal gap junctions. The density (number per micron2) of intra-membrane particles of horizontal cell soma gap junctions was significantly lower in light-adapted and dopamine-treated retinas than in dark-adapted and haloperidol-treated retinas. ⋯ Unlike horizontal cell somas, horizontal cell axon terminals did not show consistent changes in gap junction particle density with light- or dark-adaptation. Although the data suggests that there may be a reduction in axon terminal gap junction particle density with dopamine treatment, this effect is not reversible with haloperidol treatment. Our results suggest that the regulation of gap junctions may differ at two sites within the same cell.
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Thalamocortical projections to four tonotopic fields (A, AI, P, and VP) of the cat auditory cortex were studied by using combined microelectrode mapping and retrograde axonal transport techniques. Horseradish peroxidase (HRP) or HRP combined with either tritiated bovine serum albumin or nuclear yellow was injected into identified best-frequency sites of one or two different fields in the same brain. Arrays of labeled neurons were related to thalamic nuclei defined on the basis of their cytoarchitecture and physiology. ⋯ Field P receives a major projection from the caudal half of V, and from a thin band along the dorsal border of rostral V. Field AI receives a major projection from most of the rostral one-half of V, and smaller areas in Po and the caudal half of V exclusive of its caudal pole. Field A receives a major projection from most of Po.(ABSTRACT TRUNCATED AT 400 WORDS)