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Vis Neurosci. 1990 Apr;4(4):367-77.

A correlative study of the physiology and morphology of the retinotectal pathway of the perch.

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Department of Physiological Sciences, University of Manchester, United Kingdom.


The anatomy and physiology of the retinotectal pathway of the perch was investigated using physiological and histological techniques. Massed responses of the optic nerve to single shocks exhibited five distinct peaks. Single-unit responses to shocks indicate two groups of fast fibers correlating well with peaks I and II of the massed response. The flash-evoked response in nerve and tectum has three major phases (PSPI-III), with a marked low-threshold fast component. Patterns of flash-evoked response from single fibers vary, but the responses of fast transient fibers coincide with the timing of PSPI, and longer latency groups with PSPII-III. Units reflexly activated by efferents were also seen, and 12% of units were photically inexcitable. Surprisingly, few fibers responded well to a scanned spot light, unlike tectal cells, and receptive fields were often large (greater than 70 deg). ON/OFF responses, evoked either by whole field or local illumination, were much commoner than pure ON or OFF responses. Effects of electrical stimulation or cautery of the tectum on the flash-evoked response of fiber bundles, via the efferents were marginal, but repetitive stimulation or section of the optic nerve produced clear-cut deficits in the slow components of the flash-evoked response of the nerve. Stimulation of the eighth nerve produced a complex long-latency, large-amplitude response in the optic nerve. The fiber spectrum of the optic nerve taken from electron micrographs revealed the presence of a relatively small group (less than 1%) of thick fibers with diameters between 3 microns and 10 microns that could be correlated with fast responses recorded from the optic nerve, and the remainder with axon diameters down to 0.2 microns providing the slow responses. The distribution of cell-body diameters from sectioned and wholemount material indicated a marked distinction between small and large ganglion cells. The total number of fibers in the nerve was estimated 868,840.

[Indexed for MEDLINE]

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