Elsevier

Neuroscience

Volume 5, Issue 6, June 1980, Pages 1067-1084
Neuroscience

Quantitative analysis of optic terminal profile distribution within the pigeon optic tectum

https://doi.org/10.1016/0306-4522(80)90187-6Get rights and content

Abstract

Two regions of the pigeon optic tectum, caudoventral and rostrodorsal, were examined electron microscopically in an attempt to clarify quantitatively previous findings on the distribution of optic afferent terminal profiles within the retino-receptive zone. Major terminations of optic axons were found in sublaminae IIb, c and d of both the caudoventral and the rostrodorsal tectum. Multiple peaks of such terminal concentrations occur in sublayers a, b and c: in the rostrodorsal field they lie largely centrally within sublayers b and c, whereas in the caudoventral tectum they lie at the a/b, b/c and c/d boundaries. The distribution to sublayer IId tends to be maximal within its superficial and deep extremities, especially in the caudoventral tectum. Sublayer f contains a more noticeable concentration of optic terminals in the caudoventral than in the rostrodorsal tectum. The retinal input is distributed more nearly equally between sublayers a, b and c combined and sublayer d in the rostrodorsal tectum than in the caudoventral field, where sublayer d is the major target. Other differences exist between the two regions: the caudoventral tectum shows a higher density of terminal profiles/unit area than the rostrodorsal tectum, and, in the deeper parts of the retino-receptive zone, a higher density per unit volume; in general the profiles in deeper sublayers are also larger than those in the rostrodorsal tectum. Numbers of synaptic thickenings (as profiles) per terminal profile show less clear differences between tectal regions. Interlaminar differences in the synaptic thickening/terminal profile ratios are more obvious: in sublamina IIb especially, terminal profiles with multiple synaptic thickenings are more common than elsewhere.

The results are discussed in relation to previous morphological and electrophysiological studies and an attempt is made to resolve some of the discrepancies in the previous studies.

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