Tectospinal Tract

Retrograde labeling of tectospinal tract neurons could not show any differences between the normal and reeler mice, suggesting that the deep layers of the reeler SC are cytoarchitectually normal.  

TO1 neurons have widefield dendritic trees that arborize in the layers of retinal afferents and form a neuropil in the superficial layer; axons constitute the crossed tectospinal tract. Dendrites of TO2 cells have the largest dendritic trees that arborize in the intermediate and deep layers of retinal afferents; axons constitute a lateral uncrossed tectospinal tract. TO3 cells have widefield dendritic trees that arborize in the deep layer of retinal afferents and in the layer of tectal efferents; axons constitute a superficial uncrossed tectospinal tract. TO4 cells have slender primary dendrites and small-field dendritic trees that arborize in the intermediate layers of retinal afferents; axons constitute another lateral uncrossed tectospinal tract.  

Here we show that a behavioural specialization in mammals, predation, is associated with species differences in the fine structure of a single neural pathway, the tectospinal tract. Expansion of these analyses to consider comparisons between taxa at a variety of taxonomic levels gave further support to the idea of a relation between predatory habits and the evolution of the tectospinal tract. In addition, within the primates, the number of neurons in the tectospinal tract was significantly correlated with the proportion of prey in the diet.  

Based on retrograde labeling from the high cervical spinal cord, the inter- and intra-laminar distributions of tectospinal tract (TST) somata within the tectum of 23 mammals and one reptile are described. In general, the present results uphold the idea that the significance of the TST somata, and perhaps of the tectospinal tract itself, is to be found in directing the head so that the retinal area of best vision can be brought to bear on stimuli either almost outside, or about to pass outside, of the area of best vision. The larger and possibly universal predominance of TST somata subserving the lower visual field suggests that the tectospinal tract may be primarily concerned with adjusting the step dimensions of the forelegs to accommodate obstacles to normal progression..  

In seven experiments, multiple injections of PHA-L into different regions of the SC labelled a total of 172 axons in the predorsal bundle; yet only 11 tectospinal tract (TST) axons were found in the upper cervical spinal cord.  

After unilateral ablation of the superior colliculus (SC) in neonatal or adult rats, the reorganization of the tectospinal tract (TST) was examined using the technique of anterograde transport of horseradish peroxidase to which wheat germ agglutinin had been conjugated (WGA-HRP).  

Neither the evolutionary increase in the tectospinal tract along the Carnivora lineage nor the slight decrease along Man's lineage is altered by mathematical corrections for allometric or scaling factors. Of an array of morphological, visual, motor, and ecological traits tested statistically as a possible source of the variation in size of the tectospinal tract, only a primarily carnivorous feeding preference was found to be reliably related. The relatively small number of tectospinal fibers in most mammals in our sample, including the primates, suggests that the tectospinal tract in Man may be quite small, perhaps far too small to warrant continuing description as a "major descending tract.".  

By the 4th postnatal day myelination had commenced in many sensory tracts and in the trigeminal root, in the tectospinal tract, in the inferior cerebellar peduncle and in the roots of most cranial motor nerves.  

Two sizes of electrode were implanted in the tectospinal tract of rats and the average currents to produce circling at 0.2 and 0.4 turns/s were measured.  

Pretectal axons to NRTP descend lateral to the MLF and tectospinal tract.  

In tests on 111 units this has provided a basis for differentiating between cells of origin of the tectospinal tract and the tectoreticular system within the superior colliculus. Evidence has also been obtained to suggest that the tectoreticular system, in part, consists of collaterals of the tectospinal tract..  

Such descending axons can be grouped into two major bundles or tracts, i.e., the ipsilateral tectopontine-tectobulbar tract and the crossed tectospinal tract (or the predorsal bundle). Axons which comprise the tectospinal tract, or the predorsal bundle, cross within the dorsal tegmental decussation and descend within the brainstem in a position slightly lateral to the midline.  

At necropsy a single small pontine end-zone infarction was found, involving the medial part of the right paramedian pontine reticular formation, the tectospinal tract and the ventral part of the right medial longitudinal fasciculus.  

Cells of origin of the tectospinal tract were identified within the superior colliculus and tegmentum by antidromic excitation from the upper cervical cord. Almost 50% of the cells of origin of the tectospinal tract receive a convergent input from extraocular muscle and neck muscle afferents and from the retina.  

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