Retrograde degeneration of primary optic fibers in the cat

A re-evaluation of the question of ascending fibers in the pyramidal tract

In 1952 we published a study in the cat with the Glees method, demonstrating the occurrence of degenerating fibers in the pyramidal tract rostral to transections of the tract in the spinal cord. These fibers were interpreted as spinocortical fibers, which have also been described in man. However, other authors have disputed the existence of such fibers. In an attempt to provide more information about this subject, multiple injections of horseradish peroxidase (free and lectin-labeled) were made in the sensorimotor cortex of 4 cats. No retrogradely labeled cells were found in the spinal cord in these cases. Our present and previously reported findings are discussed in the light of other studies of pathological changes in fiber tracts within the central nervous system. Although the present experiments were negative, the degenerating axons previously observed by us in silver sections from the pyramid, pons and internal capsule after lesions of the pyramidal tract in the spinal cord, can not be satisfactorily explained as evidence of retrograde, indirect Wallerian, degeneration of corticospinal fibers.

The possibility of centrifugal projections to the retina in the rat

In rats, glutamic acid decarboxylase activity increased in the proximal portion of the optic nerve after its ligation, whereas the activities of choline acetyltransferase and tyrosine hydroxylase remained constant. Possible centrifugal neurons to the retina are GABAergic.

The accessory optic fiber system of the golden hamster with special reference to retinohypothalamic projection

The hamster accessory optic fiber system has been investigated with the use of de Olmos-Ingram and Fink-Heimer silver methods following the production of unilateral ocular enucleation. It was found that this fiber system consists of both crossed and uncrossed inferior and superior fasciculi. The fibers of the inferior fasciculus (anterior accessory optic tract) run along the medial edge of the cerebral peduncle and terminate within the medial terminal nucleus of the accessory optic system. The fibers of the superior fasciculus (posterior accessory optic tract) leave the main optic tract, pass superficially over the medial geniculate nucleus and the cerebral peduncle; they synapse within the dorsal, the lateral and the medial terminal accessory optic nuclei. The presence of a retinohypothalamic tract could not be confirmed.

Thalamic projections of the dorsomedial prefrontal cortex in the rhesus monkey (Macaca mulatta)

Cortical aspirations were made of the dorsomedial prefrontal sector in the rhesus monkey and the resultant anterograde and retrograde degeneration plotted. Retrograde changes were mapped using both cresyl violet and modified Fink-Heimer techniques. Following large dorsomedial lesions, small numbers of degenerating fibers were traced through the medial part of the magnocellular ventral anterior nucleus (VAmc) and the ventral part of the internal medullary lamina surrounding the anterior nuclei. Degenerating fibers were also traced medially through the inferior thalamic peduncle and rostrodorsally through the basal thalamic region into the mediodorsal nucleus. All pathways converged on areas in the dorsal part of the parvocellular mediodorsal nucleus (MDpc) containing fine-grain dust and argyrophilic neurons, reactions usually associated with retrograde degenerative changes. Sparse fiber degeneration was also noted in the ventral part of the magnocellular mediodorsal nucleus (MDmc). After a longer survival period, slight to moderate cell loss and gliosis were seen in MDpc along with an increase in the number of degenerating fibers passing through the medial part of VAmc. Rostral dorsomedial lesions resulted in small numbers of degenerating fibers in the medial part of VAmc; no degenerating fibers appeared in the basal thalamic region. Fine-grain dust was noted in the dorsal part of MDpc along with sparse preterminal degeneration in the dorsal and ventral parts of MDpc and MDmc respectively. Following caudal dorsomedial lesions, fiber degeneration was traced through the medial part of VAmc and through the inferior thalamic peduncle and basal thalamic regions to areas of degenerating preterminals in the dorsal part of MDpc. Sparse fiber degeneration was also noted in MDmc. No evidence of cell loss and gliosis or increased numbers of degenerated fibers was noted following longer survival periods. Dorsolateral and orbital lesions resulted in large areas of fine-grain dust, argyrophilic neurons, and severe cell loss in MDpc and MDmc respectively. A large combined dorsolateral and orbital lesion made 32 days prior to sacrifice of the animal resulted in coarse fiber degeneration in the medial part of VAmc and in the anterior nuclear capsule. Severe cell loss and fiber degeneration were evident in the entire MD. These results suggest that the rostral dorsomedial prefrontal sector receives projections from MDpc while the caudal sector does not. This projection courses dorsally and rostrally through the ventral part of the capsule surrounding the anterior nuclei and into the medial part of VAmc. The entire dorsomedial sector projects sparsely to both MDpc and MDmc. The projection from the rostral medial surface passes through the medial part of VAmc while that from the caudal surface reaches MD both by the dorsal approach through VAmc and through a ventral approach via the inferior thalamic peduncle and the basal thalamic region.

Retrograde changes in the nerve fibers of the dorsal spinocerebellar and spinocervical tracts in the cat

The potential retrograde changes that occur in the proximal segment of transected nerve fibers found in the region of the spinocervical tract (SCT) and in the region of the dorsal spinocerebellar tract (DSCT) after unilateral dorsolateral column (DLC) lesions were studied in kittens and adult cats. Nerve fibers in the region of the SCT and DSCT in the spinal segments caudal to the lesion were studied in transverse sections of Epon embedded material that had been fixed by vascular perfusion with a 4% buffered paraformaldehyde solution, post-fixed in osmium tetroxide, and stained with Azur II-methylene blue. T8 level DLC lesions in the 10-week old kitten resulted in a 14 to 25% decrease in mean fiber diameter in the SCT fibers (larger than or equal to 5 mu) of the T13 level. Retrograde fiber degeneration occurred in the small and large caliber fibers of the DSCT. A 15 to 30% decrease in mean fiber diameter occurred in the DSCT fibers (greater than or equal to 5 mu). The fiber density of the DSCT decreased by 20 to 30% and this could be correlated with a 20% loss of class C neurons (Loewy, '70) and a severe atrophy affecting the remaining 80% of the surviving class C neurons in the L3 segment. Mid-cervical DLC lesions in the 10-week old kitten resulted in a 10% decrease in mean fiber diameter in the SCT fibers (less than or equal to 5 mu), a 15% decrease in mean fiber diameter in the DSCT fibers (less than or equal to 5 mu), and no change in fiber density could be determined despite the finding that these lesions produced about a 10% loss of class C neurons. A T1 level lesion in a 20-week old kitten produced no change in the SCT fibers suggesting that the changes seen in the 10-week old kitten after midcervical lesions were probably age-dependent changes. A 20% decrease in mean fiber diameter (less than 5 mu) and a 6% decrease in fiber density was detected in the DSCT. T13-L1 level DLC lesions in the adult cats resulted in degeneration of some of the large and medium size fibers in the DSCT which was most noticeable at 20 to 25 days after surgery. DLC lesions did not cause degenerative changes in the SCT fibers 5 to 25 days after surgery.