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Orthograde labeling and immunocytochemical techniques were used to study the postnatal spatial and temporal development of corticospinal projections in cats. Findings from the orthograde labeling studies indicate that there are three major phases in the spatial development of corticospinal projections: an early period (1-10 postnatal days) when cortical axons grow into the spinal gray from the white matter; an intermediate period (2-5 postnatal weeks) where corticospinal axons develop terminal arborizations in a rostral to caudal, medial to lateral and intermediate gray to dorsal and ventral horn sequence; and, a late period (6-7 postnatal weeks) during which some corticospinal projections are eliminated. The time period over which cortical axons grow into the spinal cord was determined immunocytochemically using a monoclonal antibody against a microtubule associated protein (MAP 1B) present in growing axons. The corticospinal tracts were strongly immunoreactive for MAP 1B during the first three postnatal weeks. MAP 1B immunostaining of these tracts started to decline in the fourth postnatal week and was completely absent by five weeks of age. These findings indicate that the postnatal development of corticospinal projections is spatially and temporally protracted in cats.

The goal of this study was to develop an aggressive running regimen for modeling osteoarthritis (OA) in rats. Twelve Wistar rats were randomly placed into either a running group or a non-running group to serve as the control. The running rats used a motorized treadmill to run either 30 km in 3 weeks or 55 km in 6 weeks. Each week, the prints of hind paws were obtained when rats were made to walk through a tunnel. The resulting prints were digitalized for analyses of stride length and step angle. The histology of the knees was examined at 3 and 6 weeks and the OA pathology in the knees was quantified by Mankin's score. Osteoarthritic pathology developed in the knees of the running rats, including decreased proteoglycan content, uneven type II collagen distribution in the cartilage matrix, increased MMP-13 expression, expanded calcified cartilage zone, and clefts and defects in articular cartilage. The pathology worsened from running for 3 to 6 weeks. Gait analysis revealed an inverse correlation between paw angle and the grades of OA pathology. In conclusion, excessive running induces joint degeneration and a unique gait pattern in rats.

The organization of the cerebellar nucleocortical projection in the cat and the monkey has been studied using orthograde and retrograde neuroanatomical tracing techniques. Injections of tritiated leucine in the cat cerebellar nuclei orthogradely labeled nucleocortical fibers throughout their course to the cerebellar cortex. Their branch points in the corpus medullare, in the folial white matter, and in the granular layer were evident from the dense, continuous distribution of silver grains overlying these labeled axons. The results from the cat showed that the cerebellar nucleocortical projection is organized principally into three rostrocaudally oriented longitudinal cortical zones. Fastigial nucleocortical fibers were directed principally to the medial 1.5-2.5 mm of the ipsilateral vermis, with a lighter projection to the lateral vermis ipsilaterally and to the medial area of the vermis contralaterally. The interposed nuclei projected mainly to the paravermis-medial hemispheric zone of the cerebellar cortex. Nucleocortical fibers from the posterior interposed nucleus projected principally to the paramedian lobule, to the medial hemispheric area of Crus I and the lobus simplex, and to the flocculus and paraflocculus. Nucleocortical projections from the anterior interposed nucleus coursed to the anterior lobe paravermis and to the ventral folia of the paramedian lobule. A lighter projection from the interposed nuceli was found to the lateral edge of the vermis and into intermediate areas of the hemisphere. Dentatocortical fibers were directed into the lateral folia of Crus I and Crus II of the lateral hemispheric zone, with a ligher projection to intermediate areas of the hemisphere of the posterior lobe and along the lateral edge of the anterior lobe hemisphere. Along the periphery of each cortical zone, the nucleocortical projection from adjacent deep nuclei overlapped slightly. The retrograde transport of horseradish peroxidase (HRP) from injection sites in the lateral hemisphere, in the medial hemisphere--paravermis, and in the vermis labeled neurons localized mainly within the dentate, interposed, and fastigial nuclei, respectively. Retrograde labeling experiments carried out in monkeys indicated that the organization of the nucleocortical projection in this species is different than that of the cat. In the primate, the nucleocortical projection to the lateral hemisphere, to the medial hemisphere--paravermis, and to the vermis appeared to arise principally from the dentate nucleus. There was a secondary input to the paravermis and vermis arising from the interposed and fastigial nuclei, respectively. This evidence suggests that the cerebellar nucleocortical system undergoes a significant phylogenetic change in its organization between the cat and primate. These organization differences are discussed in light of possible functional implications.

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