William J. Anderson

Early effects of x-irradiation of the cerebellum in infant rats: Decimation and reconstitution of the external granular layer

Abstract The cerebellum of rats was irradiated daily with 200 r x-ray from the day of birth, with the number of exposures ranging from one to ten. The animals were killed 2 and 24 hours, and 4 days after the last exposure, and at the constant ages of 8 and 10 days. The cell population of the external granular layer was drastically reduced 24 hours after irradiation with a single dose of 200 r, and it was subtotally and maximally destroyed 24 hours after the second exposure. In animals exposed up to 5 × 200 r, recovery of the external granular layer was evident 4 days after the last irradiation; the extent of recovery was inversely related to the number of doses received. The width of the external granular layer was normal or supernormal by 10 days of age in all these groups, though planimetric measurements showed that the total area occupied by this proliferative matrix was subnormal (due to the decreased surface area of the cerebellum) and it was inversely related to the number of doses received. Some evidence was obtained that after some delay the recovered cells differentiated, and led to the development of the molecular and internal granular layers. Several abnormalities were noted in the morphology of the developing cerebellar cortex after exposure to a higher number of x-ray doses, such as abnormal folding of the cerebellar cortex and the massing and disoriented growth of Purkinje cells, and explanations were offered for these effects.

Irradiation of the cerebellum in infant rats with low-level X-ray: Histological and cytological effects during infancy and adulthood

Abstract We examined the morphological consequences of focal irradiation of the cerebellum with successive daily doses of low-level X-ray in 10-, 30-, and 90-day-old rats. The subtotally eliminated external granular layer was reconstituted by 10 days in animals exposed to 1–2 × 200 r and there was little or no reduction in the total area of the cerebellar cortex and its various layers at 30 and 90 days. With higher number of successive daily doses there was (in the affected lobes) decreasingly less regeneration of the external granular layer at 10 days, and there was a proportional reduction in the areas occupied by the molecular and internal granular layers at 30 and 90 days. The reduction in the population of granule cells in adult rats was also proportional to the number of daily exposures during infancy. These lasting effects were attributed not to greater damage done to the germinal layer by the higher number of daily exposures but to a postponement of recovery and hence reduction in the time left for regeneration when cerebellar neurogenesis comes to an end (about 21 days). Even with the highest number of exposures, the number of Purkinje cells was not affected. In the animals exposed to more than two doses of 200 r, lasting morphological and cytological changes were produced. The abnormalities could be traced to events associated with the time course of cell death and regeneration in the external granular layer and to the autonomous but disoriented growth of the Purkinje cells.

Morphological characteristics of dendrite bundles in the lumbar spinal cord of the rat

The finding of motoneuron dendrites organized into small compact bundles in cats, monkeys and pigs suggested that a study of this phenomenon in rats should be undertaken. An analysis was performed with electron microscopy, light microscopy and Golgi methods. An extensive dendrite bundle organization was found in the sixth lumbar segment of the spinal cord. Two discrete bundles were localized bilaterally: a lateral bundle in the ventrolateral gray substance, and a medial bundle in the ventral funiculus. The lateral bundle was found to consist of longitudinally oriented dendrites, neurocytons, glial cells and capillaries. As many as 1678 closely packed dendrites were observed in the lateral bundle. The medial bundle contained dendrites directed across the midline and also longitudinally oriented dendrites. Neurocytons in the medial dendrite bundle were found singly or in clusters, and many radiating bundles of dendrites were observed projecting toward the lateral bundle. Golgi analysis confirmed that neurons in the lateral bundle had most of their dendrites oriented longitudinally. It was possible to trace several dendrites into the lateral bundle from dorsally and medially lying neurons. Electron microscopy substantiated the fact that the bundles were composed of dendrites. It also revealed numerous dendrodendritic and dendrosomatic contacts which were desmosomal in type as well as an abundance of small unidentified processes. Various functions which have been attributed to the dendrite bundles are discussed.

Retardation of cerebellar and motor development by focal X-irradiation during infancy

Abstract The cerebellum of rats was irradiated daily with 150 r X-ray from birth for 2, 4, 6, 8 and 10 days. This led to a proportional decrease in the mature weight of the cerebellum due to interference with the acquisition of cerebellar microneurons. The motor development of these animals was observed from 11–30 days in an open field situation. It was also assessed in tests in which they had either to climb up on a rod or descend on a rope. The animals exposed to the highest number of doses persisted longer in displaying infantile motor patterns and showed a reduced frequency or duration in the exhibition of various motor skills. They also tended to drag their hindfeet, fell during locomotion and were severely handicapped in climbing. The deficits of the intermediate radiation groups was of a lower magnitude, and the low radiation groups were handicapped only in tasks which depend predominantly on the coordination of the hindlimbs.

Retardation of cerebellar and motor development in rats by focal X-irradiation beginning at four days

Abstract The cerebellum of rats was irradiated daily from four to thirteen days of age. This resulted in subtotal elimination of the postnatally-formed interneurons, with minimal distortion of the lobular and laminar organization of the cerebellar cortex. The population of Purkinje and Golgi cells was slightly reduced, and Purkinje cells were found in various pathological states. The motor development of these animals was observed between 14–30 days of age by recording various spontaneous activities, and were tested on a vertical rope on which they had to descend to the ground, and a vertical rod on which they had to climb up to a landing platform. The irradiated animals tended to be more active than the controls in locomotion, but they displayed severe coordination difficulties which gradually imporved in some tests as they became older. They fell more while in motion or at rest and displayed difficulty in transferring their body from a rod on which they had climbed up, to a landing platform, because of the inability of the hindlimbs to support the body.