Effects of low-level x-irradiation on cat cerebella at different postnatal intervals. III. Changes in the morphology of interneurons in the molecular layer

Naturally occurring parvovirus-associated feline hypogranular cerebellar hypoplasia-- A comparison to experimentally-induced lesions using immunohistology

Three cases of feline cerebellar hypoplasia are presented. At the time of examination, the ages of the cats ranged from 2 months to 1 year. Necropsy revealed cerebellar and pons hypoplasia. Polymerase chain reaction for parvoviral deoxyribonucleic acid was positive in cerebellar tissue. Cell-specific immunolabeling was used to characterize the lesions, which were characterized into 2 types. In type 1 lesions, the cortex was nearly agranular, with an extremely thin molecular layer; the Purkinje cells were randomly placed and oriented, and their stunted main dendrite produced a thorn-covered atrophic dendritic tree; the basket cell axons ran randomly and had dysmorphic endings; and myelinated fibers were severely reduced in folia axes. In type 2 lesions, the cortex was hypogranular; the Purkinje cells were linearly organized, but their main dendrite extended too far in the molecular layer before giving up smooth, bent secondary dendrites; many basket cells were located along the cerebellar surface, and their axons ran at right angle to the surface; myelinated fibers were moderately reduced. Defects in climbing fiber synapse translocation and elimination were evident in both types of lesion. This immunohistologic study allowed a comparison between lesions in these spontaneous cerebellar hypoplasia cases with those documented when using silver impregnation studies after perinatal experimental cerebellar damage. Such a comparison is consistent with viral infection that occurs before birth in all 3 cases. Progress in parvovirus biology knowledge suggests that viral NS1 protein cytotoxicity might explain degenerative changes in the Purkinje cells that were present, in addition to the development defect.

Alterations in the postnatal development of the cerebellar cortex due to zinc deficiency. III. Impaired dendritic differentiation of basket and stellate cells

The effects of zinc deficiency and undernutrition on the dendritic differentiation of basket and stellate cells were studied in 21-day-old rats. A morphometric analysis of the dendritic branching of basket and stellate neurons was used that took into account the cell's position in the molecular layer. Zinc deficiency and undernutrition during the suckling period impaired the dendritic differentiation of cerebellar basket and stellate cells. The effects of zinc deficiency were not due totally to the reduced food intake of lactating dams. In the lower 65-75% of the molecular layer of zinc-deficient (ZD) pups, the dendritic field area, the total dendritic length and the number of branches per interneuron were reduced by 45-61%. In the lower 50-60% of the molecular layer, undernutrition reduced the dendritic field area, the total dendritic length and the number of branches per neuron by 32-44%. A comparison of ZD and undernourished (pair-fed) pups indicated that the dendritic field area and total dendritic length of neurons of ZD animals were 43% and 30% smaller in the lower half of the molecular layer. The number of branches per neuron was not significantly different between ZD and undernourished animals. The area of the soma was unaffected by dietary treatment. A delay in the onset of dendritic differentiation and a retarded rate of dendritic growth were considered possible mechanisms for the impaired dendritic differentiation.

Effects of low-level x-irradiation on cat cerebella at different postnatal intervals. II. Changes in Purkinje cell morphology

The whole-head of infant kittens was irradiated with fractionated doses of 150 R and 200 R at different postnatal intervals. Experimental age conditions consisted of an irradiated newborn, 1-week, 2-week, 3-week, and a 4-week age condition while the age of sacrifice remained constant at 70 days. The molecular layer thickness was reduced by 47% in the newborn, 40% in the 1-week group, 17% in the 2-week group, 19% in the 3-week group and by 9% in the 4-week group. An evaluation of Golgi impregnated material revealed that the dendritic arborizations of purkinje cells were consistently reduced the earlier the age at which radiation was begun. A reduction in spiny branchlets was seen in all of the experimental conditions. All experimental age conditions displayed the phenomenon of dendritic "damming" at the pial surface, which consisted of an excessive crowding of spiny branches at this level. An increased growth of the primary dendrite before branching tood place was seen in the newborn and 1-week group. This became less but was still significant in the 2-week group. A correlation of this phenomenon with the presence or lack of stellate cells is disclssed. Purkinje cells with two or more dendrites emerging from their soma were classified and analyzed separately. It was found that the primary dendritic branching in these cells often followed separate morphological patterns and appeared to be independent of each other. Climbing fibers were found to conform to the abnormal dendritic arborizations of the Purkinje cells, and were reduced in complexity in the early radiation treatment groups. This suggested that climbing fibers had no influence upon the dendritic growth pattern, but instead were under the influence of the Purkinje cell dendritic growth.

Effects of low-level x-irradiation on cat cerebella at different postnatal intervals. I. Quantitative evaluation of morphological changes

Whole head fractionated doses of 200 r and 150 r were initiated postnatally in five experimental age groups (birth, 1-week, 2-week, 3-week and 4-week) and continued over a period of 14 or 20 days to prevent reconstitution of the external granular layer. Animals irradiated at birth displayed minor deficits in behavior, which included ataxia, tremor, hypertonus and dysmetria, while animals irradiated at 1-week showed only mild symptoms of hypermetria. All other animals displayed no motor deficits. Animals irradiated at birth had smaller eyes and ears, a reduction in the size of the entire head and were susceptible to seizures. All animals were sacrified at 70 days of age. The cerebellum was found to be reduced in size and weight, the greatest deficit being seen in animals x-irradiated at the very early ages. Newborn condition animals were found to have large compliments of interneurons in the molecular layer, an established internal granular layer, and Purkinje cells were found to have a normal orientation, position, and to be unreduced in number or size. Total granule cell deficits were found to range from 83% at birth to 29% at four weeks. Quantitative changes for the molecular layer, internal granular layer, medullary layer, Purkinje cell to granule cell ratio, and granule cell density, all depicted the greatest changes in the newborn, 1-week and 2-week conditions. This experiment confirmed that the critical period in the development at which damage would result in behavioral abnormalities was from birth to five days, while for neuroanatomical abnormalities, this critical period was from birth to 18 days.