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J Clos

Publications and source records attributed to J Clos.

72 records · Page 4Linked to original sources
PubMed1980

Effects of thyroid state on the formation and early morphological development of Bergmann glia in the developing rat cerebellum.

The formation and morphological maturation of Bergmann glia cells, which might play an important role in the histogenesis of the cerebellar cortex, was studied by histological and electron microscopic techniques in the cerebellum of normal young rats and animals made hypothyroid since the 18th day of gestation or hyperthyroid since birth. In comparison with controls, an acceleration in the morphological development of Bergmann glia cells was observed in the hyperthyroid animals; on the contrary, in the thyroid-deficient rats, the formation and morphological maturation of these cells were retarded and their final number was increased.

Animals↗
PubMed1979

Uptake and metabolism of exogenous and endogenous thyroxine in the brain of young rats.

The uptake of labelled exogenous thyroxine by the brain was determined in 10- and 30-day-old rats. It was three times higher and thyroxine was more deiodinated on day 10 than on day 30. On the other hand, the endogenous hormonal iodine content was estimated in both the brain and the isolated cortical neurones in the young rats of the same ages equilibrated with 125I. On day 10, brain and neurones contained five times more thyroid hormones than on day 30. These results are discussed in the context of the relations previously discovered between development of thyroid function and brain maturation.

Aging↗
PubMed1977

Effects of undernutrition on cell formation in the rat brain and specially on cellular composition of the cerebellum.

In 35-day-old rats which were undernourished by quantitative restriction of the mother's diet from the 6th day of gestation, the wet weight and the DNA content of the cerebellum were slightly more decreased than those of the cerebrum. Cell growth (estimated from the DNA concentration and form the ratios of RNA and protein to DNA) was significantly affected by food deprivation only in the cerebellum. In the cerebullar cortex, the number of Purkinje, Golgi and stellate cells were unchanged. The numbers of other cell tyes were affected to various extents: there were significantly less granules and basket cells per Purkinje cell, and a still more marked hypoplasia of glia involving the glial cells of the molecular layer, as well as the astrocytes of the internal granular layer and the Bergmann cells of the Purkinje cell layer. Finally, the total number of glial cells within the cortex was decreased by 44% against 13% for neurones. These effects of undernutrition on cell acquisition within the brain, and on the cellular composition of the cerebellum, contrast with those of thyroid deficiency.

Animals↗
PubMed1977

Effects of methylazoxymethanol given at different stages of postnatal life on development of the rat brain. Comparison with those of thyroid deficiency.

Newborn rats were treated at different stages of their development with low doses of methylazoxymethanol acetate. The postnatal increase of the DNA content of the cerebrum did not differ from that of controls. In the cerebellum, the DNA content was transitorily reduced, but later, the external granular layer became thicker and DNA deposition increased in comparison with controls; finally, the cerebellar DNA returned to a normal value. Morphological abnormalities of the cerebellum, abnormal orientation of migrating cells, scattering of Purkinje cell bodies within the internal granule cells and specially striking abnormalities of the morphology and orientation of Purkinje cell dendrites were noted in rats treated with MAM from birth to day 3. The effects of the Purkinje cell morphogenesis persisted but were much less marked when MAM was given from 4 to 7 or from 8 to 11 days. Neonatal thyroid deficiency, as MAM-treatment between days 0 and 3, leads to an abnormal position of Purkinje cell bodies within the cerebellar cortex; it also leads to morphological abnormalities of their dendritic arborization which closely resemble those observed after MAM-treatment during the second postnatal week. It also alters the cell formation in the cerebellum. Thyroid deficiency probably exerts its effect on cell formation earlier than previous biochemical studied have shown. On another hand, the morphological abnormalities of Purkinje cell arborizations in the thyroid-deficient animals may be partly due to the perturbations of cell formation which persist later in the cerebellum.

Animals↗
PubMed1976

Thyroid hormone and cell formation in the developing rat cerebellum.

Effects of neonatal hyperthyroidism on cell formation in the developing rat cerebellum were reinvestigated. Administration at birth of excessive doses of thyroxine or triiodothyronine led to an early stimulation of cell acquisition, followed by a permanent deficit of cells in the cerebellum. The corrective effects of physiological doses of thyroxine on the troubles of the histological and biochemical development of the cerebellum in thyroid-deficient animals were also studied. As early as 6 days, cell maturation and formation were already retarded in animals treated with propylthiouracil, but, as previously reported, cell formation was prolonged and the final number of cells was normal. Administration to thyroid-deficient animals of progressively increasing doses of thyroxine, nearly equal to the amounts of hormone secreted by the thyroid gland of the developing normal rat, returned the evolution of the cerebellar wet weight and of the cerebellar DNA to normal, as well as the histological maturation of the cerebellum, even if it did not entirely correct the retardation of body growth. These results are consistent with the view that thyroid hormone early stimulates maturation of the cerebellar germinative cells and subsequently interacts with cell formation in the cerebellum, and that this action is physiological.

Animals↗
PubMed1975

[Effect of cortisol on the cellular proliferation and maturation in the cerebrum and the cerebellum of the rat: Importance of the age of the animals at the beginning of treatment].

Young rats were given either a single subcutaneous injection (1 mg at 0, 1, 4 or 8 days), or four consecutive daily injections (0.2 mg/day between 0 and 3 days; 0.4 mg/day between 4 and 7 days; 0.6 mg/day between 8 and 11 days) of cortisol acetate in order to test the influence of age on the action of corticosteroids on the biochemical maturation of the cerebrum and cerebellum in terms of their DNA, RNA, and protein contents. The results showed that: 1 The diminution of the DNA content at 35 days was greater in the cerebellum (- 16 to - 32%) than in the cerebrum (- 9 to 20%); the DNA content of the cerebrum was more affected by treatment at birth, whereas that of the cerebellum was more affected by the delayed treatments. Results were different when expressed in terms of reduction of the normal increase: the gain of DNA decreased more in the cerebrum (-70%) than in the cerebellum (-40%); but the most delayed treatment induced a greater effect in both organs. These abnormalities were not always accompanied by a significant decrease of the body weight. 2 Generally, the treatments led to an increase of the mean cell territory, expressed either in terms of decrease of the DNA concentration, or in terms of increase of the organ weight/DNA ratio. Moreover, the increase of the RNA/DNA and the protein/DNA ratios constituted an indication of an accelerated cellular maturation.

Age Factors↗
PubMedDate not supplied

Localization of S100 protein in the rat cerebellum: an immunoelectron microscope study.

Immunoelectron microscopy has shown that, in adult rat cerebellum, S100 protein is localized exclusively in the astroyctes of both the cortex and the white matter. The labelling pattern was unaffected by the inclusion of glutaraldehyde in the primary paraformaldehyde fixative. The immunoperoxidase reaction product is observed over both the perikaryal cytoplasm of astrocytes and their processes. S100 proteins was not found in neuronal structures nor in oligodendrocytes.

Animals↗
PubMedDate not supplied

Histochemical and biochemical studies of butyrylcholinesterase activity in adult and developing cerebellum. Effects of abnormal thyroid state and undernutrition.

The cellular and subcellular localization of BuchE activity (EC.3.1.1.8) was studied in the developing and adult rat cerebellum at light and electron microscope levels. In the adult cerebellum, BuchE activity was exclusively localized to glial cells, myelin and endothelial cells. In the immature cerebellum, BuchE activity was additionally found transiently localized to the neuroblasts of the external germinative layer and in Purkinje cells of the nodulus. In both the immature and the adult animals, the main part of the activity seemed to be membrane-bound. The developmental pattern of cerebellar BuchE activity was assayed in developing normal, hypothyroid, thyroxine-treated and undernourished rats. In normal newborn rats, the specific activity was higher than in adults and it showed one characteristic peak at 6 days (1.8 times the adult value reached at 30 days). At the age of 5 days, the ratio of BuchE-containing astrocytes (numbered in the ganglionic layer) to Purkinje cells was the same as the ratio of Bergmann astrocytes to Purkinje cells determined at 35 days in Nissl preparations; their nucleus size already represented 80% of the adult value and their processes were well developed. The three experimental conditions modified the timing of BuchE development. During the early post-natal period, it was accelerated in the thyroxine-treated and undernourished animals, while in the hypothyroid rats it was delayed. During the same period, the number of labelled astrocytes per Purkinje cell was modified only by hypothyroidism and undernourishment. On the basis of these histochemical and biochemical results, BuchE can be considered as a good marker for the study of Bergmann glia development in the early post-natal period.

Animals↗
PubMedDate not supplied

Effects of thyroid state and undernutrition on S100 protein and astroglia development in rat cerebellum.

The developmental pattern of S100 protein, a specific marker of astroglia, was studied by radioimmunoassay in the cerebellum of thyroid-deficient, thyroxine-treated and undernourished rats during development. In the control animals, the S100 protein content of the cerebellum increased maximally after the 3rd postnatal week, i.e., after cell multiplication had stopped and when the cerebellum had acquired more than 70% of its adult weight and protein content. This developmental pattern of S100 protein reflected essentially the maturation of astroglia. In the thyroxine-treated rats the total amount and the concentration of S100 protein were higher than in controls during the first 3 weeks of postnatal life and returned to normal values thereafter. In the thyroid-deficient rats both the amount and concentration were lower than in controls throughout development. In the undernourished animals the amount of S100 protein per organ was also lower than in controls during the whole experimental period studied; the S100 protein concentration was higher during the first 2 postnatal weeks and became lower thereafter. These results are discussed taking into consideration previous histological and ultrastructural observations on the effects of altered thyroid state and undernutrition on the formation and maturation of cerebellar astrocytes.

Animals↗