Cerebellum: certain features of its development and biochemistry

Glycoprotein expression in mouse cerebellum: effects of inhibitors of N-linked glycosylation

1. Explants of cerebellum from foetal mouse were cultured in vitro for 10 days in the presence of one of 4 inhibitors of N-linked glycosylation (castanospermine, deoxymannojirimycin, swainsonine, and tunicamycin). 2. The effects of the inhibitors were compared with respect to: (a) the activity of enzymes involved in glycoprotein biosynthesis and degradation; (b) the expression of N-linked glycoproteins; (c) the morphology and ultrastructure of the treated cerebellar explants.

Glycoprotein expression in mouse cerebellum: effects of inhibitors of vesicle function

1. Explants of cerebellum from foetal mouse were cultured in vitro for 10 days in the presence of one of 5 inhibitors of vesicle function (ammonia, brefeldin A, carbonyl cyanide m-chlorophenylhydrazone, diethylcarbamazine, and monensin). 2. The effects of the inhibitors were compared with respect to: (a) the activity of enzymes involved in glycoprotein biosynthesis and degradation; (b) the expression of N-linked glycoproteins; (c) the morphology and ultrastructure of the cerebellar explants.

Relative cerebellar weight: a potential indicator of developmental neurotoxicity

Overt malformations do not always accompany behavioral changes resulting from perinatal exposure to certain drugs. However, the central nervous system (CNS) is the anatomical substrate for behavior, and functional defects may be accompanied by more subtle, structural alterations of the brain. The purpose of this study was to determine if changes in the weights of certain brain regions occur in rats exposed prenatally and/or perinatally to propylthiouracil (PTU) which retards functional development of the brain. Pregnant rats were dosed with PTU during gestation and/or lactation, and on postnatal day 28, auditory startle responses were measured to determine if PTU altered functional development. The brains of all pups were then dissected into 10 separate regions, dried and individually weighed. Brain weights were expressed in absolute and relative (to total brain weight) terms. Pups that were exposed to PTU from days 10 to 21 of gestation grew normally, but their startle responses to auditory stimuli were significantly different (p less than 0.05) from controls. Thus, for the purpose of this experiment, PTU acted as a developmental neurotoxicant because it altered performance on a test of neuromuscular function without being overtly teratogenic. The weights of most brain regions in PTU-treated rats were statistically comparable to controls. However, relative cerebellar weight was significantly (p less than 0.05) different. Therefore, these data suggested that relative cerebellar weight might be used to predict functional defects that appear during development following prenatal or perinatal exposure to certain neurotoxicants. Although cerebellar weight and auditory startle responses were altered by PTU, this study does not establish a causal relationship between the anatomical and functional changes that occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of a developmental stage-specific antigen by neuronal precursor cells of human fetal cerebellum

A monoclonal antibody that was prepared against human neuroblastoma cells was shown to react strongly with fetal brain and moderately with adult brain by quantitative absorption testing. Immunoperoxidase staining demonstrated expression of the antigen by neuronal precursor cells in the cerebellar external granular layer of a 24- to 26-week fetus but not by their mature derivatives in the granular and molecular layers of adult cerebellum. The antigen was also present on subventricular cells of fetal cerebral cortex, as well as adult and fetal astrocytes. The expression of this antigen by neuronal precursor cells in the external granular layer but not their mature derivatives suggests that it is a stage-specific marker for cerebellar neuronal development.

Effects of methylmercury on the morphogenesis of the rat cerebellum

Developing rat cerebellums were examined following continuous methylmercury exposure via maternal drinking water at 12.5 ppm during gestation and the suckling period. The continuous exposure resulted in reductions of the total cerebellar cell population and higher mercury tissue burdens than previous acute-dose studies. Cell necrosis was not evident, but rather alterations in the pattern of mitotic figures were observed. A decreased number of cells in the methylmercury exposed cerebellums was associated with an increased number of mitotic figures in the early stages of mitosis and a decrease in the number in the middle and late stages. These in vivo exposure observations are consistent with in vitro cell cycle studies in which the cells were found to have accumulated in G2 and early M phases. Impaired cell proliferation is suggested to be a major mechanism of developmental neurotoxicity following continuous low-dose exposure to methylmercury.

Substrate specificity and developmental aspects of a presynaptic GABA receptor regulating glutamate release in the rat cerebellum

In order to better characterize the presynaptic GABA receptors regulating glutamate release in the cerebellum [Levi and Gallo, 1981], a number of GABA agonists and GABA transport inhibitors were tested for their ability to potentiate the depolarization-induced release of the glutamate analog D-[3H]aspartate from superfused cerebellar synaptosomes. Of all the compounds tested, only those which are known to interact specifically with GABA receptors were effective when tested on synaptosomal preparations. The order of effectiveness found was the following: muscimol congruent to 3-APS greater than or equal to P4S greater than isoguvacine greater than THIP. GABA uptake inhibitors were unable to enhance D-[3H]aspartate evoked release from synaptosomes, but were effective when tested in cerebellar slices; in the latter case, the activation of the GABA receptors may be achieved indirectly, through an increase of the extracellular GABA concentrations. The substrate specificity of the presynaptic GABA receptors regulating cerebellar acidic amino acid release appears to be similar to that reported for GABA receptors in radioligand binding studies and for GABA autoreceptors. Studies on synaptosomes from immature cerebella suggested that the presence of the potentiating effect on the acidic amino acid release by GABA agonists is correlated with the development of the parallel fiber terminals, which are believed to be the main site from which glutamate is released in the adult cerebellum.

Ontogeny of receptor binding sites for [3H]glutamic acid and [3H]kainic acid in the rat cerebellum

The development of the specific binding sites for L-[3H]glutamic acid (KD = 370 nM) and for [3H]kainic acid (KD = 39 nM) was studied in the rat cerebellum. Specific binding at both sites remains low during the first week after birth but increases markedly during the second and third weeks after birth, when glutamatergic parallel fiber synaptogenesis occurs. The development of the kainate site lags behind that of the glutamate site, indicating their autonomy.