Mary Lou Oster-Granite

Glutamic acid: Selective depletion by viral induced granule cell loss in hamster cerebellum

Abstract Cerebellar hypoplasia in the hamster induced by rat virus strain PRE 308 was used as a model system in which greater than 95% of the cerebellar granule cell population can be selectively depleted at an early stage of development. Electron microscopic examination of infected hamster cerebella indicated a significant reduction of parallel fiber synapses and granule cell dendrites in glomeruli. All other cell types occurred in approximately normal numbers and formed proper synaptic connections. To attempt to identify the transmitter of the cerebellar granule cell, we examined the uptakes of amino acids and amines into synaptosomes in the cerebella of hamsters with granuloprival cerebellar hypoplasia and their littermate controls. The high affinity uptakes of glutamic and aspartic acids were reduced by 70% in infected animals. No significant reductions occurred in the uptakes of a variety of other amino acids, putative neurotransmitters and their precursors. Endogenous glutamic acid was decreased by 43%, although endogenous protein concentration was not altered. Analysis of the free cerebellar amino acid content of infected animals revealed a selective decrease in glutamic acid and no decrease in other amino acids, in particular aspartic acid. Partial granule cell depletions were also produced and the extent of granule cell loss correlated with the decrease in endogenous glutamic acid and high affinity glutamic acid uptake. Granule cells are excitatory in function; the neurophysiologic action of glutamic acid is also excitatory. Our findings suggest that glutamic acid is the natural neurotransmitter of the cerebellar granule cell.

The neurobiologie consequences of down syndrome

Trisomy of the whole or distal part of human chromosome 21 (HSA 21) (Ts21) results in Down Syndrome (DS), which is characterized in part by mental retardation and associated neurological abnormalities. Structural abnormalities observed frequently include reduced brain weight, decreased number and depth of sulci in the cerebral cortices, neuronal heterotopias, and reduced numbers of specific populations of neurons, such as granule cells, in the cerebral cortices. Abnormalities in the structure of cells, primarily of the dendrites, are observed in portions of the neuraxis, such as the hippocampus, cerebellum, and cerebral cortices. Functional abnormalities in membrane properties in peripheral structures and in neurotransmitter enzyme systems in both peripheral and central structures are observed also. Brains of DS individuals over the age of 40 exhibit the characteristic neuropathologic and neurochemical stigmata of Alzheimers disease (AD). The cholinergic and noradrenergic systems appear to be particularly vulnerable. To elucidate the mechanisms responsible for these abnormalities, identification of the genes located in the distal part of HSA 21 and the systematic study of animal model systems with close genetic homology are essential.

Autosomal aneuploidy in mice: generation and developmental consequences

Spontaneous aneuploidy in the mouse is uncommon, but specific mating schemes have been developed that produce aneuploid conceptuses at high frequencies. The most commonly reported aneuploid condition in the mouse is autosomal trisomy, in which there is an extra copy (in whole or in part) of a chromosome. In this review, we present several of the schemes used in producing trisomic, partially (tertiary) trisomic, and monosomic conceptuses and summarize the developmental consequences that are associated with each of the autosomal trisomies of the mouse.

Down syndrome, Alzheimer's disease and the trisomy 16 mouse

Abstract Recent findings have implicated genes on human chromosome 21 as important in the pathophysiology of Alzheimers disease (AD). These include the high incidence of the pathological features characteristic of AD in individuals with Down syndrome (trisomy 21) and the localization of both a familial AD gene and the gene encoding amyloid precursor protein on chromosome 21. Substantial genetic homology exists between human chromosome 21 and mouse chromosome 16, including the gene encoding the amyloid precursor protein. Mice that are trisomic for chromosome 16 offer a genetic model for studies relevant to Down syndrome that may also help to clarify molecular mechanisms involved in Alzheimers disease.

Cell lineage analysis of cerebellar Purkinje cells in mouse chimeras.

Abstract Murine chimeras provide an experimental system in which cell lineage analysis of the mammalian central nervous system (CNS) can be accomplished. Utilizing a cell marker system that permits the identification of cells of each genotype in various cell populations present in histologic sections of the CNS at different developmental periods, fate maps of the mammalian CNS can be constructed. Thus, the presence or persistence of clones of cells can be readily visualized in simply organized CNS regions, like the cerebellar cortex. The electrophoretic variants of the glycolytic enzyme, glucosephosphate isomerase (GPI, E.C. 5.3.1.9; GPI-1A, GPI-1B), are the genotype-specific cell markers most commonly used by experimental mammalian embryologists in studies of cell lineage utilizing mammalian chimeras. We have adapted this cell marker system to permit the visualization and unequivocal identification of cells containing the GPI-1B variant throughout the CNS of adult BALB cBy J a3 C57BL 6J chimeric mice. Utilizing allozyme-specific anti-GPI-1B antisera in immunocytochemical (PAP) staining techniques, we can score small as well as large cell populations, neurons as well as glia. We have reconstructed and statistically analyzed the location and distribution of chimerism present in the Purkinje cell population of four of these chimeric mice. We found the Purkinje cells in each of these animals existed as small (3–8) cell patches of like genotype that were not randomly arranged. This suggests that clones of cells may persist as contiguous groups of cells throughout mammalian cerebellar development.

Gamma-aminobutyric acid (GABA) receptor binding selectively depleted by viral induced granule cell loss in hamster cerebellum

Excitatory and inhibitory synaptic interconnections and related neurotransmitters have been more thoroughly studied in the cerebellum than in any other brain region. Of the 5 intrinsic neuronal types in the cerebellar cortex, four (the Purkinje, Golgi, basket and stellate cells) are inhibitory and appear to utilize GABA as their neurotransmitter4,5,9,11,17-19. The remaining inhibitory element is composed of noradrenergic fibers which arise from the locus coeruleus and comprise about 1 of the climbing fiber populationL There are 3 excitatory elements in the cerebellar cortex, the granule cells which appear to use glutamic acid as their transmitter 21 and the mossy and climbing fibers whose transmitters are unknown. All cerebellar neurons seem to receive GABA containing inhibitory terminals 5. Those on the granule cell dendrites appear to arise predominantly and probably exclusively from the Golgi I! cells. The density of GABA receptors upon various cell types in the cerebellum may regulate the prevalence of various types of inhibitory synaptic interconnections. Recently, we have identified selective binding of GABA to its postsynaptic receptor sites in the brain6,7, 22. To ascertain the density of GABA receptors associated with various cell types in the cerebellum, it would be desirable to destroy individual cell types selectively. Several experimental models have been developed to deplete selectively cerebellar granule cells. In the present study we have examined synaptic receptor binding of GABA in the cerebella of hamsters treated with a parvovirus, rat virus, which selectively destroys the rapidly dividing external germinal cells to produce a cerebellum in which only the granule cell population is depleted. We report a selective decline in synaptic GABA receptor binding which parallels the decrease in granule cell number. Granuloprival hypoplasia of the Syrian hamster cerebellum resulted after intracerebral injection of rat virus strain PRE (HA titer 2 -12) into the left hemisphere 21 of

Developmental expression of somatostatin in mouse brain. II. In situ hybridization

The distribution and the levels of expression of preprosomatostatin (PPSOM) mRNA were examined during pre- and postnatal development of the mouse brain using the in situ hybridization technique. The signal obtained by in situ hybridization of embryonic tissues at day 14 and day 17 of gestation was highest over the neurons of the pyriform cortex, amygdala, and entopeduncular nucleus. The signal was very low over cells of the neocortex and the developing hippocampal formation. The density of grains overlying the neurons of the amygdala and pyriform cortex continued to be high during early postnatal life, but decreased as the animals became adults. A progressive increase of PPSOM mRNA expression was observed in postnatal animals in the stratum oriens and dentate gyrus of the hippocampal formation. In the cerebral cortex and striatum, the number of these neurons became maximal between postnatal weeks 1 and 3. In the diencephalon, the highest densities of grains were found over neurons in the nucleus reticularis thalami and zona incerta at postnatal day 21; these levels declined slightly thereafter. The cells of the periventricular nucleus of the hypothalamus had high densities of grains as early as postnatal week 1 and continued to have high densities of grains in adult animals. These patterns of hybridization density parallelled the distribution of SOM-like immunoreactivity in the mouse brain. When PPSOM mRNA expression was examined in the cerebral cortices of mice that received lesions of the nucleus basalis of Meynert as neonates, a transient increase in the number of cells expressing PPSOM mRNA was observed in the frontoparietal cortex ipsilateral to the lesion at postnatal day 10, but not at postnatal day 30. Importantly, the density of grains over the individual cells was not altered in lesioned animals at these two ages.

Neurogenesis of the basal forebrain in euploid and trisomy 16 mice: An animal model for developmental disorders in down syndrome

The neurogenesis and early histochemical differentiation of the basal forebrain in trisomy 16 fetal mice and their euploid littermates were examined by combining [3H]thymidine autoradiography with acetylcholinesterase histochemistry. Neurons of the basal forebrain were being born between embryonic day 11 and 15 in both chromosomally normal (euploid) and aneuploid mice. In euploid littermate controls, neurogenesis proceeded along a caudal to rostral gradient with the peak on embryonic day 11 for caudal portions and embryonic day 13 for rostral portions of the basal forebrain. In contrast, in trisomy 16 mice, rostral sections exhibited a peak of neurogenesis on embryonic day 11, 2 days earlier than in their euploid littermate controls. Hypocellularity of the basal forebrain region was noted in trisomy 16 mice; particularly dramatic was the reduction of the population of cells that expressed acetylcholinesterase. This reduction in cell number in the trisomics was not accompanied by a reduction in cell size or by a dramatic change in the distribution of residual neurons when compared to that of euploid littermate controls. Since trisomy 16 mice do not survive the perinatal period, we examined the pattern of acetylcholinesterase expression in normal C57B1/6J mice from embryonic day 16 to postnatal day 5 to determine the postnatal disposition of these neurons. Already at embryonic day 16, fibers staining for acetylcholinesterase penetrated the striatal anlage, in their course towards targets in the cerebral cortices. By postnatal day 5, the previously expansive distribution of basal forebrain neurons had become consolidated in a more ventral and rostral position by the extensive outgrowth of the striatal neurons, a pattern resembling that seen in adult animals.

Histological changes after transection of the spinal cord of fetal and neonatal mice.

Abstract The spinal cords of fetal (days 12 to 17 gestation) and neonatal (0 to 3 days postnatal) mice were transected and examined histologically to as long as 4 months postoperatively. Serial reconstructions were made of spinal cord sections which were prepared within the vertebral column. Based upon the application of several histological stains, we found: (i) Several months after transection the cut ends of the spinal cord were separated by a space of as many as one to two vertebral segments in transection animals and two to four vertebral segments in resection animals. (ii) After complete transection, the lesion site contained longitudinally oriented glial processes which occasionally connected the rostral and caudal segments of the spinal cord. (iii) Very few nerve fibers traversed the lesion site continuously from one stump to the other. (iv) Connective tissue scarring at the site of transection was absent and neuroglial scar formation minimal to both fetal and neonatal mice. (v) In the undamaged regions of the spinal cord, microcysts occurred more frequently in neonatal than in fetal animals. (vi) Dorsal root fibers regenerated across the gap between the ends of the cord and reentered the rostral stump of the cord. We conclude that despite the absence of connective tissue and glial scars, there was insignificant outgrowth of spinal nerve fibers. Thus, there is no greater regenerative capacity in the fetal and neonatal spinal cords than in the adult spinal cord.

Genetic linkage in the mouse of genes involved in down syndrome and Alzheimer's disease in man

Recently, the gene encoding the cerebrovascular and neuritic plaque amyloid, a pathologic stigma of Alzheimers disease (AD), has been molecularly cloned and mapped to human chromosome 21, band q21. Changes in the brains of individuals with trisomy 21 (Down syndrome, DS) over 35 years of age closely resemble AD neuropathology. Genetic homology which exists between human chromosome 21 (HSA 21) and mouse chromosome 16 (MMU 16) has led to the use of mice with trisomy 16 as a model system for studies relevant to DS. Mice with Ts16 exhibit numerous developmental abnormalities that can be correlated with features observed in DS, including neurochemical and neuroanatomic alterations. In this study, we show that the genetic homology between HSA 21 and MMU 16 extends to the gene encoding the amyloid peptide. The homologous mouse gene, designated Cvap, for cerebrovascular amyloid peptide, is localized on MMU 16 band C3----ter, and is in close proximity to both superoxide dismutase-1 (Sod-1), and the protooncogene, Ets-2, two of the genes known to localize to the DS region of HSA 21. Linkage of these genes has been maintained since the divergence of the common ancestor of mouse and man, despite a chromosomal rearrangement which has changed the gene order between the two species. These findings expand the region of HSA 21 with known homology to MMU 16, and provide a genetic basis to suggest that studies of the trisomy 16 mouse, in addition to being relevant to DS, may also clarify the role of abnormal gene expression in AD.