Self-injurious behavior: gene-brain-behavior relationships

This paper summarizes a conference held at the National Institute of Child Health and Human Development on December 6-7, 1999, on self-injurious behavior [SIB] in developmental disabilities. Twenty-six of the top researchers in the U.S. from this field representing 13 different disciplines discussed environmental mechanisms, epidemiology, behavioral and pharmacological intervention strategies, neurochemical substrates, genetic syndromes in which SIB is a prominent behavioral phenotype, neurobiological and neurodevelopmental factors affecting SIB in humans as well as a variety of animal models of SIB. Findings over the last decade, especially new discoveries since 1995, were emphasized. SIB is a rapidly growing area of scientific interest to both basic and applied researchers. In many respects it is a model for the study of gene-brain-behavior relationships in developmental disabilities.

Administration of unmodified prolactin (U-PRL) and a molecular mimic of phosphorylated prolactin (PP-PRL) during rat pregnancy provides evidence that the U-PRL:PP-PRL ratio is crucial to the normal development of pup tissues

During rat pregnancy initial high concentrations of prolactin (PRL) decline by about day 9, concomitant with an increase in the ratio of unmodified to phosphorylated PRL. The physiological significance of both the decline in total PRL and the change in ratio of the two PRLs is unknown. To test the importance of each, either unmodified PRL (U-PRL) or a molecular mimic of phosphorylated PRL (PP-PRL) were continuously administered to rats throughout pregnancy. A dose of 6 microg/24 h resulted in circulating concentrations of 50 ng/ml of each administered PRL and had little effect on the pregnancy itself. After birth, pups were killed and various tissues examined. In the pup lungs, exposure to additional PP-PRL caused a reduction in epithelial integrity and an increase in apoptosis, whereas exposure to additional U-PRL had beneficial, anti-apoptotic effects. In the heart, PP-PRL caused an apparent developmental delay, whereas U-PRL promoted tissue compaction. In the blood, U-PRL increased the number of mature red blood cells at the expense of white blood cell production. Within the white blood cell population, myelopoiesis was favored at the expense of lymphopoiesis. PP-PRL, in contrast, had a less dramatic influence on the hematopoietic compartment by promoting red blood cell maturation and granulocyte production. In the thymus, exposure to PP-PRL caused accumulation of apoptotic thymocytes in enlarged glands, whereas exposure to U-PRL resulted in smaller thymi. In the spleen, exposure to U-PRL increased cellularity, with the majority of cells belonging to the erythroid series - a finding consistent with increased red blood cells in the circulation. Exposure to PP-PRL was without discernible effect. In all of these tissues, the contrasting effects of the two PRLs indicate that the absolute concentration of PRL is not crucial, but that the ratio of U-PRL to PP-PRL has a profound effect on tissue development. In brown fat, both PRL preparations decreased the number of lipid droplets. This result is therefore probably a consequence of the increase in total PRL. The results of this study attest to the importance of the U-PRL:PP-PRL ratio normally present during pregnancy and have provided clues as to the possible pathogenesis of a variety of neonatal problems.

Mouse molecular cytogenetic resource: 157 BACs link the chromosomal and genetic maps

We have established a collection of strong molecular cytogenetic markers that span the mouse autosomes and X chromosome at an average spacing of one per 19 Mb and identify 127 distinct band landmarks. In addition, this Mouse Molecular Cytogenetic Resource relates the ends of the genetic maps to their chromosomal locations. The resource consists of 157 bacterial artificial chromosome (BAC) clones, each of which identifies specific mouse chromosome bands or band borders, and 42 of which are linked to genetic markers that define the centromeric and telomeric ends of the Whitehead/MIT recombinational maps. In addition, 108 randomly selected and 6 STS-linked BACs have been assigned to single chromosome bands. We have also developed a high-resolution fluorescent reverse-banding technique for mouse chromosomes that allows simultaneous localization of probes by fluorescence in situ hybridization (FISH) with respect to the cytogenetic landmarks. This approach integrates studies of the entire mouse genome. Moreover, these reagents will simplify gene mapping and analyses of genomic fragments in fetal and adult mouse models. As shown with the MMU16 telomeric marker for the trisomy 16 mouse model of Down syndrome, these clones can obviate the need for metaphase analyses. The potential contribution of this resource and associated methods extends well beyond mapping and includes clues to understanding mouse chromosomes and their rearrangements in cancers and evolution. Finally it will facilitate the development of an integrated view of the mouse genome by providing anchor points from the genetic to the cytogenetic and functional maps of the mouse as we attempt to understand mutations, their biological consequences, and gene function.

Impairments in learning and memory accompanied by neurodegeneration in mice transgenic for the carboxyl-terminus of the amyloid precursor protein

In Alzheimer's disease (AD), a progressive decline of cognitive functions is accompanied by neuropathology that includes the degeneration of neurons and the deposition of amyloid in plaques and in the cerebrovasculature. We have proposed that a fragment of the Alzheimer amyloid precursor protein (APP) comprising the carboxyl-terminal 100 amino acids of this molecule (APP-C100) plays a crucial role in the neurodegeneration and subsequent cognitive decline in AD. To test this hypothesis, we performed behavioral analyses on transgenic mice expressing APP-C100 in the brain. The results revealed that homozygous APP-C100 transgenic mice were significantly impaired in cued, spatial and reversal performance of a Morris water maze task, that the degree of the impairment in the spatial learning was age-dependent, and that the homozygous mice displayed significantly more degeneration of neurons in Ammon's horn of the hippocampal formation than did heterozygous or control mice. Among the heterozygotes, females were relatively more impaired in their spatial learning than were males. These findings show that expression of APP-C100 in the brain can cause age-dependent cognitive impairments that are accompanied by hippocampal degeneration.

Characterization of N-methyl-d-aspartate receptors in the hyperammonemic sparse fur mouse

The N-methyl-d-aspartate (NMDA) receptor, a glutamate receptor subtype, is a ligand-gated ion channel. Overstimulation of NMDA receptors may increase intracellular Ca2+ concentrations to lethal levels in neurodegenerative disorders affecting the basal ganglia. Such excitotoxicity may also contribute to the loss of medium spiny neurons in the striata of the hyperammonemic sparse fur (spf/Y) mouse, a model of the X-linked disorder of the urea cycle, ornithine carbamoyltransferase deficiency (OCTD). Levels of quinolinic acid (QA), a potent NMDA agonist, are elevated in the brains of spf/Y mice. Further, direct injection of QA into the striatum produces selective degeneration of medium spiny neurons. Microglia, an endogenous source of QA in the brain, are abundant in spf/Y mice during the period of neuronal degeneration. The location and density of NMDA receptors was visualized by gold labelled immunocytochemistry with a polyclonal antibody to the NMDAR1 receptor subtype and their distribution quantified. A 58% reduction was found in the median density value in the layer V pyramidal neurons in fronto-parietal cortex (p<0.001), but no significant change was observed in the striatum. NMDA receptor binding was examined using [3H]dizocilpine ([3H]MK-801). Receptor density (Bmax) in the striata of clinically stable spf/Y mice and +/Y littermates was unchanged, but was decreased 15% (p<0.01) in the fronto-parietal cortices in clinically stable spf/Y mice compared with +/Y littermate controls.

Dendritic alterations in cortical pyramidal cells in the sparse fur mouse

Ornithine carbamoyltransferase deficiency, an X-linked trait, leads to toxic hyperammonemia in sparse fur (spf/Y) mice. Quantitative analysis of the basilar dendritic tree of layer V pyramidal cells in frontoparietal cortex stained by the Golgi Kopsch method revealed a significant decrease in both the complexity of the dendritic arbor and in dendritic terminal spine density (60%) in spf/Y mice compared with controls. Such reductions may contribute to behavioral dysfunction observed in spf/Y mice.

Age-dependent neuronal and synaptic degeneration in mice transgenic for the C terminus of the amyloid precursor protein

The molecular basis for the degeneration of neurons and the deposition of amyloid in plaques and in the cerebrovasculature in Alzheimer's disease (AD) is incompletely understood. We have proposed that one molecule common to these abnormal processes is a fragment of the Alzheimer amyloid precursor protein (APP) comprising the C-terminal 100 amino acids of this molecule (APP-C100). We tested this hypothesis by creating transgenic mice expressing APP-C100 in the brain. We report here that aging (18-28 month) APP-C100 transgenic mice exhibit profound degeneration of neurons and synapses in Ammon's horn and the dentate gyrus of the hippocampal formation. Of the 106 transgenic mice between 8 and 28 months of age that were examined, all of those older than 18 months displayed severe hippocampal degeneration. The numerous degenerating axonal profiles contained increased numbers of neurofilaments, whorls of membrane, and accumulations of debris resembling secondary lysosomes near the cell body. The dendrites of degenerating granule and pyramidal cells contained disorganized, wavy microtubules. Cerebral blood vessels had thickened refractile basal laminae, and microglia laden with debris lay adjacent to larger venous vessels. Mice transgenic for Flag-APP-C100 (in which the hydrophilic Flag tag was fused to the N terminus of APP-C100) showed a similar degree of neurodegeneration in the hippocampal formation as early as 12 months of age. The 45 control mice displayed only occasional necrotic cells and no extensive cell degeneration in the same brain regions. These findings show that APP-C100 is capable of causing some of the neuropathological features of AD.

Transgenic mice expressing APP-C100 in the brain

The classic hallmarks of Alzheimer's disease are the deposition of amyloid in plaques and in the cerebrovasculature, and the emergence of neurofibrillary tangles in neurons. The interplay between these two pathologic processes, on the one hand, and the degeneration of neurons and loss of cognitive functions on the other, remains incompletely understood. We have proposed that one crucial component of this interplay is a fragment of the Alzheimer amyloid protein precursor (APP) comprising the carboxyterminal 100 amino acids of this molecule, which we term APP-C100 (or, more simply, C100). This fragment, which comprises the 42-amino acid amyloid protein (A beta) and an additional 58 amino acids carboxyterminal to it, was found to be toxic specifically to nerve cells in vitro. We developed transgenic mouse models to test the hypothesis that APP-C100 causes Alzheimer's disease neuropathology. APP-C100 was delivered to the mouse brain via a transgene expressing C100 under the control of the dystrophin brain promoter. These transgenic animal models for the action of APP-C100 in the brain exhibited some of the neuropathological features characteristic of Alzheimer disease brain. The animal models that we have created can be used to test hypotheses concerning the mechanism by which C100 interacts with a neuronal receptor to kill neurons.

Evidence of excitotoxicity in the brain of the ornithine carbamoyltransferase deficient sparse fur mouse

Ornithine carbamoyltransferase deficiency (OCTD) is the most common inborn error of urea synthesis. An X-linked disorder, OCTD males commonly present with hyperammonemic coma in the newborn period. There is a high rate of mortality and morbidity, with most survivors sustaining severe brain damage and resultant developmental disabilities. Although ammonia is presumed to be the principal neurotoxin, there is evidence that other neurochemical alterations may also be involved. The OCTD sparse fur (spf/Y) mouse has proven to be a useful model of this disease with similar metabolic and neurochemical alterations to those found in the human disease. In this study, the levels of the tryptophan derived excitotoxin quinolinic acid were examined in the brains of spf/Y mice. In addition, the neuropathology was examined using both light and electron microscopic approaches. Consistent with reports in children with urea cycle disorders, the levels of tryptophan and quinolinic acid were increased two-fold in various brain regions of the spf/Y mouse. Quinolinic acid, an agonist at the N-methyl-D-aspartate (NMDA) receptors, is known to produce selective cell loss in the striatum. We found a significant loss of medium spiny neurons and increased numbers of reactive oligodendroglia and microglia in the striatum of spf/Y mice. These neurochemical and neuropathological observations are consistent with an excitotoxic influence on brain injury in OCTD. It leads us to suggest that administration of NMDA receptor antagonists may ameliorate brain damage in children with inborn errors of urea synthesis.

Abnormal production of interleukin-1 by microglia from trisomy 16 mice

The production of interleukin-1 (IL-1) was examined in cultured CNS microglia obtained from trisomy 16 (Ts16) fetal mouse brain, a model system for studies relevant to Down syndrome (DS). When compared to microglia from their normal littermates, Ts16 microglia produced significantly higher levels of IL-1 activity both before and following stimulation with lipopolysaccharide (LPS). IL-1 release was stimulated by alpha/beta interferon (IFN) in the normal but not Ts16 microglial cultures. The overall level of IL-1 production in normal littermates, however, was still less than that seen in Ts16. Thus, microglia from Ts16 mice may function in an inappropriate manner and, if this abnormality occurs in vivo, may have wide ranging effects on a developing nervous system.

Developmental expression of the gene encoding growth-associated protein 43 (Gap43) in the brains of normal and aneuploid mice

The gene encoding growth-associated protein 43 (Gap43), a neuronal phosphoprotein associated with axonal outgrowth and synaptic plasticity, is located on mouse chromosome 16 (MMU16). We examined the developmental expression of Gap43 in normal, trisomy 16 (Ts16), and trisomy 19 (Ts19) mouse brain using northern blot analysis and in situ hybridization as a first step toward understanding the neurobiologic consequences of increased gene dosage on brain development. Gap43 expression was detected by in situ hybridization throughout the mesencephalon, rhombencephalon, spinal cord, and first branchial arch in whole embryos as early as day 10 of gestation (E10). By E15, Gap43 expression was localized to cells in the retina, the olfactory bulbs, and anterior olfactory structures, the cortical plate, the basal telencephalon, diencephalon, midbrain, hindbrain, and spinal cord. Northern blot analysis detected a three-fold increase in Gap43 mRNA levels in the brains of normal mice between E12-E18. At E15, Gap43 mRNA levels were increased 35-40% in Ts16 mouse brain and decreased 10% in Ts19 mouse brain, relative to euploid littermate controls. Using in situ hybridization we found that overexpression of Gap43 occurred in the diencephalon, medial and lateral basal telencephalon, and cortical plate region in Ts16 mice relative to littermate controls. Thus, the degree of overexpression of Gap43 mRNA in Ts16 mice is consistent with that expected from gene dosage effects.

Expression of the amyloid precursor protein gene in mouse oocytes and embryos

The amyloid precursor protein (APP) is thought to be processed aberrantly to yield the major constituent of the amyloid plaques observed in the brains of patients with Alzheimer disease and Down syndrome. However, the gene encoding APP is expressed widely in normal human tissues and in adult and fetal mouse tissues and is alternatively spliced in a tissue-specific pattern in the adult. There is evidence that APP may function as a growth factor and as a mediator of cell adhesion and in these roles could be important in morphogenesis. As a step toward determining the role of APP in development and in determining how the adult pattern of tissue-specific splicing is established, we have used reverse transcription and the polymerase chain reaction to demonstrate APP expression in mouse oocytes, preimplantation embryos, and postimplantation embryonic stages to the late embryonic period. All three splicing forms described in mouse were present at each stage, although there were changes in the ratios of the splicing forms at different stages. Screens for APP clones in embryonic cDNA libraries from the egg cylinder stage and the early somite stage were used to confirm the results of the polymerase chain reaction, and APP clone abundance was found to increase 10-fold between the two stages.

Newborn basal forebrain lesions disrupt cortical cytodifferentiation as visualized by rapid Golgi staining

We have previously shown that neonatal lesions of the basal forebrain cholinergic afferents result in transient cholinergic depletion concomitant with abnormal morphogenesis of cerebral cortex in Balb/CByJ mice (Höhmann et al., 1988). Here, we have utilized the rapid Golgi method to further characterize these previously observed abnormalities. We compared layer V pyramidal neurons in somatomotor cortex ipsi- and contralateral to the lesion at postnatal days (PND) 7 and 14. Quantitative evaluations showed a significant reduction in all aspects of the dendritic tree as well as in cell body size in ipsilateral cortex at PND 7. Differences between ipsi- and contralateral pyramidal cells had attenuated by PND 14, but significant somatic size differences persisted, as did changes in the apical branching pattern. Qualitative differences between ipsilateral and contralateral hemispheres included the relatively more immature appearance of ipsilateral neurons at both ages, in addition to unusual dendritic morphology, particularly at PND 14. A close correlation was apparent between the magnitude of cholinergic depletion in cortex (larger at PND 7 than at PND 14) and the severity of abnormalities in pyramidal cell morphogenesis. We conclude that a normal cholinergic innervation to neocortex is instrumental in the timely differentiation of cortical neurons, because neonatal nBM lesions disrupted the time schedule of differentiation, but did not preclude the pyramidal neurons from further differentiation at a later time.

Enhanced production of superoxide anion by microglia from trisomy 16 mice

Disruption of normal oxygen radical metabolism in the CNS may contribute to the neuropathological changes associated with Down syndrome (trisomy 21) and its mouse counterpart, the trisomy 16 (Ts16) mouse. One potent source of oxyradicals is the CNS-specific macrophage, the microglial cell. We prepared primary glial cultures from the cerebral cortices of Ts16 and normal littermate mice taken at day 15 of gestation. Microglia were isolated from confluent cultures after 14 days in vitro and assayed for superoxide anion production using a cytochrome C reduction assay. Stimulation by either opsonized zymosan (OPZ) or phorbol myristate acetate (PMA), produced significantly higher levels (2.8-20 fold) of superoxide per mg protein in Ts16 microglial cultures. Resting, i.e. unstimulated secretion, was not significantly different from littermate controls. Astrocyte enriched cultures, stimulated by OPZ, exhibited low levels of superoxide production which was higher in Ts16 mice than normal littermates. Microglial enriched cultures from rat neonatal cerebral cortices were exposed for 24 h to medium from the Ts16 glial cultures. Superoxide production in the Ts16 media treated rat microglia was significantly higher than in those treated with littermate conditioned media.

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.

Increased number of somatostatin-immunoreactive neurons in primary cultures of trisomy 16 mouse neocortex

The gene encoding for pre-prosomatostatin is located on chromosome 16 of the mouse. To determine the effect of an extra copy of this gene on somatostatin expression in neurons, primary disaggregated cultures of neocortex prepared from 15 days gestational Trisomy 16 mice and their littermate euploid controls were subjected to immunocytochemical staining for somatostatin, neuropeptide Y and glutamic acid decarboxylase. The results demonstrate a selective and significant increase in the number of somatostatin-immunoreactive neurons.

Developmental expression of the amyloid precursor protein, growth-associated protein 43, and somatostatin in normal and trisomy 16 mice

The expression during development of 3 genes located on mouse chromosome 16 (MMU 16) which are implicated in neurobiological processes was examined by blot hybridization beginning at early gestational ages in the mouse. The 3 genes, amyloid precursor protein (App), preprosomatostatin (Smst), and growth-associated protein 43 (Gap43), exhibited distinct profiles of expression. App expression increased steadily throughout fetal and postnatal development. Smst expression peaked during the third postnatal week, then reached a plateau at a slightly lower level in adults, and Gap43 expression was highest in the early postnatal period, declining in adults to levels below those seen at the earliest timepoints examined. Smst message levels exhibited a 1.5-fold increase in the brains of trisomy 16 (Ts16) mice as compared to normal littermates on day 15 of gestation, while Gap43 and App message levels were elevated approximately 2-fold.

Neurotoxicity of a fragment of the amyloid precursor associated with Alzheimer's disease

Amyloid deposition in senile plaques and the cerebral vasculature is a marker of Alzheimer's disease. Whether amyloid itself contributes to the neurodegenerative process or is simply a by-product of that process is unknown. Pheochromocytoma (PC12) and fibroblast (NIH 3T3) cell lines were transfected with portions of the gene for the human amyloid precursor protein. Stable PC12 cell transfectants expressing a specific amyloid-containing fragment of the precursor protein gradually degenerated when induced to differentiate into neuronal cells with nerve growth factor. Conditioned medium from these cells was toxic to neurons in primary hippocampal cultures, and the toxic agent could be removed by immunoabsorption with an antibody directed against the amyloid polypeptide. Thus, a peptide derived from the amyloid precursor may be neurotoxic.

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.

Genetic mapping and analysis of somatostatin expression in Snell dwarf mice

Mice homozygous for the gene dwarf (dw) have elevated levels of somatostatin (SS) in extra-hypothalamic brain regions. By in situ hybridization, increased levels of SS mRNA were observed in regions shown previously to contain higher levels of the SS peptide. Thus, the rate of transcription and/or the stability of SS mRNA are affected by the dw mutation. Since both dw and the gene encoding SS, Smst, are located on mouse chromosome 16, two backcrosses segregating dw and Smst were used to determine whether dw is an allele of Smst. In one backcross, an inbred strain derived from the subspecies Mus musculus molossinus was used to provide a high degree of DNA sequence polymorphism. The gene order and map distances determined on this backcross were: (centromere) - Prm-1 - 7 - Igl-1 - 3 - Smst - 29 - dw - 15 - Sod-1 - 4 - Ets-2, demonstrating clearly that Smst and dw are distinct genes. Additional evidence against a primary role for SS excess in the pathogenesis of dw/dw mice was obtained by injecting normal newborn mice with a potent SS analog (cyclo II). In contrast to the pattern of cell loss observed in the dwarf anterior pituitary, the pituitaries of injected mice were indistinguishable from normal controls, further suggesting that the Smst locus is not the primary site of dw gene action.

Neuroanatomical localization and quantification of amyloid precursor protein mRNA by in situ hybridization in the brains of normal, aneuploid, and lesioned mice

Amyloid precursor protein mRNA was localized in frozen sections from normal and experimentally lesioned adult mouse brain and from normal and aneuploid fetal mouse brain by in situ hybridization with a 35S-labeled mouse cDNA probe. The highest levels of hybridization in adult brain were associated with neurons, primarily in telencephalic structures. The dense labeling associated with hippocampal pyramidal cells was reduced significantly when the cells were eliminated by injection of the neurotoxin ibotenic acid but was not affected when electrolytic lesions were placed in the medial septum. Since the gene encoding amyloid precursor protein has been localized to mouse chromosome 16, we also examined the expression of this gene in the brains of mouse embryos with trisomy 16 and trisomy 19 at 15 days of gestation. RNA gel blot analysis and in situ hybridization showed a marked increase in amyloid precursor protein mRNA in the trisomy 16 mouse head and brain when compared with euploid littermates or with trisomy 19 mice.

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 Alzheimer's 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.

Developmental consequences of autosomal aneuploidy in mammals

Autosomal aneuploidy in mammals adversely affects developmental processes. In human beings, for example, trisomy 21 is the most frequent aneuploidy detected among newborns and the most common known genetic cause of mental retardation. In this review, several hypotheses are discussed that have been proposed to explain the mechanisms by which aneuploidy (especially trisomy) disrupts development. These mechanisms included specific gene dosage effects, generalized disruption of genetic homeostasis, and the influence of the parental origin of the duplicated chromosome. The availability of specific chromosomal rearrangements in mice, coupled with selective breeding schemes, permits generation of aneuploidy of specific chromosomes or chromosomal segments on controlled genetic backgrounds, thus enabling the systematic study of the causes and consequences of defined aneuploidy. Phenotypic characteristics associated with a number of specific aneuploidies in the mouse are discussed. Emphasis is placed on the effects of trisomy 16. Genetic homology between mouse chromosome 16 and human chromosome 21 has led investigators to suggest that analogous mechanisms will be responsible for the developmental abnormalities produced in these respective aneuploidies. Analysis of trisomy 16 mice from the organismal to the subcellular level has revealed a number of phenotypic characteristics (particularly neurobiologic ones) shared with human trisomy 21. The dosage effects of shared genes (or their products) may contribute to the development of these features.

Neurochemical characterization of embryonic brain development in trisomy 19 (Ts19) mice: implications of selective deficits observed for abnormal neural development in aneuploidy

In this study, we examined the neurochemical profiles of selected brain regions (cerebral hemispheres, diencephalon/brainstem) in fetal (day 14 to 18 gestation) trisomy 19 (Ts19) mice. The neurochemical characteristics we observed in Ts19 mice were quite different from those we observed previously in Ts16 mice. Choline acetyltransferase (ChAT) activity was reduced significantly in the cerebral hemispheres, but not in the brainstem/diencephalon, of the fetal Ts19 mouse brain, suggesting a selective vulnerability of telencephalic cholinergic neurons. Additionally, the activity of glutamic acid decarboxylase (GAD) was reduced significantly in both hemispheres and diencephalon/brainstem of late gestation Ts19 fetuses, suggesting a selective vulnerability of GABAergic neurons as well. While the levels of catecholaminergic and dopaminergic markers were reduced significantly at late gestational ages, the relative rate of turnover of dopamine (DA), measured by the ratio of DOPAC/DA, was elevated significantly in Ts19 mice. Neither reduction in the thickness of various cellular zones of the cerebral cortex nor reduced cell density of the cerebral cortex accounts for the alterations in neurochemical parameters observed in Ts19 mice. These results suggest that the effects of the triplication of specific genes on the respective chromosomes, rather than a generalized disruption of developmental homeostasis resulting from extra chromosomal material, may produce selective alterations in neurochemical and neuroanatomical markers observed in these two mouse trisomies.

The neurobiologic 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 Alzheimer's 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.

Selective culture medium enhances survival of neuroblasts from postnatal rodent brain

One of the major limitations to the study of the development of the nervous system in aneuploid mammalian embryos is that the aneuploid condition is usually lethal in utero. Liveborn aneuploid individuals often succumb rapidly because they have a constellation of malformations incompatible with postnatal survival. We have developed a selective tissue culture medium (D-val) which can be used with fetal calf serum or in a serum-free defined composition and which permits neuroblasts and glioblasts present in postnatal rodent (rat, mouse) brain to proliferate and differentiate in vitro. These cells contain D-amino acid oxidase, but fibroblasts do not. In this medium, fibroblasts cannot grow and are eliminated from the cultures without the use of deleterious compounds such as antimitotic or chemotherapeutic agents. With this medium, cultures containing neuroblasts can be established from normal rat and mouse brain as late as postnatal days 11-20. Cultures with significant numbers of proliferating cells can also be established from perinatal aneuploid mouse embryos, 'rescuing' the cells for further study.

Mouse chimeras composed of trisomy 16 and normal (2N) cells: preliminary studies

Many humans with trisomy 21 (Down Syndrome (DS)) have psychomotor and cognitive retardation, congenital heart disease, and hematologic abnormalities. Partial genetic homology exists between mouse chromosome 16 and human chromosome 21; thus, studies of the development of mice with trisomy 16 (Ts16) may provide important insights into the pathogenesis of these defects and into the mechanisms by which they arise in humans. Since Ts16 mice do not survive the late fetal period, chimeras have been formed between Ts16 and normal (2N) mouse embryos to rescue the Ts16 cells for postnatal studies. In this preliminary study of the postnatal development of such chimeras, we examined the proportion of Ts16 cells in a variety of tissues, including the coat, blood, placenta, heart, and brain. The Ts16 cells made significant contributions to almost all tissues examined. Aspects of the behavior and the neurochemistry of adult Ts16 less than-greater than 2N chimeras were found to differ significantly from control (2N less than-greater than 2N) chimeras and from animals of the two donor embryo strains. Ts16 cells comprised a substantial, but not predominant, proportion of cells in each brain region examined. Suggestions for definitive analyses are reviewed.

Peripheral-type benzodiazepine receptors: autoradiographic localization in whole-body sections of neonatal rats

We have developed a procedure that allows the autoradiographic localization of benzodiazepine receptors in whole-body sections of neonatal rats. Central-type benzodiazepine receptors, visualized with [3H]methylclonazepam, are restricted to nervous tissue. In contrast, peripheral-type benzodiazepine receptors, visualized with [3H]Ro5-4864, occur widely, but with discrete localizations throughout the body. Peripheral-type benzodiazepine receptors are most concentrated in the adrenal cortex and the skin. Substantial levels of these receptors are also evident in the heart, the salivary glands, discrete regions of the kidney, the epithelium of the lung, the nasal and lingual epithelia, the lining of the pulmonary arteries, the thymus, the hair follicles of the vibrissae, the tooth buds and the bone marrow. Considerable binding of [3H]Ro5-4864 is observed in the brown fat pads, the liver and the spleen, but high levels of nonspecific binding preclude accurate evaluation of the actual specific binding in these organs. Only low levels of [3H]Ro5-4864 binding sites are found in the brain and they are virtually undetectable in the skeletal muscle, the eye, the inner ear and the gastrointestinal tract. High levels of peripheral-type benzodiazepine receptor appear present in tissues that derive their metabolic energy primarily from oxidative phosphorylation, whereas only low levels are present in tissues that can derive their metabolic energy largely from glycogenolysis. Association of these receptors with mitochondria and a possible role in modulation of energy metabolism is suggested further by the observation that the histochemically visualized distribution of cytochrome oxidase activity overlaps the autoradiographic pattern of [3H]Ro5-4864 binding sites.

The treatment of 179 blunt trauma-induced liver injuries in a statewide trauma center

The records of 179 patients who were admitted to a statewide trauma center with liver injuries from blunt abdominal trauma are reviewed. The overall mortality for the 119 men and 60 women was 35 per cent. The simpler forms of injury (classes 1, 2, and 3) were easily treated and yielded good results, whereas treatment for major injuries, involving lobar destruction and vena caval injury (classes 4 and 5), yielded poor results. Hepatic artery ligation was successful in only 7 of 17 cases, hepatic lobectomy was successful in 3 of 16 cases, and intracaval shunting was successful in both in which it was attempted. Anatomic variation, severity of injury from blunt abdominal trauma, and perhaps rapidity of evacuation combine to give poor results in these injury categories. While 26 per cent of all mortality occurred in patients with severe head injuries, hemorrhage was the most frequent cause of death (49%). In 19 of these 30 patients, the hemorrhage was from the liver. Infection played a significant role in the deaths of 27 patients. In eight of these 27 patients, the infections were related directly to the liver injury. The number of associated injuries per patient appeared unrelated to the overall outcome of the injury.

Superior mesenteric artery and vein injuries from blunt abdominal trauma

During an 8-year period, from 1974 to 1982, 13 patients were treated for superior mesenteric vascular injury secondary to blunt abdominal trauma. Ten male and three female patients ranged in age from 18 to 68 years (average age, 42.7 years). Six patients presented in profound shock, two presented in cardiopulmonary arrest, and five presented with mild shock. The 13 patients had an average of 3.2 associated intra-abdominal injuries. Six patients had devitalized bowel as a direct consequence of injury to the superior mesenteric vessels. One patient developed intestinal necrosis postoperatively from thrombosis of the superior mesenteric vein which led to extensive small bowel resection. The blood replacement ranged from 2 to 30 units, averaging 11.7 units per patient. Operative procedures included lateral arteriorrhaphy (five patients) and venorrhaphy (11 patients). Four patients required combined vessel repair and one patient required ligation of both vessels and bowel resection. The mortality rate of 57% was primarily due to massive acute hemorrhage, which was larger than could be accounted for by the associated intraabdominal injuries. Free intraperitoneal hemorrhage from the valveless portal system, which can carry up to 60% of cardiac output, causes massive bleeding until abdominal tamponade supervenes.

Neurochemical changes in murine trisomy 16: delay in cholinergic and catecholaminergic systems

Two strains of Mus musculus musculus, C57BL/6J and CD-1, and Mus musculus poschiavinus, the tobacco mouse, were used to study the effects of increased gene dosage of mouse chromosome 16 (MMU 16). A developmental delay has been found in the brains of murine trisomy 16 (Ts16) fetuses. Both the brain weight (in all three strains) and DNA content (in CD-1) were reduced, while protein content was unchanged in Ts16 compared to normal littermates. The daily increments of weight and protein (except in M. m. poschiavinus) were significantly greater in Ts16. The activities of choline acetyltransferase and acetylcholinesterase and muscarinic receptor binding were reduced. Their daily increments were also reduced to less than 56% that of littermates in Ts16 brains. The rate limiting enzymes of catecholaminergic neurons, tyrosine hydroxylase and dopamine beta-hydroxylase, and the concentration of catecholamines in the brains of Ts16 animals were lower. The activities of three other catecholaminergic enzymes, DOPA decarboxylase, catechol O-methyltransferase, and monoamine oxidase, were generally elevated in Ts16 brain, as were their daily increments. These observations indicate a significant developmental alteration in the maturation of the trisomic brain and suggest future avenues for defining the effect of increased gene dosage of MMU 16 in the CNS.

Phorbol ester receptors: autoradiographic identification in the developing rat

Autoradiography with 3H-labeled phorbol dibutyrate was used for the light microscopic detection of phorbol ester receptors in rat fetuses. In 15- and 18-day fetuses, as well as in adult rats, receptors were found to be concentrated in the central nervous system. The localization of receptors in the ventral marginal zone of the fetal neural tube, the lens of the eye, and other sites suggests a role for phorbol ester receptors in cellular process extension and cell-cell interaction.

An in vitro assay for K-papovavirus of mice

Primary cultures of mouse embryo cells were inoculated with K virus, a murine papovavirus, and were examined for cytopathic effect (CPE) of for the development of fluorescent antibody staining specific for K virus V antigen. CPE was not observed. However, numerous cells in infected cultures exhibited positive nuclear fluorescence, and the presence of papovavirus virions was demonstrated by electron microscopy. Extracts from infected cultures produced typical K virus pneumonia in newborn mice. Inoculation of cultures with serial dilutions of virus demonstrated that these cells provide a fluorescent antibody assay for K virus equal in sensitivity to animal inoculation methods. Although specific K virus fluorescence was also detected in cultures of fetal mouse endocardial cells, livers, placentas, and brains, positive cells were much less abundant in these cultures than in cultures of mouse embryo cells. The mouse embryo culture assay described in the present paper represents the first method of measuring K virus infectivity in vitro.

Immunoreactivity of the two common allozymes of murine glucosephosphate isomerase

There are two common electrophoretic variants (allozymes) of murine glucosephosphate isomerase (GPI). In order to develop immunocytochemical procedures that are allozyme-specific, the two variants (GPI-1A and GPI-1B) were purified from skeletal muscle of several mouse strains and used as antigens for the elicitation of antibodies. The allozymes were purified to a specific activity of 800 units/mg by substrate elution from cellulose phosphate. When the purified allozymes were presented as antigens to goats, rabbits, and mice (both syngeneically and allogeneically), the goats and rabbits produced high titers of anti-GPI antibody, but no humoral antibody was detected in the mice, as determined by radioimmunoassays. Antisera specific for the GPI-1B variant were enriched by absorbing selected sera with GPI-1A conjugated to Sepharose 4B. No antisera specific for GPI-1A were detected following the immunizations. The specificity of the anti-GPI-1B antisera provides a unique opportunity for the development of immunocytochemical procedures for studying the distribution fo this allozyme in chimeric mouse tissues.

Age-related pigmentation changes in the coats of allophenic mice

Hair pigmentation and patterns of pigmentation change with age in the coats of BALB/cByJ in equilibrium C57BL/6J allophenic mice. These changes are particularly evident on the dorsum where there is an increase in the proportion of white areas at the expense of agouti and black areas. The most plausible explanation for these changes is that they represent a continuous selection for one of the two genotypes of cells from which the melanoblasts and hair follicles of these animals are derived.

An immunofluorescence procedure for the tissue localization of glucosephosphate isomerase

Anti-glucosephosphate isomerase antibodies have been used to reveal the presence of the glycolytic and gluconeogenic enzyme, glucosephosphate isomerase (GPI) in mouse tissues by an indirect immunofluorescence technique. The enzyme was localized in 6-micron sections from tissues embedded in paraffin. GPI was observed in the sarcoplasm of skeletal muscle, all hepatocytes of the liver, and in the granulosa cells and oocytes of growing ovarian follicles. The immunofluorescence procedure circumvents the problems associated with the conventional localization of GPI by histochemistry and appears to be a more sensitive procedure for the detection of low concentrations of GPI, as demonstrated by the staining of the ovarian follicles.

Immunofluorescence and histochemical localization of glucosephosphate isomerase in neural tissues

The distribution of glucosephosphate isomerase (GPI, D-glucose-6-phosphate ketol isomerase) in mouse nervous tissue has been determined at the light microscopic level by immunofluorescence and histochemical procedures. The fluorescence procedure, which utilizes anti-GPI antibodies, detected lower levels of GPI than the histochemical procedure, which relies upon the catalytic activity of the enzyme. The distribution of GPI in nervous tissue is very similar to that of hexokinase. High levels of GPI were found in the Purkinje cells, the molecular layer, and the glomeruli of the granular layer in the cerebellar cortex; the pontine nuclei and the inferior olivary nuclei of the pons and medulla; the neurons of the thalamus and hypothalamus; the pyramidal cells, the dentate nuclei, and Ammons' horn of the cerebral cortex; the ventral horn cells of the spinal cord; and ventricular cells, choroid plexus cells, and the leptomeninges. The neuropil throughout the central nervous system (CNS) stained uniformly with moderately high levels of GPI. No GPI was observed in the myelin sheaths of the CNS.

Studies of cultured human and simian fetal brain cells. II. Infections with human (BK) and simian (SV40) papovaviruses

Both simian virus 40 (SV40) and BK viruses infected and lysed not only oligodendroblasts and astrocytes, but also neuroblasts and epithelioid or mesenchymal cells in cultures of fetal brain cells derived from human, rhesus, and cynomolgus hosts. Lytic infections of these four cell types differed ultrastructurally in the amount and arrangement of virions in the nucleus, the extent of nuclear membrane redundancy, the presence of nuclear virion arrays, and the amounts of virions in the cytoplasm. However, major differences were not noted between SV40 and BK viruses, nor between different species of origin or region of brain explanted. Modified astrocytic cells persisted in cultures from all three sources after infection by either virus. These cells stained for glial fibrillary acidic protein (GFAP) and polyomavirus tumour (T) antigen, but did not subculture indefinitely.

Studies of cultured human and simian fetal brain cells. I. Characterization of the cell types

Explant cultures of the cerebral subventricular zone and cerebellar external germinal layer were established from fetal human, rhesus and cynomolgus monkey brains. Using comparable gestational ages, the morphogenesis of the cultures from these three sources was almost indistinguishable. Four cell types were distinguished by electron microscopy. Germinal cells or neuroblasts were confined largely to the primary explant and extended into a transitional outgrowth region. Astrocytes, which stained for glial fibrillary acidic protein, grew out of the explants and these could be distinguished from the large, mesenchymal epithelioid cells. A fourth cell type, not identified in previous studies, had the ultrastructural characteristics of an oligodendrocyte, but did not produce myelin in these culture conditions.

Presence of radial glia in foetal mouse cerebellum

The ventricular layer (VL) of foetal mouse cerebellum at days 13--15 of gestation was studied by light and electron microscopy. In Golgi-stained material, round or ovoid cells are located in the VL. These cells have ascending processes, which extend to the pial surface. Ultrastructurally, the ascending processes are electron-lucent, contain microfilaments, some smooth endoplasmic reticulum and scant free ribosomes. They appear to be immature glial processes, oriented radially away from the ventricle. The perikarya of these glial cells lie either in the ventricular or subventricular zones. Juxtaposed along the length of these radially oriented glial processes are unidentified cells, some of which are attached to the immature glial fibres by puncta adhaerentia. These cells are elongated or ovoid with a thin rim of cytoplasm containing few organelles. These unidentified cells may represent neuroblasts (Purkinje cells, Golgi cells, cells of the deep cerebellar nuclei) or glioblasts, (precursors of astrocytes and/or oligodendrocytes) at very early stages of development.