Nervous system ganglioside composition of normothermic and hibernating dormice (Glis glis)

The ganglioside pattern of seven different regions, olfactory bulb, forebrain cortex, midbrain (corpora quadrigemina), cerebellum, brain stem, pons and spinal cord, of nervous system of normothermic and hibernating dormice (Glis glis) were investigated by two dimensional thin layer chromatography and densitometric quantification. Up to thirty different ganglioside spots were resolved, fifteen of which belonging to alkali labile species. Alkali labile gangliosides were present in all the regions obtained from normothermic animals, and their content, expressed as percentage of total ganglioside-bound sialic acid, ranged from a minimum of 10.2% in olfactory bulb, to a maximum of 30.1% in spinal cord. The most abundant alkali labile gangliosides were O-Ac-GT1b, O-Ac-GQ1b and an unidentified one, we coded I3. Alkali labile gangliosides were practically undetectable in hibernating dormice. They could be recognized only in brain stem, 3.3% and olfactory bulb, 0.6%.     

Distribution and Ontogeny of 1S,3R-1-Aminocyclopentane-1,3-Dicarboxylic Acid-Sensitive and Quisqualate-Insensitive [3H]Glutamate Binding Sites in the Rat Brain

Abstract: Displacement of [³H]glutamate by 1 S ,3 R -1-aminocyclopentane-1,3-dicarboxylic acid and quisqualate (in the presence of saturating concentrations of ionotropic glutamate receptor agonists) was used to characterize optimal ionic conditions, distribution, and the ontogeny of glutamate receptor binding sites in rat brain. Using rat forebrain membranes or receptor autoradiography, optimal 1 S ,3 R -1-aminocyclopentane-1,3-dicarboxylic acid-sensitive [³H]glutamate binding was found in the presence of 100 m M bromide ions and in the absence of calcium ions. Under these conditions, [³H]glutamate binding was relatively quisqualate insensitive. In regions of the neonatal (11-day-old) and adult rat brain, this [³H]glutamate binding was highest in forebrain (striatum, cerebral cortex, and hippocampus) and hypothalamus/midbrain but was lower in the cerebellum, olfactory bulb, and pons/medulla regions. 1 S ,3 R -1-aminocyclopentane-1,3-dicarboxylic acid-sensitive and quisqualate-insensitive [³H]glutamate binding was present in the rat forebrain at 1 day of age and gradually increased more than twofold by day 50 (adult). Thus, in the presence of bromide ions and in the absence of calcium ions, [³H]glutamate labels a subpopulation of metabotropic glutamate receptors that are sensitive to 1 S ,3 R -1-aminocyclopentane-1,3-dicarboxylic acid but insensitive to quisqualate. Expression of [³H]glutamate binding under these conditions was both regionally and developmentally regulated in rat brain, suggesting that [³H]glutamate is labeling a distinct population of metabotropic glutamate receptors.     

Regional distribution of metallothionein, zinc, and copper in the brain of different strains of rats

The regional brain distribution of metallothionein (MT), zinc, and copper in the brain was determined in nine anatomical regions (olfactory bulb, cortex, corpus striatum, hippocampus, thalamus plus hypothalamus, pons plus medulla oblongata, cerebellum, midbrain, and white matter) and was compared between two different strains of rat (Sprague-Dawley [SD] and Lewis). No significant difference was observed in the whole-brain MT level between the two strains (17.8 ± 3.4 μg/g in SD rats and 20.3 ± 2.3 μg/g in Lewis rats). In SD rats, however, MT was more highly expressed in the white matter than in the other regions studied. In contrast, MT concentration was highest in the cortex and lowest in the olfactory bulb in Lewis rats. The MT levels in the cortex, corpus striatum, hippocampus, and thalamus plus hypothalamus were significantly lower in SD rats than in Lewis rats. In both strains, the olfactory bulb contained markedly higher levels of both zinc and copper than the other regions (27.9 ±6.8 μg/g zinc in SD rats and 27.6 ± 6.9 μg/g zinc in Lewis rats, and 5.2 ± 1.5 μg/g copper in SD rats and 11.1 ± 4.8 μg/g copper in Lewis rats). The next high-est zinc levels were seen in the hippocampus, whereas the next highest copper levels were in the corpus striatum in both SD and Lewis rats. The high levels of zinc and copper in the olfactory bulb were not accompanied by concomitant high MT concentrations. These results indicate that the strain of rat as well as the anatomical brain region should be taken into account in MT and metal distribution studies. However, the highest concentrations of zinc and copper in olfactory bulb were common to both SD and Lewis rats. The discrepancy between MT and the metal levels in olfactory bulb suggests a role for other proteins in addition to MT in the homeostatic control of zinc and copper.     

DCC plays a role in navigation of forebrain axons across the ventral midbrain commissure in embryonic xenopus

In the developing vertebrate brain, growing axons establish a scaffold of axon tracts connected across the midline via commissures. We have previously identified a population of telencephalic neurons that express NOC-2, a novel glycoform of the neural cell adhesion molecule N-CAM that is involved in axon guidance in the forebrain. These axons arise from the presumptive telencephalic nucleus, course caudally along the principal longitudinal tract of the forebrain, cross the ventral midline in the midbrain, and then project to the contralateral side of the brain. In the present study we have investigated mechanisms controlling the growth of these axons across the ventral midline of the midbrain. The axon guidance receptor DCC is expressed by the NOC-2 population of axons both within the longitudinal tract and within the ventral midbrain commissure. Disruption of DCC-dependent interactions, both in vitro and in vivo, inhibited the NOC-2 axons from crossing the ventral midbrain. Instead, these axons grew along aberrant trajectories away from the midline, suggesting that DCC-dependent interactions are important for overcoming inhibitory mechanisms within the midbrain of the embryonic vertebrate brain. Thus, coordinated responsiveness of forebrain axons to both chemostimulatory and chemorepulsive cues appears to determine whether they cross the ventral midline in the midbrain.     

Phylogeny, expression and enzyme activity of zebrafish cyp19 (P450 aromatase) genes

The cyp19 encodes P450 aromatase, the enzyme catalyzing the conversion of estrogens from androgens. Estrogens affect the dimorphic, anatomical, functional and behavioral aspects of development of both males and females. In zebrafish, two cyp19 genes, cyp19a and cyp19b were found. They are expressed in ovary and brain, respectively. Expression of cyp19b can be detected by 11 days post-fertilization (dpf) by in situ hybridization in the olfactory bulbs, ventral telencephalic region and the hypothalamus of the brain in both male and female, where it is generally known to be affecting the reproductive function and sexual behavior. COS-1 clones permanently expressing the enzymes have been isolated. Both aromatase enzymes encoded by these two genes are functional in COS-1 cells and they can use androstenedione and testosterone equally efficiently. The presence of two functional cyp19 in zebrafish has its evolutionary and physiological importance.     

Role of morphogens in brain growth

During the last century, experiments on the chick embryo established that the ballooning expansion of the early forebrain and midbrain vesicles is dependent on the underlying axial (notochordal) mesoderm. Transient separation of the early midbrain primordium from the notochord causes subsequent collapse of both midbrain and forebrain (telencephalic) vesicles, accompanied by pronounced folding of the neural epithelium. More recent experiments have shown that vesicle collapse is caused by defective Sonic Hedgehog (Shh) signaling from the notochord and floor plate. Separation of the notochord from the brain causes loss of ventral Shh expression, resulting in reduced cell proliferation and increased cell death in the expanding neural epithelium, and culminating in vesicle collapse. These experiments are reviewed here, and set in the context of other studies illustrating the wide range of molecular and cellular processes that cause abnormal brain morphogenesis when perturbed. We also speculate that variation in the regulation of signaling pathways such as Hedgehog may have played a significant part in generating rapid morphogenetic changes during the evolution of the vertebrate brain.     

The mouse Dlx-2 (Tes-1) gene is expressed in spatially restricted domains of the forebrain, face and limbs in midgestation mouse embryos

The pattern of RNA expression of the murine Dlx-2 (Tes-1) homeobox gene is described in embryos ranging in age from E8.5 through E11.5. Dlx-2 is a vertebrate homologue of the Drosophila Distal-less (Dll) gene. Dll expression in the Drosophila embryo is principally limited to the primordia of the brain, head and limbs. Dlx-2 is also expressed principally in the primordia of the forebrain, head and limbs. Within these regions it is expressed in spatially restricted domains. These include two discontinuous regions of the forebrain (basal telencephalon and ventral diencephalon), the branchial arches, facial ectoderm, cranial ganglia and limb ectoderm. Several mouse and human disorders have phenotypes which potentially are the result of mutations in the Dlx genes.     

Expanded expression of Sonic Hedgehog in Astyanax cavefish: multiple consequences on forebrain development and evolution

Ventral midline Sonic Hedgehog (Shh) signalling is crucial for growth and patterning of the embryonic forebrain. Here, we report how enhanced Shh midline signalling affects the evolution of telencephalic and diencephalic neuronal patterning in the blind cavefish Astyanax mexicanus, a teleost fish closely related to zebrafish. A comparison between cave- and surface-dwelling forms of Astyanax shows that cavefish display larger Shh expression in all anterior midline domains throughout development. This does not affect global forebrain regional patterning, but has several important consequences on specific regions and neuronal populations. First, we show expanded Nkx2.1a expression and higher levels of cell proliferation in the cavefish basal diencephalon and hypothalamus. Second, we uncover an Nkx2.1b-Lhx6-GABA-positive migratory pathway from the subpallium to the olfactory bulb, which is increased in size in cavefish. Finally, we observe heterochrony and enlarged Lhx7 expression in the cavefish basal forebrain. These specific increases in olfactory and hypothalamic forebrain components are Shh-dependent and therefore place the telencephalic midline organisers in a crucial position to modulate forebrain evolution through developmental events, and to generate diversity in forebrain neuronal patterning.     

The Vascularization of the Anuran Brain: Olfactory Bulb and Telencephalon: A scanning electron microscopical study of vascular corrosion casts

Lametschwandtner, A., Albrecht, U., Adam, H. 1980. The vascularization of the anuran brain. Olfactory bulb and telencephalon. A scanning electron microscopical study of vascular corrosion casts. (Department of Zoology, University of Salzburg, Austria.) — Acta zool. (Stockh.) 61(4): 225–238. The vascularization of the olfactory bulb and the telencephalon of the anuran brain is studied by means of scanning electron microscopy of vascular corrosion casts.—The olfactory bulb is supplied via a terminal branch of the ramus hemisphaerii medialis ventralis, while the drainage is via the lateral telencephalic vein. The vascular plexus which caps the olfactory bulb shows “basket-like” vascular formations facing the rostral olfactory bulb. This plexus is supplied via two sources which are a) terminal branches of the ramus hemisphaerii medialis ventralis and b) a branch of the inner carotid artery. — In the telencephalon the vascular pattern of medial and lateral cortex, the striatum, the septum, and the amygdala are described. It is demonstrated that in the cerebral cortex of the anuran brain the centrifugal blood flow is not present in that strictness found in the other parts of the brain. The arterial supply is via the ramus hemisphaerii medialis ventralis and the posterior telencephalic artery (ramus hemisphaerii medialis dorsalis) and their branches as well as by branches of the preoptic artery. The venous drainage of the telencephalon is by the lateral telencephalic vein.     

Expression pattern of Wnt inhibitor factor 1(Wif1) during the development in mouse CNS

Wnt inhibitor factor-1 (WIF-1) is an extracellular antagonist of Wnts secreted proteins. Here we describe the expression pattern of Wif1 throughout the development of the mouse central nervous system (CNS). Wif1 mRNA can be detected as early as the developmental stage E11, and expression persists to adulthood. In embryonic stages, the level of Wif1 expression was very prominent in several areas including the cerebral cortex, the diencephalon and the midbrain, with the strongest level in the hippocampal plate and the diencephalon. However, after birth, the expression level of Wif1 decreased in the cortex and diencephalon. By adulthood, Wif1 is mainly expressed in the medial habenular nucleus (MHb) in the epithalamus, the mitral layer cells in the olfactory bulb and a few nuclei in the hypothalamus. Our data shows that the expression of Wif1 was very strong during embryonic development of the CNS and suggests that Wif1 may play an essential role in the spatial and temporal regulation of Wnt signals.     

Spatiotemporal selectivity of response to Notch1 signals in mammalian forebrain precursors

The olfactory bulb, neocortex and archicortex arise from a common pool of progenitors in the dorsal telencephalon. We studied the consequences of supplying excess Notch1 signal in vivo on the cellular and regional destinies of telencephalic precursors using bicistronic replication defective retroviruses. After ventricular injections mid-neurogenesis (E14.5), activated Notch1 retrovirus markedly inhibited the generation of neurons from telencephalic precursors, delayed the emergence of cells from the subventricular zone (SVZ), and produced an augmentation of glial progeny in the neo- and archicortex. However, activated Notch1 had a distinct effect on the progenitors of the olfactory bulb, markedly reducing the numbers of cells of any type that migrated there. To elucidate the mechanism of the cell fate changes elicited by Notch1 signals in the cortical regions, short- and long-term cultures of E14.5 telencephalic progenitors were examined. These studies reveal that activated Notch1 elicits a cessation of proliferation that coincides with an inhibition of the generation of neurons. Later, during gliogenesis, activated Notch1 triggers a rapid cellular proliferation with a significant increase in the generation of cells expressing GFAP. To examine the generation of cells destined for the olfactory bulb, we used stereotaxic injections into the early postnatal anterior subventricular zone (SVZa). We observed that precursors of the olfactory bulb responded to Notch signals by remaining quiescent and failing to give rise to differentiated progeny of any type, unlike cortical precursor cells, which generated glia instead of neurons. These data show that forebrain precursors vary in their response to Notch signals according to spatial and temporal cues, and that Notch signals influence the composition of forebrain regions by modulating the rate of proliferation of neural precursor cells.     

Expression of extracellular matrix molecules in the embryonic rat olfactory pathway

Primary olfactory neurons arise from placodal neuroepithelium that is separate from the neuroepithelial plate that forms the neural tube and crest. The axons of these neurons course along a stereotypical pathway and invade the rostral telencephalic vesicle where they induce the formation of the olfactory bulb. In the present study we examined the expression of several extracellular matrix constituents during formation of the olfactory nerve pathway in order to identify putative developmentally significant molecules. Double-label immunofluorescence was used to simultaneously map the trajectory of growing primary olfactory axons by expression of growth associated protein 43 (GAP-43) and the distribution of either laminin, heparan sulfate proteoglycans (HSPG), or chondroitin sulfate proteoglycans (CSPG). At embryonic day 12.5 (E12.5) primary olfactory axons have exited the olfactory neuroepithelium of the nasal pit and formed a rudimentary olfactory nerve. These axons together with migrating neural cells form a large mass outside the rostral surface of the telencephalon. This nerve pathway is clearly defined by a punctate distribution of laminin and HSPG. CSPG is selectively present in the mesenchyme between the olfactory nerve pathway and the nasal pit and in the marginal zone of the telencephalon. At E14.5 primary olfactory axons pierce the telencephalon through gaps that have emerged in the basement membrane. At this age both laminin and HSPG are colocalized with the primary olfactory axons that have entered the marginal zone of the telencephalon. CSPG expression becomes downregulated in this same region while it remains highly expressed in the marginal zone adjacent to the presumptive olfactory bulb. By E16.5 most of the basement membrane separating the olfactory nerve from the telencephalon has degraded, and there is direct continuity between the olfactory nerve pathway and the central nervous system. This strict spatiotemporal regulation of extracellular matrix constituents in the olfactory nerve pathway supports an important role of these molecules in axon guidance. We propose that laminin and HSPG are expressed by migrating olfactory Schwann cells in the developing olfactory nerve pathway and that these molecules provide a conducive substrate for axon growth between the olfactory neuroepithelium and the brain. CSPG in the surrounding mesenchyme may act to restrict axon growth to within this pathway. The regional degradation of the basement membrane of the telencephalon and the downregulation of CSPG within the marginal zone probably facilitates the passage of primary olfactory axons into the brain to form the presumptive nerve fiber layer of the olfactory bulb. © 1996 John Wiley & Sons, Inc.     

[3H]Homoquinolinate Binds to a Subpopulation of NMDA Receptors and to a Novel Binding Site

Abstract: NMDA receptors mediate several important functions in the CNS; however, little is known about the pharmacology, biochemistry, and function of distinct NMDA receptor subtypes in brain tissue. To facilitate the study of native NMDA receptor subpopulations, we have determined the radioligand binding properties of [³H]homoquinolinate, a potential subtype-selective ligand. Using quantitative receptor autoradiography, NMDA-specific [³H]homoquinolinate binding selectively labeled brain regions expressing NR2B mRNA (layers I–III of cerebral cortex, striatum, hippocampus, and septum). NMDA-specific [³H]homoquinolinate binding was low in brain regions that express NR2C and NR2D mRNA (cerebellar granular cell layer, NR2C; glomerular layer of olfactory bulb, NR2C/NR2D; and midline thalamic nuclei, NR2D). In forebrain, the pattern of NMDA-specific [³H]homoquinolinate binding paralleled NR2B and not NR2A distribution. In addition to NMDA-displaceable binding, there was a subpopulation of [³H]homoquinolinate binding sites in the forebrain, cerebellum, and choroid plexus that was not displaced by NMDA or l -glutamate. In contrast, we found that the derivative of homoquinolinate, 2-carboxy-3-carboxymethylquinoline, markedly inhibited the NMDA-insensitive binding of [³H]homoquinolinate without inhibiting the NMDA-sensitive population. [³H]Homoquinolinate may be useful for selectively characterizing NR2B-containing NMDA receptors in a preparation containing multiple receptor subtypes and for characterizing a novel binding site of unknown function.     

Region specific gene expressions in the central nervous system of the ascidian embryo

The vertebrate brain is regionalized during development into forebrain, midbrain and hindbrain. Fibroblast growth factor 8 (FGF8) is expressed in the midbrain/hindbrain boundary (MHB) and functions as an organizer molecule. Previous studies demonstrated that the brain of basal chordates or ascidians is also regionalized at least into fore/midbrain and hindbrain. To better understand the ascidian brain regionalization, the expression of the Ciona Fgf8/17/18 gene was compared with the expression of Otx, En and Pax2/5/8 genes. The expression pattern of these genes resembled that of the genes in the vertebrate forebrain, midbrain, MHB and hindbrain, each of those domains being characterized by sole or combined expression of Otx, Pax2/5/8, En and Fgf8/17/18. In addition, the putative forebrain and midbrain expressed Ci-FgfL and Ci-Fgf9/16/20, respectively. Therefore, the regionalization of the ascidian larval central nervous system was also marked by the expression of Fgf genes.     

Region specific gene expressions in the central nervous system of the ascidian embryo

The vertebrate brain is regionalized during development into forebrain, midbrain and hindbrain. Fibroblast growth factor 8 (FGF8) is expressed in the midbrain/hindbrain boundary (MHB) and functions as an organizer molecule. Previous studies demonstrated that the brain of basal chordates or ascidians is also regionalized at least into fore/midbrain and hindbrain. To better understand the ascidian brain regionalization, the expression of the Ciona Fgf8/17/18 gene was compared with the expression of Otx, En and Pax2/5/8 genes. The expression pattern of these genes resembled that of the genes in the vertebrate forebrain, midbrain, MHB and hindbrain, each of those domains being characterized by sole or combined expression of Otx, Pax2/5/8, En and Fgf8/17/18. In addition, the putative forebrain and midbrain expressed Ci-FgfL and Ci-Fgf9/16/20, respectively. Therefore, the regionalization of the ascidian larval central nervous system was also marked by the expression of Fgf genes.     

Cloning and expression of a novel zinc finger gene, Fez, transcribed in the forebrain of Xenopus and mouse embryos

We have identified and cloned a novel zinc finger gene, Fez (forebrain embryonic zinc-finger), as a potential downstream determinant of anterior neural plate formation in Xenopus. Fez was isolated as one of several neural-specific genes that was induced by the neuralizing factor, noggin (Smith and Harland, 1992. Cell 70, 829-840), in uncommitted ectoderm. Fez has an open reading frame comprising 466 amino acids, and contains six C(2)H(2) type zinc finger domains, which are highly conserved among Drosophila, zebrafish, mouse, and human. In Xenopus, the expression of Fez begins at stage 12 in the rostral end of the neural plate, and by stage 45, it is localized to several telencephalic regions, including the olfactory bulbs, nervus terminalis, and ventricular zone. The mouse homologue of Fez is similarly expressed in the mouse forebrain by embryonic day 11.