Mapping of the presumptive brain regions in the neural plate of Xenopus laevis

Two cell autonomous fluorescent labels (DiI and Hoechst) were used as vital markers in a fate map study of the Xenopus neural plate and ridge. Most areas of the brain derive from the neural plate in a fate map that is consistent with the topology of a sheet rolling into a tube, i.e., neighboring areas are maintained as neighbors. This has enabled us not only to plot the fates of larval brain structures, but also to suggest their primordial orientation in the neural plate. Since overlapping areas of the plate gave rise to overlapping regions of the central nervous system (CNS), we have been able to construct a space-filling model of the neural plate, whereby the number of founder cells for each brain region fate-mapped may be estimated roughly. Much of the telencephalon, ventral forebrain, and dorsal brain stem derives from the neural ridge and not the neural plate in the stage 15 Xenopus embryo. The structures of the forebrain were examined in detail because there were indications of substantial cell movements in this region. The anterior pituitary arises from the mid-anterior ridge, while hypothalamic structures arise from the midline regions of the anterior neural plate. Consistent groups of ventral hypothalamic structures were labeled when fluorescent markers were applied to these parts of the neural plate, indicating stereotyped cell movements. Detailed comparisons were made between the fate map of the Ambystoma neural plate (Jacobson, 1959) and that of Xenopus.     

Fate of the anterior neural ridge and the morphogenesis of the xenopus forebrain

The fate of the anterior neural ridge was studied by following the relative movements of simultaneous spot applications of DiI and DiO from stage 15 through stage 45. These dye movements were mapped onto the neuroepithelium of the developing brain whose shape was gleaned from whole-mount in situs to neural cell adhesion molecule and dissections of the developing nervous system. The result is a model of the cell movements that drive the morphogenesis of the forebrain. The midanterior ridge moves inside and drops down along the most anterior wall of the neural tube. It then pushes forward a bit, rotates ventrally during forebrain flexing, and gives rise to the chiasmatic ridge and anterior hypothalamus. The midanterior plate drops, forming the floor of the forebrain ventricle, and, keeping its place behind the ridge, it gives rise to the posterior hypothalamus or infundibulum. The midlateral anterior ridge slides into the lateral anterior wall of the neural tube and stretches laterally into the optic stalk and retina, and then rotates into a ventral position. The lateral anterior ridge converges to the most anterior part of the dorsal midline during neural tube closure, then rotates anteriorly, and gives rise to telencephalic structures. Whole-mount bromodeoxyuridine labeling at these stages showed that cell division is widespread and relatively uniform throughout the brain during the late neurula and early tailbud stages, but that during late tailbud stages cell division becomes restricted to specific proliferative zones. We conclude that the early morphogenesis of the brain is carried out largely by choreographed cell movements and that later morphogenesis depends on spatially restricted patterns of cell division. © 1995 John Wiley & Sons, Inc.     

Differential Effect of Cerebral Ischemia on Monoamine Content of Discrete Brain Regions of the Mongolian Gerbil (Meriones unguiculatus)

The effect of bilateral cerebral ischemia on noradrenaline, dopamine, and serotonin concentrations in six brain regions (i.e., the cerebral cortex, striatum, hippocampus, midbrain-diencephalon, cerebellum, and pons-medulla oblongata) was examined in the gerbil stroke model. The relative changes in regional cerebral blood flow after bilateral common carotid occlusion were also assessed using the radioactive microsphere technique. At 1 h after bilateral carotid occlusion, a significant decrease of monoamine concentration was observed in the cerebral cortex, striatum, hippocampus, and midbrain-diencephalon whereas no significant change was detected in the cerebellum and pons-medulla oblongata. The fall in NA content was most prominent in the cerebral cortex and hippocampus and percentage reductions of dopamine and serotonin were greatest in the striatum and cerebral cortex, respectively. These results suggest that the monoamine neurons in various brain regions might have different vulnerabilities to ischemic insult and show no evidence of transtentorial diaschisis.     

Regional development of catecholamine biosynthesis in rat brain

Abstract— The ontogenetic development of norepinephrine and dopamine and their associated biosynthetic and degradative enzymes was investigated in five anatomical regions of the rat brain. Clear regional differences were found in the development of both norepinephrine and tyrosine hydroxylase (EC 1.14.3.1). In the case of both norepinephrine and tyrosine hydroxylase, brainstem structures achieved adult levels well before forebrain structures. The development of DOPA decarboxylase (EC 4.1.1.26), monoamine oxidase (EC 1.4.3.4) and catechol-0-methyl transferase (EC 2.1.1.6) did not appear to differmarkedly from area to area. Further analysis of the data revealed that in forebrain structures both the amines and the biosynthetic enzymes developed concurrently. By contrast, in the brainstem structures, there was a dissociation of amine and enzyme development with development of tyrosine hydroxylase, in particular, markedly preceding that of norepinephrine and of DOPA decarboxylase. The bases for both the lower amine levels in the infant brain and the regional developmental differences are discussed in relation to the anatomical organization of the central catecholamine-containing neurons.     

Monitoring the Stimulated Release of Dopamine with In Vivo Voltammetry. I: Characterization of the Response Observed in the Caudate Nucleus of the Rat

Microvoltammetric electrodes were employed in the brain of an anesthetized rat to monitor chemical substances in extracellular fluid following electrical stimulation of the medial forebrain bundle. An increase in concentration of an easily oxidized substance is observed in the caudate nucleus and in the nucleus accumbens. A large amount of evidence suggests that the substance that is observed following stimulation is dopamine. (1) The location of the stimulating electrode must be in known dopaminergic tracts to induce release. (2) Release is most easily observed in brain regions that contain significant numbers of dopamine-containing neurons. (3) Two voltammetric electrodes with very different electrochemical responses provide voltammograms of the released species that are unique for catechols in one case and catecholamines in another case. (4) The amount of 3,4-dihydroxyphenylacetic acid found in striatal tissue by postmortem analysis correlates with the calculated amount of dopamine released. (5) Inhibition of tyrosine hydroxylase, and thus dopamine synthesis, decreases the observed release while inhibition of monoamine oxidase, and thus formation of dopamine metabolites, does not. (6) The dependence of release on stimulation parameters agrees with results obtained with perfusion techniques. Thus, a new method has been developed to characterize endogenous dopamine release in the rat brain and can be used on a time scale of seconds.     

Unique and combinatorial functions of Fgf3 and Fgf8 during zebrafish forebrain development

Complex spatiotemporal expression patterns of fgf3 and fgf8 within the developing zebrafish forebrain suggest their involvement in its regionalisation and early development. These factors have unique and combinatorial roles during development of more posterior brain regions, and here we report similar findings for the developing forebrain. We show that Fgf8 and Fgf3 regulate different aspects of telencephalic development, and that Fgf3 alone is required for the expression of several telencephalic markers. Within the diencephalon, Fgf3 and Fgf8 act synergistically to pattern the ventral thalamus, and are implicated in the regulation of optic stalk formation, whereas loss of Fgf3 alone results in defects in ZLI development. Forebrain commissure formation was abnormal in the absence of either Fgf3 or Fgf8; however, most severe defects were observed in the absence of both. Defects were observed in patterning of both the midline territory, within which the commissures normally form, and neuronal populations, whose axons comprise the commissures. Analysis of embryos treated with an FGFR inhibitor suggests that continuous FGF signalling is required from gastrulation stages for normal forebrain patterning, and identifies additional requirements for FGFR activity.     

POLYAMINES OF THE HUMAN BRAIN DURING NORMAL FETAL AND POSTNATAL GROWTH AND DURING POSTNATAL MALNUTRITION

Abstract— The concentrations of the polyamines and putrescine were measured in the brains of human infants during fetal and early postnatal development. The concentrations of the amines were also measured in the brains of children who were malnourished during the first 2 years of life. In the brains of the adequately-nourished infants there were differences in the developmental profiles of the amines between different regions of the brain, and the changes in polyamine concentrations paralleled changes in nucleic acid accumulation. The concentration of putrescine was much higher than that of the polyamines in all regions of the brain, and in the brain stem there were marked increases in putrescine concentration at the time of most rapid rate of myelination. Putrescine also increased markedly in the forebrain at the time of neuroblast multiplication in the fetus. In children malnourished during the first year of life there were reductions in the concentrations of spermidine and putrescine in the forebrain and brainstem, but spermine was unaffected. Malnutrition had no effect on the concentration of any of the amines in the cerebellum.     

EphB1 and EphB2 intracellular domains regulate the formation of the corpus callosum and anterior commissure

The two cortical hemispheres of the mammalian forebrain are interconnected by major white matter tracts, including the corpus callosum (CC) and the posterior branch of the anterior commissure (ACp), that bridge the telencephalic midline. We show here that the intracellular signaling domains of the EphB1 and EphB2 receptors are critical for formation of both the ACp and CC. We observe partial and complete agenesis of the corpus callosum, as well as highly penetrant ACp misprojection phenotypes in truncated EphB1/2 mice that lack intracellular signaling domains. Consistent with the roles for these receptors in formation of the CC and ACp, we detect expression of these receptors in multiple brain regions associated with the formation of these forebrain structures. Taken together, our findings suggest that a combination of forward and reverse EphB1/2 receptor‐mediated signaling contribute to ACp and CC axon guidance. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 405–420, 2016     

Presenilin-1/Presenilin-2双基因敲除小鼠脑中单胺类神经递质变化的研究

条件性presenilins双基因敲除小鼠(dKO小鼠)表现出类似阿尔茨海默症(AD)的大部分神经退行性病症,如Tau 蛋白磷酸化、神经元凋亡、皮层萎缩以及认知能力受损等．为探讨presenilins功能缺失、神经退行性症状与单胺类递质变化的相关性,利用毛细管电泳法检测6、9和12月龄dKO小鼠皮层、海马及其他前脑部位中各单胺类神经递质的含量．结果显示,与对照组相比,dKO小鼠皮层中单胺类神经递质在6月龄时显著降低,而随着年龄的增长,神经退行性病变加剧,递质浓度也均明显上升,在海马区,dKO小鼠单胺类递质则呈上升趋势,但仅6月龄时5-羟色胺和肾上腺素及12月龄时各递质的上升有统计学意义,前脑其他部位5-羟色胺和多巴胺递质在6、9月龄时与对照组相近,在12月龄时则显著降低,而去甲肾上腺素和肾上腺素在6月和12月龄时均呈降低趋势,且均有统计学差异(6月龄肾上腺素除外)．实验表明,单胺类神经递质在presenilins双基因敲除的小鼠前脑各区域中的水平均发生了随龄化的变化,且在前脑皮层、海马与前脑其他区域的变化趋势各有不同,而单胺类递质的变化是presenilins双基因敲除导致的直接结果还是间接结果,单胺类递质在AD样神经退性行病变中的作用如何,还有待于进一步的研究．     

Hedgehog regulated Slit expression determines commissure and glial cell position in the zebrafish forebrain

Three major axon pathways cross the midline of the vertebrate forebrain early in embryonic development: the postoptic commissure (POC), the anterior commissure (AC) and the optic nerve. We show that a small population of Gfap+ astroglia spans the midline of the zebrafish forebrain in the position of, and prior to, commissural and retinal axon crossing. These glial ;bridges' form in regions devoid of the guidance molecules slit2 and slit3, although a subset of these glial cells express slit1a. We show that Hh signaling is required for commissure formation, glial bridge formation, and the restricted expression of the guidance molecules slit1a, slit2, slit3 and sema3d, but that Hh does not appear to play a direct role in commissural and retinal axon guidance. Reducing Slit2 and/or Slit3 function expanded the glial bridges and caused defasciculation of the POC, consistent with a ;channeling' role for these repellent molecules. By contrast, reducing Slit1a function led to reduced midline axon crossing, suggesting a distinct role for Slit1a in midline axon guidance. Blocking Slit2 and Slit3, but not Slit1a, function in the Hh pathway mutant yot (gli2DR) dramatically rescued POC axon crossing and glial bridge formation at the midline, indicating that expanded Slit2 and Slit3 repellent function is largely responsible for the lack of midline crossing in these mutants. This analysis shows that Hh signaling helps to pattern the expression of Slit guidance molecules that then help to regulate glial cell position and axon guidance across the midline of the forebrain.     

Slit proteins prevent midline crossing and determine the dorsoventral position of major axonal pathways in the mammalian forebrain.

We report that Slit proteins, a family of secreted chemorepellents, are crucial for the proper development of several major forebrain tracts. Mice deficient in Slit2 and, even more so, mice deficient in both Slit1 and Slit2 show significant axon guidance errors in a variety of pathways, including corticofugal, callosal, and thalamocortical tracts. Analysis of multiple pathways suggests several generalizations regarding the functions of Slit proteins in the brain, which appear to contribute to (1) the maintenance of dorsal position by prevention of axonal growth into ventral regions, (2) the prevention of axonal extension toward and across the midline, and (3) the channeling of axons toward particular regions.     

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.     

以田鼠作为动物模型来研究社会行为的进化:基因、脑与行为

田鼠属的一些近缘种间具有独特的社会行为多态性。例如Microtusochrogaster和M .pinetorum为一夫一妻制 ,而M .montanus和M .pennsylvanicus则为独居和一夫多妻制。无论是在野外还是人工饲养的条件下 ,单配制的田鼠其雌、雄成年个体一经交配即在两者之间形成长期的配偶关系并且双亲共同哺育后代。已证明神经多肽加压素 (Vasopressin)参与了田鼠单配制行为的神经调控。本篇综述了过去以及近期关于加压素调控田鼠配偶关系形成的研究结果和进展。首先 ,阐述了加压素V1a受体 (V1aR)在脑分布的种间差异 ,并以此来鉴别特定脑区在配偶关系形成中的功能 ;其次 ,探讨了运用V1aR拮抗物的药理学方法来决定究竟哪些脑区参与配偶关系的形成 ,还描述了田鼠种间V1aR基因结构和功能的不同 ,以及这些不同对V1aR在大脑的分布和行为调控潜在的作用机制 ;最后 ,讨论了最新的研究结果 ,即对一夫多妻制田鼠进行脑V1aR基因的改造 ,从而使之表现出一夫一妻制田鼠的行为。总之 ,了解复杂的社会性行为的遗传和神经机制可以加深我们对种间和种内行为分歧进化的理解     

Galanin-Like Immunoreactivity Is Increased in the Postmortem Cerebral Cortex from Patients with Alzheimer's Disease

Abstract: Galanin is a peptide that is associated with cholinergic neurons of the basal forebrain and, thus, of interest for the neuropathology of Alzheimer's disease. In the present study, human galanin-like immunoreactivity was measured in postmortem human cerebral cortical tissues by using a homologous radioimmunoassay. In an initial study, six cerebral cortical regions were evaluated from nine elderly controls, 13 neuropathologically verified Alzheimer's disease patients, and 19 elderly schizophrenics. A significant 65% increase in galanin was found in frontal cortex Brodmann area 8 of Alzheimer's disease patients compared with controls. In contrast, cerebral cortical tissues from elderly schizophrenics were not different from those from elderly controls in any region. In a second study, 10 cerebral cortical regions were evaluated from 50 neuropathologically verified Alzheimer's disease patients and nine elderly controls. Concentrations of galanin were increased significantly 26–61% in six of 10 cerebral cortical regions examined (Brodmann areas F8, F44, T20, T21, T36, and P22). Purification of brain extracts by size-exclusion Sephadex G-50 chromatography revealed that human galanin-like immunoreactivity eluted in two peaks of different molecular weights. These studies reveal increased concentrations of galanin in the cerebral cortex of Alzheimer's disease, similar to previous findings in basal forebrain tissue. Because galanin inhibits cholinergic neurotransmission, these findings may have important implications in the understanding of Alzheimer's disease neuropathology and associated cognitive deficits.     

Blood-Brain Barrier Monoamine Oxidase: Enzyme Characterization in Cerebral Microvessels and Other Tissues from Six Mammalian Species, Including Human

We studied the enzyme monoamine oxidase (MAO) in isolated cerebral microvessels, and in mitochondria-enriched brain and liver preparations from six mammalian species, including human. We also studied MAO distribution in various tissues and in discrete brain regions of the rat. MAO was assessed by measuring the specific binding of [3H]pargyline, an irreversible MAO inhibitor, and the rates of oxidation of known MAO substrates: benzylamine, tyramine, tryptamine, and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Molecular forms of MAO were examined by using specific MAO inhibitors, and by polyacrylamide gel electrophoresis after [3H]pargyline binding. In general, the liver from all species had higher MAO levels than the brain, with minor variation among species in their brain and liver MAO content. However, there were remarkable species differences in brain microvessel MAO, with rat microvessels having one of the highest MAO activity among all tissues, whereas MAO activities in brain microvessels from humans, mice, and guinea pigs were very low. In most rat tissues, including the brain, there was a preponderance of MAO-B over MAO-A. The only exceptions were the heart and skeletal muscle. Estimates of MAO half-life in rat brain microvessels, rat brain, and rat liver indicated that microvessel MAO had a higher turnover rate. The reasons underlying the remarkable enrichment of rat cerebral microvessels with MAO-B are unknown, but it is evident that there are marked species differences in brain capillary endothelium MAO activity. The biological significance of these findings vis a vis the role of MAO as a "biochemical blood-brain barrier" that protects the brain from circulating neurotoxins and biogenic amines should be investigated.     

Clonal and molecular analysis of the prospective anterior neural boundary in the mouse embryo

In the mouse embryo the anterior ectoderm undergoes extensive growth and morphogenesis to form the forebrain and cephalic non-neural ectoderm. We traced descendants of single ectoderm cells to study cell fate choice and cell behaviour at late gastrulation. In addition, we provide a comprehensive spatiotemporal atlas of anterior gene expression at stages crucial for anterior ectoderm regionalisation and neural plate formation. Our results show that, at late gastrulation stage, expression patterns of anterior ectoderm genes overlap significantly and correlate with areas of distinct prospective fates but do not define lineages. The fate map delineates a rostral limit to forebrain contribution. However, no early subdivision of the presumptive forebrain territory can be detected. Lineage analysis at single-cell resolution revealed that precursors of the anterior neural ridge (ANR), a signalling centre involved in forebrain development and patterning, are clonally related to neural ectoderm. The prospective ANR and the forebrain neuroectoderm arise from cells scattered within the same broad area of anterior ectoderm. This study establishes that although the segregation between non-neural and neural precursors in the anterior midline ectoderm is not complete at late gastrulation stage, this tissue already harbours elements of regionalisation that prefigure the later organisation of the head.     

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.     

Parallel increases in lipid and protein oxidative markers in several mouse brain regions after methamphetamine treatment

The neurotoxic actions of methamphetamine (METH) may be mediated in part by reactive oxygen species (ROS). Methamphetamine administration leads to increases in ROS formation and lipid peroxidation in rodent brain; however, the extent to which proteins may be modified or whether affected brain regions exhibit similar elevations of lipid and protein oxidative markers have not been investigated. In this study we measured concentrations of TBARs, protein carbonyls and monoamines in various mouse brain regions at 4 h and 24 h after the last of four injections of METH (10 mg/kg/injection q 2 h). Substantial increases in TBARs and protein carbonyls were observed in the striatum and hippocampus but not the frontal cortex nor the cerebellum of METH-treated mice. Furthermore, lipid and protein oxidative markers were highly correlated within each brain region. In the hippocampus and striatum elevations in oxidative markers were significantly greater at 24 h than at 4 h. Monoamine levels were maximally reduced within 4 h (striatal dopamine [DA] by 95% and serotonin [5-HT] in striatum, cortex and hippocampus by 60-90%). These decrements persisted for 7 days after METH, indicating effects reflective of nerve terminal damage. Interestingly, NE was only transiently depleted in the brain regions investigated (hippocampus and cortex), suggesting a pharmacological and non-toxic action of METH on the noradrenergic nerve terminals. This study provides the first evidence for concurrent formation of lipid and protein markers of oxidative stress in several brain regions of mice that are severely affected by large neurotoxic doses of METH. Moreover, the differential time course for monoamine depletion and the elevations in oxidative markers indicate that the source of oxidative stress is not derived directly from DA or 5HT oxidation.     

Oxidation of β-Phenylethylamine by Both Types of Monoamine Oxidase: Examination of Enzymes in Brain and Liver Mitochondria of Eight Species

Abstract: β-Phenylethylamine (PEA) was characterized as a substrate for type A and type B monoamine oxidase (MAO) in brain and liver mitochondria of eight species at different substrate concentrations. In all species, at 10.0 μM, PEA was almost specific for type B MAO. At 1000 μM, however, the amine was common for both types of MAO in rat brain and liver, human brain and liver, mouse brain, guinea pig brain and liver, and bovine brain, while it was specific for type B MAO in mouse liver, rabbit brain and liver, bovine liver, pig brain and liver, and chicken brain and liver. From the present study, when PEA is used as a type B substrate, it is recommended that the substrate concentration should be sufficiently low to avoid the effects of species and tissue differences.