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1.
The Notch signalling pathway plays essential roles during the specification of the rostral and caudal somite halves and subsequent segmentation of the paraxial mesoderm. We have re-investigated the role of presenilin 1 (Ps1; encoded by Psen1) during segmentation using newly generated alleles of the Psen1 mutation. In Psen1-deficient mice, proteolytic activation of Notch1 was significantly affected and the expression of several genes involved in the Notch signalling pathway was altered, including Delta-like3, Hes5, lunatic fringe (Lfng) and Mesp2. Thus, Ps1-dependent activation of the Notch pathway is essential for caudal half somite development. We observed defects in Notch signalling in both the caudal and rostral region of the presomitic mesoderm. In the caudal presomitic mesoderm, Ps1 was involved in maintaining the amplitude of cyclic activation of the Notch pathway, as represented by significant reduction of Lfng expression in Psen1-deficient mice. In the rostral presomitic mesoderm, rapid downregulation of the Mesp2 expression in the presumptive caudal half somite depends on Ps1 and is a prerequisite for caudal somite half specification. Chimaera analysis between Psen1-deficient and wild-type cells revealed that condensation of the wild-type cells in the caudal half somite was concordant with the formation of segment boundaries, while mutant and wild-type cells intermingled in the presomitic mesoderm. This implies that periodic activation of the Notch pathway in the presomitic mesoderm is still latent to segregate the presumptive rostral and caudal somite. A transient episode of Mesp2 expression might be needed for Notch activation by Ps1 to confer rostral or caudal properties. In summary, we propose that Ps1 is involved in the functional manifestation of the segmentation clock in the presomitic mesoderm. 相似文献
2.
The rostral cartilages of batoid fishes were examined to elucidate their development, morphology and homology. Comparison of a variety of rostral cartilages among elasmobranchs with other groups of vertebrates shows that rostral cartilages originate embryologically from the trabecula and/or lamina orbitonasalis. Because different morphogenetic patterns of the derivatives of the two embryonic cartilages give rise to a wide variety of forms of rostral cartilages even within elasmobranchs, and because morphogenesis involves complex interactions among participating structures in the ethmo-orbital area, we put forward conceptual and empirical discussions to elucidate the homology of the rostral cartilages in batoid fishes. With six assumptions given in this study and based on recent discussions of biological and historical homology, our discussions centre on: (1) recognition of complex interactions of participating biological entities in development and evolution; (2) elucidation of a set of interacting biological and evolutionary factors to define a given morphological structure; (3) assessment of causal explanations for similarities or differences between homologous structures by determining genetic, epigenetic and evolutionary factors. Examples of conceptual approaches are given to make the approaches testable. Although a paucity of knowledge of rostral cartilage formation is the major obstacle to thorough analysis of the conceptual framework, several tentative conclusions are made on the homology of rostral cartilages that will hopefully attract more research on development and evolution in vertebrate morphology. These are: (1) the rostral cartilage in each group of vertebrates examined can be defined by both developmentally associated and adult structural attributes, yet such data do not allow us to assess homology of a variety of forms of rostral cartilages at higher taxonomic categories; (2) the entire rostral cartilage in elasmobranchs is formed by the contribution of the embryonic trabecula and lamina orbitonasalis. The status of the development and homology of the rostral cartilage in holocephalans remains uncertain; (3) there is no simple picture of evolution of rostral cartilages among three putative monophyletic assemblages of elasmobranchs, galeomorphs, squaloids (possibly plus Squatina, Chlamydoselachus and hexanchoids as the orbitostylic group) and batoid fishes. It is highly likely that rostral cartilages in each subgroup or subgroups of these assemblages may be of phylogenetic significance but that it may not serve as a basis to unite these assemblages into much higher assemblages; (4) the tripodal rostral cartilage is unique in form in the group including some carcharhinoid and lamnoid sharks. The status of the analogous tripodal cartilage in some squaloids remains uncertain. The unfused tripodal cartilage of the electric ray Narke is interpreted as developmentally equivalent to, but not homologous with, the unfused or fused ones in the sharks; (5) the rostral cartilage in the electric ray Torpedo is uniquely formed because of its embryonic origin solely from the ventro-medial part of the lamina orbitonasalis, but it is regarded as homologous with the rostral cartilages which are formed by the trabecula and other components of the lamina orbitonasalis in other batoid fishes; (6) the cornu trabecula contributes to the formation of the ventral stem of the rostral cartilage at least in elasmobranchs, especially to a particular set of rostral cartilages, i.e. the tripodal rostral cartilage in the shark Scyliorhinus and dorso-ventrally flattened rostral shaft in the narcinidid electric rays; (7) there is a unique form of a rostral shaft with rostral appendix in skates and probably guitarfishes; (8) there is no rostral cartilage in adult benthic stingrays, pelagic stingrays Dasyatis violacea and Myliobatidae, although it is present in embryonic stages; (9) there is a unique form of the rostral cartilage as a rostral projection from the dorso-lateral part of the lamina orbitonasalis in pelagic stingrays Rhinopteridae and Mobulidae, which together with part of the pectoral fins, forms a pair of cephalic fins; (10) different developmental mechanisms may be responsible for the absence or loss of rostral cartilages in different groups, i.e. absence of the cartilage derived from the medial area of the trabecula in Torpedo vs absence of the rostral cartilage in benthic stingrays; (11) the rostral cartilages in some placental mammals (cetaceans and sirenians) arise only from the medial area of the trabecula because monotreme and placental mammals do not form the trabecula cranii; (12) some actinopterygians and sacropterygians possess a rostral cartilage which originates only from the medial area of the trabecula. One scombroid group, including Sardini and Thunnini, Scomberomorus, Acanthocybium, Istiophoridae and Xiphias, possesses a unique larval beak composed of the rostral cartilage, ethmoid cartilage and premaxillar bone. The development and homology of other rostral cartilages remain to be further elucidated; (13) urodeles possess a medial rostral process whose anlage is probably developmentally equivalent to that in batoid fishes but the occurrence in urodeles is either atavistic or unique (autapomorphic); (14) the upper jaw of tadpoles is unique in possessing the suprarostral cartilage; the anlage of the cartilage is probably developmentally equivalent to the outgrowth of the cornu trabecula in batoid fishes. 相似文献
3.
采用免疫组织化学PAP/DAN-镍加强技术和形态计量法研究了中国树鼩下丘脑加压素(VP)能和催产素(OT)能视上核主部(SONp)、视上核交叉后部(SONr)和室旁核(PVN)的平均矢轴长度,SONp,SONr和PVN内VP能和OT能神经元胞体截面积的平均值;SONp,SONr和PVN的VP能和OT能神经元总数;各校团的各个系列节段内VP能和OT能神经元的比较计数。发现,SONp前1/3部分OT能神经元明显多于VP能的,而后2/3部分则相反;SONr前2/3部分VP能神经元明显多于OT能的,而后1/3部分两者差别不明显;PVN前2/3部分OT能神经元明显多于VP能的,而后1/3部分则相反。本文就中国树下丘脑SON和PVN内VP能和OT能神经元的形态计量学资料与大鼠的进行了比较。 相似文献
5.
By means of intracerebral microdialysis effects of cholecystokinin peptides and neurotensin administered via the microdialysis probe have been studied on dopamine release and metabolism in the nucleus accumbens and neostriatum of the halothane anaesthetized male rat. Levels of extra cellular dopamine (DA) and its metabolites 3,4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were assessed in nuc. accumbens (rostral and caudal part) using high performance liquid chromatography in combination with electrochemical detection. (1) In the rostral part of the nuc. accumbens CCK-8 (10 and 100 μM), CCK-33 (100 μM) but not CCK-4 (10 and 100 μM) increased the levels of DA in the perfusate without increasing the extracellular levels of DOPAC and HVA. (2) In the caudal nuc. accumbens CCK-8 and CCK-4 in concentrations of 10 μM and 100 μ M of CCK-33 had no effect on DA release and metabolism, since the extracellular levels of DA, DOPAC and HVA were not changed. (3) In the rostral nuc. accumbens perfusion with 10 μM of neurotensin but not with any other concentration of neurotensin (0.01, 0.1, 1 and 100 μM) increased the levels of DA in the extracellular fluid. (4) In the caudal nuc. accumbens a 40 min perfusion with neutrotensin produced a concentration dependent increase of the levels of DA in the perfusate (peak action at 10 μ M) which in this case was associated with increases in the extracellular levels of DOPAC and HVA. (5) By means of receptor autoradiography using (3-[125I]iodotyrosyl3) neurotensin it was found that a 40 min perfusion with this radioligand in the rostral nuc. accumbens reached a total volume of 0.051 mm3. The diffusion of the radioligand was limited to the rostral or caudal part of the nuc. accumbens depending upon the site of placement of the dialysis probe. The results indicate the existence of cholecystokinin (CCK) receptors in the rostral nuc. accumbens, which are sensitive to CCK-8 and CCK-33 but not to CCK-4, and which facilitate DA release without producing any detectable increase in DA metabolites. In contrast, such receptors do not appear to play a similar role in the regulation of DA release in the caudal nuc. accumbens, where DA terminals contain CCK-like immunoreactivity. Furthermore, the results indicate that neurotensin receptors exist both in the rostral and caudal nuc. accumbens, where they inter alia enhance the release of DA. In the caudal nuc. accumbens these effects of neurotensin are also associated with an increase of DA metabolites, possibly suggesting that in this region neurotensin receptors may also control DA synthesis. 相似文献
6.
本文解剖观察了我国有代表性的鲨类脑颅共32种,分隶于8目14科24属。研究结果认为鲨类的脑颅共可分为9个式型和12个亚型。现存虎鲨目、须鲨目的鲸鲨科和扁鲨目吻软骨缺如,六鳃鲨目、须鲨目、角鲨目和锯鲨目均具一吻软骨,它们是一些古老和一些特化的类群。现存大多数种类均具3根吻软骨。在各不同分类阶元常有其不同的形态特征,可作为分类依据之一,亦可显示其亲缘关系。 相似文献
7.
应用计算机图形技术在大鼠脑的连续冠状切片Nissl染色的基础上通过Onyx2超级图形工作站对大鼠脑的纹状体进行了三维重建。结果提示:大鼠纹状体由尾壳核、苍白球和边缘区三部分组成,其中边缘区位于尾壳核和苍白球之间,被二完全包绕;尾壳核呈近似的内凹半球形,嘴尾径最大的为6.2mm;背腹径最大为4.9mm;宽度(冠状平面上的内外径)为3.5mm。从嘴侧到尾侧随着脑平面的增宽,尾壳核逐渐向外侧(即靠近外轮廓的方向)移位。苍白球呈块形,嘴尾径最大为4.4mm,背腹径最大为2.6mm,宽度(冠状平面上的内外径)最大为1.5mm。位于尾壳核的内侧,除内侧外基它三个方向均被尾壳核包绕。边缘区呈现一个片状扇形结构,嘴侧背腹径大,最大为2.2mm,宽约0.17mm;尾侧背腹径小,为0.8mm,宽约0.13mm。同属壳核和苍白球一样,从嘴侧到尾侧随着脑平面的增宽边缘区亦逐渐向外侧(即靠近外轮廓的方向)移位,其移位的幅度亦明显大于脑平面增宽的幅度;整个边缘区从嘴侧到尾侧呈均匀变化,其片状逐渐变宽,长度(背腹径)逐渐变小,从而形成一个盘状结构。 相似文献
8.
BackgroundPeripheral auditory deafferentation and central compensation have been regarded as the main culprits of tinnitus generation. However, patient-to-patient discrepancy in the range of the percentage of daytime in which tinnitus is perceived (tinnitus awareness percentage, 0 – 100%), is not fully explicable only by peripheral deafferentation, considering that the deafferentation is a stable persisting phenomenon but tinnitus is intermittently perceived in most patients. Consequently, the involvement of a dysfunctional noise cancellation mechanism has recently been suggested with regard to the individual differences in reported tinnitus awareness. By correlating the tinnitus awareness percentage with resting-state source-localized electroencephalography findings, we may be able to retrieve the cortical area that is negatively correlated with tinnitus awareness percentage, and then the area may be regarded as the core of the noise cancelling system that is defective in patients with tinnitus. Methods and FindingsUsing resting-state cortical oscillation, we investigated 80 tinnitus patients by correlating the tinnitus awareness percentage with their source-localized cortical oscillatory activity and functional connectivity. The activity of bilateral rostral anterior cingulate cortices (ACCs), left dorsal- and pregenual ACCs for the delta band, bilateral rostral/pregenual/subgenual ACCs for the theta band, and left rostral/pregenual ACC for the beta 1 band displayed significantly negative correlations with tinnitus awareness percentage. Also, the connectivity between the left primary auditory cortex (A1) and the rostral ACC, as well as between the left A1 and the subgenual ACC for the beta 1 band, were negatively correlated with tinnitus awareness percentage. ConclusionsThese results may designate the role of the rostral ACC as the core of the descending noise cancellation system, and thus dysfunction of the rostral ACC may result in perception of tinnitus. The present study also opens a possibility of tinnitus modulation by neuromodulatory approaches targeting the rostral ACC. 相似文献
9.
Summary 1. The lateral hypothalamus (LH) and the dorsal periaqueductal gray area (dPAG) are two important brain structures involved in central cardiovascular control.2. In the present study, we searched for possible rostrocaudal somatotopy in the neural connections from the three subdivisions of the LH (anterior—LHa; tuberal—LHt and posterior—LHp) to the different rostrocaudal portions of the dPAG.3. The bidirectional neuronal tracer biotinylated-dextran-amine (BDA) was microinjected into different rostrocaudal coordinates of the dPAG (AP 3.4–2.7 mm) of male Wistar rats. One week later, animals were sacrificed and brain slices were processed and analyzed to detect neuronal efferent projections from the LH to the dPAG.4. Neuronal cell body staining was observed along all the rostrocaudal axis of the LH when BDA was microinjected in more rostral dPAG coordinates. When the BDA was microinjected into more caudal dPAG regions, labeled neurons were observed only in the caudal portion of the LH.5. Efferent projections from the LHa were directed only to the rostral portion of the dPAG. Projections from the rostral and medial portions of the LHt were also directed to the rostral dPAG, whereas both rostral and caudal dPAG received projections from the caudal portion of the LHt. Efferent projections from the anterior portion of the LHp were directed to both rostral and caudal dPAG, whereas projections from the caudal LHp were only directed to the rostral portion of the dPAG.6. The results suggest a somatotopic correlation in LH projections to the dPAG with main connections to the rostral dPAG, which are efferent from the three divisions of the LH. More caudal regions of the dPAG received afferents only from posterior sites in the LH.7. Moreover, the results point out to extensive and complex neural somatotopic projections from all LH subdivisions to different rostrocaudal portions of the dPAG, reinforcing the idea of significant functional interactions between the brain structures. 相似文献
10.
The aperC (abnormal proboscis extension reflex C) mutation in Drosophila melanogaster causes a defect in the proboscis extension reflex (PER) in aged flies. Young flies of the mutant show an apparently normal PER. When aperCTF36 mutants were reared at 25 degrees C, the flies became unable to extend the proboscis at Day 5 of eclosion, but within a few days, many of them recovered the PER. When reared at 18 degrees C, the mutants showed a defective PER, but did not show the recovery. At 29 degrees C, only a limited number of the mutant flies showed the defective PER. Histological inspection of the mutant revealed that the degeneration occurs in a pair of muscles, the rostral protractors, which are involved in the extension of the rostrum. The degeneration of the muscle was observed in the mutant by polarizing light microscopy. The cross striation disappeared from the central portion of the muscle fibers at Day 3. Birefringence of the fibers also disappeared. At Day 10 the degenerated muscle fibers showed regeneration. The PER was closely correlated with the degree of muscle degeneration and regeneration. Temperature-shift experiments indicated that the temperature-sensitive-period of the aper CTF36 mutation occurs around Days 2-4 after eclosion. Results indicate that the aperC+ gene regulates the posteclosional maintenance of the muscle fibers. 相似文献
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