Migratory patterns and developmental potential of trunk neural crest cells in the axolotl embryo.

Using cell markers and grafting, we examined the timing of migration and developmental potential of trunk neural crest cells in axolotl. No obvious differences in pathway choice were noted for DiI-labeling at different lateral or medial positions of the trunk neural folds in neurulae, which contributed not only to neural crest but also to Rohon-Beard neurons. Labeling wild-type dorsal trunks at pre- and early-migratory stages revealed that individual neural crest cells migrate away from the neural tube along two main routes: first, dorsolaterally between the epidermis and somites and, later, ventromedially between the somites and neural tube/notochord. Dorsolaterally migrating crest primarily forms pigment cells, with those from anterior (but not mid or posterior) trunk neural folds also contributing glia and neurons to the lateral line. White mutants have impaired dorsolateral but normal ventromedial migration. At late migratory stages, most labeled cells move along the ventromedial pathway or into the dorsal fin. Contrasting with other anamniotes, axolotl has a minor neural crest contribution to the dorsal fin, most of which arises from the dermomyotome. Taken together, the results reveal stereotypic migration and differentiation of neural crest cells in axolotl that differ from other vertebrates in timing of entry onto the dorsolateral pathway and extent of contribution to some derivatives.     

Collateral projections of trigeminal ganglion neurons to both the principal sensory trigeminal and the spinal trigeminal nuclei in the rat

Employing a combination of fluorescent retro grade double labelling and immunofluorescence histo chemistry for substance P (SP) and calcitonin gene-relat ed peptide (CGRP), we examined collateral projections from single neurons in the trigeminal ganglion (TG) of the rat to both the principal sensory trigeminal nucleus (Vp) and the oral, interpolar or caudal subnuclei of the spinal trigeminal nucleus (Vo, Vi or Vc). In the rats that were unilaterally injected with fast blue (FB) into the Vp and with diamidino yellow (DY) into the Vo, Vi or Vc, neurons labelled with FB and/or DY were observed in the TG ipsilateral to the injections. Of the labelled TG neurons, about 2% were double labelled with both trac ers in the rats that were injected with FB into the Vp and with DY into the Vo or Vi, and about 10% were double labelled in the rats that were injected with FB into the Vp and with DY into the Vc. The results indicate that TG neurons sending their axons to the Vp project, by way of axon collaterals, to the Vc more frequently than to the Vo or Vi.Some of the TG neurons double labelled with FB and DY exhibited SP-or CGRP-like immunoreactivity (LI): Of the TG neurons that were double labelled with FB injected into the Vp and with DY injected into the Vo, Vi or Vc, about 38%, 49% and 42%, respectively, displayed SP-LI, and about 54%, 58% and 59%, respectively, showed CGRP-LI. Some of the SP-or CGRP-LI TG neurons that were double labelled with FB and DY were assumed to mediate pain signals to both the Vp and the spinal trigeminal nucleus (Vo, Vi and/or Vc) by way of axon collaterals.Yun-Qing Li is on leave from the Department of Anatomy, The Fourth Military Medical University, Xian, People's Republic of China     

The formation of the superior and jugular ganglia: Insights into the generation of sensory neurons by the neural crest

The superior and jugular ganglia (S/JG) are the proximal ganglia of the IXth and Xth cranial nerves and the sensory neurons of these ganglia are neural crest derived. However, it has been unclear the extent to which their differentiation resembles that of the Dorsal Root Ganglia (DRGs). In the DRGs, neural crest cells undergo neuronal differentiation just after the onset of migration and there is evidence suggesting that these cells are pre‐specified towards a sensory fate. We have analysed sensory neuronal differentiation in the S/JG. We show, in keeping with previous studies, that neuronal differentiation initiates long after the cessation of neural crest migration. We also find no evidence for the existence of migratory neural crest cells pre‐specified towards a sensory phenotype prior to ganglion formation. Rather our results suggest that sensory neuronal differentiation in the S/JG is the result of localised spatiotemporal cues. Developmental Dynamics 239:439–445, 2010. © 2009 Wiley‐Liss, Inc.     

背侧抑制性轴突导向蛋白的表达与鸡胚脊髓神经嵴细胞迁移的空间及时间相关性

目的:探讨正常鸡胚脊髓发育过程中背侧抑制性轴突导向蛋白的表达时间和表达部位与鸡胚脊髓神经嵴细胞迁移过程的相关性。方法:应用原位杂交、免疫组织化学等方法,观察鸡胚脊髓内背侧抑制性轴突导向蛋白的表达时间和表达部位及神经嵴细胞迁移路径,同时比较两者在时间和空间分布上的相关性;应用免疫组织化学、电穿孔的方法在正常鸡胚一侧脊髓内过表达背侧抑制性轴突导向蛋白,观察背侧抑制性轴突导向蛋白过表达对鸡胚脊髓内神经嵴细胞迁移的影响。结果:正常鸡胚脊髓发育过程中,背侧抑制性轴突导向蛋白的表达时间早于神经嵴细胞开始迁移的时间。背侧抑制性轴突导向蛋白表达由颅侧向尾侧呈节段性分布,而神经嵴细胞在节段性分布的背侧抑制性轴突导向蛋白之间进行迁移;电穿孔过表达背侧抑制性轴突导向蛋白引起相邻部位神经嵴细胞迁移路径的异常。结论:背侧抑制性轴突导向蛋白的表达时间和表达部位与脊髓神经嵴细胞的迁移密切相关。     

Morphological and developmental characterization of local-circuit neurons in lamina III of the rat spinal cord

Using the Golgi silver impregnation technique the present study examines the morphology and development of presumptive local circuit neurons in lamina III of the rat lumbar spinal cord. These neurons generate local axonal plexuses which remain within the gray matter and dendritic trees which arborize in lamina III and the inner zone of lamina II. Analysis of developmental stages supports the contention that these neurons have local axons which do not enter the white matter. These cells undergo axonal and dendritic maturation during the postnatal period, well after the maturation of long axon neurons. This pattern parallels the development of local circuit neurons in lamina II.     

Mechanisms mediating the brain stem control of somatosensory transmission in the dorsal horn of the cat's spinal cord: an intracellular analysis

Summary The effect of brainstem stimulation was studied on neurones recorded intracellularly in the superficial and deeper laminae of the lumbosacral dorsal horn of the spinal cord in anaesthetised cats. Stimulation in the nucleus locus coeruleus (LC) produced a hyperpolarisation in 4/13 multireceptive neurones and produced a biphasic action consisting of a hyperpolarisation which was followed by a depolarisation in 3/13 neurones. These actions were produced irrespective of whether the multireceptive neurone was located in the superficial or deeper laminae of the dorsal horn. Stimulation failed to produce postsynaptic potentials in the remaining 6/13 multireceptive neurones. The amplitude of hyperpolarisation was increased by the passage of depolarising pulses through the recording microelectrode and decreased by hyperpolarising pulses. Stimulation in other brainstem areas such as, the lateral (FTL), paralemniscal (FTP) and central (FTC) divisions of the tegmental field and the nuclei raphe magnus (NRM) and reticularis magnocellularis (RMc) also hyperpolarised neurones in the dorsal horn. The polarity of hyperpolarisation evoked from some brainstem areas (FTP, FTC, RMc) could be reversed to depolarisation by the passive diffusion of ions from the recording microelectrode containing 3M-KCl. Brainstem (LC, NRM, FTP, FTL) stimulation generated long lasting (700 ms) hyperpolarisation on 4/4 selectively nocireceptive neurones of lamina I. There was, however, no effect on the activity of 5/5 neurones recorded in laminae I/II which in addition to receiving excitatory cutaneous inputs were inhibited by heat stimuli. Stimulation in LC also produced dorsal root potentials (DRPs) and reduced the amplitude of simultaneously recorded excitatory postsynaptic potentials (EPSPs) generated by the activation of primary afferent fibres in 3 multireceptive neurones. It is concluded that inhibition of nociceptive transmission in the spinal cord from LC and other brainstem areas may involve both pre- and postsynaptic mechanisms.     

不同发育时期鸡胚脊髓内背侧抑制性轴突导向蛋白的表达和神经嵴细胞迁移之间的相关性

目的 探讨不同发育时期的鸡胚脊髓内背侧抑制性轴突导向蛋白（draxin）表达与神经嵴迁移之间在空间分布上的相关性。方法 选
取HH 15-16、HH19-20阶段鸡胚各10只,应用原位杂交、免疫组织化学等方法,观察各阶段鸡胚脊髓内draxin的表达部位及神经嵴细胞迁移路
径,同时比较两者在空间分布上的相关性;应用活组织切片与碱性磷酸酶标记的draxin融合蛋白（draxin-AP）体外孵育的方法,检测迁移路
径内的神经嵴细胞是否具有与draxin蛋白直接结合的能力。结果 随着发育时间的推移,鸡胚脊髓内draxin的表达和神经嵴迁移都具有明显的
由颅侧向尾侧渐进性分布的特性,且draxin的表达部位位于神经管背侧、顶板和背侧生皮肌节之间,这些部位恰均位于神经嵴迁移路径的周围;
同时迁移路径内的神经嵴细胞具有与draxin蛋白体外直接结合的能力。结论 draxin表达在神经嵴迁移路径周围且部分神经嵴具有与draxin蛋白
体外直接结合的能力,推测draxin可能在鸡胚脊髓神经嵴迁移过程中发挥重要的调节作用。     

Distribution,morphology, and central projections of mesencephalic trigeminal neurons in the frog Rana ridibunda

The distribution, morphology, and central projections of the mesencephalic trigeminal neurons in the frog Rana ridibunda were studied with tracing techniques. Retrograde tracing with horseradish peroxidase (HRP) or the fluorescent tracer Fluorogold, and anterograde tracing by means of Phaseolus vulgaris leucoagglutinin, the fluorescent dye Dil, and HRP were used. The mesencephalic trigeminal nucleus (MesV) of Rana ridibunda is formed by a population of 100 to 125 unipolar or multipolar cells that are scattered on both sides of the rostral mesencephalic tectum. Subpopulation of Mes V cells were labeled after tracer application to ophthalmic, maxillary, and mandibular trigeminal branches, separately. Differences in the morphology and distribution of cells in these experiments were not evident but the number of neurons labeled via the maxillary nerve was always the highest. Mes V cells have a single central branch that courses caudally in the brainstem. At different levels, it bifurcates into a peripheral branch, which leaves the brain via the trigeminal root, and a descending branch, which terminates in a region in, or close to, the trigeminal motor nucleus and in a supratrigeminal location. The lack of a distinct somatotopy in the distribution of Mes V cells and the lack of projections caudal to the trigeminal motor nucleus as revealed in this study with a wide variety of tracers are in striking contrast to previous data provided for other amphibians. © 1993 Wiley-Liss, Inc.     

Our current understanding of the lymphatics of the brain and spinal cord

The lymphatic system, segregated from the blood vascular system, is an essential anatomical route along which interstitial fluid, solutes, lipids, immune cells, and cellular debris, are conveyed. However, the way these mechanisms operate within the cranial compartment is mostly unknown. Herein, we review current understanding of the meningeal lymphatics, described anatomically over a century ago yet still poorly understood from a functional standpoint. We will delineate the cellular mechanisms by which the meningeal lymphatics are formed and discuss their unique anatomy. Furthermore, this review will discuss the recently‐coined “glymphatic system” and the manner by which cerebrospinal fluid (CSF) and interstitial fluid (ISF) are exchanged and thus drained by the meningeal lymphatic vasculature as a key route for conveying cellular waste, solutes, and immune traffic to the deep cervical lymph nodes. The clinical relevance of the meningeal lymphatics will also be described, as they are relevant to various common defects of the lymphatic system. Clin. Anat. 32:117–121, 2019. © 2018 Wiley Periodicals, Inc.     

Bone morphogenetic protein signaling is required in the dorsal neural folds before neurulation for the induction of spinal neural crest cells and dorsal neurons

Bone Morphogenetic Protein (BMP) activity has been implicated as a key regulator of multiple aspects of dorsal neural tube development. BMP signaling in the dorsal‐most neuroepithelial cells presumably plays a critical role. We use tissue‐specific gene ablation to probe the roles of BMPR1A, the type 1 BMP receptor that is seemingly the best candidate to mediate the activities of BMPs on early dorsal neural development. We use two different Cre lines expressed in the dorsal neural folds, one prior to spinal neurulation and one shortly afterward, together with a Bmpr1a conditional null mutation. Our findings indicate that BMPR1A signaling in the dorsal neural folds is important for hindbrain neural tube closure, but suggest it is dispensable for spinal neurulation. Our results also demonstrate a requirement for BMP signaling in patterning of dorsal neural tube cell fate and in neural crest cell formation, and imply a critical period shortly before neural tube closure. Developmental Dynamics 240:755–765, 2011. © 2011 Wiley‐Liss, Inc.     

Development of specific connectivity between premotor neurons and motoneurons in the brain stem and spinal cord

Astounding progress has been made during the past decade in understanding the general principles governing the development of the nervous system. An area of prime physiological interest that is being elucidated is how the neural circuitry that governs movement is established. The concerted application of molecular biological, anatomical, and electrophysiological techniques to this problem is yielding gratifying insight into how motoneuron, interneuron, and sensory neuron identities are determined, how these different neuron types establish specific axonal projections, and how they recognize and synapse upon each other in patterns that enable the nervous system to exercise precise control over skeletal musculature. This review is an attempt to convey to the physiologist some of the exciting discoveries that have been made, within a context that is intended to link molecular mechanism to behavioral realization. The focus is restricted to the development of monosynaptic connections onto skeletal motoneurons. Principal topics include the inductive mechanisms that pattern the placement and differentiation of motoneurons, Ia sensory afferents, and premotor interneurons; the molecular guidance mechanisms that pattern the projection of premotor axons in the brain stem and spinal cord; and the precision with which initial synaptic connections onto motoneurons are established, with emphasis on the relative roles played by cellular recognition versus electrical activity. It is hoped that this review will provide a guide to understanding both the existing literature and the advances that await this rapidly developing topic.     

Immunoreactive calcitonin gene-related peptide and substance P coexist in sensory neurons to the spinal cord and interact in spinal behavioral responses of the rat

Using immunohistochemistry evidence was obtained for the coexistence of calcitonin gene-related peptide (CGRP)- and substance P (SP)-like immunoreactivity in spinal sensory neurons. Analysis of caudally directed biting and scratching (CBS) behavior was carried out after intrathecal administration of CGRP and SP alone or in combination. Thus, SP (up to 20 micrograms) alone caused CBS only for a few minutes after injection, whereas SP (10 micrograms) plus CGRP (20 micrograms) caused a response with a duration up to 40 min. CGRP (20 micrograms) alone had no effects in this model. These findings provide support for a possible interaction of the two peptides at synapses in the dorsal horn of the spinal cord.     

The topographical organization of neurons in the dorsal hypothalamic area that project to the spinal cord or to the nucleus raphé pallidus in the rat

Summary The present study was undertaken using retrograde labeling techniques to clarify whether the neurons in the dorsal hypothalamic area (DHA) that project to the spinal cord are the same as those that project to the nucleus raphé pallidus (NRP). Following an injection of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) in the NRP many labeled small neurons (6–13×9–22 m) with an oval shape were found in the ventromedial part of the DHA. At the level of the dorsomedial hypothalamic nucleus, they formed a distinct and compact cell cluster. Labeled neurons, which were large in size (9–22×11–36 m) with oval and triangular shapes, were found mainly in the dorsolateral part of the DHA after injections of horseradish peroxidase (HRP) in the spinal cord. In a double-labeling experiment, Fast Blue or True Blue, and Nuclear Yellow were injected in the NRP and in the spinal cord, respectively. A large number of blue-fluorescent neurons were located mostly in the ventromedial part of the DHA, while yellow-fluorescent ones were found in the dorsolateral part of the DHA. However, no double-labeled neurons were found in the DHA. These results show that the neurons of the DHA projecting to the NRP are essentially different from those which project to the spinal cord.     

Retinoic acid induced the differentiation of neural stem cells from embryonic spinal cord into functional neurons in vitro

Retinoic acid is an important molecular taking part in the development and homeostasis of nervous system. Neural stem cells (NSCs) are pluripotent cells that can differentiate into three main neural cells including neuron, astrocyte and oligodendrocyte. However, whether retinoic acid can induce NSCs derived from embryonic spinal cord differentiating into functional neurons and its efficiency are not clear. In this experiment, NSCs were isolated from embryonic 14 d spinal cord of rats. The growth and neuronal differentiation of NSCs induced by 500 nM RA was examined in vitro. It was indicated that compared with the control group, there were more differentiated cells with longer cytodendrites in the medium treated with RA at different time. And more, there were more neuronal marker positive cells in 500 nM RA group than the control group seven days after differentiation. At the same time, the expression of β-tublin III protein in RA group was higher than those in control group, which was contrary to the expression of astrocyte marker GFAP protein at seven days after differentiation. However the differentiated neurons, whether treated with RA or not both exhibited biological electrical reactivity after stimulated by glutamine. Therefore, these findings indicated that RA could promote growth of cellular dendrites and neuronal differentiation of NSCs, which also induce functional maturation of differentiated neurons finally.     

Distribution of serotonergic neurons and processes in the lamprey spinal cord

The distribution of serotonin in the spinal cord in two species of lamprey, Ichthyomyzon unicuspis and Petromyzon marinus, was studied by indirect immunofluorescence techniques. Multipolar cell bodies containing serotonin-like immunoreactivity were found along the length of the spinal cord, along the midline and slightly ventral to the central canal. These cell bodies send a diffuse projection of processes throughout the spinal cord, including: (1) a dense projection to the ventral surface; (2) a strong projection to the ventromedial longitudinal fiber tracts; (3) a less intense projection to the dorsal longitudinal fiber tracts; and (4) a weak projection to the lateral fiber tracts. Lesion experiments showed that processes descending from the brain or rostral spinal cord provide a major projection to the lateral fiber tracts and smaller contributions to the dorsal and ventromedial fiber tracts. Fluorescent processes were also observed in the dorsal roots and serotonergic peripheral cell bodies were seen adjacent to the dorsal roots.Our results suggest that the serotonergic innervation of the lamprey spinal cord arises from three sources: spinal interneurons, descending tracts and peripheral (possibly sensory) input. This provides an anatomical substrate for our recent finding^12,13 that serotonin modulates the central pattern generator for locomotion in the lamprey spinal cord.     

Microglia in antiviral immunity of the brain and spinal cord

Viral infections of the central nervous system (CNS) are a significant cause of neurological impairment and mortality worldwide. As tissue resident macrophages, microglia are critical initial responders to CNS viral infection. Microglia seem to coordinate brain-wide antiviral responses of both brain resident cells and infiltrating immune cells. This review discusses how microglia may promote this antiviral response at a molecular level, from potential mechanisms of virus recognition to downstream cytokine responses and interaction with antiviral T cells. Recent advancements in genetic tools to specifically target microglia in vivo promise to further our understanding about the precise mechanistic role of microglia in CNS infection.     

人胎儿和新生儿脊髓和DRG内nNOS阳性神经元的表达和分布

目的：观察24～27w人胎儿和新生儿的脊髓和背根神经节(DRG)内神经元型一氧化氮合酶(nNOS)阳性神经元的表达和分布。方法：ABC免疫细胞化学方法。结果：(1)24～27w人胎儿胸髓和腰1～3节段的中间带外侧核和前角Ⅷ层和Ⅸ层内可观察到nNOS阳性神经元。颈、胸、腰各段DRG内nNOS免疫阳性神经元占DRG细胞总数的84％～88％。(2)新生儿脊髓和DRG内nNOS免疫阳性神经元的分布情况与上述胎儿相似。但DRG内nNOS免疫阳性神经元的体积有所增加,数量明显减少,约占DRG细胞总数的70％～73％。结论：人胎儿脊髓和DRG在发育的24～27w至出生时,nNOS阳性神经元的表达在定位分布上无差异,但随胚胎发育阳性神经元的数量明显减少。