Morphological stabilization of the glycocalyces of 23 strains of five Bacteroides species using specific antisera

Cells of five Bacteroides species were examined following treatment with homologous antisera and staining with ruthenium red. They were enveloped by glycocalyces and these extensive fibrous exopolysaccharide matrices were fully retained as an integral "capsule" by some cells, while other cells showed "capsule" as well as detached glycocalyx components forming an intercellular "slime.". These extensive glycocalyces collapsed during dehydration for electron microscopy and formed electron-dense accretions on cell surfaces and electron-dense reticula in intercellular spaces when the cells were treated with heterologous antiserum or when antibody stabilization was omitted. The glycocalyces of all strains, both stabilized and unstabilized, were observed outside the outer membranes of cell walls that showed the "classic" gram-negative structural organization. Appropriate modifications of the indirect fluorescent antibody test demonstrated an integral "capsule" on all strains examined; detached glycocalyx and varying amounts of slime were demonstrated after stabilization with homologous, but not heterologous, antiserum.     

On the neurosecretory system of Dendrobaena atheca Cernosvitov

Four kinds of neurosecretory cells A, B, U and C are distinguished in the central nervous system of Dendrobaena atheca Cernosvitov. A cells, which show different morphological characteristics under different physiological states and during their cyclic changes, are the most active neurosecretory cells. They form the outer layer of the cortical cell zone in the cerebral ganglion. B cells are large and medium sized and are distributed in all parts of the central nervous system. U cells are found only in the sub-pharyngeal ganglion while C cells are distributed in the sub-pharyngeal as well as in the ventral nerve cord ganglion. The number and secretory activity of C cells decrease in caudal direction. Further, Gomori-positive cells are also observed in the ganglia of the vegetative nervous system. A rudimentary neurohaemal organ, the storage zone, has been observed in the cerebral ganglion and there appears to be another neurohaemal area in the ventral nerve cord ganglion. The storage zone is formed by the terminal ends of the axons of A cells. The chrome alum haematoxylin phloxin (CHP) and aldehyde fuchsin (AF) positive substances in the form of granules are found in this area. The cerebral ganglion is richly supplied by blood capillaries. The distal end of the axons of B cells are swollen like a bulb while in some cases the axons are united to form an axonal tract. Extra-cellular material is abundant in different parts of the nervous system. In all cell types, the perinuclear zone is the first to show activity in the secretory cycle. It appears that the nucleus may be involved in the elaboration of the neurosecretory material in the cells.     

Fine structure of smooth muscle and neuromuscular junctions in the foot of Helix aspersa

Summary The smooth muscle cells in the foot of Helix aspersa are arranged in bundles which interweave to form a complex mesh. In the peripheral cytoplasm of the muscle cells there is a system of interconnected obliquely and longitudinally orientated tubules. The full extent of this system has not been determined; its possible function in relation to Ca⁺⁺ storage and excitation-contraction coupling is discussed. Longitudinal tubules are present among the myofilaments and in association with mitochondria. Distributed throughout the myofilaments are elliptically shaped dense bodies, the fine structure of which resembles an accumulation of thin filaments. Located on the plasma membrane of the muscle cells are dense areas; the fine structure and relationships of these cellular elements resemble desmosomes. They may serve as attachment points for thin, cytoplasmic filaments (not necessarily myofilaments). The muscle cells are innervated by axons which diverge from a coarse, neural plexus (the sole plexus). The axons initially come into close contact with the muscle cells and then pass over their surfaces for up to 35 before being gradually enveloped by flange-like protrusions of the muscle cells. These axons contain either, (i) agranular vesicles (600 Å in diameter), (ii) agranular and very dense granular vesicles (1000 Å in diameter) or (iii) agranular and less dense, granular vesicles (1000 Å in diameter). The possible role of these inclusions as sites of excitatory and inhibitory transmitters is discussed.I wish to thank Professor G. Burnstock for making laboratory facilities available. This work has been supported by the Australian Research Grants Committee.     

Ultrastructural study of contacts between cells of the dorsal ectoderm and chordamesoderm during gastrulation in Xenopus laevis

In gastrulae of Xenopus laevis, various morphological types of intercellular approximation occur between the dorsal ectoderm and chordamesoderm. Ruthenium red staining reveals that in some areas the glycocalyces of heterotypic cells appear to come into contact. These observations, in conjunction with the results of previous studies, suggest that cell contacts offer a possible pathway for the transmission of inductive stimuli, and that they may be important in the regionalization of the neuralized ectoderm.     

Quantitative analysis of the structure of the varicose dilatations in the nerve fibers of the rabbit coronary artery (according to the results of three-dimensional reconstruction)]

Axoplasmic vesicles and microtubes in varicosities of axonal plexus in the external sheath of the rabbit coronary artery have been studied. Comparing serial sections and examining three-dimensional reconstruction of small nerve plexus, it was demonstrated that various varicosities differed only in their correlation of the amount of small (30-80 nm) and large (80-180 nm) vesicles. Average diameters in profiles of small and large vesicles are 56.3 nm and 115.6 nm, respectively. There are varicosities containing about 250 or more than 1,000 vesicles. Evenly distributed vesicles throughout the volume of varicosities and lack of specialized structures on the axolemma are supposed to demonstrate the absence of special areas for the mediator removal in the axons studied. The microtubes in the varicosities are peripherally arranged, next to the axolemma and form 1-1.5 wide coils. A suggestion is made that the varicosities in neighbouring axons of the same nerve plexus, with specific structural organization, are special functional units and appear to be peculiar not only for nerve plexus of the coronary artery, but also for other parts of the peripheral vegetative nerve system.     

Information of the structuro-functional characteristics of sympathetic afferents

Visceral nerves have a lot of sensitive conductors of double nature. One of them are presented by dendrites of pseudounipolar cells of cerebrospinal nodes, others - in the form of amyelinic (or, sometimes, fine myelinic) fibres - are axons of peripheral sensitive neurons (of the IId Dogil's type). By means of experimental morphological and electrod physiological analyses performed in 36 dogs, a possible connection of intraenteric neurons of the IId Dogiel's type with the spinal cord is demonstrated, at least with in the level of 5-10 thoracic segments. The centripetal fibres from the jejunum go together with the intestinal, coeliac nerves, intranodular, white and grey connective branches of the sympathetic trunk and, further - with posterior and anterior roots of the cerebrospinal nerves. The coeliac nerves serve as an important collector of the sympathetic afferents along their way from the peritoneal cavity. A part of axons of the peripheral sensitive neurons end in presynaptic buds of a terminal type on the motoneurons in the prevertebral (coeliac plexus) and the paravertebral (thoracic sympathetic trunk) sympathetic ganglia accepting the positoin of the afferent link in the systems of extracentral reflex arcs. Owing to this sign, sensitive cells of the IId Dogiel's type are justly named "sympathetic afferent neurons". Elements of the peripheral (sympathetic) afferent system are remarkable for their diffuse localization, that is corroborated by: an extreme dispersity of trophic centers (cells of the IId Dogiel' type); their axons form synapses with motor cells of numerous and sometimes unstable, individually changeable sympathetic ganglia; transfer of the centripetal sensitive fibres into the spinal cord via posterior and anterior roots.     

Termination in the prevertebral abdominal sympathetic ganglia of axons arising from the local (terminal) vegetative plexus of visceral organs

Summary Degeneration of synaptic axon terminals in the prevertebral (celiac and superior mesenteric) ganglia, occurring after operative interferences on visceral organs, shows that processes of ganglion cells (probably of Dogiel type II) located in the terminal ganglia of the gallbladder and the small intestine reach and establish synapses in the prevertebral ganglia. This finding is in accordance with the persistence of delicate axons in the peripheral stumps of visceral nerves two weeks after removal of the celiac ganglion. These results speak in favour of the existence of peripheral reflex arcs in the vegetative nervous system.     

Pathfinding, target recognition, and synapse formation of single regenerating fibers in the adult grasshopper Schistocerca gregaria

After lesion of the peripheral tympanal nerve of the adult locust (Schistocerca gregaria), sensory axons regenerate into their original target areas. We examined the individual behavior of single regenerating auditory afferents during pathway and target selection by intracellularly recording and labeling them at different times postlesion. During axotomy, spontaneous activity is not increased in either the distal or proximal part of the cells. Stimulus response properties of lesioned cells with or without regenerating axons are not influenced. Surprisingly, only 55% of sensory neurons regenerate through the lesion site and often give rise to more than one axonal fiber. Within the central nervous system, 70% of regenerated axons consistently follow an incorrect pathway to reach the correct target region. Often, one of two processes formed by a cell chooses the correct pathway, and the other the incorrect one. In the target region, regenerated axons reconstitute somatotopically ordered projections and form synapses that resemble those of intact fibers in number and structure. The regeneration process does not induce a detectable expression of antigens that are known to be expressed during neural development in these neurons. Our study clearly demonstrates that precise synaptic regeneration is possible in adult animals within a completely differentiated central nervous system, although pathfinding and formation of arborizations are disturbed in a particular and probably system-related manner. The results strongly suggest that accurate pathfinding is unlikely to be a decisive factor in target area recognition and synaptogenesis.     

Expression of L1 and N-CAM cell adhesion molecules during development of the mouse olfactory system

The expression of the neural adhesion molecules L1 and N-CAM has been studied in the embryonic and early postnatal olfactory system of the mouse in order to gain insight into the function of these molecules during development of a neural structure which retains neuronal turnover capacities throughout adulthood. N-CAM was slightly expressed and L1 was not significantly expressed in the olfactory placode on Embryonic Day 9, the earliest stage tested. Rather, N-CAM was strongly expressed in the mesenchyme underlying the olfactory placode. In the developing nasal pit, L1 and N-CAM were detectable in the developing olfactory epithelium, but not in regions developing into the respiratory epithelium. At early developmental stages, expression of the so-called embryonic form of N-CAM (E-N-CAM) coincides with the expression of N-CAM, whereas at later developmental stages and in the adult it is restricted to a smaller number of sensory cell bodies and axons, suggesting that the less adhesive embryonic form is characteristic of morphogenetically dynamic neuronal structures. Moreover, E-N-CAM is highly expressed at contact sites between olfactory axons and their target cells in the glomeruli of the olfactory bulb. L1 and N-CAM 180, the component of N-CAM that accumulates at cell contacts by interaction with the cytoskeleton are detectable as early as the first axons extend toward the primordial olfactory bulb. L1 remains prominent throughout development on axonal processes, both at contacts with other axons and with ensheathing cells. Contrary to N-CAM 180 which remains detectable on differentiating sensory neuronal cell bodies, L1 is only transiently expressed on these and is no longer detectable on primary olfactory neuronal cell bodies in the adult. Furthermore, whereas throughout development L1 has a molecular form similar to that seen in other parts of the developing and adult central nervous systems, N-CAM and, in particular, N-CAM 180 retain their highly sialylated form at least partially throughout all ages studied. These observations suggest that E-N-CAM and N-CAM 180 are characteristic of developmentally active structures and L1 may not only be involved in neurite outgrowth, but also in stabilization of contacts among fasciculating axons and between axons and ensheathing cells, as it has previously been found in the developing peripheral nervous system.     

An identified cell is required for the formation of a major nerve during embryogenesis in the leech

Investigations of the cues by which axonal growth cones navigate long distances to their targets have revealed the use of a rich and complex diversity of cellular and extracellular information. In the present study we describe one of the most conceptually simple pathfinding cues: a single identified cell in the leech, Hirudo medicinalis, that may guide axons several hundred micrometers to innervate a particular target. One of the stereotyped nerves of H. medicinalis is a "sex nerve" that projects from the anterior root of ganglion 6 [SNA (6)] to the male reproductive structures in the adjacent anterior segment. The pathway for SNA (6) is completely underlain by a single peripheral cell, here called the axonal runway cell (ARC), before axons enter the pathway. The ARC is apparently a nonneuronal cell that stains with a monoclonal antibody that recognizes leech muscle cells. The importance of the ARC for establishing SNA(6) was tested by ablating it before axons entered the pathway. When the ARC was killed either by physical disruption with a microelectrode, or by photoablation after filling it with the fluorescent dye Lucifer yellow, SNA(6) always failed to form, whereas all other nerves formed normally. Killing other peripheral cells in proximity to the ARC did not interfere with SNA(6) formation. Ablation of possible "pioneer neurons" for SNA(6) also did not prevent its formation. These results show that formation of a particular nerve requires only a single cell to serve as a guide for outgrowing processes.     

Axon branch removal at developing synapses by axosome shedding

In many parts of the developing nervous system, the number of axonal inputs to each postsynaptic cell is dramatically reduced. This synapse elimination has been extensively studied at the neuromuscular junction, but how axons are lost is unknown. Here, we combine time-lapse imaging of fluorescently labeled axons and serial electron microscopy to show that axons at neuromuscular junctions are removed by an unusual cellular mechanism. As axons disappear, they shed numerous membrane bound remnants. These "axosomes" contain a high density of synaptic organelles and are formed by engulfment of axon tips by Schwann cells. After this engulfment, the axosome's contents mix with the cytoplasm of the glial cell. Axosome shedding might underlie other forms of axon loss and may provide a pathway for interactions between axons and glia.     

Engulfment of Axon Debris by Microglia Requires p38 MAPK Activity

The clearance of debris after injuries to the nervous system is a critical step for restoration of the injured neural network. Microglia are thought to be involved in elimination of degenerating neurons and axons in the central nervous system (CNS), presumably restoring a favorable environment after CNS injuries. However, the mechanism underlying debris clearance remains elusive. Here, we establish an in vitro assay system to estimate phagocytosis of axon debris. We employed a Wallerian degeneration model by cutting axons of the cortical explants. The cortical explants were co-cultured with primary microglia or the MG5 microglial cell line. The cortical neurites were then transected. MG5 cells efficiently phagocytosed the debris, whereas primary microglia showed phagocytic activity only when they were activated by lipopolysaccharide or interferon-β. When MG5 cells or primary microglia were co-cultured with degenerated axons, p38 mitogen-activated protein kinase (MAPK) was activated in these cells. Engulfment of axon debris was blocked by the p38 MAPK inhibitor SB203580, indicating that p38 MAPK is required for phagocytic activity. Receptors that recognize dying cells appeared not to be involved in the process of phagocytosis of the axon debris. In addition, the axons undergoing Wallerian degeneration did not release lactate dehydrogenase, suggesting that degeneration of the severed axons and apoptosis may represent two distinct self-destruction programs. We observed regrowth of the severed neurites after axon debris was removed. This finding suggests that axon debris, in addition to myelin debris, is an inhibitory factor for axon regeneration.Axon degeneration is an active, tightly controlled, and versatile process of axon segment self-destruction. The lesion-induced degeneration process was first described by Waller (1) and has since been known as Wallerian degeneration (2, 3). This degeneration involves rapid blebbing and fragmentation of an entire axonal stretch into short segments, which are then removed by locally activated phagocytic cells. Phagocytic removal of damaged axons and their myelin sheaths distal to the injury is important for creating a favorable environment for axonal regeneration in the nervous system. Although the debris of degenerated axons and myelin is cleared by phagocytes in the peripheral nervous system (PNS), the debris is removed very slowly in the central nervous system (CNS)³ (4, 5). This is considered to be one of the obstacles for regeneration of the injured axons in the CNS.Apoptotic neurons are also engulfed by activated phagocytic cells. Apoptosis is very well documented in the CNS where a significant proportion of neurons undergo programmed cell death (6). To prevent the diffusion of damaging degradation products into surrounding tissues, dying neurons are phagocytosed. In the brain, apoptotic cells are engulfed mainly by the resident population of phagocytes known as microglia. Microglia are generally considered to be immune cells of the CNS (7). They respond to any kind of pathology with a reaction termed “microglial activation.” After injuries to the CNS, microglia react within a few hours with a migratory response toward the lesion site.Although insight into the mechanism of phagocytosis of dying cells by microglia has improved, little is known about the mechanism of clearance of degenerated axons and myelin debris by microglia after axonal injury in the CNS. Interestingly, the axons undergoing Wallerian degeneration do not seem to possess detectable activation of the caspase family (8), suggesting that Wallerian degeneration and apoptosis may represent two distinct self-destruction programs. Thus, the mechanism of microglial phagocytosis of dying cells might be different from that of axon/myelin debris. We aimed to elucidate the mechanism of debris clearance by microglia after an axonal injury. We established an in vitro assay system to estimate phagocytosis of degenerated axon debris. We found that p38 mitogen-activated protein kinase (MAPK) was critical for the phagocytic activity of microglia. Treatment with lipopolysaccharide (LPS) or interferon-β (IFN-β) was necessary for the primary microglia to become phagocytic. In addition, clearance of degenerated axon debris allowed axonal growth from the severed neurites, suggesting that removal of the axon debris provides a favorable environment for axonal regeneration.     

CHARACTERIZATION OF AN UNUSUAL CATECHOLAMINE-CONTAINING CELL TYPE IN THE TOAD HYPOTHALAMUS : A Correlated Ultrastructural and Fluorescence Histochemical Study

A nucleus of catecholamine-containing cells bordering the preoptic recess of the toad hypothalamus has been studied by both fluorescence histochemical and electron microscopic methods. The perikarya of these cells form one to three rows immediately subjacent to the ependyma. They send brightly fluorescent apical processes between the ependymal cells to the ventricular surface, and also give rise to long basal processes, the proximal portions of which are also fluorescent. These cells contain two distinctive constitutents: juxtanuclear bundles of tightly packed filaments, the members of which are separated from one another by only ~100 A, and large numbers of dense-cored vesicles (400–2200 A in diameter), which appear to arise from an agranular tubular reticulum distinct from the Golgi apparatus. Axons containing either clear vesicles alone or clear and dense-cored vesicles form synapses on the subependymal cells, but no evidence has been found that the subependymal cells themselves form presynaptic contacts, or that axons originate from them. The cytological characteristics of these catecholamine-containing cells, plus the fact that they border directly on the cerebrospinal fluid, suggest that they may be more closely related to peripheral chromaffin cells than to the other cell types intrinsic to the central nervous system, and the name "encephalo-chromaffin cells" is therefore proposed for them. The possible functions of such cells in the central nervous system are discussed.     

Control of the development of the ipsilateral retinothalamic projection in Xenopus laevis by thyroxine: results and speculation

The ipsilateral retinothalamic projection of the frog Xenopus laevis is formed by the axons of a subset of retinal ganglion cells which are found throughout peripheral and non-nasodorsal retina. Unlike the crossed retinotectal and retinothalamic projections, which begin to form during early embryonic stages, the ipsilateral projection does not begin to develop until late in tadpole life, at stages when thyroxine first becomes detectable in the circulation. Blocking the production of thyroid hormone in tadpoles prevents the development of the ipsilateral projection, in a reversible manner. Intraocular injection of thyroxine can "rescue" the development of the projection in tadpoles which otherwise remain premetamorphic. In addition, the projection from one eye of a metamorphically-blocked tadpole can be induced to form by an intraocular injection of thyroxine at a dose which has no detectable effect on retinal development in the other, untreated eye. These results indicate that the development of the ipsilateral retinothalamic projection is dependent upon thyroxine, and strongly suggest that the hormone acts at the level of the eye, rather than at the optic chiasm or thalamic target, to bring about the development of a new pathway. A number of ways in which thyroxine might act in the system are discussed.     

Organization of LHRH cells: differential apposition of neurotensin, substance P and catecholamine axons

A wealth of evidence suggests that catecholamines (particularly norepinephrine) influence gonadotropin secretion via a direct interaction with the LHRH neurons. Neuropeptides such as neurotensin (NT) and substance P (SP) are likewise implicated in the control of LHRH secretion, based on pharmacological and preliminary anatomical studies. Since sub-populations of LHRH neurons project to areas of the brain other than the median eminence, a detailed analysis of the topography of axonal interactions of catecholamines (CA), substance P and neurotensin with LHRH cells was conducted in adult male mice using dual immunocytochemical techniques. An analysis of the patterns of apparent contact of NT or SP axons on LHRH cells as determined by close apposition of immunoreactive axons to LHRH cells when viewed under a light microscope at high magnification revealed that the density of NT or SP axons was not a reliable index of the degree of contact; in many locations, NT and SP had similar densities yet a greater portion of the LHRH cells appeared contacted by SP than NT. NT axons were in close contact with up to one-third of the LHRH cells. Analysis of the location of these "contacted" cells did not reveal a discrete subnucleus controlled by NT. Rather, the NT-contacted cells were scattered throughout the LHRH cell field. Interactions of LHRH cells with SP axons were likewise uniform throughout most of the LHRH cell field, with the exception of the most anterior portion of the field. In the anterior septum, few SP axons appeared to contact LHRH cells. Elsewhere, most of the LHRH cells were in contact with SP axons. For the CAs, the fiber density in the regions of the LHRH cells was uniformly moderate, yet the pattern of cells contacted showed variation across the LHRH cell field, with most of the "contacted" cells located near the OVLT and medial preoptic area. These data suggest that LHRH cells may be differentially regulated by NT, SP and the CAs.     

Why Are Sensory Axons More Vulnerable for Ischemia than Motor Axons?

Objective

In common peripheral neuropathies, sensory symptoms usually prevail over motor symptoms. This predominance of sensory symptoms may result from higher sensitivity of sensory axons to ischemia.

Methods

We measured median nerve compound sensory action potentials (CSAPs), compound muscle action potentials (CMAPs), and excitability indices in five healthy subjects during forearm ischemia lasting up to disappearance of both CSAPs and CMAPs.

Results

Ischemia induced: (1) earlier disappearance of CSAPs than CMAPs (mean ± standard deviation 30±5 vs. 46±6 minutes), (2) initial changes compatible with axonal depolarization on excitability testing (decrease in threshold, increase in strength duration time constant (SDTC) and refractory period, and decrease in absolute superexcitability) which were all more prominent in sensory than in motor axons, and (3) a subsequent decrease of SDTC reflecting a decrease in persistent Na⁺ conductance during continuing depolarisation.

Interpretation

Our study shows that peripheral sensory axons are more vulnerable for ischemia than motor axons, with faster inexcitability during ischemia. Excitability studies during ischemia showed that this was associated with faster depolarization and faster persistent Na⁺ channel inactivation in sensory than in motor axons. These findings might be attributed to differences in ion channel composition between sensory and motor axons and may contribute to the predominance of sensory over motor symptoms in common peripheral neuropathies.     

Dichotomy of the glial cell response to axonal injury and regeneration

Neurons in the mammalian central nervous system (CNS) have a poor capacity for regenerating their axons after injury. In contrast, neurons in the CNS of lower vertebrates and in the peripheral nervous system (PNS) of mammals are endowed with a high posttraumatic capacity to regenerate. The differences in regenerative capacity have been attributed to the different compositions of the respective cellular environments and to different responses to injury the nonneuronal cells display, which range from supportive and permissive to nonsupportive and hostile for regeneration. The same cell type may support or inhibit regeneration, depending on its state of maturity or differentiation. Astrocytes and oligodendrocytes are examples of cells in which such a dichotomy is manifested. In developing and in spontaneously regenerating nerves, these cells support (astrocytes) and permit (oligodendrocytes) growth. However, in nonregenerating adult mammalian nerves, astrocytes form the nonsupportive scar tissue; and the mature oligodendrocytes inhibit axonal growth. Maturation of these cells may be regulated differently during development than after injury. Among the putative regulators are factors derived from astrocytes, resident microglia; or cytokines produced by macrophages. During development, regulation leads to a temporal separation between axonal growth and maturation of the cellular environment, which might not occur spontaneously after injury in a nonregenerating CNS without intervention at the appropriate time. Data suggest that temporal intervention aimed at the glial cells might enhance the poor regenerative capacity of the mammalian CNS. Possible regulation of the nonneuronal cell response to injury via involvement of protooncogenes is proposed.     

Changes in goldfish retinal ganglion cells during axonal regeneration

Recent work suggests that mammalian retinal ganglion cells may become more like developing ganglion cells in form while regenerating through a peripheral nerve graft. We have injected Lucifer Yellow into regenerating ganglion cells of goldfish to look for similar changes. Within three weeks of injury, we saw dye-coupling to nearby cells, which is a common developmental feature in many species. Dendrites and axons, which in most mature ganglion cells are smooth, became varicose and hairy, like those examined in mammalian development. Secondary axons arose later, not only as side-branches of the primary axon but also from the soma, as in mammalian development and regeneration. Since, in fish, these responses are clearly an intrinsic part of functional regeneration, their equivalence in fish and mammals strengthens the view that a similar regenerative competence may exist in the retinal ganglion cells of all vertebrates.     

Adhesive Papillae of Phallusia mamillata Larvae: Morphology and Innervation

The swimming larvae of most solitary ascidians belonging to the Ascidiidae family bear three anterior, simple conic adhesive papillae. They secrete adhesive substances that are used to effect transitory settlement at the beginning of the metamorphosis.The adhesive papillae of newly hatched Phallusia mamillata larvae examined by the SEM are covered by the tunic. When the larvae are about to settle, the tunic becomes fenestrated over the central part of the papilla and bulb-ended microvilli protrude through the holes. These papillae have two types of elongated cells: many peripheral cells and few larger central cells with microvilli and bundles of microtubules oriented along the major axis of the cells.We have done immunofluorescence experiments with an anti-beta-tubulin monoclonal antibody (clone 2-28-33) reacting with axonal microtubules. Only the central cells of the papillae were stained and the axons appeared to arise from the proximal ends of these cells. These axons form a long nerve that reaches the brain vesicle. Branches of the same nerve appear to connect to the basal ends of the peripheral cells. By confocal laser microscopy we were able to follow the course of the papillary nerve. The two nerves connecting the dorsal papillae fuse together into a single nerve that runs posteriorly. The nerve connecting the ventral papilla runs posteriorly for a long tract before fusing with the nerve of the dorsal papillae just near the brain.The reported observations raise the hypothesis that the central cells of the adhesive papillae might be primary sensory neurons and that they may have chemosensory function.     

NG2 cells response to axonal alteration in the spinal cord white matter in mice with genetic disruption of neurofilament light subunit expression

Background

Chondroitin sulphate proteoglycan (NG2) expressing cells, morphologically characterized by multi-branched processes and small cell bodies, are the 4^th commonest cell population of non-neuronal cell type in the central nervous system (CNS). They can interact with nodes of Ranvier, receive synaptic input, generate action potential and respond to some pathological stimuli, but the function of the cells is still unclear. We assumed the NG2 cells may play an active role in neuropathogenesis and aimed to determine if NG2 cells could sense and response to the alterations in the axonal contents caused by disruption of neurofilament light subunit (NFL) expression.

Results

In the early neuropathological development stage, our study showed that the diameter of axons of upper motor neurons of NFL-/- mice decreased significantly while the thickness of their myelin sheath increased remarkably. Although there was an obvious morphological distortion in axons with occasionally partial demyelination, no obvious changes in expression of myelin proteins was detected. Parallel to these changes in the axons and their myelination, the processes of NG2 cells were disconnected from the nodes of Ranvier and extended further, suggesting that these cells in the spinal cord white matter could sense the alteration in axonal contents caused by disruption of NFL expression before astrocytic and microglial activation.

Conclusion

The structural configuration determined by the NFL gene may be important for maintenance of normal morphology of myelinated axons. The NG2 cells might serve as an early sensor for the delivery of information from impaired neurons to the local environment.