Ultrastructure of the circumoral nerve ring and the radial nerve cords in holothurians (Echinodermata)

The circumoral nerve ring and the radial nerve cords (RNCs) of Eupentacta fraudatrix and Pseudocnus lubricus (Holothuroidea) were examined as an example of holothurian nervous tissue. The RNC is composed of outer ectoneural and inner hyponeural layers, which are interconnected with one another via short neural bridges. The circumoral nerve ring is purely ectoneural. Both ectoneural and hyponeural components are epithelial tubes with a thick neuroepithelium at one side. A thin ciliated non-neuronal epithelium complements the neuroepithelium to form a tube, thereby enclosing the epineural and hyponeural canals. The whole of the ectoneural and hyponeural subsystems is separated from the surrounding tissue by a continuous basal lamina. The nerve ring and the ectoneural and hyponeural parts of the radial nerves are all neuroepithelia composed of supporting cells and neurons. Supporting cells are interpreted as being glial cells. Based on ultrastructural characters, three types of neurons can be distinguished: (1) putative primary sensory neurons, whose cilium protrudes into the epineural or hyponeural canal; (2) non-ciliated neurons with swollen rough endoplasmic reticulum cisternae; (3) monociliated neurons that are embedded in the trunk of nerve fibers. Different types of synapses occur in the neuropile area. They meet all morphological criteria of classical chemical synapses. Vacuolated cells occur in the neuroepithelium of E. fraudatrix, but are absent in P. lubricus; their function is unknown. The cells of the non-neuronal epithelia that overlie the ectoneural and hyponeural canals are hypothesized to belong to the same cell type as the supporting cells of the neuroepithelium.     

Ultrastructure of the Statocysts in the Apodous Sea Cucumber Leptosynapta inhaerens (Holothuroidea, Echinodermata)

The burrowing sea cucumber Leptosynapta inhaerens possesses five pairs of statocysts, one pair on either side of each radial nerve cord where it arises from the circumoral nerve ring. The nerve cords exhibit only ectoneural components at the level of the statocysts. A sinus-like epineural canal lies superjacent to each cord. This canal is lined by a robust monociliated neuroepithelium which lacks any special support cells. Beneath the neuroepithelium, the somata of the ectoneural neurons form a perikaryal layer whereas the axons are located within the proximal parts of the cords. Glial cells have not been found. Each statocyst is a hollow sense organ. Its central cavity is lined by a monolayer of monociliated parietal cells. Axons of these parietal cells extend towards the statocyst nerve which connects each statocyst with the ectoneural pathways of the cord. A single lithocyte floats within each central statocyst cavity. This unciliated cell contains a voluminous vacuole with the statolith and several smaller vacuoles. It is concluded that statocysts do not belong to the basic organization of the Holothuroidea but have been evolved within this group. The statement, that the statocysts of apodous sea cucumbers and that of the enigmatic Xenoturbella bocki are homologous organs, is rejected.     

The giant neurone system in ophiuroids

Summary The nervous system of Ophiura texturata contains nerve fibres and cell bodies that are an order of magnitude larger than anything previously described in the Asteroidea and Echinoidea. These large nerve cells are designated giant fibres. Giant nerve cells are present in both the ectoneural and hyponeural nervous system. The layout of these nerve cells is described and it is shown that the organization is repeated in each segmental ganglion that makes up the radial nerve cord. The circumoral nerve ring is composed, in the main, of tracts of nerve fibres joining the radial nerves, and it contains only limited areas of neuropil associated with the alimentary canal and muscles of the disc and jaws. Degeneration studies have shown that each segmental ganglion of the radial nerve cords contains a discrete population of neurones separate from adjacent ganglion and that there are not anatomically continuous giant fibres along the whole length of the nerve cord.     

The fine structure of the buccal tentacles of Holothuria forskali (Echinodermata,Holothuroidea)

Summary Ultrastructural study of the buccal tentacles of Holothuria forskali revealed that each tentacle bears numerous apical papillae. Each papilla consists of several differentiated sensory buds.The epidermis of the buds is composed of three cell types, i.e. mucus cells, ciliated cells, and glandular vesicular cells (GV cells). The GV cells have apical microvilli; they contain bundles of cross striated fibrillae associated with microtubules. Ciliated cells have a short non-motile cilium. Bud epidermal cells intimately contact an epineural nervous plate which is located slightly above the basement membrane of the epidermis. The epineural plate of each bud connects with the hyponeural nerve plexus of the tentacle. This nerve plexus consists of an axonic meshwork surrounded in places by sheath cells. The buccal tentacles have well-developed mesothelial muscles. Direct innervation of these muscles by the hyponeural nerve plexus was not seen.It is suggested that the buccal tentacles of H. forskali are sensory organs. They would recognize the organically richest areas of the sediment surface through the chemosensitive abilities of their apical buds. Tentacles presumably trap particles by wedging them between their buds and papillae.     

Light and electron microscopic localization of GABA-like immunoreactivity in myenteric plexus of chicken

Summary Whole-mounts of 1-day-old chicken midgut were incubated with an antiserum against GABA-glutaraldehyde-BSA conjugate. The immunoreaction was visualized by using the peroxidase-antiperoxidase method, and processed for consecutive light and electronmicroscopic observation. GABA was selectively localized in some of the varicose and nonvaricose nerve fibres of the myenteric plexus. The varicose fibres formed dense networks within the myenteric ganglia, some of which — mainly in duodenum — also contained immunopositive nerve cell bodies. Some of the varicose fibres projected out from the myenteric plexus into the circular muscle layer. At the electronmicroscopic level, labelled axon terminals formed synaptic contact with unlabelled perikarya and vica versa. At the same time, no labelled terminals were found on immunostained cells. In a few cases, axon terminals with GABA positivity were situated close to the smooth muscle cells in the circular muscle layer, suggesting a prejunctional GABA effect on the neighbouring nerve terminals on the release of their transmitters.     

The morphology of the axial complex and associated structures in Asterozoa (Asteroidea,Echinoidea, Ophiuroidea)

The representatives of Asterozoa (Asteroidea, Echinoidea, and Ophiuroidea) have a similar structural plan of the axial complex with minor differences within each class; this structural scheme substantially differs from that in Crinozoa and Holothurozoa. The axial complex consists of the coelomic organs and the haemocoel (blood) structures, which are morphologically and functionally integral. The coelomic organs are the stone canal, axial coelom, perihaemal coeloms (axocoel perihaemal ring and somatocoel perihaemal ring), water ring, and pericardial and genital coeloms. These organs are closely associated with the epigastric and hypogastric coeloms and with the perioral coelomic ring. The haemocoel structures of the axial complex include the oral haemal ring, heart, axial organ, genital haemal ring, and gastric haemal ring. The epineural canals of echinoids and ophiuroids are of a noncoelomic nature. They are formed by the invagination of the ectoneural cord and closing of the epidermis above it. The possible functions of the axial complex in Asterozoa are blood circulation and excretion.     

Ultrastructural Study of the Filum Terminate and Caudal Ampulla of the Spinal Cord of Amphioxus (Branchiostoma lanceolatum Pallas)

The filum terminale and caudal ampulla of amphioxus were studied by electron microscopy. The filum terminale consists of ependymal cells whose cilia are directed caudally. Remarkably, nerve fibres course through the filum terminale and caudal ampulla and end on the basal lamina forming neuro-connective structures. Moreover, these nerve boutons are divisible into several classes according to their vesicle content. Boutons containing large dense-cored vesicles are very similar in appearance to the neurosecretory terminals found in the caudal spinal cord of some vertebrates. These observations on nerve fibres suggest that a primitive neurosecretory system similar to the fish urophysis is present in the amphioxus.     

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea)

Abstract. Antibodies against the echinoderm-specific neuropeptide S1 and against 5HT were used to examine the fate of the larval nervous system during metamorphosis in the ophiuroid Ophiactis resiliens . In contrast to most echinoderms, the onset of peptidergic and serotonergic expression was delayed to the advanced ophiopluteus stage, in particular for 5HT. In advanced ophioplutei, peptidergic immunoreactivity was located in simple fibres associated with the ciliated bands, a stomach nerve ring, and cells along the antero-lateral arms. 5HT immunoreactivity was concentrated in 2 oral ganglia in the adoral projections, located at the posterior rim of the mouth. Clusters of 5HT-positive cells were also found along the antero-lateral arms. The ophiopluteus lacked a serotonergic (or peptidergic) anterior ganglion. In echinoids, holothuroids, and crinoids, anterior ganglia are thought to have a sensory role in settlement and metamorphosis. Given that ophioplutei metamorphose in the plankton and that larval structures degenerate before settlement, the absence of apical ganglia correlates with the lack of a functional role for larval structures in substrate selection and settlement. Although most of the larval nervous system degenerated during metamorphosis, the adoral projections and associated oral ganglia appeared to be incorporated into the juvenile mouth, suggesting a potential role for larval neurons in contributing to oral neuronal structures in the adult. S1-positive neurons and fibres in the rudiment developed de novo and in parallel with development of the epineural canal. This structure gives rise to the primordia of the adult circumoral nerve ring and radial nerves, indicating that differentiation of the adult nervous system begins in the early stages of metamorphosis.     

Patterns of bromodeoxyuridine incorporation and neuropeptide immunoreactivity during arm regeneration in the starfish Asterias rubens

Regeneration of the arm of the starfish, Asterias rubens (L.) (Echinodermata: Asteroidea) was examined using two preparations. The first involved regeneration of the entire arm tip and its associated sensory structures and the second examined regeneration of a small section of radial nerve cord in the mid-arm region. Cell cycle activity was investigated by incorporation of the thymidine analogue, bromodeoxyuridine (BrdU). Details of neuroanatomy were obtained by immunocytochemistry (ICC) using an antiserum to the recently isolated starfish neuropeptide, GFNSALMFamide (S1). BrdU labelling indicated that initial events occur by morphallaxis, with cell cycle activity first apparent after formation of a wound epidermis. As regeneration proceeded, BrdU immunoreactive (IR) nuclei revealed cell cycle activity in cells at the distal ends of the radial nerve cord epidermis, in the coelomic epithelium, the perihaemal and water vascular canal epithelia, and in the forming tube feet of both preparations. By varying the time between BrdU pulses and tissue fixation, the possible migration or differentiation of labelled cells was investigated. Neuropeptide ICC indicated the extension of S1-IR nerve fibres into the regenerating area, soon after initial wound healing processes were complete. These fibres were varicose and disorganized in appearance, when compared to the normal pattern of S1-IR in the radial nerve. S1-IR was also observed in cell bodies, which reappeared in the reforming optic cushion and radial nerve at later stages of regeneration. Double labelling studies with anti-BrdU and anti-S1 showed no co-localization in these cell bodies, in all the stages examined. It appeared that S1-IR cells were not undergoing, and had not recently undergone, cell cycle activity. It cannot be confirmed whether S1-IR neurons were derived from proliferating cells of epithelial origin, or from transdifferentiation of epithelial cells, although the former mechanism is suggested. Differentiation of the regenerating structures to replace cells such as S1-containing neurons, is thought to involve cell cycle activity and differentiation of epithelial cells in the epidermal tissue, possibly in association with certain types of coelomocytes which move into the regenerating area.     

Nervous network in larvae of the ascidian Ciona intestinalis

 With the use of the monoclonal antibody UA301, which specifically recognizes the nervous system in ascidian larvae, the neuronal connections of the peripheral and central nervous systems in the ascidian Ciona intestinalis were observed. Three types of peripheral nervous system neurons were found: two located in the larval trunk and the other in the larval tail. These neurons were epidermal and their axons extended to the central nervous system and connected with the visceral ganglion directly or indirectly. The most rostral system (rostral trunk epidermal neurons, RTEN) was distributed bilateral-symmetrically. In addition, presumptive papillar neurons in palps were found which might be related to the RTEN. Another neuron group (apical trunk epidermal neurons, ATEN) was located in the apical part of the trunk. The caudal peripheral nervous system (caudal epidermal neurons, CEN) was located at the dorsal and ventral midline of the caudal epidermis. In the larval central nervous system, two major axon bundles were observed: one was of a photoreceptor complex and the other was connected with RTEN. These axon bundles joined in the posterior sensory vesicle, ran posteriorly through the visceral ganglion and branched into two caudal nerves which ran along the lateral walls of the caudal nerve tube. In addition, some immunopositive cells existed in the most proximal part of the caudal nerve tube and may be motoneurons. Received: 8 September 1997 / Accepted: 14 December 1997     

Comparative morphology of echinoderm calcified tissues: Histology and ultrastructure of ophiuroid scales (Echinodermata,Ophiuroida)

Summary The calcified body wall of an ophiuroid was investigated by a new method and compared with that of other echinoderms. The previous opinion that the epidermis of ophiuroid arm shields consists of a reduced syncytium continuous with the underlying dermis is incorrect. The epidermis is distinctly separated from the dermis by a basal layer and consists of (1) supporting cells which bear the cuticle, (2) ciliated cells (hitherto unknown and probably sensory), (3) gland cells, and (4) nerve cells with the basal nerve plexus. The overall structure of the epidermis is a three-dimensional tube system (marked by the basal lamina) which penetrates the dermal tissue of the scale's pore space and continues with nerve cords situated below the scale. This arrangement is unique in echinoderms.The dermal sclerocytes largely conform with those of the echinoid Eucidaris. The mineral skeleton is produced intracellularly or intrasyncytially. Moreover, dermal sclerocytes were found to release extracellular microfibrils which have nothing to do with calcite deposition. The attachment of the cuticle to the dermis is achieved by means of epidermal coupling areas. Collagen fibers fasten the scale to the underlying connective tissue sheath. The supposed fibrocytes within this sheath resemble sclerocytes. Each collagen bundle is provided with a strand of nerve fibers which, in contrast to the basal nerve plexus, are naked. They are said to infuence the mechanical properties of the connective tissue.Structures associated with cilia occur in cell types which normally lack a cilium. This finding suggests that most echinoderm cells are potentially monociliate.Abbreviations A apical shield - asp secretory products - B bacteria - bb basal body - bl basal lamina - C ciliated cell - ca coupling area - ci cilium, - cf collagen fibrils - cs cell surface - CTS connective tissue sheath - cu _i inner cuticular layer - cu _m middle cuticular layer - dp distal processes (Sc) - EC epineural canal - G Golgi complex - gv granular vesicle - H haemal vessel - hb homogeneous body - hl horizontal lamina (Su) - j cell junction - L lateral shield - le boundary layer (Sc) - lo distal lobe (Su) - M intervertebral muscle or its attachment - m mitochondrium - mf microfibrils - mu mucus - mv microvilli - mvb multivesicular body - N nerve cell - n nucleus - nf neurofibrils - ng neurogranules - nn naked neurofibrils - O oral shield - P tube foot - Pc phagocyte - pg pigment granules - rl rootlet - RN radial nerve - RV radial vessel - Sc sclerocyte - sh cytoplasmic sheath (Sc) - sj septate junction - Su supporting cell - sv secretory vesicle - T calcite trabeculum - V vertebral ossicle - v vesicle (Su)     

Distribution and morphology of the ampullary organs of the salmontail catfish,Arius graeffei

Whole body staining of Arius graeffei revealed that ampullary pores cover the body with their highest densities occurring on the head and lowest densities on the mid‐ventral surface. Each ampullary organ consists of a long canal (0.2–1.75 mm) passing perpendicular to the basement membrane, through the epidermis into underlying dermal connective tissues, curving thereafter to run roughly parallel to the epidermis. Histochemical staining techniques (Alcian blue and Lillie′s allochrome) indicate that the canals contain a neutral to acidic glycoprotein‐based mucopolysaccharide gel that varies in composition along the length of the canal. Collagen fibers, arranged in a sheath, surround a layer of squamous epithelium that lines each ampullary canal. At the proximal end of the canal, squamous cells are replaced by cuboidal epithelial cells that protrude into the lumen, thus constricting the lumen to form a small pore into the ampulla. The ampulla is lined with receptor and supportive cells. The numerous (60–120) pear‐shaped receptor cells bear microvilli on their luminal surface. Two forms of receptor cells exist in each ampullary organ: basal and equatorial receptor cells. Each receptor cell is connected to an unmyelinated nerve. Each receptor cell is surrounded by supportive cells on all but the apex. Tight junctions and underlying desmosomes occur between adjacent receptor and supportive cells. This form of ampullary organ has not previously been described for teleosts. J. Morphol. 239:97–105, 1999. © 1999 Wiley‐Liss, Inc.     

Fine structure of ocelli of an anthomedusan,Nemopsis dofleini,with special reference to synaptic organization

Summary An ocellus of an anthomedusan, Nemopsis dofleini, is composed of sensory and pigment cells and underlain by a nerve plexus and a muscle sheet. A sensory cell is divided into three parts: an apical part from which a single cilium arises, a slender middle part with numerous microtubules and an enlarged basal part that contains an oval nucleus but does not send out an axon. The ocellar cup is occupied by variously remodelled ciliary sheaths that are covered by a few lysosomal projections from the pigment cells. Three modes of synaptic connections — centripetal, centrifugal and two-way — are found between sensory cells and either dendrites or somata of second order neurons. Synaptic vesicles in sensory cells are larger in number, smaller in size and more uniform in shape than those of second order neurons. The soma of a second order neuron lies below the surface layer of an ocellar cup and gives rise to a single cilium that lacks rootlets and the second centriole. The possibility of multimodal sensory perception in and around the ocellar region is discussed.The work was supported by research grants from the Ministry of EducationFormerly Tamano Marine Laboratory     

On the ampullary organs of the South-American paddle-fish Sorubim lima (Siluroidea,Pimelodidae)

Summary Ampullary organs were found in the epidermis of the paddle-fish Sorubim lima; they are distributed all over the skin surface of the fish but are particularly densely grouped in the head region and on the dorsal surface of the paddle. Histological and electron microscopical observations show that their structure is similar to the type of cutaneous ampullary organs characteristic of other Siluroidea. Composed of a relatively large mucus-filled ampulla, the organ possesses a short and narrow canal which leads to the outer epidermal surface. The wall of the ampulla is formed of several layers of flat epidermal cells. In general four sensory cells, each one surrounded by supporting cells, compose the sensory epithelium at the bottom of the ampulla. The inner surface of the sensory cells in contact with the ampullary mucus bears only microvilli. The contact between the nerve endings and the sensory cells show the characteristic structure of an afferent neuro-sensory junction. Two ampullae are innervated in some cases by the same afferent nerve fibre.The author expresses her gratitude to Dr. Szabo for his scientific advice during her stay in Gif sur Yvette     

Nervous system of ascidian larvae: Caudal primary sensory neurons

Summary In larvae of Diplosoma macdonaldi one sensory nerve extends along the dorsal midline of the tail and another extends along the ventral midline. Each nerve is composed of 50–70 naked axons lying in a groove in the base of the epidermis, and each projects to the visceral ganglion. The cell bodies of the caudal sensory neurons occur in pairs within the epidermis, and are situated along the courses of the nerves. A single cilium arises from an invagination in the soma of each neuron, passes through the inner cuticular layer of the tunic and enters a tail fin formed by the outer cuticular layer. We propose that these cells are mechanoreceptors. The caudal sensory system is similar in representative species of ten families of ascidians.Abbreviations a axial complex of the tail - ac accessory centriole - ax axon - bb basal body - bl basal lamina - c cilium - cep common epidermal cells - cs ciliary sheath - dcv dense-cored vesicles - dsn dorsal sensory nerve - ec ependymal cells - ep epidermis - gj gap junction - h hemocoel - hc hemocoelic chamber - icl inner cuticular layer of the tunic - m caudal muscle - nc dorsal nerve cord - ncl neurocoel - no notochord - ocl outer cuticular layer of the tunic - sc sensory cell - sn sensory nerve - sv sensory vesicle - vg visceral ganglion - vsn ventral sensory nerve     

Morphological studies of the spinal cord in tetraodontiformes fishes

The spinal cord of two tetraodontiform fishes, the Japanese file fish (Navodon modestus) and the panther puffer (Takifugu pardalis), are unusual among vertebrates in having a markedly abbreviated spinal cord with a long and flattened filum terminale. Only the rostral short part of the cord of both species is cylindrical; the greater part of the cord is markedly flat. The majority of the spinal nerve roots leave the short cylindrical part. The flattened part of the cord contains the central canal, myelinated nerve fibers, and a few motoneurons surrounding the cauda equina, and it is histologically similar to the filum terminale of amphibians and mammals. The spinal cords of other teleosts, the sun-fish and angler, also are abbreviated and possess a filum terminale and cauda equina. These orders possess an enormous head and short trunk. However, the correlation between this body form and an abbreviated cord is not causal, since the tetraodontiform species described here show ordinary body proportions. The spinal cord may be abbreviated in tetraodontiform fishes in general.     

Catecholamine-containing,serotonin-like and neuropeptide FMRFamide-like immunoreactive cells and processes in the nervous system of the pilidium larva (Nemertini)

Summary Pilidium larvae at different developmental stages have been investigated for the occurrence of glyoxylic acid induced fluorescence in catecholamines (CA), and serotonin-like (5-HT) and neuropeptide FMRFamide-like (FMRFamide) immunoreactivity (ir). The distribution of CA, 5-HT-ir and FMRFamide-ir cells and processes was compared with the location of nerve processes as found by transmission electron microscopy (TEM). In the pilidium larvae the marginal and oral nerves contain CA and 5-HT-ir processes and 5-HT-ir unipolar cells. The posterior suboral nerve contain CA and 5-HT-ir processes, whereas in the anterior suboral nerve neither CA nor 5-HT-ir and FMRFamide-ir were observed. The lateral helmet nerve contains FMRFamide-ir processes and unipolar cells. In the epidermis CA and 5-HT-ir multipolar cells were found. The juvenile worm that develops inside the pilidium larva was found to contain only 5-HT-ir. A pair of lateral cords extent the whole length of the juvenile and anteriorly they form the anterior ventral cerebral commissure. Also, from the anterior part of the lateral cords projects a pair of circumrhynchodeal processes which dorsally form the dorsal cerebral commissure. A pair of proboscis processes originate from the circumrhynchodeal processes and extend the whole length of the probosics. From the dorsal cerebral commissure cephalic processes project rostrally and ventrally. Only unipolar 5-HT-ir cells were observed, and they were located along the lateral cords into which their processes extend.Abbreviations AEC 3-amino-9-ethylcarbazole - ap apical plate - arp anterior accessory ridge processes - ason anterior suboral nerve - CA catecholamines - cd cephalic discs - cp cephalic processes - crp circumrhynchodeal processes - DAB 3,3'-diaminobenzidine - dc dorsal cerebral commissure - epi epidermis - es oesophagus - fl fore lobe - FMRFamide phe—met—arg—phe—NH₂ - Go goat - GS goat serum - hl hind lobe - int intestine of the juvenile - lhn lateral helmet nerve - lhp lateral helmet processes - ll lateral lobe - lp lateral processes of the juvenile - mcb marginal ciliary band - me mesoderm - mn marginal nerve - moc monociliary cell - mp marginal processes - mu muscle - muc multiciliary cell - n 1, n 2, n 3 division of marginal nerve - on oral nerve - op oral processes - pb proboscis - pp proboscis processes - pson posterior suboral nerve - psop posterior suboral processes - Ra rabbit - sd stomodeum - st stomach - td trunk discs - tr trunk - TRITC tetramethylrhodamine isothiocyanate - vc ventral cerebral commissure - z 1, z 2 ciliary zones of marginal ciliary band - 5-HT serotonin     

Developmental origin of the adult nervous system in a holothurian: an attempt to unravel the enigma of neurogenesis in echinoderms

In adult echinoderms, the nervous system includes the ectoneural and hyponeural subsystems. The former has been believed to develop from the ectoderm, whereas the latter is considered to be mesodermal in origin. However, this view has not been substantially supported by embryological examinations. Our study deals with the developmental origin of the nervous system in the direct-developing sea cucumber Eupentacta fraudatrix. The rudiment of the adult nervous system develops from ectodermally derived cells, which ingress into the primary body cavity from the floor of the vestibule. At the earliest stages, only the rudiment of the ectoneural nerve ring is laid down. The radial nerve cords and tentacular nerves grow out from this subcutaneous rudiment. The ectoneural cords do not develop simultaneously but make their appearance in the following order: unpaired mid-ventral cord, paired dorsal lateral cords, and ventral lateral cords. These transitional developmental stages probably recapitulate the evolution of the echinoderm body plan. The holothurian hyponeural subsystem, as other regions of the metazoan nervous system, has an ectodermal origin. It originally appears as a narrow band of tissue, which bulges out of the basal region of the ectoneural neuroepithelium. Our data combined with those of other workers strongly suggest that the adult nervous tissue in echinoderms develops separately from the superficial larval system of ciliary nerves. Therefore, our data are neither in strict accordance with Garstang's hypothesis nor do they allow to refuse it. Nevertheless, in addition to ciliary bands, other areas of neurogenetic epidermis must be taken into account.     

Special cutaneous receptor organs of fish. VII. Ampullary organs of mormyrids

Ampullary receptor organs of African mormyrids consist of a cavity beneath the epidermis. The wall of the cavity contains embedded receptor cells and two types of supporting cells. A canal extends from the cavity to an opening at the surface. The lumen of the canal and the ampulla are filled with a jelly-like material and dense cylinders apparently secreted by two types of supporting cells. Flattened cells of the canal wall are joined by occluding junctions. Synapses between receptor cells and the afferent nerve fiber are characterized by a presynaptic dense body, but presynaptic vesicles were not observed. Degenerating receptor cells are occasionally seen among normal receptor cells in the base of the organ.     

NG2 and phosphacan are present in the astroglial scar after human traumatic spinal cord injury

Background

A major class of axon growth-repulsive molecules associated with CNS scar tissue is the family of chondroitin sulphate proteoglycans (CSPGs). Experimental spinal cord injury (SCI) has demonstrated rapid re-expression of CSPGs at and around the lesion site. The pharmacological digestion of CSPGs in such lesion models results in substantially enhanced axonal regeneration and a significant functional recovery. The potential therapeutic relevance of interfering with CSPG expression or function following experimental injuries seems clear, however, the spatio-temporal pattern of expression of individual members of the CSPG family following human spinal cord injury is only poorly defined. In the present correlative investigation, the expression pattern of CSPG family members NG2, neurocan, versican and phosphacan was studied in the human spinal cord.

Methods

An immunohistochemical investigation in post mortem samples of control and lesioned human spinal cords was performed. All patients with traumatic SCI had been clinically diagnosed as having "complete" injuries and presented lesions of the maceration type.

Results

In sections from control spinal cord, NG2 immunoreactivity was restricted to stellate-shaped cells corresponding to oligodendrocyte precursor cells. The distribution patterns of phosphacan, neurocan and versican in control human spinal cord parenchyma were similar, with a fine reticular pattern being observed in white matter (but also located in gray matter for phosphacan). Neurocan staining was also associated with blood vessel walls. Furthermore, phosphacan, neurocan and versican were present in the myelin sheaths of ventral and dorsal nerve roots axons. After human SCI, NG2 and phosphacan were both detected in the evolving astroglial scar. Neurocan and versican were detected exclusively in the lesion epicentre, being associated with infiltrating Schwann cells in the myelin sheaths of invading peripheral nerve fibres from lesioned dorsal roots.

Conclusion

NG2 and phosphacan were both present in the evolving astroglial scar and, therefore, might play an important role in the blockade of successful CNS regeneration. Neurocan and versican, however, were located at the lesion epicentre, associated with Schwann cell myelin on regenerating peripheral nerve fibres, a distribution that was unlikely to contribute to failed CNS axon regeneration. The present data points to the importance of such correlative investigations for demonstrating the clinical relevance of experimental data.