Structure of the nervous system of Myzostoma cirriferum (Annelida) as revealed by immunohistochemistry and cLSM analyses

The nervous systems of juvenile and adult Myzostoma cirriferum Leuckart, 1836, were stained with antisera against 5-HT (5-hydroxytryptamine, serotonin), FMRFamide, and acetylated alpha-tubulin in combination with the indirect fluorescence technique and analyzed by confocal laser scanning microscopy. The central nervous system consists of two small cerebral ganglia, connected by a dorsal commissure, a ventral nerve mass, and a pair of long circumesophageal connectives joining the former to the latter. The two neuropil cords within the ventral nerve mass curve outward and are joined to one another anteriorly and posteriorly. They are connected by 12 commissures, forming a ladder-like system. A single median nerve runs along the midventral axis. In addition to the circumesophageal connectives, 11 peripheral nerves arise from each main cord. The first innervates the anterior body region. The others form five groups of two nerves each, the first and thicker nerve of which is the parapodial nerve, innervating the parapodium and two corresponding cirri. Except for those in the most posterior group, the second nerves innervate the lateral organs and the body periphery. Serotonergic perikarya are arranged in six more or less distinct clusters, the first lying in front of and the other five between the main nerve cords. The distribution pattern of the FMRFamidergic perikarya is less clear and the somata lie between and outside the cords. One pair of dorsolateral longitudinal nerves was visualized by tubulin staining. Peripheral nerves and the commissures, in particular, demonstrate a segmental organization of the nervous system of M. cirriferum. Furthermore, their arrangement indicates that the body consists of six segments, the first of which is identifiable only by the first pair of peripheral nerves, the first two commissures, and the anteriormost ventral ganglion. The nervous system M. cirriferum thus exhibits several structures also found in the basic plan of the polychaete nervous system.     

Larval neurogenesis in Sabellaria alveolata reveals plasticity in polychaete neural patterning

The investigation of neurogenesis in polychaetes not only facilitates insights into the developmental biology of this group, but also provides new data for phylogenetic analyses. This should eventually lead toward a better understanding of metazoan evolution including key issues such as the ontogenetic processes that underlie body segmentation. We here document the development of the larval nervous system in the polychaete Sabellaria alveolata using fluorescence-coupled antibodies directed against serotonin, FMRFamide, and tubulin in combination with confocal laser scanning microscopy and 3D reconstruction software. The overall pattern of neurogenesis in S. alveolata resembles the condition found in other planktonic polychaete trochophores where the larval neural body plan including a serotonergic prototroch nerve ring is directly followed by adult features of the nervous system such as circumesophageal connectives and paired ventral nerve cords. However, distinct features are also found in S. alveolata, such as the innervation of the apical organ with ring-shaped neurons, the low number of immunoreactive perikarya, and the lack of a posterior serotonergic cell. Moreover, in the larvae of S. alveolata, two distinct modes of neuronal development are expressed, viz. the simultaneous formation of the first three segmental neurons of the peripheral nervous system on the one hand versus the sequential appearance of the ventral commissures on the other. This highlights the complex mechanisms that underlie annelid body segmentation and indicates divergent developmental pathways within polychaete annelids that lead to the segmented nervous system of the adult.     

Observations of serotonin and FMRFamide-like immunoreactivity in palp sensory structures and the anterior nervous system of spionid polychaetes

Evidence suggests that ciliated sensory structures on the feeding palps of spionid polychaetes may function as chemoreceptors to modulate deposit-feeding activity. To investigate the probable sensory nature of these ciliated cells, we used immunohistochemistry, epi-fluorescence, and confocal laser scanning microscopy to label and image sensory cells, nerves, and their organization relative to the anterior central nervous system in several spionid polychaete species. Antibodies directed against acetylated alphatubulin were used to label the nervous system and detail the innervation of palp sensory cells in all species. In addition, the distribution of serotonin (5-HT) and FMRFamide-like immunoreactivity was compared in the spionid polychaetes Dipolydora quadrilobata and Pygospio elegans. The distribution of serotonin immunoreactivity was also examined in the palps of Polydora cornuta and Streblospio benedicti. Serotonin immunoreactivity was concentrated in cells underlying the food groove of the palps, in the palp nerves, and in the cerebral ganglion. FMRFamide-like immunoreactivity was associated with the cerebral ganglia, nuchal organs and palp nerves, and also with the perikarya of ciliated sensory cells on the palps.     

On the Microanatomy of the Cephalic Nervous System of Nereidae (Polychaeta), with a Preliminary Discussion of Some Earlier Theories on the Segmentation of the Polychaete Brain

Abstract Earlier papers dealing with the microanatomy of the nereid brain have been studied. On this basis a re-investigation of the cephalic nervous system and of the innervation and homologues of the anterior end appendages of these animals appeared necessary: the existing literature proved insufficient for detailed comparisons with other polychaete families and many earlier statements were quite contradictory. In the present paper, the brain commissures and the innervation of, inter alia, the antennae and the palps of Neanthes virens and Nereis pelagica are described. Special attention was paid to the roots of the circum-oesophageal connectives and the ganglia in this part of the nervous system. The results, summarized in schematic diagrams and tables, are compared with corresponding observations in 14 other polychaete families. In a discussion of the architecture of the polychaete nervous system as a phylogenetic instrument, the supposed segmentation of the polychaete brain is questioned and the idea that the configuration of the polychaete nervous system offers support to the cyclomer theory is rejected. Other conclusions concerning the relationships within the Polychaeta are pointed out.     

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     

Electron microscopic immunolocalization of basic fibroblast growth factor in peripheral nerves

In spite of ample information about the distribution and the effects of basic fibroblast growth factor (bFGF) in the central nervous system, few data are available concerning the localization of this protein in the peripheral nervous system. In view of the role of bFGF in the regulation of trophic and non-trophic functions, we focused on the presence and precise localization of this growth factor in normal peripheral nerves at the electron microscopic level. The study shows that bFGF is mainly located in the Schwann cells, especially in the nuclei. There is slight labeling in the myelin sheath and in the axon cytoplasm. The study provides morphologic evidence for an association between bFGF expression and Schwann cells. Such as association argues for a role of this peptide in the maintenance or regeneration of peripheral nerves.     

Neurosteroids: trophic effects in the nervous system]

Some steroids, named "neurostero?ds", can be synthesized from cholesterol within both the central and peripheral nervous systems. Thus, pregnenolone and progesterone persist in the brain and in peripheral nerves long after removal of the steroidogenic endocrine glands by castration and adrenalectomy. The role of neurosteroids during the development of the nervous system is not well known, although they are synthesized by glial cells and some populations of neurons already during embryonic life. Cell culture experiments suggest that neurosteroids may influence the survival and differentiation of neurons and glial cells. In the adult nervous system, neurosteroids play an important role during regeneration. Progesterone is indeed synthesized by Schwann cells in peripheral nerves, where it plays an important role in the formation of new myelin sheaths after lesion. This is the first demonstration of a vital role for a neurosteroid in the nervous system.     

Homologous patterns in the embryonic development of the peripheral nervous system in the grasshopper Schistocerca gregaria and the fly Drosophila melanogaster.

To determine the generality of developmental mechanisms involved in the construction of the insect nervous system, the embryonic development of the peripheral nervous system in the grasshopper Schistocerca gregaria was characterized at the level of identified neurons and nerve branches and then compared to that previously described from the fly Drosophila melanogaster. For this, immunocytochemistry using a neuron-specific antibody was carried out on staged grasshopper embryos. Our results show that initially a simple peripheral nerve scaffolding is established in each segment of the animal. This scaffolding consists of a pair of intersegmental nerves that are formed by identified afferent and efferent pioneer neurons and a pair of segmental nerves that are formed by afferent pioneers situated in limb buds. Subsequently, identified sets of sensory neurons differentiate in a stereotyped spatiotemporal pattern in dorsal, lateral and ventral clusters in each segment and project their axons onto these nerves. Although segment-specific differences exist, serial homologs of the developing nerves and sensory neurons can be identified. A comparison of these results with those obtained from Drosophila shows that virtually the same pattern of peripheral nerves and sensory structures is formed in both species. This indicates that the construction of the peripheral nervous system in extremely divergent modern insects relies on conserved developmental mechanisms that evolved in ancestral insects over 300 million years ago.     

Spontaneous and Experimental Neuritis and the Distribution of the Myelin Protein P2 in the Nervous System

The P2 contents of nervous tissues from the human, rabbit, guinea pig, and Lewis rat were measured by radioimmunoassay. The ventral spinal roots contained more P2 than any other tissue. Human dorsal roots and peripheral nerves contained 41-65% of the amount in human ventral roots. Human olfactory and optic nerves and brain contained 1.1-2.7%, spinal cord, 2.8%, cranial nerve VIII, 11%, and cerebral grey matter, 0%. The relative amounts in the rabbit nervous system were similar except that the spinal cord contained 20% of the amount in the ventral roots. Qualitative estimates in the guinea pig showed that the spinal roots and peripheral nerves contained more P2 than the spinal cord, and that none was present in the brain. In the Lewis rat, P2 could be detected in the spinal roots and peripheral nerves but not in the CNS. The distribution of P2 in the human nervous system parallels the incidence and severity of lesions in acute polyradiculoneuritis. It also explains the absence of any lesions in the CNS when experimental allergic neuritis is induced in the Lewis rat.     

The central and peripheral nervous system of <Emphasis Type="Italic">Cephalodiscus gracilis</Emphasis> (Pterobranchia,Deuterostomia)

Nervous systems are important in assessing interphyletic phylogenies because they are conservative and complex. Regarding nervous system evolution within deuterostomes, two contrasting hypotheses are currently discussed. One that argues in favor of a concentrated, structured, central nervous system in the last common ancestor of deuterostomes (LCAD); the other reconstructing a decentralized nerve net as the nervous system of the LCAD. Here, we present a morphological analysis of the nervous system of the pterobranch deuterostome Cephalodiscus gracilis Harmer, 1905 based on transmission electron microscopy, confocal laser scanning microscopy, immunohistochemistry, and computer-assisted 3D reconstructions based on complete serial histological sections. The entire nervous system constitutes a basiepidermal plexus. The prominent dorsal brain at the base of the mesosomal tentacles contains an anterior concentration of serotonergic neurons and a posterior net of neurites. Predominant neurite directions differ between brain regions and synapses are present, indicating that the brain constitutes a centralized portion of the nervous system. Main structures of the peripheral nervous system are the paired branchial nerves, tentacle nerves, and the ventral stalk nerve. Serotonergic neurites are scattered throughout the epidermis and are present as concentrations along the anterior border of the branchial nerves. Serotonergic neurons line each tentacle and project into the brain. We argue that the presence of a centralized brain in C. gracilis supports the hypothesis that a nerve center was present in the LCAD. Moreover, based on positional and structural similarity, we suggest that the branchial nerves in C. gracilis could be homologous to branchial nerves in craniates, a hypothesis that should be further investigated.     

Nervous System of the Larva of the Ascidian Molgula citrina(Alder and Hancock, 1848)

Features of the nervous system, especially those of the peripheral nervous system, are described in the larva of Molgula citrina . In the peripheral nervous system, antibodies raised against acetylated α–tubulins mark a pair of rostral nerves arising from 8 to 10 sensory cells in the trunk epithelium, and a pair of tail nerves. In the sensory vesicle of the trunk, a pair of antennal cells is associated with the statocyte, and a tuft of ca. 150 cilia is labelled inside the hypophysial duct. A dorsal bundle of fibres forms a plexus over the surface of the sensory vesicle which extends caudally over the visceral ganglion. The latter contains somala that were back-filled by Co²⁺–lysine through the cut tip of the tail. Antibodies directed against the transmitter candidates: peptides substance P, FMRFamide, somatostatin, neuropeptide Y, CGRP, VIP, and the amines: 5-HT, dopamine, noradrenaline and GABA, all failed to demonstrate immunoreactivity anywhere in the nervous system. The trunk epithelium is ciliated uniformly but lacks papillae; this is remarkable given the presence of rostral nerves. The latter are presumed to be sensory, and can be compared with those in larvaceans and the larva of amphioxus. Sensory cells in the tail nerve, if present, lack cilia. The tail nerves are lateral in this species and presumed to be motor. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd     

Distribution of prosaposin in the rat nervous system

Prosaposin is the precursor of four sphingolipid activator proteins (saposins A, B, C, and D) for lysosomal hydrolases and is abundant in the nervous system and muscle. In addition to its role as a precursor of saposins in lysosomes, intact prosaposin has neurotrophic effects in vivo or in vitro when supplied exogenously. We examined the distribution of prosaposin in the central and peripheral nervous systems and its intracellular distribution. Using a monospecific antisaposin D antibody that crossreacts with prosaposin but not with saposins A, B, or C, immunoblot experiments showed that both the central and peripheral nervous systems express unprocessed prosaposin and little saposin D. Using the antisaposin D antibodies, we demonstrated that prosaposin is abundant in almost all neurons of both the central and peripheral nervous systems, including autonomic nerves, as well as motor and sensory nerves. Immunoelectron microscopy using double staining with antisaposin D and anticathepsin D antibodies showed strong prosaposin immunoreactivity mainly in the lysosomal granules in the neurons in both the central and peripheral nervous systems. The expression of prosaposin mRNA, examined using in situ hybridization, was observed in these same neurons. Our results suggest that prosaposin is synthesized ubiquitously in neurons of both the central and peripheral nervous systems. Funding: This study was supported by the Ehime University INCS and in part by grants-in-aid for Scientific Research to S.M. (Exploratory Res. 19659380) from the Japan Society for the Promotion of Science and to AS (Priority Areas 18023029) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.     

Do salivary neurotrophic factors provide neurotrophic support to neurons of the central and peripheral nervous systems including nerves innervating papillae on the tongue?

Xerostomia, or loss of saliva, can lead to degeneration of taste papillae on the tongue. Saliva contains neurotrophic factors such as nerve growth factor and epidermal growth factor. These neurotrophic factors are likely to be important for the maintenance of the peripheral nervous system. Furthermore, neurotrophic support of peripheral nerves by salivary neurotrophic factors may then be translated into neurotrophic support of the central nervous system. We propose that artificial saliva used to treat xerostomia should also contain suitable neurotrophic factors to prevent loss of taste sensation and possibly also prevent neuropathy of the central and peripheral nervous systems.     

Localization of nerve growth factor-like immunoreactivity in rat nervous tissue

The use of immunofluorescence with affinity-purified antibodies enabled cytological localization of nerve growth factor-like material in the rat. Immunoreactivity was observed along various nerve tracts of the foetal rat brain and spinal cord at day 15 of gestation. Longitudinal pathways in ventral and dorsal spinal cord, ventral lower brain stem, posterior commissure, retroflex fascicle and in the olfactory bulb were all positive. A weaker and more widely spread immunostaining was visible in many areas in the central nervous system. Cranial nerves were strongly immunoreactive. Neuronal perikarya in the retina and the olfactory mucosa as well as filae olfactoriae and the olfactory nerve all the way to the olfactory bulb were also positive. In sensory ganglia and peripheral nerves most immunoreactivity was confined to supporting tissues, probably including Schwann cells. In irides, the pattern of immunoreactivity was similar to that of the sensory and autonomic innervation. More intensively fluorescent material was found in regrowing nerve fibres in iris transplants. Our histochemical results suggest that nerve growth factor and/or a related protein is present in large amounts along nerve pathways in supportive tissues of the peripheral nervous system as well as in the central nervous system during early development.     

豚鼠在体肠系膜下神经节细胞兴奋的来源

本文运用在体细胞内记录法,观察了与肠系膜下神经节（ＩＭＧ）相连的四组神经对ＩＭＧ神经元电位活动的影响。结果显示切断或阻滞任一组神经均使ＩＭＧ细胞电活动受抑。其中结肠神经（ＣＮ）和腹下神经（ＨＮ）分别传导源自结肠尾段和膀胱等盆腔脏器的外周性兴奋,节间神经（ＡＭＮ）同时传导源自脊髓的中枢性和结肠的外周性兴奋。定量研究表明外周比中枢的影晌更重要。因此ＩＭＧ不仅是传统认为的“信息传递站”,而且对中枢和外周信息有整合作用。     

Sympathetic innervation of lymphoreticular organs is rate limiting for prion neuroinvasion

Transmissible spongiform encephalopathies are commonly propagated by extracerebral inoculation of the infectious agent. Indirect evidence suggests that entry into the central nervous system occurs via the peripheral nervous system. Here we have investigated the role of the sympathetic nervous system in prion neuroinvasion. Following intraperitoneal prion inoculation, chemical or immunological sympathectomy delayed or prevented scrapie. Prion titers in spinal cords were drastically reduced at early time points after inoculation. Instead, keratin 14-NGF transgenic mice, whose lymphoid organs are hyperinnervated by sympathetic nerves, showed reduction in scrapie incubation time and, unexpectedly, much higher titers of prion infectivity in spleens. We conclude that sympathetic innervation of lymphoid organs is rate limiting for prion neuroinvasion and that splenic sympathetic nerves may act as extracerebral prion reservoirs.     

Monoamines and neuropeptides as transmitters in the sedentary polychaete Sabellastarte magnifica: actions on the longitudinal muscle of the body wall.

Pharmacological studies on the body wall musculature of the sedentary polychaete Sabellastarte magnifica show a potential neurotransmitter role for monoamines and neuropeptides in this organism. All catecholamines induced contraction of longitudinal muscle strips, while serotonin and the neuropeptides FMRFamide and substance P caused a relaxation of both resting and active muscle. In addition, we demonstrate catecholaminergic and serotonergic pathways in the nervous system of this sabellid, using immunohistochemistry and catecholamine-induced fluorescence. The presence of neuropeptide-containing fibers in the nervous system of this polychaete has been previously reported. Together these results suggest that catecholamines act as excitatory transmitters on the longitudinal muscle cells of the body wall of S. magnifica, while serotonin and FMRFamide, and possible substance P, are inhibitory transmitters. The possibility of coexistence of serotonin and FMRFamide within the same neuronal cell bodies and fibers of this polychaete is also explored.     

Molecular architecture of myelinated peripheral nerves is supported by calorie restriction with aging

Peripheral nerves from aged animals exhibit features of degeneration, including marked fiber loss, morphological irregularities in myelinated axons and notable reduction in the expression of myelin proteins. To investigate how protein homeostatic mechanisms change with age within the peripheral nervous system, we isolated Schwann cells from the sciatic nerves of young and old rats. The responsiveness of cells from aged nerves to stress stimuli is weakened, which in part may account for the observed age-associated alterations in glial and axonal proteins in vivo . Although calorie restriction is known to slow the aging process in the central nervous system, its influence on peripheral nerves has not been investigated in detail. To determine if dietary restriction is beneficial for peripheral nerve health and glial function, we studied sciatic nerves from rats of four distinct ages (8, 18, 29 and 38 months) kept on an ad libitum (AL) or a 40% calorie restricted diet. Age-associated reduction in the expression of the major myelin proteins and widening of the nodes of Ranvier are attenuated by the dietary intervention, which is paralleled with the maintenance of a differentiated Schwann cell phenotype. The improvements in nerve architecture with diet restriction, in part, are underlined by sustained expression of protein chaperones and markers of the autophagy–lysosomal pathway. Together, the in vitro and in vivo results suggest that there might be an age-limit by which dietary intervention needs to be initiated to elicit a beneficial response on peripheral nerve health.