Ultrastructure of glial cells in the nervous system of <Emphasis Type="Italic">Grillotia erinaceus</Emphasis>

Until now, there has been no answer to the question of whether specialized glial cells exist in the nervous system of platyhelminths. The identification of these cells in parasitic flatworms is difficult due to their organization as parenchymal animals. The goal of this study was to reveal and describe structural elements corresponding to the term glia in the CNS of the parasitic flatworm Grillotia erinaceus (Cestoda: Trypanorhyncha). Three types of glial cells are revealed. The first type consists of fibroblast-like cells located in the cerebral ganglia that contain fibrils and excrete onto the surface fibrillar material and possess desmosomes; the presumable function of fibroblast-like glial cells is the isolation and support of ganglionar neurons. Glial cells of the second type form a myelin-like envelope of giant axons and bulbar nerves of the scolex and have laminar cytoplasm; they are numerous and exceed the number of neurons in the composition of nerves. Glial cells of the third type form multilayer envelopes in the main nerve cords and make contacts with the excretory epithelium; however, specialized junctions with neurons were not found. The existence of glia in other free living and parasitic flatworms is discussed.     

Organization of the orthogon – main and minor nerve cords

The central nervous system of flatworms has been regarded as comprised of the bilobed brain, the longitudinal cords and the connecting transverse commissures forming a so called orthogon. The peripheral nervous system comprises the submuscular and subepidermal plexuses. As a confusion in the terminology of the longitudinal nerve cords has prevailed, two concepts have been introduced, the main nerve cords (MCs) and the minor cords. The MCs have been defined as the pair of longitudinal nerve cords that (1) start with strongest roots in the brain, (2) consist of wide fibre bundles and (3) are associated with more neurons (particularly amninergic marker neurons) than the other cords. Longitudinal nerve cords in other positions are thinner and have less pronounced contact with the brain. They have collectively been named minor cords. Support for the special status of the MCs has been obtained from studies of the neuroanatomy of Catenulida, Macrostomida, Proseriata, Tricladida and Lecithoepitheliata and of parasitic flatworms. Using the above mentioned criteria for the MCs and the results of recent studies, we present the following hypothese: The MCs in all flatworms correspond to each other and have a common origin. This revised version was published online in July 2006 with corrections to the Cover Date.     

No news on the flatworm front! Nitric oxide synthase in parasitic and free-living flatworms

The free radical nitric oxide (NO) has emerged as a simple and unique signalling molecule that can serve as neurotransmitter, paracrine substance or hormone. NO is a gas, formed by various neuronal cells, both centrally and peripherally. NO regulates cyclic GMP synthesis. The production of NO can be detected using the NADPH diaphorase (NADPH-d) histochemical stain for nitric oxide synthase (NOS). NOS was detected in two parasitic flatworms, Diphyllobothrium dendriticum and Hymenolepis diminuta, and two free-living flatworms, Planaria torva and Girardia tigrina. The staining for NOS was very strong in the nervous system of both parasitic worms. The main nerve cords, the transverse ring commmissures, nerves in association with the musculature, especially the cirrus musculature and sensory nerve endings showed NADPH-d staining. The NADPH-d staining in the free-living flatworms was much weaker. Still NOS activity was found in the neuropile of the brain and in association with the pharynx musculature. The demonstration of NOS in flatworms, indicates that NO is an old signal molecule in evolutionary terms. This revised version was published online in July 2006 with corrections to the Cover Date.     

Immunocytochemical localization of histamine in flatworms

Summary Specific antibodies against histamine were used to demonstrate the occurrence and cellular distribution of histamine-like immunoreactivity in three species of flatworms (phylum Platyhelminthes). In the parasitic cestode Diphyllobothrium dendriticum, histamine-reactivity was found in neurons of the main nerve cords, and in cells lining the central and peripheral excretory ducts. In the free-living microturbellarian Microstomum lineare and in the planarian Polycelis nigra, histamine-immuno-reactivity was restricted to cells and fibres of the nervous system. The occurrence of histamine or a related substance in the nervous system of flatworms, which represent primary bilateria, indicates the importance of this neuroactive substance in the animal kingdom.     

The pattern of neuropeptide F and RF-amide in two tapeworms

Two years ago the first platyhelminth regulatory peptide, neuropeptide F (NPF), was isolated from the tapeworm Moniezia expansa by Maule et al. (1991). NPF is a 39 amino acid peptide with a C terminal phenylalaninamide. NPF is the first platyhelminth neuropeptide to be sequenced fully. Preabsorption with NPF quenches the immunostaining with anti-FMRF-amide and anti-bovine PP (Halton et al. 1992). As the first authentic flatworm neuropeptide, the occurence and distribution of NPF along the whole flatworm line are under investigation. Both free-living and parasitic flatworms are being studied. So far NPF-immunoreactivity has been reported from three free- living flatworms (see Grahn et al., 1995) and from four parasitic flatworms (Marks et al., 1993).FMRF- and RF-amide immunoreactive (IR) nerve cells and fibres are common in the gull-tapeworm Diphyllobothrium dendriticum. In order to test whether the patterns for NPF- and RF-immunoreactivity co- localize in the gull-tapeworm, immunostaining with anti-NPF and anti-RF were performed. To broaden the study, adult Proteochepalus exiguus from the intestine of whitefish were included in the experiment.The study was performed on whole mounts of skinned worms (Gustafsson, 1991). Anti-NPF was used in concentrations 1:500 and 1:1000. Controls included liquid phase absorption with the homologous antigen (1000 ng ml^–1).In D. dendriticum NPF-immunoreactivity occurs in nerve cells and varicose nerve fibres of larval and adult worms. The NPF-IR cell bodies are more common in the peripheral nerve cords than along the main nerve cords, which contain nerve fibres with large varicosities. The cell bodies in the PNS are often triangular in shape. Immediately beneath the tegumental surface a thin NPF-IR nerve fibre is observed. As to the co-localization of NPF and RF nothing definite can be said but the general pattern seems tobe the same. In the brain commissure of D. dendriticum one large ganglion cell stains with both antisera, indicating coexistence.In P. exiguus NPF- and RF-immunoreactivity was observed in the two main nerve cords situated laterally and in the pairs of thin dorsal and ventral longitudinal nerve cords. Numerous transverse commissures connect the longitudinal cords forming an orthogonal pattern. The cell bodies along the nerve cords are multipolar. Thin projections extend from the main nerve cords to the surface of the worm. The main nerve cords are lined with NPF-and RF-IR cell bodies. The general staining patterns of NPF and RF are very similar.     

Monoclonal antibodies to proteins of the myelin-like sheath of earthworm giant axons show cross-reactivity to crayfish CNS glia: An immunogold electron microscopy study

Monoclonal antibodies were generated to the proteins in myelin-like membranes isolated from the nerve cords of the earthworm,Lumbricus terrestris. One of these showing cross-reactivity to 30–32 and 40 kDa proteins was shown by immunofluorescence microscopy and immunogold electron microscopy to be bound primarily to glial cell processes and their membranes and the myelin-like layers. This antibody cross-reacted with proteins of 60–65, 42, and 40 kDa in crayfish (Procambarus clarki) nerve cord homogenates. Localization by immunoelectron microscopy showed the antibody to be bound exclusively to the membranes of the glial processes ensheathing the axons in the crayfish nerve cord. Thus, the proteins in earthworm and crayfish glial cell membranes have some epitopes in common. We suggest that this may represent an evolutionary conservation of these proteins. Special issue dedicated to Dr. Marion E. Smith.     

Electron microscopy of the mucosal plexus of the rat colon.

The ultrastructure of neurons, glial cells and axons of the mucosal plexus of the rat colon descendens was studied. Serial semithin sections and a re-embedding technique were used in order to localize the ganglia. The ganglia are free of blood vessels and connective tissue. The ratio of neurons to glial cells is approximately 1. Ganglia and nerve strands are enclosed by a basement membrane, without a well-defined perineural connective tissue. The neurons show a structure similar to other enteric plexus. Synaptic contacts were observed frequently in the neuropil, where nerve endings and varicosities show a diverse outfit in vesicles. The glial cells, which contain immunocytochemically detectable glial fibrillary protein, possess the same ultrastructural attributes in the intra- and extraganglionic localizations. In the nerves, axonic profiles and varicosities appear in close relation with glial cells or their processes. The distance between the nerves and their target cells, i.e. the enterocytes, is 0.5 microns or more with interposed basement membranes and fibroblasts.     

Some aspects of the structural organization of the arthropod ganglia

Summary This paper deals with the fine structure of the abdominal ganglia of several species of arthropods belonging to the classes Arachnida, Crustacea, Myriapoda and Insecta. The tissues were fixed in osmium tetroxide and embedded in n-butyl methacrylate or fixed in potasium permanganate and embedded in a mixture of X 133/2097 and Araldite.A comparative study was made in order to discriminate between those structural characteristics of the nervous system appearing only in determined taxonomic groups and those belonging to a fundamental plan common to the whole Phylum. This work covers the morphology of neurons, glial cells, neuropilic nerve fibers and neuronal connections.Most arthropod neurons are pear-shaped with only one prolongation and the nucleus is located in the center of the soma, enveloped by two membranes showing numerous pores. Cisternae of the ER have frequently been observed in continuity with this nuclear envelope. After osmic fixation the nuclear content appears to consist of small dense granules distributed at random in the nucleoplasm. In addition to these small perticles there are, in some species, large chromatin blocks. The use of Permanganate as fixative introduces important changes in the nuclear aspect; most of the nuclei look washed and the nuclear content acquires an homogeneous appearance.The cytoplasm of the neurons contains a complex system of internal membranes consisting of cisternae and tubuli of the ER system, lamellae of the Golgi complex and invaginations of the plasma membrane. In most species the elements of the ER system are distributed at random in the cytoplasm but in the neurons of Bothriurus bonariensis there are parallel aggregations of membranes similar to the Nissl bodies found in vertebrates.It was found in some of the species studied (Armadillidium vulgare and Lithobius Sp.) that the internal membrane system of the nerve cells is mainly represented by Golgi elements while the ER system seems to be poorly developed.Besides the membranous components, the neuronal cytoplasm contains mitochondria, multivesicular bodies and dense granules of neurosecretory material.Neuroglial cells are mainly characterized by their nuclear structure. After the action of osmium tetroxide, glial nuclei show irregular masses of chromatin inmersed in a nucleoplasm of low electron density. In permanganate fixed material these chromatin blocks appear as blank spaces.In the cytoplasm of these cells there are mitochondria, membranes pertaining to the ER system and elements of the Golgi complex but in some of the species studied gliofibrils and granules of pigment were found.Three main types of neuroglial cells have been recognized in an arthropod ganglia. These are: subcapsular glial cells, neuron satellites and nerve fiber satellites.The neuropile occupies the central region of the ganglion and consists of a great number of nerve fibers intermingled with glial processes. The neuropilic n. fibers consistently show profiles of ER membranes and tubuli pertaining to the ER system. In some of these fibers the ER reaches a high degree of development. In Armadillidium there is a special type of n. fiber containing a regular sequence of transversally oriented cisternae. Arthropod fibers sometimes contain thin parallel filaments as well as typical ER elements.Mitochondria, small vesicles and dense granules are commonly found within the neuroplasm of the neuropilic fibers. It is important to note that in arthropods, microvesicles are not restricted to the terminal region of the nerve fibers but that they may also occur all along the fibers.Arthropod neurons are enveloped by a glial insulating capsule and therefore interneuron contacts may only occur at neuropile level. These contacts are of three different morphological types: cross contacts, longitudinal contacts and end-knob contacts. At the level of longitudinal and cross contacts the neuroplasm shows no increase in the number of microvesicles or mitochondria. In the end-knob contacts, on the contrary, large numbers of microvesicles appear concentrated in the pre-synaptic fiber only, and occasionally in both fibers the pre-synaptic and the post-synaptic.It is maintained that funcional interneuron connections may result not only from contacts between fibers containing vesicles, but also between fibers in which vesicles are absent.     

Axo-glial synapses and GABA-accumulating glial cells in the embryonic neocortex of the rat

Summary On embryonic day 18, synapse-like contacts are found on certain non-neuronal cells appearing in clusters in lamina I (LI) of the parieto-occipital cortex of the rat. The structural criteria of these cells resemble those of immature glial cells: (1) The elongated nuclei containing dispersed chromatin are enclosed by a membrane showing narrow folds. (2) The cytoplasm contains many free ribosomes and a few dilated cisterns of the rough endoplasmic reticulum with granular or filamentous contents. (3) The plasma membrane forms concave adaptations toward neighboring neuronal processes. (4) At least one of the processes makes contact with the basal lamina of a vessel wall. The presynaptic elements contain a varying number of synaptic vesicles, and the pre- and postsynaptic membranes show densifications. Certain neurons and glial cells of the neocortex have the capability to accumulate GABA at day 16 of embryonic life. Only the more differentiated glial cells accumulate GABA. Many of these elements closely resemble the glial cells receiving synapse-like contacts, e.g., with respect to their cytological characteristics, clustering, and laminar position. According to recent experiments with adult ganglion cells, GABA released from glial cells might promote synaptogenesis by increasing the number of postsynaptic thickenings on the surrounding neurons. Thus, it cannot be excluded that transitory axo-glial synapses, by inducing GABA release, play a specific role in the earliest stages of synaptogenesis.     

A common origin of complex life cycles in parasitic flatworms: evidence from the complete mitochondrial genome of <Emphasis Type="Italic">Microcotyle sebastis</Emphasis> (Monogenea: Platyhelminthes)

Background  

The parasitic Platyhelminthes (Neodermata) contains three parasitic groups of flatworms, each having a unique morphology, and life style: Monogenea (primarily ectoparasitic), Trematoda (endoparasitic flukes), and Cestoda (endoparasitic tapeworms). The evolutionary origin of complex life cyles (multiple obligate hosts, as found in Trematoda and Cestoda) and of endo-/ecto-parasitism in these groups is still under debate and these questions can be resolved, only if the phylogenetic position of the Monogenea within the Neodermata clade is correctly estimated.     

Ultrathin structure of the main lateral nerve cords and accompanying elements of Triaenophorus nodulosus (Cestoda: Pseudophyllidea)

The ultrastructure of lateral nerve cords (LNC) of Triaenophorus nodulosus has been studied. 4 of the 6 types of neurones earlier reported for cerebral ganglia are present in LNC: multipolars, bipolars, unipolars and "light"; neurosecretory cells of the 7th type lie in transverse commissures. The growth and formation of LNC occur at the expense of undifferentiated cells found on the cord periphery among mature neurones. LNC are surrounded with specialized envelopes made of cell processes of excretory vessels and a fibrillar matrix formed at early stages of cestode development. In large axons, cisternae of the cross reticulum are detected, which can serve as ultrastructural marker of the synapse. Two types of muscle innervation are determined. The direct innervation of muscular fibres is realized by peripheral neurosecretory neurones, which form contacts of the paracrine type. The central or sarco-neural innervation of muscular fibers occurs in LNC via the entering muscular processes.     

Study on the fine structure of the central nervous system of Pholus labruscoe,L. (Lepidoptera)

Summary This is a preliminary electron microscope investigation in which the structure of insect neurons, neuropile, and interganglionic fibers are studied.Neurons of insect are pear-shaped and have an unique prolongation which ramifies into the neuropile. Their soma is surrounded by glial prolongations that exclude the possibility of nervous contacts. The neuronal cytoplasm is rich in granular material similar to the one described as R.N.A. by several authors; it is scattered at random or associated with endoplasmic reticulum cysternae. The latter does not adopt the regular array characterizing the vertebrate Nissl bodies.A large number of naked fibers is seen in the neuropile. The content of these fibers is different in fibers of different diameter. The thinner elements appear light and show a loose reticular matrix, few vesicles, and mitochondria. The thick fibers are characterized by a denser neuroplasm constituted by a reticular matrix and rows of tiny vesicles alternating with profils of tubuli. In some of these fibers the tubuli are seen in a central position.Three main types of contact relationships between fibers are described in the neuropile. These are; a) cross contacts; b) longitudinal contacts; and c) endknob contacts. The first type is in turn subdivided into subtypes, namely: minimum-area cross contacts and maximum-area cross contacts.A glial sheath enveloping each connective nerve fiber is described. Inside the cytoplasm of such cells there are bundles of dense, thin fibrils twisted along the nerve fibers.The criteria maintained by several authors in regard to the fine structure of the synaptic region are discussed and compared with facts reported in this paper.     

Vitellogenesis of basal trematode Aspidogaster limacoides(Aspidogastrea: Aspidogastridae)

The vitellogenesis of the trematode Aspidogaster limacoides (Aspidogastrea: Aspidogastridae), a parasite of cyprinid fishes, is described here using transmission electron microscopy. Four different stages of vitellocytes are differentiated: immature vitellocytes, early maturing vitellocytes, advanced maturing vitellocytes and mature vitellocytes. The process follows the same general pattern already described in other free-living neoophorans and parasitic flatworms (i.e. Trematoda, Monogenea and Cestoda): differentiation into mature vitelline cells involves the development of mitochondria, granular endoplasmic reticulum, Golgi complexes, lipid droplets and shell-globules. Mature vitellocytes of A. limacoides are composed of numerous shell-globule clusters, few lipid droplets and glycogen granules. They differ from those of another aspidogastrean Rugogaster hydrolagi in that they possess numerous globules tightly packed and by the presence of only one type of vitelline material. The interstitial tissue of vitelline follicles of A. limacoides contains a peripheral nucleus and long cytoplasmic projections extending between vitelline cells. Since aspidogastreans are considered as an archaic group of parasitic flatworms and thus have a strategic phylogenetic position, future works needs to pay special attention to the ultrastructural and chemical composition of mature vitellocytes within this basal group of trematodes.     

Hox genes from the Polystomatidae (Platyhelminthes, Monogenea)

Hox genes form a multigenic family that play a fundamental role during the early stages of development. They are organised in a single cluster and share a 60 amino acid conserved sequence that corresponds to the DNA binding domain, i.e. the homeodomain. Sequence conservation in this region has allowed investigators to explore Hox diversity in the metazoan lineages. Within parasitic flatworms only homeobox sequences of parasite species from the Cestoda and Digenea have been reported. In the present study we surveyed species of the Polyopisthocotylea (Monogenea) in order to clarify Hox identification and diversification processes in the neodermatan lineage. From cloning of degenerative PCR products of the central region of the homeobox, we report one ParaHox and 25 new Hox sequences from 10 species of the Polystomatidae and one species of the Diclidophoridae, which extend Hox gene diversity from 46 to 72 within Neodermata. Hox sequences from the Polyopisthocotylea were annotated and classified from sequence alignments and Bayesian inferences of 178 Hox, ParaHox and related gene families recovered from all available parasitic platyhelminths and other bilaterian taxa. Our results are discussed in the light of the recent Hox evolutionary schemes. They may provide new perspectives to study the transition from turbellarians to parasitic flatworms with complex life-cycles and outline the first steps for evolutionary developmental biological approaches within platyhelminth parasites.     

Ultrastructure of the area postrema of the monkey, Macaca fascicularis

The area postrema of the monkey, Macaca fascicularis, were a pair of oval organs at the caudal end of the floor of fourth ventricle. Their ependymal lining was covered by well-developed microvilli with occasional overlying supraependymal cells. Two types of lining cells were present: pyramidad- and flattened cells. The pyramidal cell showed a long extending basal process resting on the underlying blood vessels. In transmission electron microscopy, the organ showed numerous fenestrated sinusoids characterized by a distinct perivascular space containing mast cells, macrophages and collagen fibrils. The parenchyma of the organ was composed of neurons and glial elements. Only one type of neuron ranging from 9.5 to 15 microns could be distinguished. The neurons contained an indented nucleus surrounded by organelle rich cytoplasm. The soma of the neuron was enclosed by glial element resembling astrocyte. The glial processes terminated on the blood vessel where they were "tunnelled" by a variable number of nerve fibres some of which gained a direct access to the external basal lamina of the perivascular space. Synapses in the neuropil predominantly of the axodendritic variety were observed. Axon terminals containing round agranular vesicles were seen to make synaptic contacts with the neuronal soma. No structural changes were observed in the area postrema following bilateral cervical vagotomy. However, degenerating axon terminals were observed in the subpostremal zone 7, 14 and 21 days after vagotomy suggesting a direct afferent projection into this region.     

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.     

The embryonic development of the bodywall and nervous system of the cestode flatworm Hymenolepis diminuta

Cestodes (tapeworms) are a derived, parasitic clade of the phylum Platyhelminthes (flatworms). The cestode body wall represents an adaptation to its endoparasitic lifestyle. The epidermis forms a non-ciliated syncytium, and both muscular and nervous system are reduced. Morphological differences between cestodes and free-living flatworms become apparent already during early embryogenesis. Cestodes have a complex life cycle that begins with an infectious larva, called the oncosphere. In regard to cell number, cestode oncospheres are among the simplest multicellular organisms, containing in the order of 50-100 cells. As part of our continuing effort to analyze embryonic development in flatworms, we describe here the staining pattern obtained with acTub in embryos and larvae of the cestode Hymenolepis diminuta and, briefly, the monogenean Neoheterocotyle rhinobatidis. In addition, we labeled the embryonic musculature of Hymenolepis with phalloidin. In Hymenolepis embryos, two different cell types that we interpret as neurons and epidermal gland cells express acTub. There exist only two neurons that develop close to the midline at the anterior pole of the embryo. The axons of these two neurons project posteriorly into the center of the oncosphere, where they innervate the complex of muscles that is attached to the hooklets. In addition to neurons, acTub labels a small and invariant set of epidermal gland cells that develop at superficial positions, anteriorly adjacent to the neurons, in the dorsal midline, and around the posteriorly located hooklets. During late stages of embryogenesis they spread and form a complete covering of the embryo. We discuss these data in the broader context of platyhelminth embryology.     

Structure of the glial cells in the nervous system of parasitic and free-living flatworms

This study is devoted to ultrastructural and immunosytochemical investigation of the nervous system in parasitic and free-living platyhelminthes to learn if glial cells exist in the nervous system of flatworms. We described the ultrastructure of different types of glial cells and the peculiarities of myelinization of gigantic axons; immunoreactivity to the S100b protein is revealed. Comparative analysis of the glia structure of annelids and platods is given; structural, functional, and evolutionary aspects of myelinization of gigantic axons, which are revealed in cestodes, are discussed.     

Ultrastructure of the nerve cells and fibres in the urinary bladder wall of the cat.

The nerve elements in the urinary bladder of the cat were studied by electron microscopy. According to their ultrastructure, nerve cell somata can be classified into three types: the large cells with a cytoplasm rich in organelles, several processes and numerous synaptic contacts on their surface; the cytoplasm contained 80- 120-nm granulated vesicles. The second type is poor in cytoplasmic organelles and has very few processes and virtually no synaptic contacts on the soma. The third type contains numerous large 160- to 220-nm 'neurosecretory' vesicles in the cytoplasm. According to the morphology of the vesicle population, four types of nerve processes could be distinguished: Type a, with a dominant population of small (40-60 nm) agranular vesicles. These are thought to be sacral parasympathetic fibres. Type b, with small (40-60 nm) granular vesicles, which may be the noradrenergic sympathetic fibres. Type c, with 80- to 120-nm granulated vesicles, probably of local origin. Typed d, with large 160- to 220-nm 'neurosecretory' vesicles also of local origin. Different types of nerve fibres are converging on the local nerve cells. This suggests that the local circuits can play an important role in coordinating the function of the bladder. Therefore, ganglia may be considered as an elementary functional unit.