Distribution of serotonin-, Gamma-Aminobutyric Acid- and substance P-like immunoreactivity in the central and peripheral nervous system of Mytilus galloprovincialis

The distribution of serotonin-, GABA- and substance P-like immunoreactivity has been studied in the cerebral and visceral ganglia and in some peripheral tissues of Mytilus galloprovincialis (Moleusca, Bivalvia). Cerebral ganglia contain a developed serotonin-immunoreactive neuronal subpopulation and numerous GABA-immunoreactive neurons, whereas neurons positive for substance P are sparse. In peripheral tissues innervated by the cerebral ganglia (labial palps and oesophagus) only serotonin-immunoreactive nerve fibers were found. In the visceral ganglia, serotonin- and GABA-immunoreactive neurons are far less numerous than in the cerebral ganglia, whereas several neurons positive for substance P are scattered in all cortical zones. Serotonin-immunoreactive plexuses innervate the posterior adductor muscle and the gill filaments which contain also a developed nerve network positive for substance P. The distribution pattern of the immunoreactive elements in the ganglia and in peripheral territories indicates that GABA should exert only a central action, whereas serotonin and a substance P-like peptide are involved both in central and peripheral neurotransmission.     

Ultrastructural differences between the anterior and posterior adductors of the strawberry cockle, Fragum unedo

Adductors of Fragum unedo were observed ultrastructurally and their muscle cells were classified according to the statistically analyzed diameter of their thick myofilaments. Two types of smooth muscle cells were observed in the opaque portion of the anterior adductor: A-type cells containing thick myofilaments of about 46 nm in diameter and B-type cells having 62 nm thick myofilaments. The posterior adductor was also composed of two kinds of cells: the B-type cell, which had thick myofilaments of about 67 nm in diameter, and the C-type, containing thick myofilaments of 90 nm. Two types of oblique-striated cells were commonly recognized in the translucent portions of anterior and posterior adductors. Our observations thus indicate that the posterior adductor generally consists of cells which have thicker myofilaments than the ones of the anterior adductor.     

Out-of-the tropics or trans-tropical dispersal? The origins of the disjunct distribution of the gooseneck barnacle Pollicipes elegans

Myogenesis is currently investigated in a number of invertebrate taxa using combined techniques, including fluorescence labeling, confocal microscopy, and 3D imaging, in order to understand anatomical and functional issues and to contribute to evolutionary questions. Although developmental studies on the gross morphology of bivalves have been extensively pursued, organogenesis including muscle development has been scarcely investigated so far. The present study describes in detail myogenesis in the scallop Nodipecten nodosus (Linnaeus, 1758) during larval and postmetamorphic stages by means of light, electron, and confocal microscopy. The veliger muscle system consists of an anterior adductor muscle, as well as four branched pairs of striated velum retractors and two pairs of striated ventral larval retractors. The pediveliger stage exhibits a considerably elaborated musculature comprising the velum retractors, the future adult foot retractor, mantle (pallial) muscles, and the anterior and posterior adductors, both composed of smooth and striated portions. During metamorphosis, all larval retractors together with the anterior adductor degenerate, resulting in the adult monomyarian condition, whereby the posterior adductor retains both myofiber types. Three muscle groups, i.e., the posterior adductor, foot retractor, and pallial muscles, have their origin prior to metamorphosis and are subsequently remodeled. Our data suggest a dimyarian condition (i.e., the presence of an anterior and a posterior adductor in the adult) as the basal condition for pectinids. Comparative analysis of myogenesis across Bivalvia strongly argues for ontogenetic and evolutionary independence of larval retractors from the adult musculature, as well as a complex set of larval retractor muscles in the last common bivalve ancestor.     

Organization of the nervous system in the pygmy cuttlefish,Idiosepius paradoxus ortmann (Idiosepiidae,Cephalopoda)

The idiosepiid cuttlefish is a suitable organism for behavioral, genetic, and developmental studies. As morphological bases for these studies, organization of the nervous system was examined in Idiosepius paradoxus Ortmann, 1881, using Cajal's silver technique and immunohistochemical staining with anti-acetylated alpha-tubulin antibody. The nervous architecture is generally identical to that described in Sepia and Loligo, but some features characterize the idiosepiid nervous system. The olfactory system is highly developed in the optic tract region. The dorsolateral lobes show large neuropils, connected with each other by a novel well-fasciculated commissure. Each olfactory lobe is subdivided into two lobules. The neuropils of the anterior and the posterior chromatophore lobes are very poorly developed. Neuronal gigantism is not extensive in the brain; enlarged neuronal cells are visible only in the perikaryal layer of the posterior subesophageal mass. The giant nerve fiber system is of the Sepia type; the axons are not markedly thick and the first-order giant fibers do not fuse with each other at the chiasma. Three-dimensional images by whole-mount immunostaining clarified the innervation pattern in the peripheral nervous system in detail. Two commissural fibers link the left and right posterior funnel nerves ventrally and dorsally. The stellate commissure, which is absent in Sepia and Sepiola, connects the stellate ganglia with each other. A branch of the visceral nerve innervating the median pallial adductor muscle is characteristically thick. Tubulinergic reactivity of the cilia and axons reveals the presence of many ciliated cells giving off an axon toward brain nerves in the surface of the funnel, head integument, arm tips, and epidermal lines. Some of these features seem to reflect the inactive nekto-benthic life of the idiosepiid cuttlefish in the eelgrass bed.     

The cerebral ganglia of Milnesium tardigradum Doyère (Apochela, Tardigrada): Three dimensional reconstruction and notes on their ultrastructure

Differential interference contrast micrographs from stretched animals, serially sectioned semi-thin and ultrathin sections revealed that the cerebral ganglia (supraoesophageal mass) of the eulardigrade Milnesium tardigradum lie above the buccal tube and adjacent tissue like a saddle. It has an anterior indentation which is penetrated by two muscles that arise from the cuticle of the forehead. The cerebral ganglia consist of lateral outer lobes bearing an eye on each side, and two inner lobes which extend caudally. Between the inner lobes a cone-like projection tapers into a nerve bundle. Each outer lobe is joined with the first ventral ganglion. From the outer lobe near the eye the ganglion for a posterolateral sensory field extends to the epidermis. Anterior to the supraoesophageal mass are three dorsal ganglia for the upper three peribuccal papillae. Two additional ganglia attached to the cerebral mass supply the lateral cephalic papillae. The cerebral ganglia are covered by a thin neural lamella. The pericarya which surround the neuropil have large nuclei. Near the axons in the centre of the supraoesophageal mass the cytoplasm is crowded with vesicles of different size and appearance. Some of them resemble synaptic vesicles while others resemble dense core bodies. Structurally different types of synapses and axons can be distinguished within the neuropil.     

Morphological analysis of tendinous structure in the American alligator jaw muscles

In the American alligator, the jaw muscles show seven bundles of tendinous structure: cranial adductor tendon, mandibular adductor tendon, lamina anterior inferior, trap-shaped lamina lateralis, lamina intramandibularis, lamina posterior, and depressor mandibular tendon (originating from the musculus depressor mandibulae, m. pseudotemporalis, m. adductor mandibulae posterior, m. adductor mandibulae externus, m. intramandibularis, m. pterygoideus anterior, and m. pterygoideus posterior). These tendinous structures are composed of many collagen fibrils and elastic fibers; however, the distributions and sizes of the fibers in these tendinous components differ in comparison with those of other masticatory muscles. The differences of these properties reflect the kinetic forces or the stretch applied to each tendon by the muscle during jaw movements in spite of the simple tendon-muscle junctions. © 1993 Wiley-Liss, Inc.     

青蛤形态学初步观察

青蛤是帘蛤科中分布较广的一种埋栖双壳贝类。壳近圆形,两侧近等,无小月面,有外韧带,主齿三枚,前闭壳肌痕呈半月形,后闭壳肌痕呈椭圆形。肌肉系统由闭壳肌、足伸缩肌、外套膜肌、水管肌、足肌等组成;消化系统分为消化道和消化腺两部分。消化盲囊呈绿色,为主要的消化腺体;鳃是青蛤主要呼吸器官,同时,外套膜也起到辅助呼吸的作用;循环系统为开管式,具后动脉球,血液中含有血清蛋白而使之成为无色液体;排泄系统由肾脏和围心腔腺组成;青蛤是雌雄异体,生殖期间,精巢为乳白至乳黄色,卵巢为粉红色;系统比较简单,具有三对神经节。     

Analysis of neurotransmitter distribution in brain development of benthic and pelagic octopod cephalopods

The database on neurotransmitter distribution during central nervous system development of cephalopod mollusks is still scarce. We describe the ontogeny of serotonergic (5‐HT‐ir) and FMRFamide‐like immunoreactive (Fa‐lir) neurons in the central nervous system of the benthic Octopus vulgaris and Fa‐lir distribution in the pelagic Argonauta hians. Comparing our data to previous studies, we aim at revealing shared immunochemical domains among coleoid cephalopods, i.e., all cephalopods except nautiluses. During development of O. vulgaris, 5‐HT‐ir and Fa‐lir elements occur relatively late, namely during stage XII, when the brain neuropils are already highly differentiated. In stage XII‐XX individuals, Fa‐lir cell somata are located in the middle and posterior subesophageal mass and in the optic, posterior basal, and superior buccal lobes. 5‐HT is predominately expressed in cell somata of the superior buccal, anterior basal, and optic lobes, as well as in the subesophageal mass. The overall population of Fa‐lir neurons is larger than the one expressing 5‐HT. Fa‐lir elements are distributed throughout homologous brain areas of A. hians and O. vulgaris. We identified neuronal subsets with similar cell number and immunochemical phenotype in coleoids. These are located in corresponding brain regions of developmental stages and adults of O. vulgaris, A. hians, and the decapod squid Idiosepius notoides. O. vulgaris and I. notoides exhibit numerous 5‐HT‐ir cell somata in the superior buccal lobes but none or very few in the inferior buccal lobes. The latter have previously been homologized to the gastropod buccal ganglia, which also lack 5‐HT‐ir cell somata in euthyneuran gastropods. Among coleoids, 5‐HT‐ir neuronal subsets, which are located ventrally to the lateral anterior basal lobes and in the anterior middle subesophageal mass, are candidates for homologous subsets. Contrary to I. notoides, octopods exhibit Fa‐lir cell somata ventrally to the brachial lobes and 5‐HT‐ir cell somata close to the stellate ganglia. J. Morphol., 2012. © 2012 Wiley Periodicals, Inc.     

Evolution of the molluscan body plan: the case of the anterior adductor muscle of bivalves

The separated shell plates with the rearranged musculature (adductor muscle) is a novelty for bivalves. Despite its importance in the bivalve bodyplan, the development of the anterior adductor muscle remains unresolved. In this study, we investigate the myogenesis of the bivalve species Septifer virgatus to reveal the developmental origin of the larval muscles in bivalves, focusing on the anterior adductor muscle. We observed that larval retractor muscles are differentiated from the ectomesoderm in bivalves, and that the anterior adductor muscles are derived from primordial larval retractor muscles via segregation of the myoblast during the veliger larval stage. Through the comparative study of myogenesis in bivalves and its related taxa, gastropods, we found that both species possess myoblasts that emerge bilaterally and later meet dorsally. We hypothesize that these myoblasts, which are a major component of the main larval retractor in limpets, are homologous to the anterior adductor muscle in bivalves. These observations imply that the anterior adductor muscle of bivalves evolved as a novel muscle by modifying the attachment sites of an existing muscle.     

Alcian blue-alcian yellow mapping of neurosecretory cells in the central nervous system of the salt marsh pulmonate snail Melampus bidentatus

1. The neurosecretory system of the primitive ellobiid Melampus bidentatus (Pulmonata: Basommatophora) was investigated using Alcian blue-Alcian yellow histochemistry. 2. Putative neurosecretory cells within the central ganglia were distinguished by the criteria of cell size, position, and staining reaction. 3. The cerebral ganglia, with attached lateral lobes, contained the greatest diversity of neurosecretory cell types (at least seven), including single cells and cell clusters ranging from two to 40 cells. 4. Four neurosecretory cell types were identified in the parietal and visceral ganglia, two in the pedal ganglia, and one each in the buccal and pleural ganglia. 5. Neurosecretory system homology among pulmonate gastropods is suggested by the close similarity of the Melampus AB/AY cell map to those reported in the literature for two limnic basommatophorans and for four terrestrial stylommatophorans.     

Serotonin-like immunoreactivity in the central nervous system and gonad of the scallop,Patinopecten yessoensis

Summary The localization of neurons containing serotonin in the central nervous system and the gonad of the scallop, Patinopecten yessoensis, was examined immunohistochemically. In the central nervous system a large number of immunoreactive perikarya were observed in the following regions: a part of the anterior lobe of the cerebral ganglion; the posterior lobe of the cerebral ganglion; the pedal ganglion; and the accessory ganglion. No immunoreactive perikarya were found in the visceral ganglion. Numerous immunoreactive fibers were revealed in the neuropil of all central ganglia. In the gonadal region immunoreactive fibers were distributed around the gonoduct and along the germinal epithelium.This work was supported by a grant from the Ministry of Education, Science and Culture, Japan     

Distribution of serotonin-like immunoreactive neurons in the slug<Emphasis Type="Italic"> Limax valentianus</Emphasis>

Immunohistochemical techniques were used to study the distribution of serotonin-containing neurons in the nervous system of the slug Limax valentianus. Approximately 350 serotonin-like immunoreactive cell bodies were found in the central nervous system. These were located in the cerebral, pedal, visceral and right parietal ganglia. Most serotonin-like immunoreactive neurons had small cell bodies, which were aggregated into discrete clusters. A pair of previously identified metacerebral giant cells were found on the anterior side of the cerebral ganglion, and two additional pairs of uniquely identifiable, serotonin-like immunoreactive cells were found on the posterior side of the cerebral ganglion. The whole-mount maps of these stained neurons will be useful in further physiological and biochemical studies of olfactory learning at the cellular level in Limax valentianus.This study was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Science, Sports and Technology, Japan (nos. 12307053 and 13771353)     

THE ADDUCTOR AND RETRACTOR MUSCLES OF THE VELIGER OF PECTEN MAXIMUS (L.) (BIVALVIA)

In Pecten maximus (L.), retractor and adductor muscles becomefunctional in the early veliger larva. The twelve-day-old veligerhas four pairs of velar retractors, three pairs of retractorsattached to the posterior body wall and an anterior adductor.The pediveliger has in addition, pedal retractor muscles anda posterior adductor. The retractors consist of striated muscle:the adductors have both smooth and striated portions. The retractorsattach near the hinge, branch to a greater or lesser extent,then attach to specific areas of the velum, posterior body walland foot. Some features of the branching and of the dispositionof points of attachment form a pattern which exhibits mirrorsymmetry about the plane between the two shell valves. Thispattern is characteristic of the species. It is deduced thatretraction and protraction of the velum result from co-ordinatedsequences of muscle contractions. ^*Present address: Forest Products Research Centre, P.O. Box1358, Boroko, Papua New Guinea. (Received 15 June 1984;     

Investigation of early mussel (Perna canaliculus) development using histology,SEM imaging,immunochemistry and confocal microscopy

A comprehensive study, incorporating histology, light microscopy, scanning electron microscopy, immunochemistry and confocal microscopy, was performed to investigate embryogenesis and larval development of the New Zealand Greenshell? mussel, Perna canaliculus. Detailed observations with this multi-technique approach revealed a gastrula stage at 18 hours post-fertilization, with the appearance of a blastopore, apical sense organ and enclosing vegetal pole. Early D-stage larvae showed limited alimentary organogenesis and clear initiation of a developing nervous system. Shell morphology of D-larvae was characterized by a flat, hinged, pitted–punctate prodissoconch I shell, followed closely by commarginal growth lines within the prodissoconch II shell. Early umbo larvae had a protruding functioning velum, and well-developed posterior adductor and velar retractor muscles. Significant progression in neuronal development occurred just before the umbo stage with noticeable paired cerebral, pedal and visceral ganglia. Shell morphology was characterized by further prodissoconch II secretion with a more rounded umbonate appearance. During the transition through the pediveliger stage, rapid development of the gill rudiment, eye spot and functioning foot was observed with ongoing neuronal development. The first appearance of the dissoconch shell layer took place during this transition, at which point the nervous system was highly distinct with innervations extending throughout muscle regions and between ganglia. This study provides the first comprehensive documentation of the developmental stages of P. canaliculus larvae from fertilization to settlement. The study highlights the advantages of using a combination of techniques to understand larval development and provides crucial information to identify larval performance during larval rearing.     

The posterior intervertebral spaces of the craniovertebral joint]

Closing of the posterior intervertebral spaces of the craniovertebral joint is not performed by the classical posterior atlanto-occipital and atlantoaxial membranes. In the atlanto-occipital space, the connective laminae come from the occipital periosteum and from the anterior fascia of the rectus capitis posterior minor muscle, and pass round the anterior side of the posterior arch of the atlas to reach the spinal dura mater. In the atlantoaxial space, the anterior fasciae of the rectus capitis posterior major muscle and of the inferior oblique muscle, as well as the periosteum of the posterior arch of the atlas, extend to reach the spinal dura mater. Thus, the epidural space is sealed posteriorly by the connective laminae of the atlantoaxial space, and lets above a superior recessus containing the ganglia of the spinal nerves C1 and C2 and in which the vertebral artery transits.     

Central nervous system of Chaetoderma japonicum (Caudofoveata, Aplacophora): implications for diversified ganglionic plans in early molluscan evolution

The organization of the central nervous system of an "aplacophoran" mollusc, Chaetoderma japonicum, is described as a means to understand a primitive condition in highly diversified molluscan animals. This histological and immunocytochemical study revealed that C. japonicum still retains a conservative molluscan tetra-neural plan similar to those of neomenioids, polyplacophorans, and tryblidiids. However, the ventral and lateral nerve cords of C. japonicum are obviously ganglionated to various degrees, and the cerebral cord-like ganglia display a lobular structure. The putative chemosensory networks are developed, being composed of sensory cells of the oral shield, eight precerebral ganglia, and eight neuropil compartments that form distinct masses of neurites. In the cerebral cord-like ganglia, three anterior, posterior, and dorsal lobes are distinguished with well-fasciculated tracts in their neuropils. Most neuronal somata are uniform in size, and no small globuli-like cell clusters are found; however, localized serotonin-like immunoreactivity and acetylated tubulin-containing tracts suggest the presence of functional subdivisions. These complicated morphological features may be adaptive structures related to the specialized foraminiferan food in muddy bottoms. Based on a comparative scheme in basal molluscan groups, we characterize an independent evolutionary process for the unique characters of the central nervous systems of chaetoderms.     

The organization of corticopontine fibres in man

Patients with lesions located in the frontal and temporal lobes, in the parieto-temporo-occipital border zone, and in the anterior limb of the internal capsule, did not present ataxia or other cerebellar signs. On the other hand, patients with the ataxic hemiparesis (AH) syndrome had lesions located in the posterior limb of the internal capsule, in the corona radiata and in the central region of the cerebral cortex. These findings in man do not confirm the existence of large frontal (Arnold's bundle) and temporal (Türck's bundle) projections to the pontine nuclei and indicate that the main bulk of corticopontine fibres originates from the central region of the cerebral hemisphere and courses in the posterior limb of the internal capsule. In man, the anatomical organization of corticopontine fibres is therefore similar to that recently demonstrated in animals.     

On the fine structure of the creeping larva of Loxosomella murmanica: additional evidence for a clade of Kamptozoa (Entoprocta) and Mollusca

The creeping larva of the kamptozoan (entoproct) Loxosomella murmanica was investigated using transmission electron microscopy. The late larva exhibits a prominent apical organ connected to the ‘cerebral’ commissure of large cerebral ganglia, which supply the paired frontal organ. From the cerebral ganglia two paired nerve cords project backwards, closely resembling the tetraneuralian pattern of basal molluscs. In addition, a neural ring supplying the prototroch is present. The epidermis is composed of myoepithelial cells. Dorsally its cuticle is covered by granules of unknown composition. The prototroch consists of two ciliary rings; a downstream collecting system is not present. Although there is a one‐way gut with a lumen throughout, the larva obviously does not feed. A single pair of protonephridia is present. The foot sole shares distinct similarities with basic molluscs, particularly with those of the aplacophoran Solenogastres: The anterior part shows a huge, subepidermal pedal gland and several bundles of cirri consisting of compound cilia. The posterior part is ciliated with intraepithelial mucous cells interspersed. The dorsoventral muscle fibres show the mollusc‐like ventral intercrossing. The present results and previous findings, in particular the chitinous, non‐moulted cuticle, the sinus circulatory system, and a number of neural features shared by Kamptozoa and Mollusca, provide substantial evidence for a direct sister‐group relationship between these phyla. In addition, the basal position of the Solenogastres (Neomeniomorpha) within the Mollusca is corroborated.