Tentacle Nerves Research Articles

Identification and characterization of an output neuron from the oscillatory molluscan olfactory network

Synchronous oscillations in olfactory systems have been thought to play critical roles in encoding olfactory information. However, their role in determining behavior is unknown. As a first step toward understanding the decoding process of coherent oscillation, we looked for a neuron in the terrestrial slug Limax marginatus that receives output signals from the procerebrum (PC), which is the olfactory center of Limax. We identified a neuron in the metacerebrum that extends its neurites into both the PC and the metacerebrum, and named it the metacerebro-procerebral neuron (MPN). The MPN exhibited a membrane potential oscillation that was synchronous with the local field potential oscillation in the PC. When we cut the PC off, the membrane potential oscillation of the MPN disappeared. Numerous varicosities were found on the neurites in the metacerebrum, while no varicosities were found on the neurites inside the PC. From these morphological and physiological results, we conclude that the MPN is an output neuron from the PC. The MPN also receives monosynaptic inputs from the superior and inferior tentacle nerves. The MPN thus may receive olfactory information from two pathways, one directly from the sensory organ and the other by way of the PC, possibly functioning to integrate them.

Embryonic development of the nervous system of the temnocephalid flatworm Craspedella pedum.

The nervous system of temnocephalid flatworms consists of the brain and three pairs of longitudinal connectives extending into the trunk and tail. The connectives are crosslinked by an invariant number of regularly spaced commissures. Branches of the connectives innervate the tentacles of the head and the sucker organ in the tail. A set of nerve rings encircling the pharynx and connected to the brain and connectives constitute the pharyngeal nervous system. The nervous system is formed during early embryogenesis when the embryo represents a multilayered mesenchymal mass of cells. Gastrulation and the formation of separate epithelial germ layers that characterize most other animal groups are absent. The brain arises as a bilaterally symmetric condensation of postmitotic cells in the deep layers of the anterior region of the embryonic mesenchyme. The pattern of axon outgrowth, visualized by labeling with anti-acetylated tubulin (acTub) antibody, shows marked differences from the pattern observed in other flatworm taxa in regard to the number of neurons that express the acTub epitope. Acetylated tubulin is only expressed in neurons that form long axon tracts. In other flatworm species, such as the typhloplanoid Mesostoma and the polyclad Imogine, which were investigated by us with the acTub antibody (Hartenstein and Ehlers [2000] Dev. Genes Evol. 210:399-415; Younossi-Hartenstein and Hartenstein [2000] Dev. Genes Evol. 210:383-398), only a small number of "pioneer neurons" become acTub positive during the embryonic period. By contrast, in temnocephalids, most, if not all, neurons express acTub and form long, large-diameter axons. Initially, the brain commissure, pharyngeal nerve ring, and the connectives are laid down. Commissural tracts and tentacle nerves branching off the connectives appear later. We speculate that the precocious differentiation of the nervous system may be related to the fact that temnocephalids move by muscle action, and possess a massive and complex muscular system when they hatch. In addition, they have muscular specializations such as the anterior tentacles and the posterior sucker that are used as soon as they hatch. By contrast, juveniles of Mesostoma and larvae of polyclads move predominantly by ciliary action that may not require a complex neural circuitry for coordination.

Electrophysiological responses to thermal stimuli in peripheral nerves of the African giant snail, Archachatina marginata S.

In Archachatina marginata S. the activity of 264 single units of the lip nerves and the tentacle nerve was recorded during thermal stimulation of the lip region. 17.8% of all fibres responded with an increase in neuronal activity to temperature changes in the range from 12 to 36°C. The amount of fibres responding to peripheral warm or cold stimuli varied between the investigated nerves. In the tentacle nerve (N. olfactorius) 30.5% of the neurons responded either to peripheral warming or cooling. In the three lip nerves N. labialis internus, N. labialis externus, and N. labialis medianus 20, 17, and 9.5%, respectively, proved to be thermoresponsive. Additional behavioural tests revealed that the thermopreferendum of Archachatina marginata S. is in the broad range between 13 and 32°C.

3F1530 嗅覚神経束への局所的電気刺激に対するヤマナメクジ前脳葉ネットワーク活動の光学測定

3F1530 嗅覚神経束への局所的電気刺激に対するヤマナメクジ前脳葉ネットワーク活動の光学測定

Physiological characterization of lip and tentacle nerves in Lymnaea stagnalis.

The lip and tentacle nerves of the pond snail, Lymnaea stagnalis, were characterized using electrophysiological techniques. When the activity of those nerves was induced in lip-tentacle preparations, aversive taste signals were transmitted through all the lip and tentacle nerves, but appetitive signals could be recorded only through the superior lip nerve. In the CNS immersed in high Mg2+ -high Ca2+ saline, electrical stimuli applied to any of the nerves failed to induce action potentials in one of the regulatory neurons (cerebral giant cell: CGC) involved in feeding responses, implying that the signals are polysynaptically transmitted to the CGC. Intracellular recordings revealed that the CGCs in semi-intact half-body preparations received both appetitive and aversive taste signals not only through the superior lip nerve but also through the median lip nerve. In addition, an osphradium was ruled out as a candidate for appetitive reception. The present results, together with our preceding data arrived at by the histochemical analyses, indicate that the appetitive taste transduction responsible for generating feeding responses is performed through the superior lip nerve with some contribution of the median lip nerve. The data showing that the CGC can receive various taste signals suggests that it may play a crucial role in feeding behavior as demonstrated in the study of conditioned taste-aversion.

Histological characterization of lip and tentacle nerves in Lymnaea stagnalis

The lip and tentacle nerves of the pond snail, Lymnaea stagnalis, were characterized using histological techniques. Anatomical drawings showed the detailed distributions of the superior lip, median lip, and tentacle nerves in the lip and tentacle; in particular it was found that the mouth is mainly innervated by the superior lip nerve. The tentacle nerve was clarified to form a zigzag structure along the extension direction in a shrinking tentacle. By backfilling of the superior lip nerve and/or the median lip nerve with fluorescent dyes, the neurons in the CNS made some clusters, whereas those stained from the tentacle nerve made other clusters. These stained neurons were not part of the central pattern generator or its regulatory neurons for feeding. The present results, therefore, suggest that the superior lip nerve may be employed as a principal factor in the chemosensory transduction from the mouth, and that no direct inputs occur through the lip and tentacle nerves to the central pattern generator or its regulatory neurons for feeding.

1PA126 ヤマナメクジ前脳葉神経ネットワークの神経束電気刺激に対する応答の光学測定

1PA126 ヤマナメクジ前脳葉神経ネットワークの神経束電気刺激に対する応答の光学測定

Histochemical study on the relation between NO-generative neurons and central circuitry for feeding in the pond snail, Lymnaea stagnalis

To examine whether nitric oxide (NO)-generative neurons are included in the central circuitry for generation of feeding pattern in the pond snail, Lymnaea stagnalis, two staining techniques for NADPH diaphorase and serotonin (5-HT) were applied for its central nervous system (CNS). The former technique is known to show localization of NO synthase; the latter is well employed as a marker for the feeding circuitry because 5-HT is a main transmitter in it. In the buccal ganglion, B2 motoneuron was found to be a putative NO-generative neuron. This motoneuron is not involved directly in the coordination of feeding pattern but is activated simultaneously with the feeding to control the oesophageal and gut tissues for the digestion. Taking account of the diffusion effects of NO, the NO released from B2 motoneuron, when the feeding is started, is thought to sufficiently modulate the feeding circuitry. In the cerebral ganglion, the superior lip nerve, the median lip nerve and the tentacle nerve included both putative NO-generative fibers and serotonergic fibers. These fibers are not identical, but the NO released in the nerves may activate the serotonergic fibers, resulting in the influence upon the initiation of the feeding. Therefore, our present findings clearly showed that NO is not involved in transmission within the central circuitry for the feeding, but suggested that NO can crucially affect the feeding behavior, such as initiation and modulation of the feeding pattern.

Changes in spontaneous oscillations of the procerebral lobe depending on an stimulated region in digits of the tentacular ganglion in Limax marginatus

In terrestrial gastropod mollusks (slugs and snails), olfaction is the dominant sensory modality guiding various kinds of behavior. Anatomical studies indicate that olfactory information is processed in the brain (the cerebral ganglion) in two lobes in particular: the procerebrum (PC) and the metacerebrum (MtC). This implies that olfactory functions emerge from simultaneous and cooperative processing in the PC and the MtC. However, no previous physiological study has investigated the activity in these two lobes simultaneously. In the present study, the activity evoked by electrical stimulation of the olfactory nerves, the superior and inferior tentacle nerves, was recorded optically from the whole cerebral ganglion of the terrestrial slug, Incilaria fruhstorferi. The results indicated that the evoked activity in the PC and the MtC showed two specific spatio-temporal patterns. First, when either set of nerves was stimulated, the activity of the medial neuropilar region of the MtC (the mMtC) always preceded the activity in the PC. Second, stimulation of the superior tentacle nerves activated the medial and lateral halves of the mMtC almost evenly, whereas stimulation of the inferior tentacle nerves activated the lateral half of the mMtC more strongly than the medial half. These results suggest that the activated region of the mMtC plays an important role in olfactory processing, especially with respect to the functional differences between the superior and inferior tentacles.

FMRF amide-like-immunoreactive primary sensory neurons in the olfactory system of the terrestrial mollusc, Limax marginatus.

The distribution of FMRF amide-like immunoreactivity was investigated in the olfactory organs in the tentacle tip of the terrestrial slug, Limax marginatus. Approximately 0.7% of the neurons in the lobules of the tentacle ganglia demonstrated FMRF amide-like immunoreactivity. Most of the FMRF amide-like-immunoreactive somata lay at superficial positions within the lobules, and dendritic processes extended to the outer surface of the sensory epithelium, whereas the axons traveled toward the cerebral ganglion through the ventral part of the tentacle nerve. From their morphological features, FMRF amide-like-immunoreactive cells were considered to be primary sensory neurons.

Comparative study on neural oscillation in the procerebrum of the terrestrial slugs Incilaria bilineata and

Coherent oscillatory activities in procerebral neurones have been described in Limax maximus; however, the electrical properties of the procerebrum of other terrestrial molluscs are less well understood. We have examined oscillatory activity in the procerebrum of Incilaria bilineata and Limax marginatus. The local field potential measured in the procerebrum of I. bilineata showed repetitive peaks which had the opposite polarity from those measured in L. marginatus. Optical measurement of membrane potential using a potential-sensitive dye, di-4-ANEPPS, showed that the oscillations in I. bilineata occurred mainly in the internal mass while those in L. marginatus were located in the cell mass. An analysis of the waveform revealed that the depolarizing phase of the oscillations consists of both a slow and a rapid component in both species. The rapid component was most pronounced in the internal mass of I. bilineata but was prominent in the cell mass of L. marginatus. The superior tentacle nerve, which projects to the terminal mass, also showed oscillations in synchrony with those of the procerebrum. These results suggest that oscillations in procerebral interneurones are commonly generated in a region adjacent to the terminal mass and that these oscillations may affect the membrane potential of the neurones constituting the superior tentacle nerve.

Antho-RFamide Immunoreactivity in Neuronal Synaptic and Nonsynaptic Vesicles of Sea Anemones.

Antho-RFamide is a neuropeptide isolated from the sea anemone Anthopleura elegantissima. Antho-RFamide immunoreactivity was localized in four different populations of neuronal vesicles in the tentacle nerve plexus of Anthopleura. Small, opaque, neuronal vesicles, averaging 49 nm in diameter, were gold-labeled at two-way synapses. Heterogranular vesicles, averaging 184 nm in diameter, were gold-labeled in a neuronal swelling adjacent to a muscle cell process. These vesicles were similar in size to a third class of gold-labeled dense-cored vesicles. A fourth class of immunogold-labeled vesicles observed in neuronal swellings had light cores and averaged 129 nm in diameter. Using 5-nm gold particles, we observed a heavy labeling of the granular cores of the dense-cored vesicles, suggesting that the immunoreactivity is specific to the vesicle core. The ultrastructural demonstration of Antho-RFamide immunoreactivity in interneuronal synaptic vesicles, together with the immunofluorescence and electrophysiological studies of other investigators, suggest that Antho-RFamide plays a role in neurotransmission in sea anemones.

Structure and organization of the nervous system in the actinotroch larva of Phoronis vancouverensis

The nervous system of the earliest functional stage of the actinotroch larva of Phoronis vancouverensis is described based on ultrastructural surveys and three-dimensional reconstructions, including serial reconstructions of selected parts of the system. The central element and main source of fibres in the system is the apical organ. Nerve cell bodies were found here and in the surrounding apical epithelium, but nowhere else in the body. Given the limitations of the methods used, the presence of nerve cell bodies elsewhere in the body cannot be ruled out, but based on this work and a recent study by A. Hay-Schmidt of whole larvae, it seems unlikely they occur in any numbers. The larval nervous system is thus highly centralized, an advanced and rather specialized feature in comparison with some other larval types, specifically those of primitive spiralia and echinoderms, in which nerve cell bodies are more widely distributed in the larval epithelium. The largest single nerve in the body is the primary hood nerve, which runs around the pre-oral hood slightly back from its margin. The nerve is a compact, well-defined tract of approximately 40 fibres, with an investment of glial-like accessory cells. A second set of smaller, accessory nerves run parallel to the primary nerve between it and the hood margin. The hood nerves all join at the base of the hood on either side of the mouth to form a pair of adoral nerve centres. A number of small nerves cross the hood from the apical organ to the hood nerves. Three of these are large enough to be considered major nerves: one is medial and connects to the centre of the hood margin, the other two are dorsolateral and connect to the adoral nerve centres. Fibre tracings, which show the distribution of vesicle-filled terminals and varicosities, suggest the hood nerves are mainly involved in neuromuscular control, specifically, in lifting the hood. This involves the stimulation, in sequence, of the radial and circular hood muscles by the primary and accessory hood nerves, respectively. Cells at the hood margin are organized somewhat in the fashion of a conventional ciliary band, but there is no obvious morphological evidence that any of the hood nerves are involved in neurociliary control. A diffuse plexus of small nerves connects the above apical structures to the nerves supplying the tentacles. There are two main tentacle nerves, the primary tentacle nerve, which runs along the upper, oral margin of the tentacular ciliary band, and a smaller accessory nerve, which arises as a branch from the primary nerve, and runs along the lower, aboral margin of the band. There is also a row of uniciliate sensory receptor cells at the oral margin of the band. Each cell has a basal process ending in a vesicle-filled terminal that abuts fibres in the upper tentacle nerve, and forms junctions with them. The cells themselves produce no other fibres. They appear to be mechanosensory, and are probably involved in initiating the hood lift response, which can be triggered by touching the top surface of the tentacles. Additional large, vesicle-filled terminals branch from the fibres in the primary tentacle nerve. Their positions suggest a neurociliary function. The accessory tentacle nerve is associated mainly with muscle cells. A series of small nerves, which probably arise as branches from the larger tentacle nerves, supply the region below the tentacles, later the site of the telotroch. The comparative and phylogenetic implications of the above are discussed. Phoronids are generally interpreted as being intermediate between deuterostomes and protostomes, with a curious mixture of characteristics of both groups. Phoronids are probably only distantly related to spiralian protostomes, but they are, strictly speaking, protostomes, and their larvae resemble the trochophore-type larvae of spiralia in many respects. Regarding ciliary band substructure and patterns of innervation, the actinotroch possesses too few features that are clearly primitive to support a detailed comparison with spiralian larvae, but the pre-oral hood band shows a sufficient number of prototroch-like features, to suggest the hood band and prototroch could be homologous. There is evidence for parallel evolution, in the two groups, of an increasingly centralized nervous system that provides improved effector control via nerve cells located in and around the apical organ. No evidence was obtained to support suggested homologies between the post-oral band of the actinotroch and circumoral or post-oral feeding bands in deuterostome larvae. The two appear, in fact, to be quite dissimilar in terms of their innervation. The results thus support conventional interpretations of the relationship between phoronids and other major groups.

Interganglionic dendrites constitute an output pathway from the procerebrum of the snail Achatina fulica.

The procerebrum is an olfactory processing region that occupies approximately one-third of the total brain area in pulmonate gastropod molluscs. It has many unusual features, including a development separate from the rest of the brain and the absence of axons belonging to its intrinsic neurons. We have investigated the input and output pathways of the procerebrum in the terrestrial snail Achatina fulica by using hexamminecobalt chloride as a selective label. Both the tentacle nerve and the cerebropedal connective nerve contribute to a fine neural plexus that is distributed throughout the neuropile region of the procerebrum. The fibers from the tentacle nerve are predominantly presynaptic, whereas those from the cerebropedal connective are predominantly postsynaptic. The postsynaptic fibers (dendrites) were traced to two groups of nerve cells (total number, 20-25) near the ventral surface of the ipsilateral pedal ganglion. No evidence was obtained for any other numerically significant output pathway from the procerebrum. Since locomotion is known to be controlled by the pedal ganglion, these results provide an anatomical substrate for the strong influence of olfaction on locomotor behavior in snails. The pathway is unusual in that the dendrites are interganglionic and can be as long as 5 mm.

The Vetigastropoda and the systematics of streptoneurous Gastropoda (Mollusca)

The status of the Vetigastropoda, created 1980 to unite zeugobranch and trochoid archaeo‐gastropods, is reconsidered and confirmed in the light of recent investigations. The most important synapomorphic characters of the Vetigastropoda are the ctenidial sense organs (so‐called bursicles), the epipodial sense organs, and the special structure of the oesophagus. The conditions of the archaeogastropod oesophagus are comparatively described.An examination of the relationships of the Vetigastropoda establishes the archaeogastropod nature of the Architaenioglossa. It also demonstrates the monophyletic origin of all higher gastropods, including the Caenogastropoda (s.str.) as well as the Pentaganglionata (= Euthy‐neura). The Campanilidae, Valvatidae, Rissoellidae, Omalogyridae, and the Allogastropoda (= Architectonicoidea and Pyramidelloidea) share characteristics with both of the above‐mentioned groups, but cannot be classified within any of them. These groups are regarded as subsequent offshoots between the caenogastropod and the pentaganglionate level of organization. The level of Archaeogastropoda is redefined by the hypoathroid/dystenoid nervous system and simple tentacle nerves; the remaining Streptoneura are classified as Apogastropoda with epiathroid nervous system, parapedal commissure, and bifurcated tentacle nerves.

Chemoreception and mechanoreception in the gastropod molluscPleurobranchaea californica

1. Sensory reception in the molluscPleurobranchaea californica was studied in whole animals and surgically reduced preparations by delivering chemical and mechanical stimuli while observing behavior or recording extracellularly the responses of the corresponding nerves. Sensory structures studied included the rhinophores, tentacles and oral veil. 2. Specimens reliably (50% or more) exhibited feeding responses to 10 of 18 amino acids tested (Table 1), including alanine and glycine. In 14 electrophysiological experiments on the rhinophore, medium to high centripetal responses to alanine and/or glycine were obtained in 7 preparations (Fig. 2), while little or no response was obtained in 7 preparations. Responses to different amino acids were sometimes mediated by the same centripetal unit (Fig. 2). 3. The rhinophore nerves showed vigorous excitatory responses to variations in the salt concentration (Figs. 3, 4), osmolarity (Figs. 5, 6), and pH (Figs. 7, 8) of sea water solutions directed onto the rhinophore sensory epithelium. The rhinophore and tentacle nerves showed strong excitatory responses to various salt solutions directed onto the corresponding sensory structure, including 1 osmolar NaCl, NaBr, NaI, Na2SO4 and KCl, but not LiCl (Table 2). Curves relating extracellular discharge to stimulus strength typically showed a minimum in the physiological range and increases to either side of this range (Figs. 4, 8). 4. All nerves studied showed excitatory responses to stimulation with mechanical stimuli (Figs. 9–11). Maps of receptive fields of different nerves (Fig. 10) delineated areas of functional innervation for each nerve and showed little overlap. The same centripetal unit(s) typically responded to mechanostimulation of a wide peripheral area (Fig. 11). 5. All nerves studied showed excitatory responses to application of liquefied food substances to the sensory structures (Figs. 12–15). Dose response curves for different food stimuli (Fig. 13) were similar except at higher stimulus strengths, where mean discharge rates were significantly different for different foods. These and other data furnish neurophysiological evidence for discrimination between different food stimuli, as suggested also by earlier behavioral studies (Davis et al. 1980). 6. For all stimuli, severing the afferent nerves leading from the peripheral sensory epithelium abolished electrophysiological responses. Therefore the responses observed were mediated by the sensory epithelium rather than by direct stimulation of peripheral ganglia or nerves. 7. It is concluded that the rhinophores, tentacles and oral veil participate not only in food detection but also have the sensory capacity to detect changes in several other environmental parameters. The data are consistent with the hypothesis that incoming afferent information is processed by peripheral ganglia before it is relayed centrally.

Biphasic action of glutamic acid and synpatic inhibition in an identified serotonin-containing neurone.

IN each cerebral ganglion of the snail Helix pomatia there is a giant serotonin-containing neurone1,2. The serotonin within these giant serotonin cells (GSCs) probably serves a transmitter role3,4. Stimulation of most of the different nerve trunks entering the cerebral ganglia results in the appearance of cholinergic excitatory postsynaptic potentials (EPSPs) in these symmetrically placed neurones5. It has been found that electrical stimulation of the tentacle nerves can result in a wave of hyperpolarization and inhibition of the GSC as well as EPSPs6. Glutamate mimics the synaptic inhibition. We have reported here in more detail the effects of stimulating the different tentacle nerves, to observe the inhibitory process unaffected toy synaptic excitation, and the action of glutamic acid and related compounds on the membrane potential of the GSC. Our results show that stimulation of the cutaneous cephalicus or the external peri-tentacular nerves causes a biphasic response in each GSC and that glutamic acid brings about a very similar response. The initial phase of inhibition in both cases is mainly dependent on an increase in membrane permeability to chloride ions and that of the second phase mainly to an increase in membrane permeability to potassium ions. DL α-aminoadipic acid produces an effect which is superficially similar to the first phase of the glutamate response.

Glutamic acid mimicking of synaptic inhibition on the giant serotonin neurone of the snail.

Stimulation of the snail's tentacle nerves results in hyperpolarization and inhibition of the 'giant serotonin-containing neurone'located in the brain. Glutamic acid mimics this effect. Available data indicate that the reversal potential for the glutamic acid effect is very similar to that of the synaptic action being about 5 to 8 mV more negative than the resting potential in each case.