Cerebropleural Ganglia Research Articles

Monosynaptic connections between identified A and B photoreceptors and interneurons in Hermissenda: evidence for labeled-lines.

The cellular and synaptic organization of the eye of the nudibranch mollusk Hermissenda is well-documented. The five photoreceptors within each eye are mutally inhibitory and can be classified into two types: A and B based on electrophysiological and anatomical criteria. Two of the three type B and two type A photoreceptors can be further identified according to their medial or lateral positions within each eye. In addition to reciprocal synaptic connections between photoreceptors, photoreceptors also project to second-order neurons in the cerebropleural ganglion. The second-order neurons receive convergent synaptic input from two additional sensory pathways; however, it has not been previously established if lateral A, lateral B, or medial B photoreceptors converge onto the same second-order neurons. To determine the specific synaptic organization of these components of the visual system, we have examined monosynaptic connections between identified lateral and medial type A and B photoreceptors and second-order cerebropleural (CP) interneurons. We found that monosynaptic connections between identified lateral A and lateral and medial B photoreceptors and CP interneurons follow a labeled-line principle. Illumination of the eyes or extrinsic depolarizing current applied to identified photoreceptors evoked excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs, respectively) in different CP interneurons. The PSPs in CP interneurons followed one-for-one spikes in the photoreceptors and could be elicited in artificial seawater solutions containing high divalent cations. Identified photoreceptors projected to more than one CP interneuron and expressed both excitatory and inhibitory connections with the different CP interneurons. In examples where a monosynaptic connection between a lateral B photoreceptor and a CP interneuron was identified, lateral A, medial A, or medial B photoreceptors did not project to the same CP interneuron. Moreover, when connections between medial B and CP interneurons were identified, lateral A, medial A, and lateral B connections were not found to project to the same CP interneuron. Similar results were obtained for a lateral A and CP interneuron connection. These results indicate that divergent labeled-lines exist between specific photoreceptors and second-order CP interneurons and potential convergence of synaptic input from primary and secondary elements of the visual system must occur at sites that are postsynaptic to the CP interneurons.

Central pattern generator for escape swimming in the notaspid sea slug Pleurobranchaea californica.

Escape swimming in the notaspid opisthobranch Pleurobranchaea is an episode of alternating dorsal and ventral body flexions that overrides all other behaviors. We have explored the structure of the central pattern generator (CPG) in the cerebropleural ganglion as part of a study of neural network interactions underlying decision making in normal behavior. The CPG comprises at least eight bilaterally paired interneurons, each of which contributes and is phase-locked to the swim rhythm. Dorsal flexion is mediated by hemiganglion ensembles of four serotonin-immunoreactive neurons, the As1, As2, As3, and As4, and an electrically coupled pair, the A1 and A10 cells. When stimulated, A10 commands fictive swimming in the isolated CNS and actual swimming behavior in whole animals. As1-4 provide prolonged, neuromodulatory excitation enhancing dorsal flexion bursts and swim cycle number. Ventral flexion is mediated by the A3 cell and a ventral swim interneuron, IVS, the soma of which is yet unlocated. Initiation of a swim episode begins with persistent firing in A10, followed by recruitment of As1-4 and A1 into dorsal flexion. Recurrent excitation within the As1-4 ensemble and with A1/A10 may reinforce coactivity. Synchrony among swim interneuron partners and bilateral coordination is promoted by electrical coupling among the A1/A10 and As4 pairs, and among unilateral As2-4, and reciprocal chemical excitation between contralateral As1-4 groups. The switch from dorsal to ventral flexion coincides with delayed recruitment of A3, which is coupled electrically to A1, and with recurrent inhibition from A3/IVS to A1/A10. The alternating phase relation may be reinforced by reciprocal inhibition between As1-4 and IVS. Pleurobranchaea's swim resembles that of the nudibranch Tritonia; we find that the CPGs are similar in many details, suggesting that the behavior and network are primitive characters derived from a common pleurobranchid ancestor.

Serotonin immunoreactivity in the central nervous system of the marine molluscs Pleurobranchaea californica and Tritonia diomedea

The central nervous systems of the marine molluscs Pleurobranchaea californica (Opisthobranchia: Notaspidea) and Tritonia diomedea (Opisthobranchia: Nudibranchia) were examined for serotonin-immunoreactive (5-HT-IR) neurons and processes. Bilaterally paired clusters of 5-HT-IR neuron somata were distributed similarly in ganglia of the two species. In the cerebropleural ganglion complex, these were the metacerebral giant neurons (both species), a dorsal anterior cluster (Pleurobranchaea only), a dorsal medial cluster including identified neurons of the escape swimming network (both species), and a dorsal lateral cluster in the cerebropleural ganglion (Pleurobranchaea only). A ventral anterior cluster (both species) adjoined the metacerebral giant somata at the anterior ganglion edge. Pedal ganglia had the greatest number of 5-HT-IR somata, the majority located near the roots of the pedal commissure in both species. Most 5-HT-IR neurons were on the dorsal surface of the pedal ganglia in Pleurobranchaea and were ventral in Tritonia. Neither the buccal ganglion of both species nor the visceral ganglion of Pleurobranchaea had 5-HT-IR somata. Afew asymmetrical 5-HT-IR somata were found in cerebropleural and pedal ganglia in both species, always on the left side. The clustering of 5-HT-IR neurons, their diverse axon pathways, and the known physiologic properties of their identified members are consistent with a loosely organized arousal system of serotonergic neurons whose components can be generally or differentially active in expression of diverse behaviors.

NADPH-diaphorase localization in the CNS and peripheral tissues of the predatory sea-slugPleurobranchaea californica

The distribution of putative nitric oxide synthase (NOS)-containing cells in the opisthobranch mollusc Pleurobranchaea californica was studied histochemically via NADPH-diaphorase (NADPH-d) reduction of Nitro Blue Tetrazolium (NTB). Whole mounts and cryostat sections were prepared from the central nervous system and peripheral organs, including the buccal muscles, esophagus, salivary glands, foot, mantle, and gills. NADPH-d-positive neurons were localized predominantly to the buccal and pedal ganglia as well as to distinct areas of the cerebropleural and visceral ganglia. A variety of identified neurons were positive for NADPH-diaphorase in various central ganglia, including the metacerebral cells of the cerebropleural ganglion, putative locomotor neurons of the pedal ganglia, and buccal motoneurons. Specific staining was observed only in somata of central neurons, whereas neuropil areas remained unstained. However, NADPH-d-reactive axons were dense in buccal ganglion nerves, whereas peripheral nerves and connectives of other ganglia had few or no NADPH-d positive terminals. In the periphery, NADPH-d activity was detected only in a few neurons of the rhinophore and tentacle ganglia. NADPH-d staining was marked in the salivary glands and gills, but there was no or very little staining in the esophagus, buccal mass, and foot. Histochemical stain production required the presence of both beta-NADPH and NBT; alpha-NADPH could not substitute for beta-NADPH. The inhibitor of NOS, 2,6-dichlorophenol-indophenol, at 10(-3) M, totally abolished NADPH-d-positive staining. The apparent high activity of central NADPH-d contrasts with much lower activity in the ganglia of the related gastropod Tritonia. These data suggest a role for nitric oxide as a signal molecule in the central nervous system of Pleurobranchaea.

Neuronal elements that mediate escape swimming and suppress feeding behavior in the predatory sea slug Pleurobranchaea.

1. The white, bilaterally paired A1 interneurons of the cerebropleural ganglion of Pleurobranchaea californica fire rhythmic bursts of action potentials during escape swimming behavior. We studied the role of the A1s in swimming behavior and pattern generation in whole animal and isolated CNS preparations. 2. The escape swim is a cyclic sequence of dorsal and ventral flexions of the body. During the swim, A1 bursts precede and accompany the dorsal flexion phase of the cycle. Hyperpolarization of A1 to prevent spike activity interrupts swimming behavior in the whole animal and fictive swimming in the isolated CNS. Stimulated A1 activity was not observed to cause swimming in whole animals, and was only occasionally sufficient to trigger fictive swimming activity in the isolated CNS. 3. In quiescent whole animal preparations, stimulation of a single A1 normally causes a single dorsal flexion followed by body flexion to the side contralateral to the stimulated cell; characteristically, A1 spike activity stimulates feedback inhibition coinciding with the end of dorsal flexion and the onset of contralateral flexion. 4. A1 spike activity suppresses feeding behavior and causes proboscis retraction in whole animal preparations induced to feed. A1 activity also suppresses fictive feeding driven by stimulation of the critical phasic paracerebral neurons (PCps) of the motor network of feeding in the isolated CNS. Concomitantly, A1 spikes cause potent inhibition of the PCp interneurons. 5. The A1s are specifically excited by noxious mechanical and chemical stimuli, but are not affected by feeding stimuli or the occurrence of feeding behavior. 6. We conclude that the A1 neurons are elements of an escape swimming pattern generator, and that they are probably homologous to the similar C2 neurons of the nudibranch Tritonia diomedea. One of their functions outside of generating the swim pattern may be the suppression of feeding behavior in response to noxious stimulation. These observations provide a neural mechanism for the original observations of the dominance of escape swimming behavior over feeding.

Changes Occur in the Central Nervous System of the Nudibranch Berghia verrucicornis (Mollusca, Opisthobranchia) During Metamorphosis.

The structure of the larval and juvenile central nervous system (CNS) in Berghia verrucicornis, an aeolid nudibranch, was examined using 1-{mu}m serial sections. The CNS consists of paired optic, cerebral, pleural (also known as sub- and supra-intestinal ganglia), pedal, and buccal ganglia, and a single visceral ganglion. A pleurovisceral loop is present. The organization of the CNS changes as the nudibranch undergoes metamorphosis. In general, there is a condensation of the CNS. The cerebral and pleural ganglia fuse to form the prominent cerebropleural ganglia. The single visceral ganglion fuses with the pleural portion of the left cerebropleural ganglion. The buccal ganglia enlarge and fully organize into a cortex of nerve cell bodies and medulla of nerve fibers. Rhinophoral ganglia develop anterior to each cerebropleural ganglion and a pair of nervous processes extend from each: one to the developing rhinophore and the other anteroventral toward the mouth and associated structures. These metamorphic changes are similar to those seen in other commonly studied opisthobranch species, suggesting that Berghia verrucicornis is an appropriate model for the developmental examination of structure and function in molluscan nervous systems.

Histamine in the nervous system ofMacoma balthica (Bivalvia)

The distribution of histamine(HA)-immunoreactivity of the molluscan species Macoma balthica was mapped with an antiserum against a histamine-protein conjugate. The main ganglia of the central nervous system of M. balthica, the cerebropleural ganglia, the pedal ganglion and the visceral ganglion all contained strongly HA-positive fluorescent cell bodies. The positive cell bodies were situated in clusters in the outer region of the ganglia. Immunoreactive fibres were located in the inner neuropil region of the ganglia. Also the commissure and the connectives of the ganglia as well as many nerve roots contained HA-positive fibres. These results agree well with the recent finding of the wide distribution of histamine in the nervous system of two marine gastropod molluscs, Aplysia and Pleurobranchaea supporting the thought that histamine has an important role in many physiological function of molluscs.

Neurochemical and immunocytochemical studies of serotonin in the hermissenda central nervous system

In the preceding paper (11) we showed that serotonin mimics the effects of associative conditioning on Type B photoreceptors of Hermissenda. Here we show that serotonin is present in the Hermissenda central nervous system and that it is released in a calcium-dependent manner. A large number of serotonergic cell bodies are present in the cerebropleural ganglia (CPG). Cell bodies in the CPG are located in three small, symmetrical clusters. One cluster (2–3 cells) located at the anterior end of the CPG contains a large cell that projects to the buccal ganglion. A second cluster (2–3 cells) is located posterior to the first and near the midline of the nervous system. A third cluster (1–2 cells) was located slightly more posteriorly than the second. Type B photoreceptors and the S/E optic ganglion cell project to a region of the CPG neuropil which is heavily innervated by serotonin immunoreactive fine processes. Since serotonin mimicked the effects of associative conditioning on Type B cells, and is present in an appropriate region of the CPG neuropil, serotonin may mediate some effects of associative conditioning on Type B cells. Results supporting this hypothesis are presented in an accompanying paper.

Distribution of monoamines in the central nervous system of the nudibranch gastropod, Hermissenda crassicornis

The distribution of monoamines in the central ganglia of the nudibranch gastropod Hermissenda crassicornis was examined through the histological localization of both glyoxylic acid-induced fluorescence and serotonin-like immunoreactivity. Glyoxylic acid histochemistry revealed several clusters of catecholamine-containing cells which were located principally in the cerebropleural ganglia. One large unpaired catecholamine-containing cell was also located in the right pedal ganglion. Glyoxylic acid histochemistry and immunohistochemistry together revealed several serotonin-containing cells. The most prominent of these was a bilateral pair of cells (the metacerebral giants or MCG's) with somata located in the anterior lobes of the cerebropleural ganglia and each with a single large axon running through the ipsilateral cerebrobuccal connective to the buccal ganglia. Apart from the MCG's and a few smaller ones in the cerebropleural ganglia, most other serotonergic cells were located in the pedal ganglia. Among the serotonergic cells identified in the pedal ganglia was a single unpaired giant cell (LP1) located only on the left side. The neurites of LP1 projected through the cerebropleural ganglia to the contralateral pedal ganglion. Similarities in the distribution of monoamines in different gastropod species are discussed.

Autoradiographic measurement of tritiated agmatine as an indicator of physiologic activity inHermissenda visual and vestibular neurons

[3H]Agmatine (amino-4-guanidobutane) has been shown to be potentially useful for identifying and assessing the ACh sensitivity of specific neurons. Small cationic amines are able to permeate ACh-activated ion channels in sympathetic neurons and vertebrate endplates. Sensory neurons of the photic pathway in the nudibranch mollusc Hermissenda crassicornis are cholinergic and the synaptic interactions between the photic and vestibular systems have been well characterized electrophysiologically. We have therefore tested the feasibility of using autoradiography with [3H]agmatine, (a) to identify known ACh-responsive postsynaptic cells and (b) to examine its ability to serve as an indicator of physiologic activity within the photic and vestibular pathways under conditions of darkness and light stimulation. Scintillation counting revealed that approximately 70% of the radioactivity was associated with the CNS while approximately 30% was found in the processing fluids, indicating that routine glutaraldehyde-osmium fixation and subsequent processing for epoxy embedding allows retention of substantial amounts of the radiolabel. The autoradiographic results consistently demonstrated that the uptake patterns for [3H]agmatine did reflect some of the known neuronal interactions under the experimental conditions of light and dark. The accuracy extended to the second order cells of the optic ganglion and to putative interneurons along the photic tract in the cerebropleural ganglion. Since all the neurons in these pathways are unipolar with their synaptic interactions occurring only at the terminal endings, the radiolabel accumulated in the somata resulted from retrograde axonal transport. In the photic-vestibular pathways, the highest silver grain densities were found over structures (cell bodies or axon tracts) with increased synaptic activity coupled with higher levels of cellular activity (i.e. increased excitatory postsynaptic potentials or increased spontaneous impulse activity). Slightly less label was found in cells which received increased numbers of inhibitory postsynaptic potentials that produced hyperpolarization and a transient cessation of impulse activity under conditions of illumination. Therefore, the uptake levels of [3H]agmatine as revealed by autoradiography appear to reflect not only changes in sensitivity or density of ACh-activated channels but also changes in cellular activity as indicated by increased amounts of retrograde transport. These results represent the first example of the effective use of this radiolabel as an indicator of synaptic activity in invertebrates and in sensory systems.

Serotonin immunoreactivity in the circumesophageal nervous system of Hermissenda crassicornis

Immunohistochemical techniques were used to examine the distribution of serotonin-immunoreactive (5-HT-IR) neurons and processes in the circumesophageal nervous system of Hermissenda. Both the pedal and the cerebropleural ganglia contained immunoreactive neuronal somata, with the majority occurring in the pedal ganglia. Immunoreactive fibers and varicosities were identified in portions of the central neuropil, where we noted a consistent and specific relationship between 5-HT-IR axons, the optic nerve and the synaptic region in the neuropil near the photoreceptor terminals.

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. III. Role fo the paracerebral neurons and other identified brain neurons

Identified neurons in the cerebropleural ganglion (brain) of the mollusc Pleurobranchaea were stimulated and recorded from intracellularly while recording the identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the metacerebral giant neurons (MCGs), phasic paracerebral neurons (PCp's), polysynaptic excitors of the PCp's (PSEs), type II electrotonic neurons (ETII's), type I electrotonic neurons (ETI's) and several other identified neurons or neuronal classes. Intracellular stimulation of the above identified neurons generally elicited the ingestion motor program or its characteristic components, but never the egestion motor program and seldom its characteristic components. Intracellular recordings from these neurons in the isolated central nervous system preparation while eliciting the ingestion and egestion motor program generally showed cyclic membrane potential oscillations in phase with both motor programs, indicating that these neurons receive synaptic feedback from the ingestion and egestion central pattern generator(s). This study is therefore consistent with the view that an interrelated cluster of brain neurons is specialized to command the ingestion motor program. A neural model of motor program switching in the buccal motor system is formulated, comprising separate command pathways for ingestion and egestion that converge on a common central pattern generator(s).

Sensory, interneuronal, and motor interactions within Hermissenda visual pathway.

The visual pathway of Hermissenda was identified by means of intracellular recordings and iontophoretic injection of the fluorescent dye lucifer yellow. This pathway consisted of five neuron types, namely, type B photoreceptors and the medial type A photoreceptor within each of the two eyes, hair cells in the two statocysts, a group of interneurons in the cerebropleural ganglia, and a putative motor neuron (MN1) in each pedal ganglion. The MN1 cells responded during illumination of the eye with increased impulse and excitatory postsynaptic potential (EPSP) activity. This response was often followed by bursting activity for higher light intensities. The medial type A photoreceptor, which was found to be inhibited by medial and intermediate type B photoreceptors, was demonstrated to excite the MN1 cell indirectly via a group of identified interneurons. Hair cells were also found to excite the MN1 cell indirectly via these interneurons. Among the ipsilateral hair cells, cephalic hair cells were least frequently found to excite the MN1 cell. Among the contralateral hair cells, on the other hand, lateral hair cells were most often found to excite the MN1 cell. Interneurons that were shown to excite the MN1 cell received excitatory input from the medial type A photoreceptor and hair cells. Our observations are consistent with the interpretation that these interactions are mediated by monosynaptic chemical synapses. Electrical stimulation of the MN1 cell with positive-current injection produced turning of the posterior half of the animal's foot to the ipsilateral direction consistent with the animal's turning behavior toward light. The visual pathway identified in this experiment was considered to have some significance in explaining, at least in part, a causal role for changes within type B photoreceptors in producing Hermissenda's modified behavior following associative conditioning.

Rhythmic and Bilaterally Coordinated Motor Activity in the Isolated Brain of Pleurobranchaea

ABSTRACT Rhythmic ingestive behaviour in the predatory marine snail Pleurobranchaea is characterized by cycles of protraction and retraction of the buccal mass, during which food material is taken into the buccal cavity and swallowed (Davis & Mpitsos, 1971). Fictive feeding is demonstrable in the isolated nervous system; the rhythmic motor programme appropriate to feeding behaviour can occur spontaneously or can be elicited by stimulation of different populations of ‘command’ neurones (Davis et al. 1975; Gillette & Davis, 1977; Croll & Davis, 1981; Gillette & Gillette, 1983). Oscillatory motor output is most striking in the isolated buccal ganglion; however, cyclic activity has been recorded in the brain (the cerebropleural ganglion) when it was isolated from the buccal ganglion by cutting the cerebrobuccal connectives (CBCs) (Davis, Siegler & Mpitsos, 1973). Such cyclic activity was recorded in the nerves of the brain while the CBC was stimulated by repetitive electrical shocks. These and other results were interpreted as indicating that oscillators existed both in the brain and the buccal ganglion. Interneurones were identified in both the brain and buccal ganglion which appeared to coordinate the oscillators via axons in the CBCs (Davis et al. 1973; Gillette & Davis, 1977; Gillette, Kovac & Davis, 1978, 1982).

Control of feeding motor output by paracerebral neurons in brain of Pleurobranchaea californica.

1. A population of interneurons that control feeding behavior in the mollusk Pleurobranchaea has been analyzed by dye injection and intracellular stimulation/recording in whole animals and reduced preparations. The population consists of 12-16 somata distributed in two bilaterally symmetrical groups on the anterior edge of the cerebropleural ganglion (brain). On the basis of their position adjacent to the cerebral lobes, these cells have been named paracerebral neurons (PCNs). This study concerns pme subset pf [MCs. the large, phasic ones, which have the strongest effect on the feeding rhythm (21). 2. Each PCN sends a descending axon via the ipsilateral cerebrobuccal connective to the buccal ganglion. Axon branches have not been detected in other brain or buccal nerves and hence the PCNs appear to be interneurons. 3. In whole-animal preparations, tonic intracellular depolarization of the PNCs causes them to discharge cyclic bursts of action potentials interrupted by a characteristic hyperpolarization. In all specimens that exhibit feeding behavior, the interburst hyperpolarization is invariably accompanied by radula closure and the beginning of proboscis retraction (the "bite"). No other behavorial effect of PCN stimulation has been observed. 4. In whole-animal preparations, the PCNs are excited by food and tactile stimulation of the oral veil, rhinophores, and tentacles. When such stimuli induce feeding the PCNs discharge in the same bursting pattern seen during tonic PCN depolarization, with the cyclic interburst hyperpolarization phase locked to the bit. When specimens egest an unpalatable object by cyclic buccal movements, however, the PCNs are silent. The PCNs therefore exhibit properties expected of behaviorally specific "command" neurons for feeding. 5. Silencing one or two PCNs by hyperpolarization may weaken but does not prevent feeding induced by natural food stimuli. Single PCNs therefore can be sufficient but are not necessary to induction of feeding behavior. Instead the PCNs presumably operate as a population to control feeding. 6. In isolated nervous system preparations tonic extracellular stimulation of the stomatogastric nerve of the buccal ganglion elicits a cyclic motor rhythm that is similar in general features to the PNC-induced motor rhythm. Bursts of PCN action potentials intercalated at the normal phase position in this cycle intensify the buccal rhythm. Bursts of PCN impulses intercalated at abnormal phase positions reset the buccal rhythm. The PCNs, therefore, also exhibit properties expected of pattern-generator elements and/or coordinating neurons for the buccal rhythm. 7. The PCNs are recruited into activity when the buccal motor rhythm is elicited by stomatogastric nerve stimulation or stimulation of the reidentifiable ventral white cell. The functional synergy between the PCNs and the buccal rhythm is therefore reciprocal. 8...

Ultrastructure of photoreceptors in the eye of Hermissenda labelled with intracellular injections of horseradish peroxidase.

The terminal processes of single and of pairs of identified photoreceptors in the eyes of the nudibranch mollusc Hermissenda crassicornis were studied by light and transmission electron microscopy after their somata were labelled by intracellular iontophoresis of horseradish peroxidase (HRP). The HRP spread from the somata into the axons and fine terminal processes within the neuropil of the cerebropleural ganglia. The photoreceptors ended in extensive secondary branches in the neuropil where previous electrophysiological studies had indicated the probable site of synaptic interactions between photoreceptors. Clear round vesicles (54-126 nm diameter) within labelled processes were similar to the vesicles found in the somata and axon hillocks. The terminal processes of pairs of type B photoreceptors contained different intensities of the HRP label. Uniform intensities of the HRP label were found in the terminal processes of single type B photoreceptors. These differences in intensity suggested that the terminal processes were from different type B photoreceptors. This finding suggests that the connections between type B photoreceptors are probably monosynaptic.

Command neurons in Pleurobranchaea receive synaptic feedback from the motor network they excite.

Command neurons that cause rhythmic feeding behavior in the marine mollusc Pleurobranchaea californica have been identified in the cerebropleural ganglion (brain). Intracellular stimulation of single command neurons in isolated nervous systems, semi-intact prepartions, and restrained whole animals causes the same rhythmic motor output pattern as occurs during feeding. During this motor output pattern, action potentials recorded intracellularly from the command neurons occur in cyclic bursts that are phase-locked with the feeding rhythm. This modulation results from repetitive, alternating bursts of excitatory and inhibitory postsynaptic potentials, which are caused at least in part by synaptic feedback to the command neurons from identified classes of neurons in the feeding network. Central feedback to command neurons from the motor network they excite provides a possible general physiological mechanism for the sustained oscillation of neural networks controlling cyclic behavior.

Interaction of chemosensory, visual, and statocyst pathways in Hermissenda crassicornis.

Neurons in the cerebropleural ganglia (CPG), photoreceptors in the eye, optic ganglion cells, and statocyst hair cells of the nudibranch mollusk Hermissenda crassicornis responded in specific ways, as recorded intracellularly, to stimulation of the chemosensory pathway originating at the tentacular chemoreceptors as well as to stimulation of the visual pathway originating at the photoreceptors. Synaptic inhibition of photoreceptors occurs via the chemosensory pathway. The possible significance of such intersensory interaction is discussed with reference to preliminary investigation of the animal's gustatory behavior and possible neural mechanisms of behavioral choice.

Pleurobranchaea egg-laying hormone: Localization and partial purification

1. Egg-laying behavior in the gastropodPleurobranchaea californica is a stereotyped sequence of events lasting several hours and culminating in the extrusion of eggs and their attachment to the substrate (Fig. 1). A hormone that causes egg laying has been localized in the two pedal ganglia by means of bioassay (Table 1). One fourth, but not one eighth, of a single pedal ganglion was capable of causing egg laying (Fig. 3).Pleurobranchaea egg-laying hormone differs from that of the closely related gastropodAplysia, sincePleurobranchaea egg-laying hormone did not cause egg laying inAplysia, nor didAplysia egg-laying hormone cause laying inPleurobranchaea. 2. Pleubranchaea egg-laying hormone has a molecular weight of 4000–7000 daltons as determined by fractionation of pedal ganglia on Sephadex G-50 and subsequent bioassay of fractions (Fig. 4). The hormone stained with Coomassie blue when fractionated by SDS-polyacrylamide gel electrophoresis (Fig. 6), incorporated3H and14C labeled leucine when pedal ganglia were labeled in vitro (Figs. 7,8), and was inactivated by trypsin (Table 2). Therefore the hormone is presumably a polypeptide. The hormone was not inactivated by boiling (Table 3). 3. Bioassay and gel electrophoresis localized the hormone to the medial lobe of the pedal ganglion (Fig. 6). Histology of the pedal ganglion revealed that the surface of the medial lobe is comprised exclusively of cells 70–90μm in diameter that stained with phloxine (Fig. 9b), a substance known to stain cells containing egg-laying hormone inAplysia (Fig. 9a) and other molluscs. Therefore, the medial lobe cells that stain with phloxine are presumably the site of synthesis and storage of egg-laying hormone. 4. Whereas egg-laying hormone sufficient to cause egg laying is usally confined to the pedal ganglia, bioassay revealed hormone also in cerebropleural ganglia removed from animals in the act of laying eggs (Fig. 10). Extracts from cerebropleural ganglia of non-laying animals never caused egg laying (Table 1 and Fig. 10a), although these extracts did occasionally induce some of the components of egg-laying behavior (Fig. 10b). The greater amount of egg-laying hormone in cerebropleural ganglia of laying animals could signify the binding of hormone to target sites in this ganglion.

Motor and sensory mechanisms of feeding in Pleurobranchaea.

AbstractNerves of the cerebropleural ganglion play a major role in the sensory and motor aspects of feeding in the marine mollusk, Pleurobranchaea. Investigations of these nerves were carried out using whole‐body preparations capable of essentially normal feeding behavior. Chemosensory nerves which function in food arousal are the rhinophore, tentacle (large branch) and large oral veil nerves, and a nerve of the pedal ganglion (P3). Recordings from these nerves are consistent with previous behavioral findings concerned with the location of receptor regions.The feeding cycle of proboscis extension, thrusting, and withdrawal, is controlled primarilly by cerebral nerves. The mouth nerve and small oral veil nerve supply muscles which control the oral tube. When these muscles contract, the oral tube and mouth are pulled open, and the buccal mass, which forms the core of the proboscis, advances part way. At his time, the body wall musculature, innervated by the body wall nerve and a pedal nerve (P4), contracts behind the buccal mass, forcing it out of the open mouth. Proboscis thrusting is accomplished by rhythmic bursts of the mouth and small oral veil nerves. Withdrawal of the buccal mass is accomplished essentially by the reverse process.This conception of the feeding cycle was developed by considering the muscular anatomy and by behavior simulation. It was confirmed by recording motor nerve output and muscle activity during food stimulation.