Photoperiod controls egg laying and caudodorsal cell hormone expression but not gonadal development in the pond snail Lymnaea stagnalis.

Photoperiod is a reliable cue to regulate growth and reproduction for seasonal adaptation. Although photoperiodism has been well studied in Chordata and Arthropoda, less is known about Mollusca. We examined photoperiodic effects on egg laying, body size, gonad-somatic index, oocyte size and relative amounts of caudodorsal cell hormone mRNA in individual rearing conditions in the pond snail Lymnaea stagnalis. Twenty-five weeks after hatching, the percentages of egg-laying snails under a photoperiod of 12 h light and 12 h darkness (12L:12D) were significantly smaller than those under longer days. The total numbers of eggs and egg masses under 12L:12D were significantly smaller than those under longer days. Significant differences between 16L:8D and 12L:12D were not observed in the soft body and ovotestis weight, and the gonad-somatic index. Photoperiodic effects were also not observed in oocyte diameters twenty-two weeks after hatching. Twenty-seven weeks after hatching amounts of caudodorsal cell hormone mRNA were significantly lower in the cerebral ganglia with commissure under 12L:12D than 16L:8D. L. stagnalis exhibited a clear photoperiodic response in egg laying and the amount of caudodorsal cell hormone mRNA, but not in gonadal development. Under 12L:12D suppression of caudodorsal cell hormone expression might suppress egg laying.

The Use of Mechanistic Population Models in Metal Risk Assessment: Combined Effects of Copper and Food Source on Lymnaea stagnalis Populations.

Environmental risk assessment (ERA) of chemicals aims to protect populations, communities, and ecosystems. Population models are considered more frequent in ERA because they can bridge the gap between the individual and the population level. Lymnaea stagnalis (the great pond snail) is an organism that is particularly sensitive to various metals, including copper (Cu). In addition, the sensitivity of this species to Cu differs between food sources. The first goal of the present study was to investigate whether we could explain the variability in sensitivity between food sources (lettuce and fish flakes) at the individual level with a dynamic energy budget (DEB) model. By adapting an existing DEB model and calibrating it with Cu toxicity data, thereby combining information from 3 studies and 2 endpoints (growth and reproduction), we put forward inhibition of energy assimilation as the most plausible physiological mode of action (PMoA) of Cu. Furthermore, the variation in Cu sensitivity between both food sources was considerably lower at the PMoA level than at the individual level. Higher Cu sensitivity at individual level under conditions of lower food quality or availability appears to emerge from first DEB principles when inhibition of assimilation is the PMoA. This supports the idea that DEB explained Cu sensitivity variation between food sources. Our second goal was to investigate whether this food source effect propagated to the population level. By incorporating DEB in an individual-based model (IBM), population-level effects were predicted. Based on our simulations, the food source effect was still present at the population level, albeit less prominently. Finally, we compared predicted population-level effect concentration, x% (ECx) values with individual-level ECx values for different studies. Using the DEB-IBM, the range of effect concentrations decreased significantly: at the individual level, the difference in chronic EC10 values between studies was a factor of 70 (1.13-78 µg dissolved Cu/L), whereas at the population level the difference was a factor of 15 (2.9-44.6 µg dissolved Cu/L). To improve interstudy comparability, a bioavailability correction for differences in water chemistry was performed with a biotic ligand model. This further decreased the variation, down to a factor of 7.4. Applying the population model in combination with a bioavailability correction thus significantly decreased the variability of chronic effect concentrations of Cu for L. stagnalis. Overall, the results of the present study illustrate the potential usefulness of transitioning to a more modeling-based environmental risk assessment. Environ Toxicol Chem 2019;00:1-16. © 2019 SETAC.

Molecular cloning and functional analysis of chitinases in the fresh water snail, Lymnaea stagnalis.

Molluscan shells, consisting of calcium carbonate, are typical examples of biominerals. The small amount of organic matrices containing chitin and proteins in molluscan shells regulates calcification to produce elaborate microstructures. The shells of gastropods have a spiral shape around a central axis. The shell thickness on the internal side of the spiral becomes thinner than that on the outer side of the spiral during the growth to expand the interior space. These observations suggest that a dissolution process works as a remodeling mechanism to change shell shape in molluscan shells. To reveal the dissolution mechanism involved in the remodeling of gastropod spiral shells, we focused on chitinases in the fresh water snail Lymnaea stagnalis. Chitinase activity was observed in the acetic acid-soluble fraction of the shell and in the buffer extract from the mantle. Allosamidin, a specific inhibitor of family 18 chitinases, inhibited the chitinase activity of both fractions completely. Homology cloning and transcriptome analyses of the mantle revealed five genes (chi-I, chi-II, chi-III, chi-IV, and chi-V) encoding family 18 chitinases. All chitinases were expressed in the mantle and in other tissues suggesting that chitinases in the mantle have multiple-functions. Treatment with commercially available chitinase obtained from Trichoderma viride altered the shell microstructure of L. stagnalis. Larvae of L. stagnalis cultured in allosamidin solution had a thinner organic layer on the shell surface. These results suggest that the chitinase activities in the shell and mantle are probably associated with the shell formation process.

Radix dolgini: The integrative taxonomic approach supports the species status of a Siberian endemic snail (Mollusca, Gastropoda, Lymnaeidae).

The molecular techniques are the standard tool for the study of the taxonomic position and phylogenetic affinities of the lymnaeid genus Radix Montfort, 1810, and the majority of the European representatives of this taxon have been studied in this respect. However, a plethora of nominal species of Radix described from Northern Asia (Siberia and the Russian Far East) are still characterized only morphologically, raising some doubts concerning their validity. In this paper, we present the triple (morphological, molecular, and zoogeographical) evidence that there is at least one endemic species of Radix, Radix dolgini (Gundrizer and Starobogatov, 1979), widely distributed in Siberia and Western Mongolia. Phylogenetically, it is a sister species to the European R. labiata (Rossmaessler, 1835) [=R. peregra auct.], and their common ancestor most probably lived in the Pliocene, nearly 3.25Myr ago. Our results assume the existence of an extended dispersal barrier for freshwater hydrobionts between Europe and Siberia in the Late Pliocene that may be important for biogeographical explanations. Three other nominal Siberian species of Radix: R. kurejkae (Gundrizer and Starobogatov, 1979), R. gundrizeri (Kruglov and Starobogatov, 1983), and R. ulaganica (Kruglov and Starobogatov, 1983) proved to be the junior synonyms of R. dolgini.

Are sick individuals weak competitors? Competitive ability of snails parasitized by a gigantism-inducing trematode.

Parasitized individuals are often expected to be poor competitors because they are weakened by infections. Many trematode species, however, although extensively exploiting their mollusc hosts, also induce gigantism (increased host size) by diverting host resources towards growth instead of reproduction. In such systems, alternatively to reduced competitive ability due to negative effects of parasitism on host performance, larger size could allow more efficient resource acquisition and thus increase the relative competitive ability of host individuals. We addressed this hypothesis by testing the effect of a trematode parasite Diplostomum pseudospathaceum on the competitive ability of its snail host Lymnaea stagnalis. We experimentally examined the growth of snails kept in pairs in relation to their infection status and intensity of resource competition (i.e. food availability). We found that parasitized snails grew faster and their reproduction was reduced compared to unparasitized individuals indicating parasite-induced gigantism. However, growth of the snails was faster when competing with parasitized individuals compared to unparasitized snails indicating reduced competitive ability due to parasitism. The latter effect, however, was relatively weak suggesting that the effects of the parasite on snail physiology may partly override each other in determining competitive ability.

Sole smooth muscle states determine gliding rate in the freshwater snail Lymnaea stagnalis.

The sole of crawling gastropods is a unique model for studying the function of smooth muscles and ciliated epithelium. The gastropod snail Lymnaea stagnalis glides over the substratum without visible muscular contraction in its sole; consequently, the gliding was thought to be due to sole cilia. However, we have shown that the sole muscles in Lymnaea are phasic smooth muscles. They contribute extensively to gliding rate, which is directly correlated with the sole length (longitudinal sole muscle tonus) that varies widely during gliding. Here, we show that the linear relationship between gliding rate and sole length in Lymnaea may be modified. Serotonin increases gliding rate and has no effect on sole length. Dopamine contracts the sole and, consequently, slows the gliding rate, while ergometrine (a blocker of dopamine receptors) relaxes the sole and increases gliding rate. These influences on locomotion rate and sole length are similar to those obtained earlier for Helix lucorum, in which the substances changed the number and contraction force of muscle cells involved in peristaltic locomotory waves. Taken together, the data obtained here for Lymnaea and earlier for Helix describe the fundamental mechanisms for controlling phasic smooth muscles.

Morphological and molecular characterization of lymnaeid snails and their potential role in transmission of Fasciola spp. in Vietnam.

Freshwater snails of the family Lymnaeidae play an important role in the transmission of fascioliasis worldwide. In Vietnam, 2 common lymnaeid species, Lymnaea swinhoei and Lymnaea viridis, can be recognized on the basis of morphology, and a third species, Lymnaea sp., is known to exist. Recent studies have raised controversy about their role in transmission of Fasciola spp. because of confusion in identification of the snail hosts. The aim of this study is, therefore, to clarify the identities of lymnaeid snails in Vietnam by a combination of morphological and molecular approaches. The molecular analyses using the second internal transcribed spacer (ITS2) of the nuclear ribosomal DNA clearly showed that lymnaeids in Vietnam include 3 species, Austropeplea viridis (morphologically identified as L. viridis), Radix auricularia (morphologically identified as L. swinhoei) and Radix rubiginosa (morphologically identified as Lymnaea sp.). R. rubiginosa is a new record for Vietnam. Among them, only A. viridis was found to be infected with Fasciola spp. These results provide a new insight into lymnaeid snails in Vietnam. Identification of lymnaeid snails in Vietnam and their role in the liver fluke transmission should be further investigated.

Morphological and Molecular Characterization of Lymnaeid Snails and Their Potential Role in Transmission of Fasciola spp. in Vietnam

Freshwater snails of the family Lymnaeidae play an important role in the transmission of fascioliasis worldwide. In Vietnam, 2 common lymnaeid species, Lymnaea swinhoei and Lymnaea viridis, can be recognized on the basis of morphology, and a third species, Lymnaea sp., is known to exist. Recent studies have raised controversy about their role in transmission of Fasciola spp. because of confusion in identification of the snail hosts. The aim of this study is, therefore, to clarify the identities of lymnaeid snails in Vietnam by a combination of morphological and molecular approaches. The molecular analyses using the second internal transcribed spacer (ITS2) of the nuclear ribosomal DNA clearly showed that lymnaeids in Vietnam include 3 species, Austropeplea viridis (morphologically identified as L. viridis), Radix auricularia (morphologically identified as L. swinhoei) and Radix rubiginosa (morphologically identified as Lymnaea sp.). R. rubiginosa is a new record for Vietnam. Among them, only A. viridis was found to be infected with Fasciola spp. These results provide a new insight into lymnaeid snails in Vietnam. Identification of lymnaeid snails in Vietnam and their role in the liver fluke transmission should be further investigated.

Chromatographic assay to study the activity of multiple enzymes involved in the synthesis and metabolism of dopamine and serotonin.

Serotonin and dopamine are crucial regulators of signalling in the peripheral and central nervous systems. We present an ex-vivo, isocratic chromatographic method that allows for the measurement of tyrosine, L-3,4-dihydroxyphenylalanine (L-DOPA), dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), tryptophan, 5-hydroxytryptophan (5-HTP), serotonin and 5-hydroxy-3-indoleacetic acid (5-HIAA) in a model central nervous (CNS) system, to study the role of key enzymes involved in the synthesis and metabolism of serotonin and dopamine. By utilising a sample splitting technique, we could test a single CNS sample at multiple time points under various pharmacological treatments. In, addition, we were able to conduct this assay by utilising the endogenous biochemical components of the CNS to study the synthesis and metabolism of serotonin and dopamine, negating the requirement of additional enzyme activators or stabilisers in the biological matrix. Finally we utilised NSD-1015, an aromatic amino acid decarboxylase enzyme inhibitor used to study the synthesis of dopamine and serotonin to monitor alterations in levels of key neurochemicals. 3-hydroxybenzylhydrazine dihydrochloride (NSD-1015) was able to reduce levels of serotonin and dopamine, whilst elevating precursors L-DOPA and 5-HTP.

Organization of the serotonergic innervation of the feeding (buccal) musculature during the maturation of the pond snail Lymnaea stagnalis: a morphological and biochemical study.

The serotonergic innervation of the buccal musculature responsible for feeding (radula protraction) was investigated during the maturation of the pond snail, Lymnaea stagnalis L., applying light and electron microscopic immunohistochemistry and biochemical approaches. According to epifluorescence and laser confocal microscopy, the first 5-HT-like-immunoreactive (5-HTLIR) processes appeared on the surface of the musculature at the postmetamorphic E80% embryonic stage. Until hatching, the innervation continued to increase in density, showing axon arborizations with projections into the deeper muscle levels. An adult-like pattern of 5-HTLIR innervation appeared at P2-P3 juvenile stages. At the ultrastructural level, close (16-20 nm) but mostly unspecialized neuromuscular contacts were formed by both unlabeled and 5-HTLIR axon profiles from the E80% embryonic stage. Labeled processes were also found located relatively far from the muscle cells. An HPLC assay showed a gradual increase of the 5-HT level in the buccal mass during development. The buccal mass was characterized by a single-component high-affinity 5-HT uptake system, and 5-HT release could be evoked by 100 mM K(+) and blocked in Ca(2+) -free medium. It is suggested that 5-HT plays a wide modulatory role in the peripheral feeding system and is also involved in the functional maturation of the muscle system.

Morphological and molecular characterization of Neotropic Lymnaeidae (Gastropoda: Lymnaeoidea), vectors of fasciolosis.

Lymnaeidae play a crucial role in the transmission of fasciolosis, a disease of medical and veterinary importance. In the Neotropic, a region where fasciolosis is emergent, eight Lymnaeidae species are currently considered valid. However, our knowledge of the diversity of this taxon is hindered by the fact that lymnaeids exhibit extremely homogeneous anatomical traits. Because most species are difficult to identify using classic taxonomy, it is difficult to establish an epidemiological risk map of fasciolosis in the Neotropic. In this paper, we contribute to our understanding of the diversity of lymnaeids in this region of the world. We perform conchological, anatomical and DNA-based analyses (phylogeny and barcoding) of almost all species of Lymnaeidae inhabiting the Neotropic to compare the reliability of classic taxonomy and DNA-based approaches, and to delimitate species boundaries. Our results demonstrate that while morphological traits are unable to separate phenotypically similar species, DNA-based approaches unambiguously ascribe individuals to one species or another. We demonstrate that a taxon found in Colombia and Venezuela (Galba sp.) is closely related yet sufficiently divergent from Galba truncatula, G. humilis, G. cousini, G. cubensis, G. neotropica and G. viatrix to be considered as a different species. In addition, barcode results suggest that G. cubensis, G. neotropica and G. viatrix might be conspecifics. We conclude that conchological and anatomical characters are uninformative to identify closely related species of Lymnaeidae and that DNA-based approaches should be preferred.

[Geographic distribution features of subgenus and life forms of Lymnaeidae (Gastropoda, Pulmonata) in Eastern Europe].

Relative species richness as a ratio of species number known from the teritory norther than polar circle and species number in Eastern Europe as a whole was calculated from all subgenuses and life forms of the Lymnaeidae. The largest value of this character typical for amla-like life form. The dominance of one life form is a result of its adaptation to life in places with wave activity and for water respiration. Large relative species richness of subgenuses Lymnaea and Peregriana is a sequence of ampla-like life form dominance, wuch consist from these subgenuses.

The antidepressant fluoxetine but not citalopram suppresses synapse formation and synaptic transmission between Lymnaea neurons by perturbing presynaptic and postsynaptic machinery.

Depression is a debilitating mental disorder, and selective serotonin reuptake inhibitors (SSRIs) constitute the first-line antidepressant treatment choice for the clinical management of this illness; however, the mechanisms underlying their therapeutic actions and side effects remain poorly understood. Here, we compared the effects of two SSRIs, fluoxetine and citalopram, on synaptic connectivity and the efficacy of cholinergic synaptic transmission between identified presynaptic and postsynaptic neurons from the mollusc Lymnaea. The in vitro paired cells were exposed to clinically relevant concentrations of the two SSRIs under chronic and acute experimental conditions, and the incidence of synapse formation and the efficacy of synaptic transmission were tested electrophysiologically and with fluorescent Ca(2+) imaging. We demonstrate that chronic exposure to fluoxetine, but not to citalopram, inhibits synapse formation and reduces synaptic strength, and that these effects are reversible following prolonged drug washout. At the structural level, we demonstrate that fluoxetine, but not citalopram, prevents the expression and localization of the presynaptic protein synaptophysin. Acute exposure to fluoxetine substantially reduced synaptic transmission and synaptic plasticity (post-tetanic potentiation) in established synapses, whereas citalopram reduced synaptic transmission, but not short-term synaptic plasticity. We further demonstrate that fluoxetine, but not citalopram, directly inhibits voltage-gated Ca(2+) currents in the presynaptic neuron, as well as postsynaptic responsiveness to exogenously applied neurotransmitter. This study provides the first direct evidence that fluoxetine and citalopram exert characteristic, non-specific side effects that are unrelated to their function as SSRIs, and that fluoxetine is more detrimental to synaptic physiology and structure than citalopram.

Peripheral sensory cells in the cephalic sensory organs of Lymnaea stagnalis.

The peripheral nervous system in gastropods plays a key role in the neural control of behaviors, but is poorly studied in comparison with the central nervous system. Peripheral sensory neurons, although known to be widespread, have been studied in a patchwork fashion across several species, with no comprehensive treatment in any one species. We attempted to remedy this limitation by cataloging peripheral sensory cells in the cephalic sensory organs of Lymnaea stagnalis employing backfills, vital stains, histochemistry, and immunohistochemistry. By using at least two independent methods to corroborate observations, we mapped four different cell types. We have found two different populations of bipolar sensory cells that appear to contain catecholamines(s) and histamine, respectively. Each cell had a peripheral soma, an epithelial process bearing cilia, and a second process projecting to the central nervous system. We also found evidence for two populations of nitric oxide-producing sensory cells, one bipolar, probably projecting centrally, and the second unipolar, with only a single epithelial process and no axon. The various cell types are presumably either mechanosensory or chemosensory, but the complexity of their distributions does not allow formation of hypotheses regarding modality. In addition, our observations indicate that yet more peripheral sensory cell types are present in the cephalic sensory organs of L. stagnalis. These results are an important step toward linking sensory cell morphology to modality. Moreover, our observations emphasize the size of the peripheral nervous system in gastropods, and we suggest that greater emphasis be placed on understanding its role in gastropod neuroethology.

Different circuit and monoamine mechanisms consolidate long-term memory in aversive and reward classical conditioning.

There has been considerable recent interest in comparing the circuit and monoamine-based mechanisms of aversive and reward-associative conditioning in a number of vertebrate and invertebrate model systems. The mollusc Lymnaea stagnalis provides a unique opportunity to explore changes in the neural and chemical pathways underlying these two different types of conditioning as its feeding circuitry has been thoroughly characterised. Animals can learn after a single trial to associate the same CS (amyl acetate) either with a punishment (quinine) or reward (sucrose), showing either a reduced or an elevated feeding response, respectively, to the CS. We previously showed that reward conditioning strengthened the direct excitatory pathway from the lips to the feeding central pattern generator in the buccal ganglia through the activation of feeding interneurons in the cerebral ganglia. Now we demonstrate that aversive conditioning enhances the strength of a different inhibitory pathway that suppresses feeding but has no effect on the excitatory pathway. Here we show that consolidation of long-term memory (LTM) in reward conditioning depends on dopamine but not octopamine. In contrast, aversive LTM depends on octopamine but not dopamine. Octopamine is the invertebrate equivalent of noradrenalin, so these results on the monoamine dependence of reward and aversive conditioning in Lymnaea resemble, at the transmitter receptor level, those in mammals but are the opposite of those in another invertebrate group, the insects.

The shadow-induced withdrawal response, dermal photoreceptors, and their input to the higher-order interneuron RPeD11 in the pond snail Lymnaea stagnalis.

The shadow-induced withdrawal response in Lymnaea stagnalis is mediated by dermal photoreceptors located on the foot, mantle cavity, and skin around the pneumostome area. Here, we determined whether we could obtain a neural correlate of the withdrawal response elicited by a shadow in a higher-order central neuron that mediates withdrawal behavior. We measured the electrophysiological properties of the higher-order interneuron Right Pedal Dorsal 11 (RPeD11), which has a major role in Lymnaea withdrawal behavior. In semi-intact preparations comprising the circumesophageal ganglia, the mantle cavity and the pneumostome, but not the foot and eyes, a light-on stimulus elicited a small short-lasting hyperpolarization and a light-off stimulus elicited a depolarization of RPeD11. We also determined that dermal photoreceptors make a monosynaptic contact with RPeD11. The dermal photoreceptor afferents course to the circumesophageal ganglia via the anal and genital nerves to the visceral ganglion, and/or via the right internal and external parietal nerves to the parietal ganglion. Finally, in addition to responding to photic stimuli, RPeD11 responds to both mechanical and chemical stimuli delivered to the pneumostome.

Pituitary adenylate cyclase activating polypeptide (PACAP) and its receptors are present and biochemically active in the central nervous system of the pond snail Lymnaea stagnalis.

PACAP is a highly conserved adenylate cyclase (AC) activating polypeptide, which, along with its receptors (PAC1-R, VPAC1, and VPAC2), is expressed in both vertebrate and invertebrate nervous systems. In vertebrates, PACAP has been shown to be involved in associative learning, but it is not known if it plays a similar role in invertebrates. To prepare the way for a detailed investigation into the possible role of PACAP and its receptors in a suitable invertebrate model of learning and memory, here, we undertook a study of their expression and biochemical role in the central nervous system of the pond snail Lymnaea stagnalis. Lymnaea is one of the best established invertebrate model systems to study the molecular mechanisms of learning and memory, including the role of cyclic AMP-activated signaling mechanisms, which crucially depend on the learning-induced activation of AC. However, there was no information available on the expression of PACAP and its receptors in sensory structures and central ganglia of the Lymnaea nervous system known to be involved in associative learning or whether or not PACAP can actually activate AC in these ganglia. Here, using matrix-assisted laser desorption ionization time of flight (MALDI-TOF) and immunohistochemistry, we established the presence of PACAP-like peptides in the cerebral ganglia and the lip region of Lymnaea. The MALDI-TOF data indicated an identity with mammalian PACAP-27 and the presence of a squid-like PACAP-38 highly homologous to vertebrate PACAP-38. We also showed that PACAP, VIP, and maxadilan stimulated the synthesis of cAMP in Lymnaea cerebral ganglion homogenates and that this effect was blocked by the appropriate general and selective PACAP receptor antagonists.

Transient and big are key features of an invertebrate T-type channel (LCav3) from the central nervous system of Lymnaea stagnalis.

Here we describe features of the first non-mammalian T-type calcium channel (LCa(v)3) expressed in vitro. This molluscan channel possesses combined biophysical properties that are reminiscent of all mammalian T-type channels. It exhibits T-type features such as "transient" kinetics, but the "tiny" label, usually associated with Ba(2+) conductance, is hard to reconcile with the "bigness" of this channel in many respects. LCa(v)3 is 25% larger than any voltage-gated ion channel expressed to date. It codes for a massive, 322-kDa protein that conducts large macroscopic currents in vitro. LCa(v)3 is also the most abundant Ca(2+) channel transcript in the snail nervous system. A window current at typical resting potentials appears to be at least as large as that reported for mammalian channels. This distant gene provides a unique perspective to analyze the structural, functional, drug binding, and evolutionary aspects of T-type channels.

The suitability of gallium as a substitute for aluminum in tracing experiments.

Aluminum is a toxic metal whose complex aquatic chemistry, mechanisms of toxicity and trophic transfer are not fully understood. The only isotope of Al suitable for tracing experiments in organisms-(26)Al-is a rare, costly radioisotope with a low emission energy, making its use difficult. Gallium shares a similar chemistry with Al and was therefore investigated as a potential substitute for Al for use in aquatic organisms. The freshwater snail, Lymnaea stagnalis was exposed to either Al or Ga (0.0135 mM) under identical conditions for up to 40 days. Behavioural toxicity, metal accumulation in the tissues, and sub-cellular partitioning of the metals were determined. Al was more toxic than Ga and accumulated to significantly higher levels in the soft tissues (P < 0.05). The proportion of Al in the digestive gland (DG; detoxificatory organ) relative to other tissues was significantly lower than that of Ga (P < 0.05) from day 14 onwards. There were also differences in the proportions of Al and Ga associated with heat stable proteins (HSPs) in the digestive gland, with significantly more HSP present in the DGs of snails exposed to Al, but significantly less Al than Ga associated with the HSP per unit mass protein present. From this evidence, we conclude that Ga may be of limited use as a tracer for Al in animal systems.

Comparative neurobiology of feeding in the opisthobranch sea slug, Aplysia, and the pulmonate snail, Helisoma: evolutionary considerations.

The motor systems that generate feeding-related behaviors of gastropod mollusks provide exceptional opportunities for increasing our understanding of neural homologies and the evolution of neural networks. This report examines the neural control of feeding in Helisoma trivolvis, a pulmonate snail that ingests food by rasping or scraping material from the substrate, and Aplysia californica, an opisthobranch sea slug that feeds by using a grasping or seizing motion. Two classes of neurons that are present in the buccal ganglia of both species are considered: (1) clusters of peptidergic mechanoafferent cells that transmit sensory information from the tongue-like radula/odontophore complex to the central motor circuit; and (2) sets of octopamine-immunoreactive interneurons that are intrinsic to the feeding network. We review evidence that suggests homology of these cell types and propose that their roles have been largely conserved in the control of food-scraping and food-grasping consummatory behaviors. We also consider significant differences in the feeding systems of Aplysia and Helisoma that are associated with the existence of radular closure in Aplysia, an action that does not occur in Helisoma. It is hypothesized that a major adaptation in the innervation patterns of analogous, possibly homologous muscles could distinguish the food-scraping versus food-grasping species. It appears that although core CPG elements have been largely conserved in this system, the neuromuscular elements that they regulate have been more evolutionarily labile.