Anatomical and physiological background permitting spatial odor sensation in stylommatophoran molluscs

Earlier experiments demonstrated that in order to place protracted tentacles and thereby olfactory receptors in an appropriate position for optimal perception of odor stimuli extraordinary complex movements are required. Until recently both large scale tentacle movements and patterned tentacle movements have been attributed to the concerted involvement of the tentacle retractor muscle and muscles of tegumentum. Recently the existence of three novel muscles in the posterior tentacles of Helix has been discovered. The present review, based on experimental data obtained by our research group, outlines the anatomy, physiology and pharmacology of these muscles that enable the tentacles to execute complex movements observed during foraging both in naïve and food-conditioned snails. Our findings are also compared as far as possible with earlier and recent data obtained on innervation characteristics and pharmacology of molluscan muscles.

Intraspecific Scaling Relationships Between Crawling Speed and Body Size in a Gastropod

Across various modes of locomotion, body size and speed are often correlated both between and within species. Among the gastropods, however, current data are minimal for interspecific and intraspecific scaling relationships. In this study, we tested the relationships between various measurements of body size and crawling speed in the terrestrial snail Cornu aspersum. We also investigated the relationships between crawling speed, muscular wave frequency, and muscular wavelength, because--while these relationships within individuals are well studied--the relationships among individuals are unknown. We recorded snails crawling on both a horizontal and a vertical surface. We found that when they crawled on a horizontal surface, foot length was positively correlated with pedal wavelength and crawling speed, but was not correlated with wave frequency. In comparison, when they crawled on a vertical surface, foot length was positively correlated with wavelength, negatively correlated with wave frequency, and not correlated with crawling speed. Body mass had no correlation with crawling speed when snails were crawling on a horizontal surface, but was negatively correlated with speed when snails crawled on a vertical surface.

Novel triplet of flexor muscles in the posterior tentacles of the snail, Helix pomatia

The anatomy of three novel flexor muscles in the posterior tentacles of Helix pomatia is described. The muscles originate from the ventral side of the sensory pad and are anchored at different sites in the base of the tentacle stem. The muscles span the tentacle and always take the length of the stem which depends on the rate of tentacle protrusion indicating that the muscles are both contractile and extremely stretchable. The three anchoring points at the base of the stem determine three space axes along which the contraction of a muscle or the synchronous contraction of the muscles can move the tentacle in space.

Neural control of olfaction and tentacle movements by serotonin and dopamine in terrestrial snail

We investigated the role of serotonin (5HT) and dopamine (DA) in the regulation of olfactory system function and odor-evoked tentacle movements in the snail Helix. Preparations of the posterior tentacle (including sensory pad, tentacular ganglion and olfactory nerve) or central ganglia with attached posterior tentacles were exposed to cineole odorant and the evoked responses were affected by prior application of 5HT or DA or their precursors 5-hydroxytryptophan (5HTP) and L: -DOPA, respectively. 5HT applications decreased cineole-evoked responses recorded in the olfactory nerve and hyperpolarized the identified tentacle retractor muscle motoneuron MtC3, while DA applications led to the opposite changes. 5HTP and L: -DOPA modified MtC3 activity comparable to 5HT and DA action. DA was also found to decrease the amplitude of spontaneous local field potential oscillations in the procerebrum, a central olfactory structure. In vivo studies demonstrated that injection of 5HTP in freely moving snails reduced the tentacle withdrawal response to aversive ethyl acetate odorant, whereas the injection of L: -DOPA increased responses to "neutral" cineole and aversive ethyl acetate odorants. Our data suggest that 5HT and DA affect the peripheral (sensory epithelium and tentacular ganglion), the central (procerebrum), and the single motor neuron (withdrawal motoneuron MtC3) level of the snail's nervous system.

Mass spectrometric analysis of activity-dependent changes of neuropeptide profile in the snail, Helix pomatia

Terrestrial snails are able to transform themselves into inactivity ceasing their behavioral activity under unfavorable environmental conditions. In the present study, we report on the activity-dependent changes of the peptide and/or polypeptide profile in the brain and hemolymph of the snail, Helix pomatia, using MALDI TOF and quadrupole mass spectrometry. The present data indicate that the snails respond to low temperature by increasing or decreasing the output of selected peptides. Average mass spectra of the brain and hemolymph revealed numerous peaks predominantly present during the active state (19 and 10 peptides/polypeptides, respectively), while others were observed only during hibernation (11 and 13). However, there were peptides and/or polypeptides or their fragments present irrespective of the activity states (49 and 18). The intensity of fourteen peaks that correspond to previously identified neuropeptides varied in the brain of active snails compared to those of hibernating animals. Among those the intensity of eight peptides increased significantly in active animals while in hibernated animals the intensity of another six peptides increased significantly. A new peptide or peptide fragment at m/z 1110.7 was identified in a brain of the snail with the following suggested amino acid sequence: GSGASGSMPATTS. This peptide was found to be more abundant in active animals because the intensity of the peptide was significantly higher compared to hibernating animals. In summary, our results revealed substantial differences in the peptide/polypeptide profile of the brain and hemolymph of active and hibernating snails suggesting a possible contribution of peptides in the process of hibernation.

Humoral serotonin and dopamine modulate the feeding in the snail, Helix pomatia

We investigated the effect of elevated levels of humoral 5HT and DA on the feeding latency of Helix pomatia, 1 day, 3 days and 10 days following satiation, by injecting monoamines into the haemocoel. HPLC assay of monoamines showed that both 5HT and DA are present in pmol/ml concentrations in the haemolymph of both starved and non-starved animals. Elevated levels of 5HT and DA were most effective at decreasing the feeding latency 10 days following satiation when DA decreased the feeding latency in a concentration dependent manner between 10(-7) and 10(-5) M whereas 5HT levels decreased the feeding latency only at 10(-6) M but increased it at 10(-5) M. Immunocytochemistry revealed that both 5HT3 and D1 receptor-like immuno-reactivity are present in cell bodies located in the same areas of the buccal ganglia. Our observations suggest that both humoral DA and 5HT mutually modulate the activity of the feeding CPG through neurons which have these receptors.

Variation in spermathecal morphology is independent of sperm competition intensity in populations of the simultaneously hermaphroditic land snail Cornu aspersum

The complexity of the sperm-storing organ (spermatheca) has been hypothesized to reflect sperm competition intensity in several gastropod species. Furthermore, considerable variation in spermathecal morphology has been detected among populations of the same species. The morphological variation of the fertilization pouch was studied in five populations of the simultaneously hermaphroditic land snail Cornu aspersum (formerly, Helix aspersa). The populations studied differed in snail density and habitat humidity regimes, thus in sperm competition intensity. The study was conducted on wild adult snails and their progeny, which was reared in the laboratory for two successive generations. Finally, the morphology of the spermatheca was correlated to behavioral mating traits of the snails. The fertilization pouch consisted of a simple fertilization chamber and 4-19 blind tubules. The five studied populations did not differ in either mean number of spermathecal tubules, length of the fertilization chamber, length of the main tubule, or cumulative length of all tubules, while they differed in copulation frequency and mating propensity. No correlation was found between snail size and number of tubules, or length of any spermathecal structure measured. Additionally, no correlation was found between any behavioral trait and the morphological characteristics of the spermatheca. Strong correlations were found only among measurements of some of the spermathecal structures. Our results suggest that the complexity of the spermatheca is not related to sperm competition intensity and its structure is thus genetically determined.

Intracellular Localization of the HCS2 Gene Products in Identified Snail Neurons In Vivo and In Vitro

1. The HCS2 (Helix command specific 2) gene expressed in giant command neurons for withdrawal behavior of the terrestrial snail Helix lucorum encodes a unique hybrid precursor protein that contains a Ca-binding (EF-hand motif) protein and four small peptides (CNP1-CNP4) with similar Tyr-Pro-Arg-X aminoacid sequence at the C terminus. Previous studies suggest that under conditions of increased intracellular Ca(2+) concentration the HCS2 peptide precursor may be cleaved, and small physiologically active peptides transported to the release sites. In the present paper, intracellular localization of putative peptide products of the HCS2-encoded precursor was studied immunocytochemically by means of light and electron microscopy. 2. Polyclonal antibodies against the CNP3 neuropeptide and a Ca-binding domain of the precursor protein were used for gold labeling of ultrathin sections of identified isolated neurons maintained in culture for several days, and in same identified neurons freshly isolated from the central nervous system. 3. In freshly isolated neurons, the gold particles were mainly localized over the cytoplasmic secretory granules, with the density of labeling for the CNP3 neuropeptide being two-fold higher than for the calcium-binding domain. In cultured neurons, both antibodies mostly labeled clusters of secretory granules in growth cones and neurites of the neuron. The density of labeling for cultured neurons was the same for both antibodies, and was two-fold higher than for the freshly isolated from the central nervous system neurons. 4. The immunogold particles were practically absent in the bodies of cultured neurons. 5. The data obtained conform to the suggestion that the HCS2 gene products are transported from the cell body to the regions of growth or release sites.

Modulatory serotonin receptors on the soma of command neurons in edible snail

Local application of serotonin (5-hydroxytryptamine, 5-HT) to the soma of command neurons LPa2, LPa3, PPa3, and PPa2 of edible snail Helix lucorum reversibly decreased acetylcholine-induced inward current in these neurons. NAN-190 and methiothepin, antagonists of 5-HT1 serotonin receptors, prevented this modulatory effect of 5-HT. By contrast, LY-53.857, ICS-205.930, and SDZ-205.557, antagonists of 5-HT2, 5-HT3, and 5-HT4 serotonin receptors, respectively, produced no effect on the modulatory effect of serotonin. The data confirm the presence of modulator 5-HT1 serotonin receptor on the soma of command neurons of Helix pomatia.

Sensory innervation of the ovotestis in the snail Helix aspersa

Because oviposition in the land snail Helix aspersa is a metabolically expensive process coupled to a high fixed cost, one expects oviposition to occur only when the clutch size surpasses a minimum value at which the reproductive benefit exceeds the cost. We propose that neural innervation of the gonad allows H. aspersa to monitor oocyte production and ensure an adequate supply of gametes prior to ovulation. The ovotestis is innervated by a branch of the intestinal nerve in which the majority of axon fibres measure <0.2 μm in diameter. We found a strong positive correlation between the number of mature oocytes in the ovotestis and the frequency of spontaneous afferent spikes in the nerve branch. Tactile stimulation of the ovotestis resulted in a 20-fold increase in afferent spikes and an efferent reflex directed towards the ovotestis and the pericardium. Afferent activity also increased 10-fold after an experimentally induced increase in the volume of the ovotestis. These results suggest that the growing oocytes expand the walls of the acini and trigger action potentials in the mechanosensitive nerve terminals that lie within the acinar walls. We hypothesize that the resulting tonic signal is permissive for ovulation. In addition, a phasic sensory signal may occur during ovulation to trigger CNS motor output related to oviposition.

Shell shape of the land snail Cornu aspersum in North Africa: unexpected evidence of a phylogeographical splitting

Anatomical and molecular characters used to differentiate populations of the land snail Cornu aspersum (Helix aspersa) exhibit, in the western Mediterranean, definite and concordant patterns of correlation with geography. Scenarios involving Pliocene geological changes and postglacial expansion during the Pleistocene were proposed in previous studies to account for the establishment of this geographical structure. In the present work, we have performed a spatial analysis of variation in shell morphometrics, after the partitioning of the overall variation into size and shape components by means of a principal component-based approach (Cadima and Jolliffe, 1996). In order to know if the same historical events have also structured shell variation, the analysis includes all the populations from North Africa which were investigated for anatomical and molecular surveys. Contrary to shell size, which shows a significant spatial heterogeneity essentially related to environmental pressures, variation in shell shape components splits the populations according to a geographical pattern reflective of hypotheses suggested for molecular markers and genital anatomy. This implies that the selective forces often invoked to explain spatial changes in shell shape are not the deciding factors in the present case. Moreover, within each of the two geographical clusters defined, Mantel correlograms show that the similarity between populations declines according to an isolation by distance model. Because of the different allometric relationships between shell size and genitalia measurements in Western and Eastern entities of North Africa, mechanical constraints, possibly leading to a precopulatory isolation in the contact zone, are involved.

Complementary distribution of NADPH-diaphorase and l-arginine in the snail nervous system

Since the interneuronal messenger nitric oxide (NO) can not be stored in neurones, the regulation of the NO-producing enzyme nitric oxide synthase (NOS) is crucial. Neuronal NOS metabolises L-arginine to nitric oxide (NO) and L-citrulline in a Ca(2+)-dependent manner. Thus, availability of L-arginine to NOS may modulate NO production. In this study, we examined the cellular distribution of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase, L-arginine and L-citrulline. Using NADPH-diaphorase histochemistry to visualise putative NO-producing cells and immunocytochemistry to localise L-arginine, we showed that the distribution of L-arginine-immunoreactive neurones correlates well with those of NADPH-diaphorase-positive neurones in cerebral ganglia of the pulmonate Helix pomatia. However, substrate and enzyme were visualised in separate but adjacent neurones. We further examined whether NADPH-diaphorase-labelled cells contain the L-citrulline. Following elevation of intracellular Ca(2+) by the Ca(2+) ionophore, ionomycin, or by a high-K(+) solution, the number of L-citrulline-immunoreactive neurones in mesocerebrum and pedal lobe increased up to tenfold. Preincubation of ganglia with the NOS inhibitor N(G)-nitro-L-arginine prevented ionomycin or high-K(+) solution-induced L-citrulline synthesis. Most L-citrulline-immunoreactive neurones contain NADPH-diaphorase activity. In conclusion, these experiments indicate a complementary distribution of NOS and L-arginine and suggest an unknown signalling pathway between neurones to maintain L-arginine and NO homeostasis.

Effect of static and dynamic influences on receptors of equilibrium organ of Helix lucorum after 163-day orbital flight in "Mir" station

A 163-day orbital flight increased the baseline impulse activity of statocyst receptor cells in terrestrial pulmonata snail Helix lucorum. The maximum of reaction to step static stimuli (changes in body position in the range from 0 to 180 degrees) was significantly shifted by 30 degrees from gravitational vertical, while the reaction to dynamic stimuli (dumped sinusoidal oscillations) faded more rapidly than in control animals.

Lead reduces shell mass in juvenile garden snails (Helix aspersa)

In an earlier paper examining inherited tolerance to Pb, the shell growth of laboratory-bred offspring of Helix aspersa from contaminated sites was compared with that ofjuveniles from naive populations on dosed and undosed diets. Eight-week-old snails were fed either 500 microg g(-1) Pb or a control food in competitive trials between two populations. In the first series of trials, a parental history of exposure to Pb did not confer any advantage to either of two populations (BI and MI) competing with a naïve population (LE). whether Pb was present in the diet or not. However, in the analysis of their metal concentrations reported here, LE are found to retain higher levels of Pb in the soft tissues than either BI or MI. Compared to their siblings on the unleaded diet, dosed LE and BI juveniles had lower soft tissue concentrations of Ca and Mg. Although the growth in shell height is unaffected by diet, LE and BI juveniles build lighter shells on the Pb-dosed diet, achieving around 75% of the shell mass of their controls. In contrast, the shell weights of dosed MI juveniles are depressed by only 15% and show no change in the essential metal concentrations of their soft tissues. A second experiment using five populations fed only the dosed food show that the shell weight/soft tissue weight ratios are comparable to the dosed snails of the previous experiment. Building a lighter shell thus appears to be the common response of all Helix populations to a high Pb diet, at least amongst juveniles. The reduction in its mass means that less Ca and Mg is added to the shell and, along with the lowered soft tissue concentrations observed in some populations. may be a consequence of an increased effort to excrete Pb. The possibility that the MI population shows a genotypic adaptation. perhaps as some form of modification of its Ca metabolism, is briefly discussed.

Effects of serotonin, dopamine and ergometrine on locomotion in the pulmonate mollusc Helix lucorum

The terrestrial snail Helix lucorum crawls using waves of muscular contraction (pedal waves) that spread along the sole of its foot. Crawling speed depends on wave generation frequency (step frequency) and the distance the snail moves forwards during each wave (step length). In a previous study, video recordings of a crawling snail showed that its sole length varied over a wide range and was directly correlated with mollusc speed. Speed depended on step length, which was directly related to sole length, rather than on step frequency, which remained rather constant. In the present study, the effects of dopamine, ergometrine (a blocker of dopamine receptors in molluscs) and serotonin injection on the linear relationship between sole length and locomotor speed in Helix lucorum were studied. In crawling snails, dopamine caused sole contraction, and locomotion slowed down or ceased. Ergometrine stimulated locomotion, which resembled rapid crawling with an extended sole, as observed under normal conditions. Serotonin stimulated locomotion and accelerated crawling significantly without causing changes in sole length. The acceleration of locomotion induced by serotonin injection was due to pedal wave (step) elongation. It is proposed that, during each locomotor episode, dopamine controls snail speed by regulating sole length, which determines the amplitude of contraction of the muscle cells involved in pedal waves and, as a result, step length; serotonin determines the basic step length and shifts the linear relationship between sole length and mollusc speed upwards along the axis of mollusc speed. The efficiency of the serotonergic system depends on the physiological state of the mollusc (e.g. that characteristic of summer or winter).

Topographic organization of efferent neurons with different neurochemical characters in the cerebral ganglia of the snail Helix pomatia

This study provides a description of the organization of neurons efferent to different head areas in the cerebral ganglia of Helix pomatia, revealed by simultaneous Ni-lysine and Co-lysine back-filling of different pairs of cerebral nerves. The backfills show that labeled cerebral neurons that innervate the head areas are concentrated in seven representation foci distributed in different parts of the cerebral ganglia. Almost each head area is represented in each focus. At a gross level, the representation of the different head areas in the representation foci shows a topographic arrangement. Each focus is constituted by neurochemically different groups of neurons. All head areas are innervated by serotonin-containing fibers from a single focus (Focus 2) and by dopamine-containing fibers from Foci 1, 2, and 4. However, they are innervated by CARP and FMRFamide-containing fibers from all of the foci. The combination of retrograde labeling with 5, 6-dihydroxytriptamine induced pigment labeling of serotonin-containing neurons or with fluorescence tyrosinehydroxylase immunocytochemistry to detect dopamine-containing neurons showed that the different head areas are topographycally represented in the clusters of both the serotonin- and dopamine-containing cells. The combination of Ni-lysine backfillings from different cerebral nerves with fluorescence CARP and FMRFamide immunocytochemistry revealed that the head areas are represented also in both the CARP and FMRFamide immunoreactive groups of neurons in the different foci.

Structure and function in the cerebral ganglion

Evidence is reviewed to evaluate whether the term "brain is justified in referring to the snail's cerebral ganglion. The focus of the review is terrestrial species, with particular attention given to the genus Helix. In accordance with a standard definition of "brain, the cerebral ganglion is found to be differentiated both structurally and functionally. It receives convergent sensory inputs from a variety of anterior sensory organs plus the posterior body wall. Its outputs comprise motor commands directed towards anterior muscle systems, e.g., the tentacles and the penis, as well as premotor commands directed towards executory centers in other ganglia, e.g., the buccal, visceral, and pedal ganglia. Of the three major divisions in the ganglion, the procerebrum and the mesocerebrum are the most differentiated, whereas the metacerebrum is the least differentiated. The specializations of the procerebrum for olfactory functions, and the mesocerebrum for reproductive functions, reflect the importance of adaptations for feeding and mating in the evolution of the Gastropoda.

A conserved location for the central nervous system control of mating behaviour in gastropod molluscs: evidence from a terrestrial snail

We have investigated the role of the right mesocerebrum in the expression of mating behaviour in the garden snail Helix aspersa. Using an in vivo stimulation and recording technique, we provide evidence for both sensory and motor functions in the mesocerebral neuronal population. Some neurones were specifically sensitive to tactile stimuli delivered to the skin on the superior tentacles and around the genital pore. Electrical stimulation of the right mesocerebrum evoked genital eversion and, in combination with tactile stimulation, dart-shooting and penial eversion. Genital eversions were also elicited by injections of APGWamide. During courtship, one recorded unit increased its activity only in correlation with penial eversion, while six other units increased their activity only during dart-shooting. Three additional units increased their activity during both types of behaviour. In addition, most of the recorded units showed increased neuronal activity during times of contact with a partner. Comparison of our results with available data from other molluscs leads us to conclude that the right anteromedial region of the cerebral ganglion is an evolutionarily conserved region of the gastropod brain specialised for the control of male mating behaviour. It is striking to find such functional conservation in the central nervous system of phylogenetically distant gastropods given the large differences in behaviour during mating.

Topographic organization of serotonergic and dopaminergic neurons in the cerebral ganglia and their peripheral projection patterns in the head areas of the snail Helix pomatia

The distribution of monoaminergic neurons within the cerebral ganglia was investigated in the pulmonate snail Helix pomatia. Simultaneous serotonin and tyrosine hydroxylase double immunostaining revealed that the immunoreactive cell groups are concentrated in a putative monoaminergic center on the ventral surface of the cerebral ganglia. Simultaneous cobalt (Co)- and nickel (Ni)-lysine backfills of cerebral nerves were combined with 5, 6-dihydroxytryptamine pigment-labelling of serotonergic neurons, or with fluorescence immunocytochemistry of dopaminergic neurons. This showed that the serotonergic and dopaminergic cell groups can be divided into smaller subgroups on the basis of their axonal projections into different cerebral nerves. These subgroups show a topographic organization within the serotonergic and dopaminergic neuronal clusters. In the serotonergic system, the different regions of the head are represented in a rostrocaudal direction, whereas a caudorostral organization is characteristic for the dopaminergic system. No serotonin- or dopamine-immunoreative cell bodies but numerous fibers were observed in the head areas, indicating that these are innervated by cerebral monoaminergic neurons and show different innervation patterns. Serotonin-immunoreactive fibers mostly innervate muscle fibers, whereas dopamine-immunoreactive processes do not innervate effector cells, but terminate within the nerve branches of the head areas. On the basis of their innervation pattern, we suggest that dopaminergic neurons may take part in en route modulation of sensory afferent and efferent processes in an as yet unknown manner. The serotonergic neurons, on the other hand, may play a direct role in the modulation of muscle function.

Morphological and electrophysiological features of F76 and D1 neurones of the sub-oesophageal ganglia of Helix aspersa in vitro and in culture

Identified neurones F76 and D1 of the suboesophageal ganglia of Helix aspersa were studied in the isolated ganglia in vitro and in culture. The neurones were examined electrophysiologically with current clamp and morphologically either with intracellular injections of Lucifer Yellow or biocytin. These nerve cells had very similar resting membrane potentials and responses to injected current. The projections of D1 and F76 have been characterised, with both neurones having two main axons. The F76 neurones project to the left pallial, right pallial, anal, and visceral nerves as well as to the left and right pleural ganglia. The D1 neurones have similar projections except that they do not project to the anal and visceral nerves. The bilateral symmetry to the pallial nerves and pleural ganglia is discussed. These cells were also studied electrophysiologically after mechanical isolation and culture. F76 and D1 neurones were separated by dissection (no enzymes) and cultured in three ways. In normal snail Ringer they remained viable for up to two weeks with no development. In Ringer preincubated with a ganglia or containing endothelial growth factor, neurite outgrowths were seen. Membrane potentials were significantly lower in cultured neurones than in vitro and the after hyperpolarization never went below resting in cultured cells but it did in vitro.

Morphology of interneurons in the procerebrum of the snail Helix aspersa

Terrestrial snails have a highly developed sense of olfaction. Because the procerebrum has a large number of cells and is located at the entry site of the olfactory nerve into the brain, the structure is thought to have a significant role in the processing of olfactory stimuli. The morphology of the procerebral neurons in the snail Helix aspersa was investigated through intracellular injections of biocytin. No formal categorization of neuronal types was possible, but some cells were seen to have neurites entirely intrinsic to the procerebrum, whereas others had both intrinsic and extrinsic arborizations, and still others had only extrinsic arborizations. These interneurons were previously thought to have arborizations restricted to the procerebral lobe. We demonstrated the extent of the neurite projections outside of the procerebral lobe by making focal injections of biocytin or Neurobiotin into various regions of the cerebral ganglion. This technique revealed subsets of cells that send neurites not only in the ipsilateral ganglion but also through the cerebral commissure into the contralateral cerebral ganglion. Our results demonstrate not only that the procerebral cell population is heterogeneous but also that the procerebrum interacts more directly with the rest of the central nervous system than was formerly believed.

Distribution of catch-relaxing peptide (CARP)-like immunoreactive neurons in the central and peripheral nervous system of Helix pomatia

Immunocytochemistry was performed on the nervous system of Helix by the use of an antibody raised against a myotropic neuropeptide, the catch-relaxing peptide (CARP), isolated from Mytilus edulis. In each ganglion of the central nervous system of Helix pomatia, numerous CARP-immunoreactive cell bodies and a dense immunoreactive fiber system could be observed with a dominancy in the cerebral and pedal ganglia. The majority of the immunoreactive neurons are unipolar, although multipolar neurons also occur. In the neuropil areas, CARP-immunoreactive fibers show extensive arborization, which may indicate a central role of CARP. CARP-immunoreactive elements could be observed in each investigated peripheral nerve and peripheral areas, namely in the intestine, heart, aorta, buccal mass, lips, and foot. However, CARP-immunoreactive cell bodies could only be demonstrated in the intestine and the foot musculature. Thin varicose CARP-immunoreactive fibers were observed over both muscle and gland cells in the different peripheral organs, suggesting a peripheral role of CARP. In vivo CARP injection into the body cavity (10(-3), 10(-4), 10(-5) M) altered the general behavioral state of the animals and induced the relaxation of the musculature of the whole body wall indicating that CARP has a significant role in the regulation of muscle contraction.

The cerebral neurons of Helix aspersa during hibernation. Changes in the cytochemical detection of calmodulin, cytoskeletal components and phosphatases

Some markers of the intracellular systems that regulate neuronal activity and morphology were analyzed in the cerebral ganglion of hibernating snails (Helix aspersa), in comparison with active animals. The immunocytochemical expression of a calcium-binding protein, i.e. calmodulin, and some cytoskeletal components, i.e. 200 kDa phosphorylated neurofilament protein (pNFH), microtubule associated protein 2 (MAP2) and alpha-tubulin were analyzed by the use of a panel of antibodies raised against mammal antigens. Moreover, by enzymatic reactions the Ca(2+)-ATPase and alkaline phosphatase (AIPase) activities were demonstrated. In comparison with the active phase, the hibernation induced an increase in the immunopositivity for calmodulin in all the neurons. The increase may be linked to unmasking of immunoreactive epitopes due to conformational changes of the protein, which in turn may be a consequence of a reduction or absence of binding with calcium ions or of a real increase in the amount of calmodulin in the somata of neurons. In any event, both the hypotheses indicate that neurons have decreased or suppressed the Ca(2+)-dependent mechanisms as also shown by the lower Ca(2+)-ATPase activity. Nevertheless, the AIPase activity, which was localized in the epineural sheat, was not significantly changed during hibernation and this supports that some metabolic activities are preserved in the hibernated animals. Changes in the immunopositivity for cytoskeletal components were found. There was an increase in the epitopes recognized by the mammalian pNF antibody, that concerned both the positivity of the entire cytoplasm of some clusters of metacerebral neurons and the intensity of the reaction. This would be aimed to improve the stability of the somata and primary neurites. Moreover, the decrease of alpha-tubulin and MAP2 immunopositivity, suggests that a disassembly of microtubules have occurred. The findings indicate that the transport of vesicles in the axons is slowed down during hibernation. In fact, research in progress show that the patterns of neurotransmission and neuromodulation are also deeply modified.

Peripheral connections of FMRFamide-like immunoreactive neurons in the snail, helix pomatia: an immunogold electron microscopic study

Using a postembedding immunogold electron microscopic method, the ultrastructure and synaptic connections of FMRFamide-like immunoreactive varicosities were investigated in different peripheral organs of the snail Helix pomatia, including the heart (auricle), intestine, hepatopancreas, upper tentacle and salivary gland. The FMRFamide-like immunoreactive varicosities contained granules and vesicles as described in a previous study of the CNS of this species, and additionally, based on their granule content, two novel types of varicosities were found in the auricle. A selective accumulation of gold particles over the granules could be demonstrated. The FMRFamide-like immunoreactive varicosities formed unspecialized contacts with postsynaptic target cells in all peripheral organs investigated, with the exception of the tentacle retractor muscle. Both the neuro-muscular and the neuro-glandular contacts were characterized by either unspecialized close apposition of the 'pre- and postsynaptic' membranes or the immunoreactive elements faced the target cell(s) across a relatively wide extracellular space. In the tentacle retractor muscle some of the neuromuscular contacts showed appositions of electron dense material along the presynaptic membrane, clustering of agranular synaptic vesicles and intersynaptic cleft material. The present observations support previous electrophysiological findings and suggest a versatile modulatory role of FMRFamide and related substances in the Helix PNS.

Distribution and anatomy of GABA-like immunoreactive neurons in the central and peripheral nervous system of the snail Helix pomatia

Gamma-aminobutyric acid (GABA)-like immunoreactive neurons were studied in the central and peripheral nervous system of Helix pomatia by applying immunocytochemistry on whole-mount preparations and serial paraffin sections. GABA-immunoreactive cell bodies were found in the buccal, cerebral and pedal ganglia, but only GABA-immunoreactive fibers were found in the viscero-parietal-pleural ganglion complex. The majority of GABA-immunoreactive cell bodies were located in the pedal ganglia but a few could be found in the buccal ganglia. Varicose GABA-ir fibers could be seen in the neuropil areas and in distinct areas of the cell body layer of the ganglia. The majority of GABA-ir axonal processes run into the connectives and commissures of the ganglia, indicating an important central integrative role of GABA-immunoreactive neurons. GABA may also have a peripheral role, since GABA-immunoreactive fibers could be demonstrated in peripheral nerves and the lips. Glutamate injection did not change the number or distribution of GABA-immunoreactive neurons, but induced GABA immunoreactivity in elements of the connective tissue ensheathing the muscle cells and fibers of the buccal musculature. This shows that GABA may be present in different non-neural tissues as a product of general metabolic pathways.

Immunocytochemical distribution of neuropeptide F (NPF) in the gastropod mollusc, Helix aspersa, and in several other invertebrates

The distribution of neuropeptide F (NPF) immunoreactivity in the snail, Helix aspersa, has been demonstrated by immunocytochemistry using 2 region-specific antisera. One, designated NPF3, was raised against a synthetic N-terminal fragment of Helix aspersa NPF; the other, designated PP221, was raised against the C-terminal hexapeptide amide of mammalian pancreatic polypeptide (PP) but cross-reacts fully with the analogous C-terminal region of Helix aspersa NPF. The distribution of NPF immunoreactivity has also been compared with that of FMRFamide using alternate serial sections of Helix aspersa ganglia. Results showed that NPF immunoreactivity was abundant and widespread in the central and peripheral nervous systems and the pattern of immunostaining obtained using both region-specific antisera was similar. Likewise, immunocytochemistry of neural tissues of a congeneric species, Helix pomatia, and 2 prosobranch gastropods, Buccinum undatum and Littorina littorea, produced similar staining patterns with both antisera. However, in the cephalopod mollusc, Loligo vulgaris, and the cestode, Moniezia expansa, positive immunostaining was only obtained with the C-terminal PP antiserum. Immunostaining of alternate serial sections of Helix aspersa ganglia with NPF3, and an antiserum raised to FMRFamide, showed that while a few neurones were immunoreactive with one antiserum only, in the majority, both immunoreactivities were co-localised. NPF thus appears to be an important neuropeptide of widespread distribution in Helix aspersa and the differential immunocytochemical staining obtained using the 2 region-specific antisera would suggest a high degree of primary structural conservation within the gastropod molluscs, but lack of conservation of the N-terminal region of the peptide in other invertebrate groups.

Cardiac regulation by endogenous small cardioactive peptides and FMRFamide-related peptides in the snail Helix aspersa

The putative hepatopeptide pQDPFLRIamide, previously known only from its appearance in a cDNA clone from Helix aspersa, was isolated from circumoesophageal ganglia extracts and sequenced. Extracts of several tissues were fractionated by high performance liquid chromatography and the fractions analysed by radioimmunoassay (RIA). The results indicate that ten cardioactive peptides, FMRFamide, FLRFamide, six FMRFamide-related heptapeptides and two nonapeptide analogues of the small cardioactive peptides (SCPs), are present in the circumoesophageal ganglia (brain), the visceral nerve trunk (from which the cardiac nerve branches) and the aorta. The heart contains the two tetrapeptides, FMRFamide and FLRFamide, and the SCPs, but the heptapeptides were completely undetectable in this organ. The levels of tetrapeptide were high enough to allow their calcium-dependent release from the heart to be demonstrated. Immunohistochemistry revealed a diffuse SCP and FMRFamidergic innervation distributed throughout the heart. These data support the idea that, although the ten peptides are probably acting as neurotransmitters throughout most of the cardiovascular system, the heptapeptides probably also have a neurohormonal role on the Helix aspersa heart itself. The binding affinities of the various antisera used in these studies were examined in competitive RIAs, in non-competitive dot-blot assays or in both.

[The structural organization of the snail sensory systems]

In the paper are reviewed the author's data on the structure of peripheral nervous system of the body wall, gravitational organs--statocysts, eyes, and organs of distant chemoreception--ommatophors, or posterior head tentacles, of the snails Helix vulgaris and Helix pomatia. Localization in the CNS of central parts of the main sensory systems is shown and some structural characteristics of them are described. The data on the organization of the procerebrum which takes part in processing of information from the receptors of the head tentacles are presented. By some morphological features the procerebrum may be considered as one of the highest associative centers of the snails. The data under consideration were obtained by means of silver impregnation by Golgi, retro- and anterograde infusion of CoCl2, horseradish peroxidase and Lucifer yellow into the nerves, as well as by means of a number of other classical histological techniques.

Molecular and biochemical study of the presence and synthesis sites of methionine enkephalin-like substances in the circumoesophageal ganglia, the ovotestis and the tentacles of the snail

In situ hybridization with an oligonucleotidic 35S-labelled probe complementary to the 388-435 coding region of rat proenkephalin mRNA seems to show a colocalization between synthesis and storage sites of methionine-enkephalin(MK)-like substances only in young cellular stages of the ovotestis and in several neurons of cerebral, parietal and pleural ganglia. No positive signal can be detected neither in pedal and visceral ganglia nor in the tentacular collar cells, in spite of previous immunocytochemical data. Radioimmunoassays carried out on acidic extracts of the same organs confirm the molecular results and lead us to conclude to the presence of substances strongly related to MK in the ovotestis as well as in the circumoesophageal ganglia (COG), and to ascertain that the MK-positive tentacular collar cells do not contain authentic MK.

Neurotransmitters in the gastropod CNS: comparative immunocytochemistry

The number, distribution, morphology, and projection areas of immunoreactive neurons labelled with different antisera were analyzed in the gastropod species, Aplysia californica, Lymnaea stagnalis and Helix pomatia, representing different levels of evolutionary development of the central nervous system. Our results show that the number of small-size peptidergic interneurons increases considerably in the cerebral ganglia of Helix, when compared to serotonin-immunoreactive neurons. This phenomenon might be connected to the change from aquatic to terrestrial life, involving also a change in the composition and quality of sensory input, reaching the animal from the surrounding.

Snails and snail farming: an introduction for the veterinary profession

In the past veterinary interest in snails has been confined to their role in the transmission of disease; nowadays the trend to keep these animals in captivity--for food, for study, as 'companion animals'--means that the profession is increasingly likely to be consulted about their health, welfare or conservation. An understanding of the biology of snails is an important prerequisite to work with them. Land snails are hermaphrodite and have a complex reproductive system; other organs also show special adaptations. Management methods vary considerably and farmed snails can be maintained under extensive or intensive conditions. Methods for handling and transporting them are important considerations. There is little published information on the diseases and pathology of snails but suboptimum environment, poisons, nutritional deficiencies, predators and parasites are known to cause, or contribute, to their mortality.

Evidence for a light compensation of the inhibition of reproduction by low temperatures in the snail Helix aspersa. Ovotestis and albumen gland responsiveness to different conditions of photoperiods and temperatures

Four combinations of photoperiods and temperatures have been tested on the reproduction and on the activity of the genital apparatus of the snail Helix aspersa. The results show some interaction between photoperiod and temperature and reveal a predominant effect of photoperiod that compensates for the negative effect of low temperatures. A combination of long day (LD, 18L:6D) and a temperature of 20 degrees C is the most favorable condition for egg-laying as well as for the effective functioning of the ovotestis and albumen gland. In contrast, during a short day (SD, 8L:16D), egg-laying is completely inhibited at 15 degrees C and partly inhibited at 20 degrees C; the differentiation of gametes can be observed in the ovotestis, but the mature oocytes are not released and thus they degenerate. In the albumen gland, an important synthetic activity is noticed, but cellular multiplication and the release of the secretory products decrease. These results suggest that short photoperiods induce inhibition of the (neuro)endocrine centers responsible for the control of both ovulation and egg-laying.

Monosynaptic connections between serotonin-containing neurones labelled by 5,6-dihydroxytryptamine-induced pigmentation in the snail Helix pomatia L

Microelectrophysiological experiments were carried out on in vivo 5,6-dihydroxytryptamine-induced pigment-labelled serotonin-containing neurones of Helix pomatia. Excitatory chemical monosynaptic connections were found between the giant pedal LP3 neurone and several follower cells in the visceral and right parietal ganglia. These neurones have previously been described to be involved in regulation of visceral functions. Monitoring changes in identified monosynaptic connections between pairs of serotonin-containing neurones aids the cellular analysis of behavioural plasticity.

[Various principles of the organization of preterminal and terminal branches of afferent conductors in neuropil of the snail dorsal ganglia]

Character of ramifications in the preterminal and terminal axonal parts in the neuropil of the dorsal ganglia have been studied in 16 edible snails (Halix pomatia). The nervous tissue is impregnated with silver nitrate after Golgifast method. Serial sections are made in two projections: horizontal and vertical. The analysis of peculiarities of the spatial distribution of the afferent fibers (AF) demonstrates their several forms that are united into the following types: dominant, probable and transitional. Comparison of the edible snail AF with those in the higher vertebrata makes it possible to conclude that the character of ramification of their preterminal and terminal parts and principle of organizational connections of the AF with the postsynaptical structures are principally similar.

Gut endocrine cells in the snail Helix aspersa

A microscopic study of the endocrine cells present in the gut of the snail Helix aspersa is made. Electron microscopy is necessary in most cases to identify the enteroendocrine cells, since neither silver impregnations nor immunocytochemical staining have rendered positive results. Endocrine cells are scarce and rest on the basement membrane. They display a clear cytoplasm and variable amounts of small (143 nm) secretory granules of diverse electron-density. They are ovoid or rounded and possess apical processes which extend into the lumen of the gut. The nucleus, located in the basal region of the cell, presents characteristic cytoplasmic indentations. Intraepithelial nerve bundles in contact with endocrine cells are present.

Sensory responses and axonal morphology of two different types of cerebral neurones in Helix pomatia L

1. The mechano- and chemosensory responses of two different types of cerebral neurones responding to food stimuli were studied by microelectrophysiological techniques. This was correlated with axonal morphology investigated by intracellular Co-lysine labelling. 2. The C4 neurone responded to food stimuli applied to the lip receptors by phasic (less than 30 sec duration), while the C14 neurone by an initial phasic and a subsequent tonic longer than 10 min duration) activity change. 3. The different sensory responses of the two neurones can partly be explained by the morphological differences found between them.

Immunocytochemical and ultrastructural evidence for supra- and subesophageal localization of the dorsal-body cells of the snail Helix aspersa

Dorsal-body endocrine cells (DBEC) of the snail were studied by means of immunocytochemical and electron microscopic methods at different times of the reproductive cycle. They specifically bind the anti-methionine-enkephalin (vertebrate--opioid-pentapeptide) antibody and are located not only near the cerebral ganglia but also in the connective tissue surrounding the subesophageal ganglia. Ultrastructural characteristics of these subesophageal cells, however, confirm their clear identity with the previously described supraesophageal cells. The quantitative variations of their immunoreactive content allow us to postulate a likely involvement in reproductive physiology (mating and egg laying). These observations prove that the distribution of the classical "dorsal-body cells" is more extensive than has been admitted until now and that they synthesize methionine-enkephalin-like substance(s).

Intermediate filaments in non-neuronal cells of invertebrates: isolation and biochemical characterization of intermediate filaments from the esophageal epithelium of the mollusc Helix pomatia

To screen invertebrate tissues for the possible expression of intermediate filaments (IFs), immunofluorescence microscopy with the monoclonal antibody anti-IFA known to detect all mammalian IF proteins was used (Pruss, R. M., R. Mirsky, M. C. Raff, R. Thorpe, A. J. Dowding, and B. H. Anderton. 1981. Cell, 27:419-428). In a limited survey, the lower chordate Branchiostoma as well as the invertebrates Arenicola, Lumbricus, Ascaris, and Helix pomatia revealed a positive reaction primarily on epithelia and on nerves, whereas certain other invertebrates appeared negative. To assess the nature of the positive reaction, Helix pomatia was used since a variety of epithelia was strongly stained by anti-IFA. Fixation-extraction procedures were developed that preserve in electron micrographs of esophagus impressive arrays of IFs as tonofilament bundles. Fractionation procedures performed on single cell preparations document large meshworks of long and curvilinear IF by negative stain. These structures can be purified. One- and two-dimensional gels show three components, all of which are recognized by anti-IFA in immunoblotting: 66 kD/pl 6.35, 53 kD/pl 6.05, and 52 kD/pl 5.95. The molar ratio between the larger and more basic polypeptide and the sum of the two more acidic forms is close to 1. After solubilization in 8.5 M urea, in vitro filament reconstitution is induced when urea is removed by dialysis against 2-50 mM Tris buffer at pH 7.8. The reconstituted filaments contain all three polypeptides. The results establish firmly the existence of invertebrate IFs outside neurones and demonstrate that the esophagus of Helix pomatia displays IFs which in line with the epithelial morphology of the tissue could be related to keratin IF of vertebrates.

Intrasomatically recorded action potentials in snail neurons (Helix pomatia): different shapes with different sites of origin in the neuronal arborization. A combined morphological and electrophysiological study

Fibres of the identified neurons B1 to B3 in the buccal ganglia of Helix pomatia can be divided into three types according to their diameters. Electrical stimulation of nerves containing the different fibres induces typical fast depolarizations in the somata of neurons B1 to B3. The appearance of these depolarizations is strictly correlated to the fibre types. The depolarizations are interpreted as axonal action potentials.

Ultrastructure of synaptic connections of a bimodal pacemaker giant neuron in the central nervous system of Helix pomatia L

Following intracellular labelling with horseradish peroxidase, the arborization and synaptic connections of the bimodal pacemaker giant neuron (RPal) of Helix pomatia were investigated in the right parietal and visceral ganglia. The RPal neuron possesses extensive axonal branching, the elements of which could be observed and traced within the entire neuropil region of both ganglia. The main axonal branches showed further arborization. The thin axon processes enter the synaptic neuropil, where they receive numerous synapses. At least six ultra-structurally different terminals form synaptic contacts on peroxidase-labelled axon processes of the cell. On the basis of their vesicle and granule content, they are likely to contain different neurotransmitters. Some intraganglionic efferent contacts of the RPal neuron were also observed. It is suggested that, besides its peripheral efferent connections, this cell might also serve as an interneuron.

Organization of sensory pathways in the anterior tentacle of Helix pomatia L. A light microscopic study

Morphology of the sensory cells in the anterior tentacle and their connection with the tentacular ganglion as well as the organization of the tentacular ganglion have been investigated using double chromation method. Only one kind of sensory neurone, the primary receptor cells could be found in the sensory cup of the anterior tentacle and they were found to be arranged in columnar form. Between the sensory cells a few unipolar neurons having only dendritic process also could be found. The axonal processes of the bipolar receptor cells form the fascicles of the sensory axons which enter the peduncles of the tentacular ganglion. Inside the peduncles, two different parts could be distinguished namely one consisting of bundles of fibres and other consisting of nerve fibres with rich arborization. The tentacular ganglion near the tip of the anterior tentacle can be divided into a distal and a proximal part. The cortical layer of the ganglion contains unipolar neurons showing an uneven distribution. The well-developed neuropile is composed by sensory axons, ganglion cell processes and motor fibres of the cerebral ganglion.

[Innervation of the cutaneous integument of pulmonary mollusks]

Cellular organization of the integumental innervation apparatus was studied in Lymnaea stagnalis and Helix vulgaris by the methods of impregnation with silver nitrate after Golgi, scanning electron microscopy, phase-contrast microscopy and by the technique of semi-thin sections. The integument of the tentacles, mouth lips, head, margins and soles of the foot was subjected to the investigation. In all the areas studied, 6 types of receptors were detected; they varied in number, diameter and form of their peripheral processes, in form of the apical surface, as well as in number, length and position of the receptory cilia. The structure of the subdermal neural plexus was demonstrated. A small number of neurons was present in the distal neural parts and in the subdermal plexus. A possible functional specialization of different receptors and morphological basis for performing peripheral dermal reflexes were discussed.

The effect of adenosine triphosphate, magnesium chloride and phospholipids on crystal formation in the demineralized shell-repair membrane of the snail, Helix pomatia L. An in vitro study

The effect of adenosine triphosphate (ATP), magnesium chloride (MgCl2) and phospholipids on the calcium-binding activity and crystal formation within the decalcified shell-repair membrane of the snail, Helix pomatia, was studied in vitro. The application of ATP produced a characteristic dual effect on calcification: (1) It strongly inhibited the formation of inorganic calcium carbonate (CaCO3) crystals. (2) It stimulated the development of organic crystalline bodies and induced deposition of amorphous calcium carbonate. The demineralized shell-repair membranes became white and rigid after incubation for 7 days in the medium containing 1.0 mM ATP. The inhibitory effect of Mg2+ on CaCO3 crystal formation was diminished by reduction of the concentration of MgCl2 in the incubation solution. Thus, after incubation for only 24h, 1.0 mM MgCl2 promoted the formation of birefringent CaCO3 crystals within the repair membranes. The principal effect of phospholipids on the demineralized shell-repair membrane was stimulatory, but after application of phospholipids to the medium, the formation of crystals proceeded slowly. The very large, composite crystals that were formed within the repair membranes showed strong birefringence. In all cases the development of the crystals and the organic crystalline bodies occurred in close vicinity to the amoebocytes. The role of ATP, MgCl2 and phospholipids in the recalcification of shell-repair membrane is discussed.

[Structuro-functional analysis of identified grape snail neurons]

The study of microanatomy of central neurons in Helix pomatia showed that each identified neurone has a constant number of definitely directed processes. The branching pattern of the processes is also specific for each neurone, but in the same cell the number of the branches may vary. It is concluded, that the general morphology of the neurone is its sufficiently stable characteristic and may serve as a criterion for its identification. The possible functional role of different types of the neurone's branchings is discussed. It is suggested that the processes and branches of RPa3 neurone are axones whereas the branches in the form of fine threads are dendrites. It is shown that the neurone with such organization of process branchings play integrative and command functions.

Motor innervation of the pharynx levator muscle of the snail, Helix pomatia: physiological and histological properties

(1) Motor innervation of the pharynx levator muscle of Helix pomatia was investigated with intracellular recording and axonal iontophoresis of cobalt chloride. (2) Muscle fibers respond to direct electrical stimulation of the muscle with active graded responses or non-overshooting spike potentials. (3) Each fiber is innervated via the external and internal lip nerves by several (mostly 3) excitatory nerve fibers each. Two types of EPSPs can be distinguished according to amplitude, duration, and facilitation. (4) Axonal CoCl2-staining via an external lip nerve branch revealed many nerve fibers entering the muscle and branching there into a rich network of blebbed fibers of various diameters.