Localization of substance P- and FMRFamide-like immunoreactivity in the atrium of the snail Achatina fulica

By immunohistochemical and immunocytochemical methods localization of Substanse P (SP) and FMRFamide in the atrium of the snail Achatina fulica was investigated. Nerve fibers innervating the snail atrium contact tightly with the granular cells (GC) situated between muscle and endocardial cells, forming neuroendocrine units. Both neuromediators were found in the cells of the neuroendocrine units. By immunohistochemistry SP- and FMRFamide-immunoreactive material was revealed in the granules of the atrial GC. Elecrtonmicroscopical immunocytochemistry has confirmed the presence of SP- and FMRFamide-immunoreactive material in the granules of the GC and shown their presence in the neurosecretory granules of the nerve endings contacting both the atrial GC and cardiomyocytes.     

Localization of a substance P-like material in the central and peripheral nervous system of the snail Helix aspersa

Summary A monoclonal antibody against substance P was used for immunocytochemical staining of the central ganglia of the snail Helix aspersa and several peripheral tissues including the gut, reproductive system, cardiovascular system, tentacle and other muscles.Within the central ganglia many neurones, and many fibres in the neuropile and the nerves entering the ganglia, were stained for the SP-like material. The largest numbers of reactive cell bodies were in the pleural ganglia and on the dorsal surfaces of the pedal ganglia. A group of cells was also found, surrounding the right pedal-cerebral connective, that did not fluoresce, but were enveloped by reactive processes terminating directly onto the neurone somata.Specific staining was observed in all peripheral tissues examined and always appeared to be concentrated in nerve terminals. Most particularly these occurred in the heart and aorta, the pharyngeal retractor muscle and the tentacle. Although mostly present in muscular tissues, some fluorescence was also observed in the nervous layer surrounding the retina. The tentacular ganglion also contained immunoreactive cell bodies.     

Localization of a substance P-like material in the central and peripheral nervous system of the snail Helix aspersa

A monoclonal antibody against substance P was used for immunocytochemical staining of the central ganglia of the snail Helix aspersa and several peripheral tissues including the gut, reproductive system, cardiovascular system, tentacle and other muscles. Within the central ganglia many neurons, and many fibres in the neuropile and the nerves entering the ganglia, were stained for the SP-like material. The largest numbers of reactive cell bodies were in the pleural ganglia and on the dorsal surfaces of the pedal ganglia. A group of cells was also found, surrounding the right pedal-cerebral connective, that did not fluoresce, but were enveloped by reactive processes terminating directly onto the neurone somata. Specific staining was observed in all peripheral tissues examined and always appeared to be concentrated in nerve terminals. Most particularly these occurred in the heart and aorta, the pharyngeal retractor muscle and the tentacle. Although mostly present in muscular tissues, some fluorescence was also observed in the nervous layer surrounding the retina. The tentacular ganglion also contained immunoreactive cell bodies.     

Actions of substance P on central neurones and peripheral tissues,and co-existence of 5-hydroxytryptamine and a substance p-like peptide in the heart of the snail Helix aspersa

The actions of substance P (SP) were tested on central neurones of the snail Helix aspersa, and on the in vitro heart and pharyngeal retractor muscle (PRM). SP was found to show very limited effects in the CNS, but did produce consistent, though weak, inhibition of a group of cells in the right pedal-cerebral connective. On the isolated beating heart 5-hydroxytryptamine (5-HT) produced short latency cardioexcitation, whereas long latency excitation was produced by SP. Electrically-induced contractions of the PRM were found to be inhibited by SP and augmented by the molluscan SP analogue eledoisin, suggesting the presence of separate receptor types in this tissue.Double immunohistochemical staining of sections through the central ganglia for 5-HT and SP revealed that the 2 compounds usually occur in separate neurones, although a few examples showing coexistence were also observed. In the heart, however, all the nerve endings visible were labelled by both antibodies suggesting that two cardioexcitatory compounds, 5-HT and a SP-like peptide, occur together in the same nerve endings in the Helix heart. An assay to measure cAMP levels in homogenized tissue showed that 5-HT and dopamine stimulated cAMP production, whereas production was inhibited by SP, indicating that the actions of cAMP may be mediated via an adenylate cyclase/cAMP system.     

The pharmacological actions of 5-hydroxytryptamine,FMRF-amide and substance P and their possible occurrence in the heart of the snail Helix aspersa L.

The actions of 5-hydroxytryptamine (5-HT), FMRF-amide and substance P were tested on the isolated heart of Helix aspersa. All three compounds were found to produce positive inotropic and chronotropic effects, the order of potency being 5-HT > substance P > FMRF-amide. However, whereas the responses to 5-HT and FMRF-amide were maximal within a few seconds, the response to substance P had a longer latency. Two other similar undecapeptides, eledoisin and physalaemin, were also tested and were found to have very similar actions to those of substance P. The effects of 5-HT and FMRF-amide could be separated using the 5-HT blockers methysergide and ketanserin, which had relatively little effect on the response to FMRF-amide.Immunohistochemical staining was carried out on sections through the Helix auricle and ventricle for 5-HT, FMRF-amide and substance P. Substantial 5-HT-like and substance P-like immunoreactivity was observed, apparently concentrated in nerve endings, but the level of FMRF-amide-like immunoreactivity was considerably lower. The fluorescence produced by all three compounds was evenly distributed throughout the heart tissue. HPLC analysis of heart tissue extract demonstrated a high level of 5-HT (about 8 μg/g wet weight) but a negligible catecholamine content.     

Eye regeneration in the mystery snail

Mystery snails (Family Ampullariidae) are aquatic prosobranchs which possess structurally complex eyes at the tip of a cephalic eyestalk. No other sensory organs are found in association with this stalk. These snails possess the ability to regenerate the eye completely after amputation through the mid-eyestalk. Amputation induces gross changes in the cellular character of the entire eyestalk; in particular, an invagination of integumentary epithelium at the apex of the eyestalk stump produces a shallow cleft or "eyecup." Differentiation of all components of the eye apparently occurs by transdetermination of these epithelial cells. Retinal differentiation and the appearance of a new lens is observed as soon as 14 days postamputation. Complete eyes (by external observation), although smaller than the originals, have regenerated by 25 days postamputation. We compare this regeneration to the reconstruction of other animal tissues, in particular the regeneration of amphibian limbs.     

蜗牛的解剖

以采自新疆大学校园巴蜗牛科Bradybaenidae的一种蜗牛为例,介绍了蜗牛的一般解剖方法,并对蜗牛的内部结构进行了标注和描述。     

Influence of snail mucus trails and first snail meal on the behavior of malacophagous sciomyzid larvae

There has been considerable focus on the natural enemies of snails, particularly those of medical and veterinary significance. Much attention has focussed on members of the Family Sciomyzidae (Diptera), the majority of which feed on a range of mollusc species. However, little is known about the influence of first snail meal on subsequent prey choices, an important consideration in biocontrol. We examined neonate larval responses of Ilione albiseta to fresh and aged snail mucus trails of three snail species. Median neonate response rates to aged mucus trails for all three snail species tested were significantly (P < 0.001) weaker than for fresh mucus trails indicating a strategy which enhances the likelihood of reaching prey snail species without expending energy following “cold” trails. More than 78% of first instar larvae, fed on one snail species (Radix peregra or Stagnicola palustris) and subsequently offered a choice of these two snail species for the second snail meal, selected the snail species of the first snail meal suggesting that the first snail meal influences subsequent prey selection. However, the impact of the first snail meal on larval trail-following behavior is less clear-cut. While there may be some preference for the mucus trail of the snail species on which neonate larvae have fed, this does not exclude the larvae from following the mucus trails of other snail species. The results are discussed in the context of the potential use of I. albiseta as a biocontrol agent of vectors of snail borne diseases.     

Nematode and snail metallothioneins

Metallobiologists have, at large, neglected soil dwelling invertebrates; exceptions are the nematode (Caenorhabditis elegans) and snails (Helix pomatia and Cantareus aspersus). This review aims to compare and contrast the molecular, protein and cellular mechanisms of the multifunctional nematode and snail metallothioneins (MTs). The C. elegans genome contains two MT genes, mtl-1, which is constitutively expressed in the pharynx and likely to act as an essential and/or toxic metal sensor, and mtl-2, which plays a negligible role under normal physiological conditions but is strongly induced (as mtl-1) in intestinal cells upon metal exposure. It has been possible to follow the intricate phenotypic responses upon the knockdown/knockout of single and multiple MT isoforms and we have started to decipher the multifunctional role of C. elegans MTs. The snails have contributed to our understanding regarding MT evolution and diversity, structure and metal-specific functionality. The H. pomatia and C. aspersus genomes contain at least three MT isoform genes. CdMT is responsible for cadmium detoxification, CuMT is involved in copper homeostasis and Cd/CuMT is a putative ancestral MT possibly only of minor importance in metal metabolism. Further investigations of nematode, snail and other invertebrate MTs will allow the development of alternative biomarker approaches and lead to an improved understanding of metallobiology, protein evolution and toxicogenomics.     

Electrophysiological and neurochemical study of long-term sensitization in the snail

The long-term sensitization of avoidance reflex was produced in snail Helix pomatia, which led to the remarkable increase in the pneumostome closures period. The formation of long-term sensitization is also accompanied by increase in excitability of command neurons of this reflex. One of the possible mechanisms of this phenomenon is the depolarization of these cells. The quantitative redistribution of water-soluble proteins with relative mobility 0.54 0.42 0.40 was also observed in the identified neurons, both included in the avoidance reflex (command neurons) and non-included (bursting neurons, nerve cells of pool D). The protein with the relative mobility of 0.75 was unique for the nerve cells of neurosecretory pool D in sensitized snails, and was never found in control animals.     

Effect of x-irradiation on amoebocytopoiesis in the snail

The [3H]thymidine radioautography technique was used to study the objective laws of the renewal of blood cells (amoebocytes) of the edible snail (Helix pomatia) after X-radiation. Cells which are the precursors of amoebocytes actively proliferating beyond the limits of peripheral blood have been shown to possess a high radiosensitivity. The action of lethal doses of radiation (200-500 Gr) suppresses their proliferation and leads to the irreversible amoebocytopenia. Radioresistant cells lost the ability to the proliferation circulate in the peripheral blood.     

Interrelations in the Fasciola hepatica-water snail system

Peculiarities of relationships in the "Fasciola hepatica-Lymnaea truncatula" system were studied by means of hystological and histochemical methods. Trematodes cause deep histopathological and histochemical changes of the injured organs of L. truncatula. They are determined by mechanical destruction of mollusc's tissues under the effect of parasites and by intoxication of animals with metabolites of parasites. Under the effect of parasites the content of glycogen and phospholipids in hosts' tissues decreases while the concentration of neutral fats increases. In most cases, however, the infected hosts remain viable that under normal ecological conditions results in the preservation of the "F. hepatica-L. truncatula" system.     

Viscero-cardiac reflexes in the edible snail]

Only two inhibitory neurons in the visceral ganglia provide the viscero-cardial and cardio-cardial reflexes of Helix pomatia. These neurons are connected in parallel and do not interact with each other. The cells have extensive receptive fields in all visceral organs which are considerably overlapped. These inhibitory neurons can provide the afferent function because of a high sensitivity to tactile stimulation of their endings. The analysis of the data showed that morphological and functional characteristics of the neurons in question corresponded completely to previously identified multifunctional interneuron V21.     

Long-term potentiation in the neurons of the edible snail

A brief high-frequency stimulation of the anal nerve of the isolated nerve ring of snail Helix induced a pronounced increase in the amplitude of EPSPs, evoked in identified neurons of left parietal and visceral ganglions by low frequency (once in 5 min) stimulation of the same nerve. The amplitude of EPSP returned to the control level 30-120 min after tetanization. We called this effect long-term potentiation. A brief application of serotonin (10 microM) in the majority of neurons also induced lasting either 15-30 min or more than 2 hours facilitation of EPSP, evoked by anal nerve stimulation. Intracellular cAMP injections, being without effect on EPSP amplitude in many neurons, in certain neurons caused an increase in EPSP amplitude, lasting up to 30 min. It is suggested that the 3 factors shown to increase synaptic efficiency in molluscan neurons may have common mechanisms of action.