Degradation of the radula in the snails Biomphalaria glabrata say and Limnaea stagnalis L. (Gastropoda,Pulmonata)

Summary The radula of snails is formed at the posterior end of the radular gland or pocket, and degraded at the same rate at its anterior end. Degradation is due to different secretory activities of the inferior epithelium of the radular gland. Its secretions seem to degrade enzymatically the matrix of the radular membrane and basal plates of teeth, leaving only chitin containing microfibres and degradation products. The sclerotized parts of the teeth remain unchanged, but as they are now only loosely connected with the radular membrane. they are torn off easily during feeding movements. The rest of the degraded and frayed radular membrane and the subradular membrane are also lost by abrasion during feeding. The cells of the inferior epithelium are connected with each other by septate desmosomes and an elaborate system of deep lateral interdigitation which may provide tensile strength. Extrusion of degraded cells of the inferior epithelium into the subradular membrane takes place, although the thick basal lamina forms a continuous sheath which is closely adjoined to the basal parts of the inferior epithelium. Nerve fibres containing vesicles with electron dense neurosecretory material (deduced from the diameter of 200–250 nm) are attached to this sheath or penetrate into it; they may be involved in the regulation of production and degradation processes during radula replacement. Problems of the forward transport of radula and inferior epithelium are discussed.     

Histochemistry of glycosaminoglycans in cartilage ground substance. Alcian-blue staining and lectin-binding affinities in semithin Epon sections

The critical-electrolyte-concentration staining method using Alcian blue (AB) was applied to etched semithin Epon-embedded sections. The distribution of various glycosaminoglycans (GAGs) was studied in hyaline, elastic, cellular and fibrous cartilage obtained from humans and rodents. The staining patterns in semithin sections were found to correspond to those obtained using paraffin-embedded material. Lectin histochemistry was performed on consecutive sections. The following peroxidase-labelled lectins were used: Ricinus communis A I, Arachis hypogaea, Ulex europaeus A I, Triticum vulgaris, Helix pomatia, Limax flavus, and concanavalin A. The lectin-binding capacity of cartilaginous ground substance was found to be low, as was expected on account of the few free sugar residues of GAGs. Chondroitin sulphate, the most widely distributed GAG, did not exhibit lectin staining. The lectin-binding sites (positive staining for all lectins tested except H. pomatia) observed corresponded to areas positive for keratan sulphate, as shown by AB staining in preceding or following sections. The pronounced lectin binding seen in cellular structures and the inner territorial matrix regions is considered to be due to higher concentrations of oligosaccharides involved in the metabolism of GAGs.     

Subdomains of the rough endoplasmic reticulum in colon goblet cells of the rat: lectin-cytochemical characterization.

Using lectin binding, we characterized subdomains of the rough endoplasmic reticulum (rER) in goblet cells of the rat colon. In this cell type, special rER regions can be differentiated on the basis of their content of low electron density and dilated cisternal spaces in conventional transmission electron microscopic preparations. The fine fibrillar content of these cisternal regions demonstrated high-affinity binding with lectins from wheat germ, Helix pomatia, Griffonia simplicifolia I-A4 and -B4, and Ricinus communis I, although not with the sialic acid-specific Limax flavus lectin and the fucose-binding Ulex europaeus I lectin. Sugar-inhibitory experiments indicated that glycoconjugates packed within these regions bound the lectins with higher affinity than molecules present in the Golgi apparatus and secretory granules. Furthermore, the lectin binding patterns of the rER subdomains differed from those of the Golgi apparatus and mucin granules: the terminal sugar residues sialic acid and fucose were demonstrable in the Golgi apparatus and mucin granules and were absent from the rER, while galactose-recognizing lectins bound intensely at these rER regions, weakly to Golgi elements, and were almost absent from mucin granules.     

Basal bodies in the odontoblasts of the limpet,Patella coerulea L. (Gastropoda)

Summary The odontoblasts in the long radular gland of Patella coerulea L. are arranged in a terminal position; therefore newly formed teeth already have an upright position. The long and slender odontoblasts have only one to three lengthy and ramifying apical microvilli. Between these pinnate microvilli a fine filamentous material appears which probably corresponds to chitin microfibrils. Therefore, the pattern of chitin microfibrils seems to depend on the arrangement of odontoblasts' microvilli. For the first time, basal bodies were found in the apical part of odontoblasts which led to the assumption that the radular gland originally might have been a mucous gland, the secretion of which was transported by cilia.     

Lectin binding patterns to terminal sugars of rat lung alveolar epithelial cells.

We used post-embedding cytochemical techniques to investigate the lectin binding profiles of rat lung alveolar epithelial cells. Sections from rat lung embedded in the hydrophilic resin Lowicryl K4M were incubated either directly with a lectin-gold complex or with an unlabeled lectin followed by a specific glycoprotein-gold complex. The binding patterns of the five lectins used could be divided into three categories according to their reactivity with alveolar epithelial cells: (a) the Limax flavus lectin and Ricinus communis I lectin bound to both type I and type II cell plasma membranes; (b) the Helix pomatia lectin and Sambucus nigra L. lectin bound to type II but not type I cells; and (c) the Erythrina cristagalli lectin reacted with type I cells but was unreactive with type II cells. The specificity of staining was assessed by control experiments, including pre-absorption of the lectins with various oligosaccharides and enzymatic pre-treatment of sections with highly purified glycosidases to remove specific sugar residues. The results demonstrate that these lectins can be used to distinguish between type I and type II cells and would therefore be useful probes for investigating cell dynamics during lung development and remodeling.     

两种石磺齿舌形态差异分析

显微观察了瘤背石磺(Onchidiumstruma)和石磺(O. verruculatum)齿舌的形态结构。运用差异系数法对两种石磺齿舌参数进行比较分析。利用SPSS10.0对瘤背石磺、石磺齿舌参数(齿舌长、齿舌头宽、齿舌中宽、齿舌尾宽、横列数、每排最少齿片数和每排最多齿片数)与个体参数(体长、体宽、体高、足长、足宽和体重)作回归分析。结果表明,两种石磺齿舌都很发达,外观呈长统靴状;齿片排成许多横列,每一横列均有中央齿一枚,侧齿若干无缘齿;两种石磺的齿舌头宽、齿舌中宽和齿舌尾宽差异极显著,但差异系数小于1.28,认为两种石磺的齿片形态存在明显的种间差异,但齿舌参数不适合作为石磺属贝类的分类依据;瘤背石磺的体宽和石磺的体重在评估各自齿舌生物学性状方面起到比较重要的作用。     

Histology and regeneration of the radula of Pomacea bridgesi (Gastropoda,Prosobranchia)

Summary Histology, physiological regeneration, and degradation of the taenioglossan prosobranch radula and its concomitant epithelia were studied by light and electron microscopy (TEM, SEM), electron microprobe analysis, and autoradiography. Taenioglossa have seven multicellular odontoblastic cushions which produce the tooth matrix by apocrine secretion; many long microvilli are also incorporated. In contrast to pulmonates, the odontoblasts of prosobranchs are capable of division, and their mitoses contribute to the expansion of the cushions, but presumably also to the displacement of degenerating odontoblasts. The seven cushions are isolated from each other by separation cells. The radular membrane is produced from microvilli of membranoblasts and a substance secreted at the base of microvilli.Strands of the supraradular epithelium subsequently move in between the teeth and finally enclose them completely. They effect the hardening and mineralization of the teeth. The strands move together with the radula towards the anterior and are extruded at the opening of the radular sheath; their degeneration, however, has already started in the middle section of the sheath. Epithelial cells are produced by two completely separated mitotic centres which lie dorsolaterally at the end of the sheath.In the subradular epithelium, mitotic activity is scattered over the posterior half of the sheath but is not found in the region where the supramedian radula tensor muscle is inserted. The epithelial cells move forward, but at a much lower rate than the radula. At the opening of the sheath the subradular membrane is generated, while cells of the subradular epithelium lying between the lamellae of the subradular membrane are extruded.The subradular membrane is limited to the functional part of the radula. It is situated on the distal radular epithelium, which is obviously not a continuation of the subradular epithelium. In test animals treated with tritiated thymidine, there is a very strong stationary centre of labeled cells at the beginning of the epithelium, but so far no mitoses have been found in this centre and the labeled cells do not move on continually. In the middle of the distal epithelium mitoses do occur, and the labeled cells permit the assumption that these cells do not migrate at all to the anterior end. At least in Prosobranchia, the distal radular epithelium does not transport the radula to its degradation zone. The transport mechanism for the radula is still unknown.     

Processing of mechano- and chemosensory information in the lip nerve and cerebral ganglia of the snail Helix pomatia L.

Neurophysiologists have long been seeking out simple model systems in which to analyse the neuronal mechanisms underlying the organisation of behaviour. The feeding behaviour of molluscs has proved to be one of the most useful simple systems for the analysis of cyclical motor patterns, the interactions of central pattern generating interneurones and the role of sensory inputs in the initiation and maintenance of the behaviour. Considerable progress has been made in one or both of the first two aspects of this research in Lymnaea, Helisoma, Limax, Planorbarius, Pleurobranchaea and Tritonia (for reviews see [3, 7, 8, 15]) and more recently, in Aplysia [39] and Planorbis [1]. The role of mechano- and chemosensory inputs in the organisation of the feeding behaviour was studied in at least twenty molluscan species (for a review see [3]). However, in only less than half of them was the analysis extended to the effect of tactile and chemical inputs on identified neurones in the buccal and cerebral ganglia which contain the feeding circuitry (Aplysia: [12, 22, 36, 41]; Pleurobranchaea: [9, 16, 17]; Tritonia: [2]; Helisona: [21]; Limax: [11, 14, 35]; Helix: [6, 19, 24-26, 32, 38]). In present chapter I would like to review our earlier findings on the processing of mechano- and chemosensory information in the lip nerves and cerebral ganglia of Helix pomatia L. These findings were published in a series of papers between 1982 and 1987 [19, 20, 24-26]. The results reviewed here prepared the way for the development of new lines of research in our laboratory on the plasticity and serotonergic modulation of feeding in this widely used experimental animal [27, 40].     

Ultrastructural localization of lectin receptors on the luminal and abluminal aspects of brain micro-blood vessels

Lectin- or glycoprotein-colloidal gold complexes were used for detection of specific monosaccharide residues in mouse brain micro-blood vessels (MBVs). The lectins tested recognize the following residues: beta-D-galactosyl (Ricinus communis agglutinin-120, RCA-1), alpha-N-acetylgalactosaminyl (Helix pomatia agglutinin, HPA), alpha-D-mannosyl and alpha-D-glucosyl (Concanavalin A, Con A), sialoglycoconjugates (Limax flavus agglutinin, LFA), N-acetylglucosaminyl and sialyl (wheat germ agglutinin, WGA), and alpha-L-fucosyl (Ulex europeus agglutinin, UEA-1). Use of these lectin-gold complexes and ultrathin sections of Lowicryl K4M-embedded tissue makes it possible to gain insights into localization of lectin receptors in the entire cross-section of MBV walls. Receptors for all lectins, except UEA-1, were found on both luminal and abluminal fronts of the endothelial cells (ECs). Differential labeling of luminal and abluminal fronts of ECs with some lectins (Con A, HPL) is considered to reflect the polarity of the endothelium. Some differences noted in the distribution of lectin receptors in the wall of representatives of three types of MBVs (capillaries, arterioles, and venules) are thought to be associated with different functions performed by the above-mentioned segments of the microvasculature in maintenance of the blood-brain barrier.     

Fine structure of the epidermis of the optic tentacle in a slug, Limax flavus L.

The epidermis at the tip of the optic tentacle in Limax flavus is constructed of columnar epithelial cells, distal processes of nerve cells, and scattered processes of the collar cells. The epithelial cells extend stout microvilli called plasmatic processes by Wright perpendicularly from the free surface. Each plasmic process branches into a few terminal twigs embedded in a fuzzy filamentous substance. Most nerve cells have their nuclei under the basal lamina. The distal processes of these nerve cells reach the free surface and send long microvilli to form the spongy layer under a filamentous covering. At the side surface of the tentacle the epithelial cells are cuboidal or squamous and the neural elements are fewer. Here, no spongy layer is formed; and the collar cell processes are replaced by the lateral cell processes. Peculiar secretion granules are contained in the lateral and collar cell processes as well as in their cell bodies situated beneath the basal lamina.     

Axonal pathways and synaptic inputs of three identified neurons in the buccal ganglion of Helix pomatia.

The axonal pathways and the synaptic inputs of the identified neurons B1 through B3 in the buccal ganglia of Helix pomatia were studied. The axons of neurons B1, B2 and B3 were found to run invariably within the ipsilateral posterior oesophageal nerve, ipsi- and contralateral salivary gland nerves, and ipsilateral cerebrobuccal connective, respectively. Synaptic responses could be elicited by stimulation of most of the nerves of the buccal ganglia. These consisted of an early depolarization which was most frequently followed by a longlasting de- or hyperpolarization. The shape of the synaptic response proved to be related to the different neurons.     

嫁[虫戚]的齿舌带及其齿片的形态差异分析

在光镜和电镜下对嫁[虫戚]（Cellana toreuma）的齿舌形态进行观察研究。嫁[虫戚]的齿舌带每1横列具有2枚侧齿和2枚缘齿,缺乏中央齿,齿式为1.1.0.1.1。齿舌带前端弯曲,齿片排列松散且存在明显的磨损现象;中段齿片排列紧密、整齐;后端齿片无色且宽度有略微的缩小。侧齿呈镰刀型,具1个齿尖,基部呈三角形且具突起,尖齿部分细长;缘齿具3个齿尖,第2尖齿靠近第3尖齿。采用多个比例参数来比较嫁齿舌带及其前、中、后3段上的齿片形态,发现嫁齿舌带前、中、后3段各比例参数的值存在一定的关系,即中段大于前段、中段大于后段。     

COMPARATIVE MORPHOLOGY OF RADULAR TEETH IN CONUS: OBSERVATIONS WITH SCANNING ELECTRON MICROSCOPY

Radular teeth of 22 Indo-Pacific species of the genus Conus(Neogastropoda: Toxoglossa) were compared. On morphologicalfeatures all can be related to one of three known feeding modes:piscivorous, vermivorous and molluscivorous. Observations arereported on the radular teeth of six piscivores, thirteen vermivoresand three molluscivores. The radular teeth of piscivores areof two general types. In the first, two barbs and a posteriorly-directedprocess with a recurved tip are found at the anterior end. Inthe second, two barbs are located at the anterior end and theshaft is serrated for most of its length. An enlarged posteriorregion (terminal knob) is present in the first and absent inthe second. Molluscivores possess radular teeth with two anteriorbarbs and in some species a serrated shaft or terminal knob.The radular teeth of vermivores, which show much greater interspecificvariation than those of piscivores or molluscivores, are characterizedby one or two anterior barbs and in most species a serratedregion near the apex. A forwardly-projecting cone (basal spur)is usually located on the terminal knob. Piscivores and molluscivoreslack such basal spurs. The radular teeth of Conus are used toconvey a potent venom and hold prey firmly during feeding. Previouslyundescribed morphological features are noted on the teeth ofC. obscurus and C. lividus. Figured here for the first timeare the radular teeth of C. abbreviatus, C. aureus, C. catus,C. litoglyphus, C. pennaceus, C. rattus and C. sponsalis. ^*Present address: Department of Paleontology, University ofCalifornia, Berkeley, California 94720, U.S.A. (Received 2 April 1979;     

The dependence of thermopreferendum in Helix pomatia L. on air temperature

Behavioural tests with 192 specimen of the roman garden snail Helix pomatia L. were performed in order to clarify whether the thermopreferendum of this pulmonate is influenced not only by the temperature of the substratum but also by air temperature. For this purpose, the snails were exposed to a horizontal temperature gradient of the substratum at different air temperatures between 10 and 30 degrees C. The results show that the selection of substratum temperature depends on the air temperature: the lower the air temperature, the lower is the temperature of the substratum preferred by the snails. Obviously, the animals tend to keep the difference between air temperature and temperature of the substratum as small as possible. This behaviour might be a mechanism to reduce the temperature gradient in the snail's body and to adjust the metabolic rate to cardiac output.     

Two lectins on the surface of Helix pomatia haemocytes: a Ca2+-dependent,GalNac-specific lectin and a Ca2+-independent,mannose 6-phosphate-specific lectin which recognises activated homologous opsonins

Summary Haemocytes of the gastropod mollusc, Helix pomatia, possess on their surface a membrane-integrated GalNac-specific lectin which binds to and stimulates phagocytosis of GalNac-bearing target cells (human A erythrocytes) only in the presence of extracellular calcium ions. Target cells without GalNac moieties on their surface (human B and bovine erythrocytes) are not recognised. Helix haemocytes also possess a Ca²⁺-independent mannose-6-phosphate-specific lectin on their surface which, in the absence of extracellular calcium ions, enables recognition and phagocytosis of A rbc opsonised with agglutinins isolated from either the snail's albumin gland or serum. These opsonins, however, bind to host haemocytes only after binding to GalNac moieties on the surface of test particles. Our results indicate that such a ligand-specific opsonin/target cell interaction apparently induces a conformational change in the opsonin, resulting in exposure of mannose 6-phosphate moieties that are recognised by the Ca²⁺-independent lectin on the surface of the haemocytes.Abbreviations BSA bovine serum albumin - bv bovine - DAB 3-3-diamino-benzidine tetrahydrochloride - ELISA enzyme-linked immunosorbent assay - GalNac N-Acetyl-D-galactosamine - G6-P glucose 6-phosphate - HE haemocyte extract - HPA Helix pomatia albumin gland agglutinin - HPA PO peroxidase-labelled HPA - M6-P mannose 6-phosphate - ML monolayer - MLS monolayer supernatant - OPD orthophenylene diamine - PBS phosphate buffered saline - PMSF phenylmethylsulphonyl fluoride - PO peroxidase - rbc red blood cells - RT room temperature - SA Helix pomatia serum agglutinin - TBS Tris buffered saline     

The fine structural organization of sensory nerve endings in the lip of Helix pomatia L.

The fine structural and cytochemical characteristics of sensory nerve cells have been studied in the lip of Helix pomatia. A ruthenium red positive cuticular layer was found on the surface of the sensory epithelium. Among the undifferentiated epithelial cells two types of sensory dendrites were observed, namely ciliated and non-ciliated ones. A large amount of smooth surfaced endoplasmic reticulum, microtubes and ribosomes were present in the neuroplasm of the sensory dendrites. However, rough surfaced endoplasmic reticulum, mitochondria, and electrodense bundles of long filaments were characteristic in the simple epithelial cells. The cell bodies of the sensory dendrites lie subepithelially among the muscle cells and they generally contain empty or dense core vesicles.     

Historical and biomechanical analysis of integration and dissociation in molluscan feeding,with special emphasis on the true limpets (Patellogastropoda: Gastropoda)

Modifications of the molluscan feeding apparatus have long been recognized as a crucial feature in molluscan diversification, related to the important process of gathering energy from the environment. An ecologically and evolutionarily significant dichotomy in molluscan feeding kinematics is whether radular teeth flex laterally (flexoglossate) or do not (stereoglossate). In this study, we use a combination of phylogenetic inference and biomechanical modeling to understand the transformational and causal basis for flexure or lack thereof. We also determine whether structural subsystems making up the feeding system are structurally, functionally, and evolutionarily integrated or dissociated. Regarding evolutionary dissociation, statistical analysis of state changes revealed by the phylogenetic analysis shows that radular and cartilage subsystems evolved independently. Regarding kinematics, the phylogenetic analysis shows that flexure arose at the base of the Mollusca and lack of flexure is a derived condition in one gastropod clade, the Patellogastropoda. Significantly, radular morphology shows no change at the node where kinematics become stereoglossate. However, acquisition of stereoglossy in the Patellogastropoda is correlated with the structural dissociation of the subradular membrane and underlying cartilages. Correlation is not causality, so we present a biomechanical model explaining the structural conditions necessary for the plesiomorphic kinematic state (flexoglossy). Our model suggests that plesiomorphically the radular teeth must flex laterally as they pass over the bending plane as a result of the mechanical restrictions in the flexible but inelastic subradular membrane and close association between subradular membrane and cartilages. Relating this model to the specific character states of the clades, we conclude that lack of flexure in patellogastropods is caused by the dissociation of the subradular membrane and cartilage supports. J. Morphol. 241:175–195, 1999. © 1999 Wiley‐Liss, Inc.     

Neurogenic contractile activity of the penis retractor muscle of Helix pomatia L.

Using convential mechanical and electromyographic recording methods 2 distinct types of neurogenically elicited activity can be observed in the penis retractor muslce (PRM) of Helix pomatia: (1) rhythmic, phasic contractions correlated with single or a few compound action potentials and (2) intervening, strong, prolonged contractions accompanied by sustained, high frequency electrical muscle activity. The 2 distinct types of muscle activity which seem to play a part in the normal behaviour of the PRM in the intact animal are mediated by both the central nervous system and peripheral neurons. While central neuronal structures are involved in causing the strong, prolonged contractions, the phasic activity is initiated by peripheral neuronal structures located at the proximal end of the PRM. There is evidence that the transmission of the excitation at the neuromuscular level of central and peripheral origin is mediated by ACh.     

Anatomical correlates of venom production in Conus californicus

Like all members of the genus, Conus californicus has a specialized venom apparatus, including a modified radular tooth, with which it injects paralyzing venom into its prey. In this paper the venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy. The general anatomy of the venom apparatus resembles that in other members of the genus, but several features are described that have not been previously reported for other species. The proximal (posterior) quarter of the venom duct is composed of a complex epithelium that may be specialized for active transport rather than secretion. The distal portion of the duct is composed of a different type of epithelium, suggestive of holocrine secretion, and the cells display prominent intracellular granules of at least two types. Similar granules fill the lumen of the duct. The passageway between the lumen of the venom duct and pharynx is a flattened branching channel that narrows to a width of 10 micro m and is lined by a unique cell type of unknown function. Granular material similar to that in the venom duct was also found in the lumen of individual teeth within the radular sac. Mass spectrometry (MALDI-TOF) demonstrated the presence of putative peptides in material derived from the tooth lumen, and all of the more prominent species were also evident in the anterior venom duct. Radular teeth thus appear to be loaded with peptide toxins while they are still in the radular sac.     

Comparative lectin-histochemistry on the pre-epithelial mucus layer in the distal colon of conventional and germ-free rats

The mucin composition of the rat distal colonic pre-epithelial mucus layer (PML) was studied by lectin histochemistry in conventional (CV), and germ-free (GF) rats to define effects exerted by the gut flora. No peanut agglutinin (PNA) binding was observed in the PML of GF rats, while the PML of their CV counterparts showed a considerable PNA linkage, indicating terminal Gal-beta1,3-GalNAc residues. Soybean agglutinin (SBA) and Helix pomatia agglutinin (HPA) stained the PML mucins in CV and in GF rats, indicating terminal GalNAc moieties. A quantitative difference in the Limax flavus agglutinin (LFA) binding capacity was found between CV and GF rats, indicating terminal sialic acid moieties: the staining intensity of bound LFA/ FiTC was higher in CV rats than in GF rats. No linkage of Datura stramonium agglutinin (DSA) and of wheat germ agglutinin (WGA) was found in the PML of GF rats, indicating the absence of terminal GlcNAc, while in CV rats, a clearly marked border was visible next to the luminal content as a "nipple edge" when stained with DSA or WGA. Canavalia ensiformis agglutinin (ConA), indicative for branched mannose, stained PML mucins and goblet cell mucins of GF rat distal colon. In CV rats, both locations were free of ConA binding sites. These results suggest degrading effects, exerted by the gut flora on the rat colonic pre-epithelial mucus layer.