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This chapter discusses the carbohydrate metabolism of gastropods. D-glucose is the most common monosaccharide and has been detected in the blood and tissues of many gastropods. Other sugars also occur, in particular D-galactose, that are either stereoisomers or derivatives of monosaccharides. Glycogen and galactogen are the main storage polysaccharides. Whereas glycogen occurs in most gastropod tissues and serves as a general energy source, galactogen is generally confined to the albumen gland and eggs of adult pulmonate snails and the albumen gland region of the palliai oviduct of some prosobranchs, and it serves as a specialized energy source in reproduction. Glycogen is a branched-chain homopolysaccharide of D-glucose in α-1,4 linkage with branches joined through α-1,6 linkages. The degree of branching and the length of the outer branches of the glycogen from the snail Biomphalaria glabrata are similar to those of glycogens from other animal sources.

Carbohydrate metabolism of gastropods

Biogenic monoamines in the freshwater snail, Biomphalaria glabrata: influence of infection by the human blood fluke, Schistosoma mansoni.

Structural elucidation and immune-enhancing activity of peculiar polysaccharides fractioned from marine clam Meretrix meretrix (Linnaeus).

The localization and distribution of the serotoninergic and peptidergic elements of the nervous system of larval Schistosoma mansoni have been investigated using an indirect immunofluorescence technique in conjunction with confocal scanning laser microscopy (CSLM). A range of antisera was used, raised to the biogenic amine, 5-hydroxytryptamine (5-HT, or serotonin), the vertebrate peptides pancreatic polypeptide (PP), peptide YY (PYY) and neuropeptide Y (NPY) and to the native invertebrate peptide, FMRFamide; all these antisera were shown previously to be immunopositive in the adult worm. No immunoreactivity to 5-HT was detected in any of the larval stages, but both miracidia and cercariae were consistently immunoreactive to all 4 peptides. The peptidergic nervous system of the miracidium is relatively simple, taking the form of a central neural mass with associated paired anterior and posterior nerve tracts. The cercarial peptidergic nervous system comprises a central commissure joining paired anterior ganglia, from which emanate paired dorsal and ventral nerve tracts, which terminate at the body/tail junction. The excretory bladder region of the tail is also immunoreactive for the 4 peptides, and a fine pair of nerve tracts extends the length of the tail shaft. Immunoreactive nerve cell bodies are also evident in the midbody region of the intrasprocystic cercariae, these same structures being immunoreactive for the neuronal marker, neurone-specific enolase (NSE). The organization of the larval peptidergic nervous system is compared to that of the cholinergic nervous system and contrasted with the peptidergic system in the adult worm. The absence of immunoreactivity to 5-HT is discussed in relation to the proposed development of the aminergic nervous system upon establishment in the definitive host.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0031182000063277

A confocal scanning laser microscope study of the peptidergic and serotoninergic components of the nervous system in larval Schistosoma mansoni

The life of the schistosome miracidium begins upon its complete embryonation within the egg, some time after being produced by the female parent in the mammalian host. Its first active function in life occurs in the process of hatching; the various environmental factors that condition this process have been described and reviewed recently by Bair and Etges,l but the contribution of the miracidium to the process remains poorly understood. The existence of an unidentified hatching factor within schistosome eggs, as suggested by Kusel,2 remains hypothetical. The posthatching behavior of schistosome miracidia has been more thoroughly studied; the work of Wright: Chernin and Dunavan: MacInnis: Etges and Decker,6 among many others,T-13 serves to show that considerable attention has been given to this phase of the life cycle. Briefly stated, previous studies indicate that hatched miracidia remain infective to their molluscan host for 8-12 hr, swim in a smooth spiral path in a “ranging” phase of host location, and increase their turning rate dramatically when stimulated by chemical agents emitted by snails and other organisms (termed the “excited state”). Excited miracidia thus remain relatively close to the source of chemical stimulation and, upon chance contact with a surface, begin to rotate their bodies vigorously while maintaining contact with the surface by the anterior terebratorium. Secretions of apical glands augment the boring movements and finally permit physical entry of the entire ciliated miracidial body. Should the surface penetrated be a susceptible snail‘s tegument, the miracidia will metamorphose into a mother sporocyst; otherwise, the miracidia die. Host location, therefore, appears to be the result of characteristic ciliary locomotion of miracidia, conditioned by their orientation to various physical stimuli (light, gravity, contact, and so on), until some chemical substance stimulates them to exhibit excited locomotor behavior; Chernin* coined the term “miraxone” to refer to the undefined complex of substances emitted by host snails that produce this effect. Though some earlier

Behavioral and developmental physiology of schistosome larvae as related to their molluscan hosts.

5-hydroxytryptamine (5-HT) and dopamine (DA) have been isolated and identified in the tissues of the snail, Biomphalaria glabrata. The brain contained approximately 15 tAg, the cephalopedal region 2 ,ug, and the mantle region 1 jug of 5-HT per gram of fresh weight. The concentrations of DA in the brain and the cephalopedal region were of the same order of magnitude as those of 5-HT, and 5 times lower in the mantle region. Neither 5-HT nor DA were detectable in the hepatopancreas-ovotestis region. The distribution of these 2 biogenic amines was also studied by the histochemical fluorescence technique of Falck and Owman (1965). Only green (catecholamine) fluorescent neurons were observed in the buccal ganglia; they are tentatively considered as DA neurons. Neuropile areas probably contain a mixture of 5-HT and DA. The nerve fibers emanating from the ganglia predominantly contain DA. With the exception of the buccal ganglia, 5-HT neurons were more numerous and comparatively large in the other ganglia. Green catecholamine fluorescence was detected in areas nearest to the epithelium of the foot. The presence of two biogenic amines, 5hydroxytryptamine (5-HT) and dopamine (DA), has been demonstrated in a variety of gastropods (Carpenter et al., 1971; Cottrell and Maser, 1967; Dahl et al., 1966; Gerschenfeld, 1971; Sweeney, 1963; Twarog, 1968; Walker et al., 1968; Kerkut and Cottrell, 1963; Kerkut et al., 1966). These amines are localized predominantly in the nervous system of this class of animals, and evidence for their function as neural transmitters has been reported (Carpenter et al., 1971; Dahl et al., 1966; Gerschenfeld, 1971; Gerschenfeld and Stefani, 1968; Sweeney, 1963; Twarog, 1968). The gastropod Biomphalaria glabrata is an intermediate host of the parasitic trematode, Schistosoma mansoni. 5-HT and norepinephrine have been identified as constituents of the adult form of this parasite (Bennett et al., 1969; Bennett and Bueding, 1971). Furthermore, recent evidence indicates the presence of dopamine receptors in the longitudinal muscle of adult S. mansoni, a function of 5-HT as an excitatory neuromuscular transmitter in the parasite. (T. Tomosky et al., 1974), and a high affinity uptake Received for publication 2 November 1973. * This investigation was supported by NIH training grant AI-149, and research grants AI-03515 and AI-08022. t Present address: National Institute of Child Health and Human Development, Gerontology Research Center, Baltimore City Hospitals, Baltimore, Maryland 21224. mechanism for 5-HT providing a neurotransmitter which the adult worm cannot synthesize de novo. The question arises whether biogenic amines play a role in the development of the larval stages of schistosomes in their intermediate host; this, in turn, requires information about the distribution of these amines in B. glabrata. The present study is concerned with this problem. MATERIALS AND METHODS Biomphalaria glabrata with shell diameters of 9 to 14 mm were used. Determination of biogenic amines The tissues were dissected, quickly frozen in liquid nitrogen, and homogenized in a solution containing perchloric acid (0.4 M), ascorbic acid (10 mM), and EDTA (5.4 mM) (Anden and Magnusson, 1967) in a motor-driven all-glass homogenizer at 4 C. One ml of solution was used per 100 mg tissue. The mixture was transferred into a centrifuge tube and, after washing of the container with a measured volume of the same solution, was centrifuged at 10,000 g for 15 min at 4 C. The pH of the supernatant solution was adjusted to 5 to 6 by addition of 0.5 ml of 2 M potassium phosphate buffer (pH 6.5) and a measured volume of 2 N KOH. After centrifugation (10,000 g, 15 min, 4 C) the supernatant solution was used for the determinations of 5-HT and of DA.

5-Hydroxytryptamine and dopamine in Biomphalaria glabrata.

1. 1. The distribution of glycogen in different tissues of the snail, Biomphalaria glabrata was determined; the cephalopedal region contained 15–17 mg, the mantle region 23–29 mg, the hepatopancreas 31–45 mg, and the ovotestis 50 mg of glycogen/g wet wt. 2. 2. There was a significant decrease in the glycogen content in the cephalopedal region after incubating the snails with 5-hydroxytryptamine (4 × 10−5 M) in vivo. 3. 3. Enzymatic degradation of glycogen from different tissues revealed that the degree of branching was 9% of the total glucosyl residues, and the length of outer branches was about 40% of the total glucosyl residues. 4. 4. There was an active form of glycogen phosphorylase in the cephalopedal region and the mantle region. Phosphorylase in the hepatopancreas was generally inactive, but could be activated by an endogenous phosphorylase kinase. 5. 5. Glycogen synthetase of the snail tissues required glucose-6-phosphate to be active.

Glycogen metabolism in the snail, Biomphalaria glabrata.

Acetylcholinesterase (AChE) was demonstrated histochemically in the nervous system of the snail, Biomphalaria glabrata.AChE activity is localized in two distinct regions in each buccal ganglion.AChE activity is high in the neuropiles of cerebral and pedal ganglia; in a few instances, AChE activity is associated with axons in the neuropiles. In the pleural, visceral and parietal ganglia, AChE activity seems to be highly localized structurally.AChE activity of each ganglion is in communication with one another via connectives and commissures.AChE activity is distributed throughout the motor nerves of the snail foot, and is not exclusively associated with membranes, but can be observed also in the entire cross sections of the axons.

Peter K. Chiang

Papers

5-Hydroxytryptamine and dopamine in Biomphalaria glabrata.

Glycogen metabolism in the snail, Biomphalaria glabrata.

Histochemical distribution of acetylcholinesterase in the nervous system of the snail, Biomphalaria glabrata.