Transmitter identification in neurons involved in male copulation behavior inLymnaea stagnalis

FMRF-NH2 -related neuropeptides in Biomphalaria spp., intermediate hosts for schistosomiasis: Precursor organization and immunohistochemical localization

Freshwater snails of the genus Biomphalaria serve as intermediate hosts for the digenetic trematode Schistosoma mansoni, the etiological agent for the most widespread form of intestinal schistosomiasis. As neuropeptide signaling in host snails can be altered by trematode infection, a neural transcriptomics approach was undertaken to identify peptide precursors in Biomphalaria glabrata, the major intermediate host for S. mansoni in the Western Hemisphere. Three transcripts that encode peptides belonging to the FMRF-NH2 -related peptide (FaRP) family were identified in B. glabrata. One transcript encoded a precursor polypeptide (Bgl-FaRP1; 292 amino acids) that included eight copies of the tetrapeptide FMRF-NH2 and single copies of FIRF-NH2 , FLRF-NH2 , and pQFYRI-NH2 . The second transcript encoded a precursor (Bgl-FaRP2; 347 amino acids) that comprised 14 copies of the heptapeptide GDPFLRF-NH2 and 1 copy of SKPYMRF-NH2 . The precursor encoded by the third transcript (Bgl-FaRP3; 287 amino acids) recapitulated Bgl-FaRP2 but lacked the full SKPYMRF-NH2 peptide. The three precursors shared a common signal peptide, suggesting a genomic organization described previously in gastropods. Immunohistochemical studies were performed on the nervous systems of B. glabrata and B. alexandrina, a major intermediate host for S. mansoni in Egypt. FMRF-NH2 -like immunoreactive (FMRF-NH2 -li) neurons were located in regions of the central nervous system associated with reproduction, feeding, and cardiorespiration. Antisera raised against non-FMRF-NH2 peptides present in the tetrapeptide and heptapeptide precursors labeled independent subsets of the FMRF-NH2 -li neurons. This study supports the participation of FMRF-NH2 -related neuropeptides in the regulation of vital physiological and behavioral systems that are altered by parasitism in Biomphalaria.

An immunohistochemical analysis of peptidergic neurons apparently associated with reproduction and growth in Biomphalaria alexandrina

Peptide hormones and neurotransmitters involved in reproduction and growth have been studied extensively in certain gastropod molluscs, such as Lymnaea stagnalis and Aplysia californica. The present study employs antisera that have been used to study peptidergic neurons in those species to probe the central nervous system of another gastropod, Biomphalaria alexandrina, an intermediate host of the parasitic trematode that causes schistosomiasis in humans. Whole mount preparations of central ganglia were stained immunohistochemically, and several populations of neurons appeared to be homologous to those forming the neuroendocrine axis that has been previously described in L. stagnalis. These cells include the caudodorsal cells and the light green and canopy cells, which produce hormones that regulate ovulation and growth, respectively. Other populations of cells containing APGWamide, FMRFamide and/or related peptides are consistent with ones that innervate the penis in L. stagnalis and other gastropods. Identification of neurons that might be responsible for the control of reproduction and growth in Biomphalaria provides an important initial step toward the development of novel methods of disease control and pest management directed toward reducing snail populations.

Single-cell analysis of peptide expression and electrophysiology of right parietal neurons involved in male copulation behavior of a simultaneous hermaphrodite

Male copulation is a complex behavior that requires coordinated communication between the nervous system and the peripheral reproductive organs involved in mating. In hermaphroditic animals, such as the freshwater snail Lymnaea stagnalis, this complexity increases since the animal can behave both as male and female. The performance of the sexual role as a male is coordinated via a neuronal communication regulated by many peptidergic neurons, clustered in the cerebral and pedal ganglia and dispersed in the pleural and parietal ganglia. By combining single-cell matrix-assisted laser mass spectrometry with retrograde staining and electrophysiology, we analyzed neuropeptide expression of single neurons of the right parietal ganglion and their axonal projections into the penial nerve. Based on the neuropeptide profile of these neurons, we were able to reconstruct a chemical map of the right parietal ganglion revealing a striking correlation with the earlier electrophysiological and neuroanatomical studies. Neurons can be divided into two main groups: (i) neurons that express heptapeptides and (ii) neurons that do not. The neuronal projection of the different neurons into the penial nerve reveals a pattern where (spontaneous) activity is related to branching pattern. This heterogeneity in both neurochemical anatomy and branching pattern of the parietal neurons reflects the complexity of the peptidergic neurotransmission involved in the regulation of male mating behavior in this simultaneous hermaphrodite.

A 5-HT1A-like receptor is involved in the regulation of the embryonic rotation of Lymnaea stagnalis L

Cilia driven rotation of the pond snail Lymnaea stagnalis embryos is regulated by serotonin (5-HT). In the present study, physiological and biochemical assays were used to identify the 5-HT receptor type involved in rotation. The 5-HTergic agonists applied stimulated the rotation by 180-400% and their rank order potency was as follows: LSD>5-HT>8-OH-DPAT>WB4101>>5-CT. The applied antagonists, spiperone, propranalol and mianserin inhibited the 5-HT or 8-OH-DPAT stimulated rotation of the embryos by 50-70%. (3)H-5-HT was bound specifically to the washed pellet of the embryo homogenates. The specific binding of (3)H-5-HT was saturable and showed a single, high affinity binding site with K(d) 7.36 nM and B(max) 221 fmol/mg pellet values. This is the first report demonstrating the high affinity binding of (3)H-5-HT to the native receptor in molluscs. All of the pharmacons that stimulated the rotation or inhibited the 5-HT or 8-OH-DPAT evoked stimulation displaced effectively the binding of (3)H-5-HT. 5-HT resulted in the inhibition of forskolin stimulated cAMP accumulation, showing that 5-HT is negatively coupled to adenylate cyclase. Our results suggest that in the 5-HTergic regulation of the embryonic rotation in L. stagnalis a 5-HT(1A)-like receptor of the vertebrate type is involved.

Molluscs as multidisciplinary models in environment toxicology

The primary goal of this paper is to stimulate discussion and promote the use of mollusc models and multidisciplinary research approaches in the field of environmental toxicology. Molluscs are effective models because they are ubiquitous, have highly conserved control and regulatory pathways that are often homologous to vertebrate systems, and are extremely sensitive to anthropogenic inputs. We have attempted to provide initial references as an avenue into the literature and as a means for researchers to expand their thoughts to regions outside of their own area of expertise. The authors are particularly interested in developing multidisciplinary international collaborative efforts.

Target-dependent differentiation and development of molluscan neurons and neuroendocrine cells: use of parasitisation as a tool

Specimens of the freshwater snail Lymnaea stagnalis infected with the schistosome parasite Trichobilharzia ocellata show a strongly inhibited development of their reproductive tract. We hypothesised that the effects of the underdevelopment of targets are reflected at the level of the neuronal development of (i) the motor neurons innervating the male copulation organ and (ii) neuroendocrine cells regulating the gonad. We determined the state of neuronal development by measuring cell number, cell size and neuropeptide gene expression. Our results show that the neuronal development of both copulation controlling anterior lobe motor neurons of the right cerebral ganglion and neuroendocrine caudodorsal cells, which produce neuropeptides regulating ovulation, egg laying and accompanying behaviour, are affected in parasitised animals in which their respective target organs were not developed. The cell bodies were smaller and fewer cells were found to express neuropeptide genes compared to those in non-parasitised animals. These effects were not observed in the appropriate controls. Backfills and lesions of the penis nerve have shown that the inhibited development of central motor neurons in parasitised snails is target dependent; neighbouring neurons that have no connection with the male copulation organ are not affected. Our data suggest that this effect is established by target-derived neurotrophic factors that need this connection for being transported to the innervating motor neurons. We propose that the effect on the neuroendocrine caudodorsal cells is mediated by a humoral factor, since they have no known connection with their target. We have shown that the size and gene expression of motor neurons controlling copulation behaviour in the pond snail Lymnaea stagnalis are related to the size of their target, the copulation organ, and depend on the connection with this target.

Effects of the serotonin receptor ligand methiothepin on reproductive behavior of the freshwater snail Biomphalaria glabrata: reduction of egg laying and induction of penile erection

The biogenic monoamine serotonin (5-HT) has been reported to enhance egg laying in the freshwater gastropod Biomphalaria glabrata, an intermediate host for human blood flukes. Methiothepin, a vertebrate 5-HT(1/2) receptor ligand which binds with high affinity to a 5-HT receptor (5-HTlym) in Lymnaea stagnalis was tested for its ability to block egg laying in B. glabrata as a possible target for snail control. A single 30-min application of methiothepin (1 microM) was sufficient to prevent egg laying for over 1 week and did so in a dose-dependent fashion. Furthermore, single applications of methiothepin (1 microM and 10 microM) induced penile erection in a high percentage of snails tested. Latency to erection was long (at least 8 hr), but the duration of erection was long-lasting (up to 48 hr). Despite the erections, methiothepin-treated snails failed to achieve copulations. The pharmacological effect of methiothepin on both male and female reproductive processes is similar to that produced in other molluscs, and points to the gene for the 5-HT receptor mediating or modulating both or either processes as a potential target of snail control strategies. J. Exp. Zool. 289:202-207, 2001.

Fulicin regulates the female reproductive organs of the snail, Achatina fulica

Fulicin is a D-amino acid-containing neuropeptide that has been thought to control male copulatory behavior in the land snail, Achatina fulica. In the present study, we demonstrated that the vagina and the oviduct of Achatina were densely innervated by fulicin-like immunoreactive neuronal fibers. We confirmed that fulicin was actually present in the vagina by mass spectrometry. Furthermore, fulicin showed a profound excitatory effect on contractions of the vagina and the oviduct. These results suggest that fulicin controls female egg-laying behavior as an excitatory neuropeptide regulating the female reproductive organs of the snail.