Ultrastructural analysis of the dorsal body gland of the terrestrial snail Megalobulimus abbreviatus (Becquaert, 1948)

Abstract

The ultrastructure of the reproductive gland, dorsal body (DB), of Megalobulimus abbreviatus was analysed. Electron microscope immunohistochemistry was used to detect FMRFamide-like peptides in the nerve endings within this gland. Nerve backfilling was used in an attempt to identify the neurons involved in this innervation. In M. abbreviatus, the DB has a uniform appearance throughout their supraesophageal and subesophageal portions. Dorsal body cells have several features in common with steroid-secreting gland cells, such as the presence of many lipid droplets, numerous mitochondria with tubular cristae and a developed smooth endoplasmic reticulum cisternae. Throughout the DB in M. abbreviatus numerous axonal endings were seen to be in contact with the DB cells exhibiting a synapticlike structure. The axon terminals contained numerous electron-dense and scanty electron-lucid vesicles. In addition, the DB nerve endings exhibited FMRFamide immunoreactive vesicles. Injection of neural tracer into the DB yielded retrograde labelling of neurons in the metacerebrum lobe of the cerebral ganglia and in the parietal ganglia of the subesophageal ganglia complex. The possibility that some of these retrograde-labelled neurons might be FMRFamidelike neurons that may represent a neural control to the DB in M. abbreviatus is discussed.Keywords: mollusc, endocrine gland, FMRFamide, cerebral ganglia, reproductive control. Análise ultraestrutural da glândula corpo dorsal do caracol terrestre Megalobulimus abbreviatus (Becquaert, 1948) ResumoFoi analisada a ultraestrutura da glândula reprodutiva corpo dorsal (CD) de Megalobulimus abbreviatus. Imunoistoquímica para microscopia eletrônica foi utilizada para detectar peptídeos relacionados ao tetrapeptídeo FMRFamida nas terminações axonais existentes nessa glândula. Foi utilizada marcação neuronal retrógada com o intuito de localizar os neurônios envolvidos nesta inervação. O CD de M. abbreviatus possui um aspecto uniforme em toda sua extensão, tanto na porção supraesofágica como subesofágica. As células do CD possuem várias características de glândulas esteroidogênicas, tais como a presença de inúmeras gotículas lipídicas, numerosas mitocôndrias com cristas tubulares e cisternas bem desenvolvidas de retículo endoplasmático liso. Por toda a extensão do CD de M. abbreviatus foram encontradas numerosas terminações axonais fazendo contatos estruturalmente semelhantes a sinapses com as células do CD. As terminações axonais continham grande número de vesículas eletrodensas e esparsas vesículas eletrolúcidas. As terminações axonais no CD apresentavam vesículas com conteúdo imunorreativo à FMRFamida. A injeção de traçador neural no CD resultou em marcação retrógrada de neurônios no metacérebro dos gânglios cerebrais e nos gânglios parietais do complexo ganglionar subesofágico de M. abbreviatus. É discutida a possibilidade de que estes neurônios identificados por marcação retrógrada possam representar a via de controle neural do CD de M. abbreviatus, cujo mediador químico seria um n...

Invaginating Presynaptic Terminals in Neuromuscular Junctions, Photoreceptor Terminals, and Other Synapses of Animals

“…Most studies that we have found on invertebrate endocrine cell innervation do not show invaginating or distinctively indenting terminals. The dorsal body gland of the snail, Megalobulimus abbreviatus, adjacent to the brain, is an endocrine gland that secretes a female reproductive hormone (Moraes et al 2010). Axon terminals often appear to be deeply indenting to fully invaginating in the gland cells; in the latter case, the cell extends processes that surround the terminal.…”

“… Indented ≈ presynaptic processes run in a deep pit or groove; invaginated ≈ presynaptic varicosity is embedded within the postsynaptic process. CNS, central nervous system; en, endocrine gland cells; ex, exocrine gland cells; NMJs, neuromuscular junctions; SSR, subsynaptic reticulum; SJFs, subjunctional folds; dash indicates no information found 1 Pavans de Ceccatty (1966) 2 Horridge (1965) 3 Hernandez-Nicaise (1973) 4 Spencer (1979) 5 Westfall et al (1971) 6 Holtmann and Thurm (2001a, b) 7 Pan (1980) 8 Petralia et al (2015) 9 Reger (1965) 10 Clément (1977) 11 Duvert and Barets (1983) 12 Lacalli (1990) 13 Reger (1969), Rosenbluth (1973), Yaksta-Sauerland and Coggeshall (1973) 14 Graziadei (1966), Barber and Graziadei (1967), Rogers (1969), Økland (1980), Elekes and Ude (1994) 15 Ducros (1972), Elekes and Ude (1994) 16 Moraes et al (2010) 17 Dilly et al (1963), Case et al (1972), Cohen (1973), Haghighat et al (1984) 18 Castejón and Villegas (1964) 19 Melamed and Trujillo-Cenoz (1971), Smith (1971), Fourtner and Sherman (1973), Sherman (1973) 20 Hart et al (1980) 21 Lang (1972), Sherman and Fourtner (1972), Fourtner and Sherman (1973) 22 Filimonova and Amosova (2015) 23 Oberdorfer (1977) …”

Occurrence of Cruzia tentaculata Larvae in the Land Snail Megalobulimus abbreviatus—Influence of Natural Parasite Load on Snail Physiology

“…However, one should not rule out the possibility that the impairment of the reproductive functions performed by the albumen gland and ovotestis is due to secondary effects of the larvae presence into the nerve ring. The development and maintenance of the albumen and ovotestis depend on stimulating hormone from the dorsal body gland located close to the cerebral ganglia of M. abbreviatus (Moraes et al, 2010). The dorsal body of M. abbreviatus is highly vascularized and with a high cellular content of lipids and glycogen during the reproductive period (Zancan and Achaval, 1995).…”

“…The dorsal body of M. abbreviatus is highly vascularized and with a high cellular content of lipids and glycogen during the reproductive period (Zancan and Achaval, 1995). This gland is under the control of neuropeptides from the cerebral and right parietal ganglia (Moraes et al, 2010), and the frequent location of C. tentaculata larvae in the central nervous ganglia could interfere with the reproductive control carried out by this neuroendocrine complex of M. abbreviatus . The interference with the reproduction of Lymnaea stagnalis by Trichobilharzia ocellata cercariae could be through the neuroendocrine control functions of the cerebral ganglia of L. stagnalis (Schallig et al, 1991; de Jong-Brink et al, 1999; Hoek et al, 2005).…”