Principles of the structural organization of the chemosensory systems of freshwater gastropod mollusks

Abstract

Gastropod mollusks are a classical model system for current neurobiologists, because of their relatively simple nervous systems, the fact that neurons can be identified, and because of the generality of the fundamental principles of the organization of their nervous and sensory systems and the analogous systems of more highly organized animals. Studies of the structural organization of the sensory systems of gastropods are important both for the comparative evolutionary aspect of understanding the major principles of receptor apparatus development and for modeling reception processes.Chemoreception is a leading sensory modality in mollusks. Gastropods use their chemosensory systems to orientate themselves in space, search for food and a place to live, and for other aspects of their lives [20,22,23,26,38,40]. Chemoreceptor cells are located in gastropods in the same way as mechanoreceptor and shade cells--in the skin of virtually the whole surface of the body, head, and mantle [22,28,36]. In addition, most species have more or less advanced chemosensory organs--cephalic antennae, lips, mouth, and osphradia. Electrophysiological and behavioral investigations indicate that the cephalic antennae are chemosensors predominantly for distant stimuli, while the lips and mouth are taste organs, and the osphradia, located in the 1Department of General Physiology and Laboratory of Nervous System Physiology (Director Academician of the Russian Academy of Sciences, Professor A.

Regeneration of the visual system in gastropods (Mollusca)

“…In both species, bodies of neurons and their axons are found in all of the ganglia of the snails' nervous system, with the exception of the buccal ganglia. We, therefore, feel confident to conclude that the central visual projections in pulmonate snails are more extensive than reported in previous investigations (Zaitzeva et al 1982;Zaitzeva 1992). Axons from the eye near the optic nerve's input form a bundle of many fine branches (optic neuropil) that is very difficult to observe and to distinguish from surrounding tissue un-der the light microscope.…”

“…As for pulmonate species, in Lymnaea stagnalis (LINNAEUS, 1758) and Helix pomatia (LINNAEUS, 1758), central visual projections (Fig. 3) were identified by anterograde and retrograde transport of cobalt/nickel chloride (Tyrer & Bell 1974;Sonetti et al 1982) only in the cerebral ganglia, according to Zaitzeva et al (1982) and Zaitzeva (1992). Afferent (sensory) projections from the eye form a bud of fine axons in the region, where the optic nerve enters the ipsilateral cerebral ganglion, and then send two branches through the commissure to the contralateral ganglion.…”

“…Additionally, numerous afferent projections from the tentacles, eyes, statosysts, lips, mouth, and head skin lead to the metacerebrum (for the position of the latter, see Fig. 1), so that this structure most likely performs the function of sensory integration in pulmonates (Zaitzeva 1992;Bernocchi et al 1998).…”

“…Although studies on the regeneration of the peripheral visual system in gastropods commenced many years ago (e.g., Eakin & Brandenburger 1967;Eakin & Ferlatte 1973;Scarsso & Pellegrino de Iraldi 1973), specifically with regard to the central visual structures, we still know rather little. Investigations in this field have focused on just a handful of species (Alkon 1973;Rossner 1974;Moffett & Austin 1981;Zaitzeva et al 1982;Zaitzeva 1992;Zhukov & Tuchina 2008).…”

“…Among heterobranch gastropods, pulmonates such as Helix have a CNS that is more concentrated than what is typically found in most opisthobranchs. But the opisthobranchs Hermissenda crassicornis (E schscholtz , 1831) and Coryphella rufibranchialis (J ohnston , 1832) (Alkon 1973; Zaitzeva 1999) possess a special structure—the peripheral optic ganglion—that functions as the way‐station for processing of visual information from the eye to the brain. It usually contains 14 neurons in the cortex and a small neuropil inside (Fig.…”