Distribution of sensorin immunoreactivity in the central nervous system ofHelix pomatia: Functional aspects

Invertebrate neurons as a simple model to study the hyperexcitable state of epileptic disorders in single cells, monosynaptic connections, and polysynaptic circuits

Epilepsy is a neurological disorder characterized by a hyperexcitable state in neurons from different brain regions. Much is unknown about epilepsy and seizures development, depicting a growing field of research. Animal models have provided important clues about the underlying mechanisms of seizure-generating neuronal circuits. Mammalian complexity still makes it difficult to define some principles of nervous system function, and non-mammalian models have played pivotal roles depending on the research question at hand. Mollusks and the Helix land snail have been used to study epileptic-like behavior in neurons. Neurons from these organisms confer advantages as single-cell identification, isolation, and culture, either as single cells or as physiological relevant monosynaptic or polysynaptic circuits, together with amenability to different protocols and treatments. This review's purpose consists in presenting relevant papers in order to gain a better understanding of Helix neurons, their characteristics, uses, and capabilities for studying the fundamental mechanisms of epileptic disorders and their treatment, to facilitate their more expansive use in epilepsy research.

Characterisation of Reproduction-Associated Genes and Peptides in the Pest Land Snail, Theba pisana

Increased understanding of the molecular components involved in reproduction may assist in understanding the evolutionary adaptations used by animals, including hermaphrodites, to produce offspring and retain a continuation of their lineage. In this study, we focus on the Mediterranean snail, Theba pisana, a hermaphroditic land snail that has become a highly invasive pest species within agricultural areas throughout the world. Our analysis of T. pisana CNS tissue has revealed gene transcripts encoding molluscan reproduction-associated proteins including APGWamide, gonadotropin-releasing hormone (GnRH) and an egg-laying hormone (ELH). ELH isoform 1 (ELH1) is known to be a potent reproductive peptide hormone involved in ovulation and egg-laying in some aquatic molluscs. Two other non-CNS ELH isoforms were also present in T. pisana (Tpi-ELH2 and Tpi-ELH3) within the snail dart sac and mucous glands. Bioactivity of a synthetic ELH1 on sexually mature T. pisana was confirmed through bioassay, with snails showing ELH1-induced egg-laying behaviours, including soil burrowing and oviposition. In summary, this study presents a detailed molecular analysis of reproductive neuropeptide genes in a land snail and provides a foundation for understanding ELH function.

Characterisation of two conopressin precursor isoforms in the land snail, Theba pisana

Increased understanding of the molecular components involved in mollusc reproduction may assist in understanding the evolutionary adaptations used by animals, including hermaphrodites, to produce offspring. The neuropeptide conopressin, a member of the vasopressin/oxytocin-like peptide family, can modulate various reproductive activities in invertebrates. In this study, we used the hermaphroditic land snail, Theba pisana, to investigate the presence and tissue-specific distribution of a conopressin gene. Our transcriptomic analysis of T. pisana CNS sheath tissue has revealed two conopressin gene transcripts (Tpi-conopressin-1 and Tpi-conopressin-2), each encoding for precursors containing an identical conopressin nonapeptide and a variable neurophysin. T. pisana conopressins share high identity with other land snails and slugs, as well as other mollusc and vertebrate vasopressin/oxytocin, supported by phylogenetic analysis. Conserved residues in the T. pisana neurophysin are important for peptide binding, and we present molecular dynamic models demonstrating the most likely stable structure of the Tpi-conopressin-1 peptide when associated with neurophysin. RT-PCR shows that Tpi-conopressin-1 is additionally expressed in reproductive tissues, including the dart sac, where abundant spatial expression throughout the sac region is found; this implies a role in 'love' dart synthesis or dart injection during mating. The presence of a conopressin receptor in the CNS sheath indicates CNS neural excitation. In summary, this study represents a detailed molecular analysis of conopressin in a land snail.

Pentylenetetrazol-induced epileptiform activity affects basal synaptic transmission and short-term plasticity in monosynaptic connections

Epileptic activity is generally induced in experimental models by local application of epileptogenic drugs, including pentylenetetrazol (PTZ), widely used on both vertebrate and invertebrate neurons. Despite the high prevalence of this neurological disorder and the extensive research on it, the cellular and molecular mechanisms underlying epileptogenesis still remain unclear. In this work, we examined PTZ-induced neuronal changes in Helix monosynaptic circuits formed in vitro, as a simpler experimental model to investigate the effects of epileptiform activity on both basal release and post-tetanic potentiation (PTP), a form of short-term plasticity. We observed a significant enhancement of basal synaptic strength, with kinetics resembling those of previously described use-dependent forms of plasticity, determined by changes in estimated quantal parameters, such as the readily releasable pool and the release probability. Moreover, these neurons exhibited a strong reduction in PTP expression and in its decay time constant, suggesting an impairment in the dynamic reorganization of synaptic vesicle pools following prolonged stimulation of synaptic transmission. In order to explain this imbalance, we determined whether epileptic activity is related to the phosphorylation level of synapsin, which is known to modulate synaptic plasticity. Using western blot and immunocytochemical staining we found a PTZ-dependent increase in synapsin phosphorylation at both PKA/CaMKI/IV and MAPK/Erk sites, both of which are important for modulating synaptic plasticity. Taken together, our findings suggest that prolonged epileptiform activity leads to an increase in the synapsin phosphorylation status, thereby contributing to an alteration of synaptic strength in both basal condition and tetanus-induced potentiation.

Leaf mechanical properties modulate feeding movements and ingestive success of the pond snail, Lymnaea stagnalis

We examined the mechanical properties of Butterhead and Iceberg lettuce leaves, and the rate at which they were eaten by the pond snail Lymnaea stagnalis. The outer part of Butterhead leaves were less robust than either the inner Butterhead or outer Iceberg leaves (Young's modulus 2.8, 5.2, 7.7 MPa respectively; ultimate tensile stress 0.18, 0.34 0.51 MPa) which were also thicker. Snails ingested inner Butterhead and Iceberg strips more slowly (36 and 32%) than outer Butterhead. This was not due to differences in latency to first bite or biting rate. Rather, the drop was due to a decrease in the proportion of successful bites (inner Butterhead 84%; Iceberg 86%), to a shorter length ingested per bite (inner Butterhead 55%; Iceberg 45%) and to increased handling time (inner Butterhead 30%). We conclude that sensory input from the mechanically more robust lettuce slows the buccal central pattern generator.

Novel kruppel-like factor is induced by neuronal activity and by sensory input in the central nervous system of the terrestrial slugLimax valentianus

In the Limax central nervous system, the procerebrum is thought to be the locus of odor information processing and odor memory retention, but little is known about the input pathway of the noxious stimuli used in this learning protocol. To gain insight into the sensory information processing of the noxious stimuli involved in memory formation, we screened genes induced by artificial neuronal activity, and identified one kruppel-like factor (KLF) family transcription factor gene (Limax KLF; limKLF), which is up-regulated 30 min after depolarization. The limKLF protein fused to GFP was localized to the nucleus in COS-7 cells. We also cloned an immediate early gene, CCAAT enhancer binding protein (C/EBP), of Limax by reverse transcription-polymerase chain reaction (RT-PCR). Both genes were up-regulated by dissection of the central nervous system (CNS) out of the slug in a protein synthesis-independent manner, and also by various noxious stimuli to the slug's body. These genes may be useful as neuronal activity markers in Limax to visualize activated sensory nervous systems.