Molluscan neurons in culture: shedding light on synapse formation and plasticity

Abstract

From genes to behaviour, the simple model system approach has played many pivotal roles in deciphering nervous system function in both invertebrates and vertebrates. However, with the advent of sophisticated imaging and recording techniques enabling the direct investigation of single vertebrate neurons, the utility of simple invertebrate organisms as model systems has been put to question. To address this subject meaningfully and comprehensively, we first review the contributions made by invertebrates in the field of neuroscience over the years, paving the way for similar breakthroughs in higher animals. In particular, we focus on molluscan (Lymnaea, Aplysia, and Helisoma) and leech (Hirudo) models and the pivotal roles they have played in elucidating mechanisms of synapse formation and plasticity. While the ultimate goal in neuroscience is to understand the workings of the human brain in both its normal and diseased states, the sheer complexity of most vertebrate models still makes it difficult to define the underlying principles of nervous system function. Investigators have thus turned to invertebrate models, which are unique with respect to their simple nervous systems that are endowed with a finite number of large, individually identifiable neurons of known function. We start off by discussing in vivo and semi-intact preparations, regarding their amenability to simple circuit analysis. Despite the 'simplicity' of invertebrate nervous systems however, it is still difficult to study individual synaptic connections in detail. We therefore emphasize in the next section, the utility of studying identified invertebrate neurons in vitro, to directly examine the development, specificity, and plasticity of synaptic connections in a well-defined environment, at a resolution that it is still unapproachable in the intact brain. We conclude with a discussion of the future of invertebrates in neuroscience in elucidating mechanisms of neurological disease and developing neuron-silicon interfaces.

Previous motor activity affects transition from uncertainty to decision-making in snails

“…Lymnaea stagnalis has been used widely for analysis of the cellular and molecular mechanisms of behaviour (Dyakonova et al, 2015;Koene, 2010;Marra et al, 2013;Pirger et al, 2014;Schmold and Syed, 2012), including studies at the single-cell level (Dyakonova et al, 2009(Dyakonova et al, , 2015Dyakonova and Dyakonova, 2010;Schmold and Syed, 2012). Therefore, our findings also reveal new opportunities for investigating the cellular basis of the intriguing interplay between motor and cognitive activities, which may have deep roots in evolution.…”

Molluscan cells in culture: primary cell cultures and cell lines

“…Therefore, early on, investigators focused on isolation and cultivation of nerve cells located in defined ganglia in order to understand nerve cell growth and regeneration, neuroplasticity, and sensory connectivity to physiological processes and behavior in the intact animal. A review by Schmold and Syed (2012) details the many important contributions to neuroscience made by studying the molluscan nervous system in intact or semi-intact animals, including identification and mapping of neural circuitries controlling rhythmic behaviors such as respiration (Haque et al 2006; Bell and Syed 2009) or feeding (Yoeman et al 1995; Horn et al 2004), or more complex processes like learning and memory (Lee et al 2008 a ; Glanzman 2009; Nargeot and Simmers 2011). These types of experimental approaches are critically important as they provide the linkage between behavioral responses and the nerve centers (ganglia) involved in controlling such activities.…”

“…In other studies, in vitro vs. in vivo cellular responses to specific chemical agents were compared (Fiumara et al 2005) and found to be similar. Schmold and Syed (2012) have reviewed the extensive literature on in vitro neuronal cell research and how these simple culture models have contributed to a fundamental understanding of complex neural networks in regard to their control of behavior and learning/memory in molluscs. The following are examples of the main types of research conducted using cultured neuronal cells.…”

Interaction of leech neurons with topographical gratings: comparison with rodent and human neuronal lines and primary cells

“…The simple nervous system and cellular accessibility, together with the large size and the single neuron identifiability in vivo and in vitro, are some of the invertebrate advantages that allowed us to improve the knowledge about evolutionarily conserved neuronal mechanisms [37]. Moreover, it is worth mentioning the contribution of pioneering experimental studies performed on invertebrates that permitted the identification of the basic mechanisms of neuronal functions [38][39][40]. Both cell body and GC membranes of leech neurons express mechanosensitive cation channels with pharmacological features similar to those found in vertebrate cells [41].…”