Helix aspersa neurons maintain vigorous electrical activity when co-cultured with intact H. aspersa ganglia

Multisite Recording of Extracellular Potentials Produced by Microchannel-Confined Neurons In-Vitro

Towards establishing electrical interfaces with patterned in vitro neurons, we have previously described the fabrication of hybrid elastomer-glass devices polymer-on-multielectrode array technology and obtained single-electrode recordings of extracellular potentials from confined neurons (Claverol-Tinturé et al., 2005). Here, we demonstrate the feasibility of spatially localized multisite recordings from individual microchannel-guided neurites extending from microwell-confined somas with good signal-to-noise ratios (20 dB) and spike magnitudes of up to 300 microV. Single-cell current source density (scCSD) analysis of the spatio-temporal patterns of membrane currents along individual processes is illustrated.

Multielectrode arrays with elastomeric microstructured overlays for extracellular recordings from patterned neurons

Multielectrode array technology constitutes a promising approach for the characterization of the activity-dependent neuronal plasticity underlying information processing in the nervous system. For this purpose, long-term monitoring and stimulation of cultured neuronal networks with one-to-one neuron-sensor interfacing is advantageous. Existing neurochips that meet these specifications have made use of custom 3D structures requiring clean-room intensive microfabrication techniques. Low-cost fabrication procedures with potential for mass production would facilitate progress in the area. To this end, we have developed a sandwich structure comprising an elastomeric film, microstructured by replica moulding and microhole punching, for neuronal patterning, and a standard planar microelectrode array (MEA), for stimulation and recording. The elastomeric film includes microwells for cell body confinement, and microchannels capable of guiding neurites for network topology specification. The device is formed by overlaying the elastomeric structures on planar arrays. The combination of replica moulding, rapid prototyping and planar MEAs results in low-cost neurochips accessible to most neurophysiology labs. Single neuron patterning and recordings of extracellular potentials are demonstrated.

In vitro formation and activity-dependent plasticity of synapses between Helix neurons involved in the neural control of feeding and withdrawal behaviors

Short-term activity-dependent synaptic plasticity has a fundamental role in short-term memory and information processing in the nervous system. Although the neuronal circuitry controlling different behaviors of land snails of the genus Helix has been characterized in some detail, little is known about the activity-dependent plasticity of synapses between identified neurons regulating specific behavioral acts. In order to study homosynaptic activity-dependent plasticity of behaviorally relevant Helix synapses independently of heterosynaptic influences, we sought to reconstruct them in cell culture. To this aim, we first investigated in culture the factors regulating synapse formation between Helix neurons, and then we studied the short-term plasticity of in vitro-reconstructed monosynaptic connections involved in the neural control of salivary secretion and whole-body withdrawal. We found that independently of extrinsic factors, cell-cell interactions are seemingly sufficient to trigger the formation of electrical and chemical synapses, although mostly inappropriate--in their type or association--with respect to the in vivo synaptic connectivity. The presence of ganglia-derived factors in the culture medium was required for the in vitro reestablishment of the appropriate in vivo-like connectivity, by reducing the occurrence of electrical connections and promoting the formation of chemical excitatory synapses, while apparently not influencing the formation of inhibitory connections. These heat-labile factors modulated electrical and chemical synaptogenesis through distinct protein tyrosine kinase signal transduction pathways. Taking advantage of in vitro-reconstructed synapses, we have found that feeding interneuron-efferent neuron synapses and mechanosensory neuron-withdrawal interneuron synapses display multiple forms of short-term enhancement-like facilitation, augmentation and posttetanic potentiation as well as homosynaptic depression. These forms of plasticity are thought to be relevant in the regulation of Helix feeding and withdrawal behaviors by inducing dramatic activity-dependent changes in the strength of input and output synapses of high-order interneurons with a crucial role in the control of Helix behavioral hierarchy.

Aplysia hemolymph promotes neurite outgrowth and synaptogenesis of identified Helix neurons in cell culture

Hemolymph of adult Aplysia californica significantly affects neurite outgrowth of identified neurons of the land snail Helix pomatia. The metacerebral giant cell (MGC) and the motoneuron C3 from the cerebral ganglion and the neuron B2 from the buccal ganglion of H. pomatia were isolated by enzymatic and mechanical dissociation and plated onto poly-L-lysine-coated dishes either containing culture medium conditioned by Helix ganglia, or pre-treated with Aplysia hemolymph. To determine the extent of neuronal growth we measured the neurite elongation and the neuritic field of cultured neurons at different time points. Aplysia hemolymph enhances the extent and rate of linear outgrowth and the branching domain of Helix neurons. With the hemolymph treatment the MGC neuron more consistently forms specific chemical synapses with its follower cell B2, and these connections are more effective than those established in the presence of the conditioned medium.