Lidocaine treatment during synapse reformation periods permanently inhibits NGF-induced excitation in an identified reconstructed synapse of Lymnaea stagnalis.

PURPOSE: Nerve growth factor (NGF) has been reported to affect synaptic transmission and cause neuropathic pain. In contrast, lidocaine has been used to reduce neuropathic pain; however, the effect of NGF and lidocaine on spontaneous transmitter release and synapse excitation has not been fully defined. Therefore, the effect of NGF and lidocaine on nerve regeneration, synapse reformation, and subsequent spontaneous transmitter release was investigated. We used Lymnaea stagnalis soma-soma-identified synaptic reconstruction to demonstrate that a transient increase in both frequency and amplitude of spontaneous events of miniature endplate potentials (MEPPs) occurs following NGF treatment and a short burst of action potentials in the presynaptic cell; in addition, the effect of lidocaine on NGF-induced synapse reformation was investigated. METHODS: Using a cell culture and electrophysiological and FM-143 imaging techniques for exocytosis on unequivocally identified presynaptic visceral dorsal 4 (VD4) and postsynaptic somata left pedal (LPeE) neurons from the mollusc Lymnaea stagnalis, the effects of NGF and lidocaine on nerve regeneration, synapse reformation, and its electrophysiological spontaneous synaptic transmission between cultured neurons were described. RESULTS: NGF increased axonal growth, frequency, and amplitudes of MEPPs. Lidocaine exposure during synapse reformation periods was drastically and permanently reduced axonal growth and the incidence of synapse excitation by NGF. CONCLUSION: NGF increased amplitudes and frequencies of MEPPs and induced synaptic excitation by increasing axonal growth and exocytosis. Lidocaine exposure during synapse reformation periods permanently suppressed NGF-induced excitation by suppressing axonal growth and exocytosis of presynaptic neurons in the identified reconstructed synapse of L. stagnalis.

Clinical dose of lidocaine destroys the cell membrane and induces both necrosis and apoptosis in an identified Lymnaea neuron.

PURPOSE: Although lidocaine-induced cell toxicity has been reported, its mechanism is unclear. Cell size, morphological change, and membrane resistance are related to homeostasis and damage to the cell membrane; however, the effects of lidocaine on these factors are unclear. Using an identified LPeD1 neuron from Lymnaea stagnalis, we sought to determine how lidocaine affects these factors and how lidocaine is related to damage of the cell membrane. METHODS: Cell size and morphological form were measured by a micrograph and imaging analysis system. Membrane potential and survival rate were obtained by intracellular recording. Membrane resistance and capacitance were measured by whole-cell patch clamp. Phosphatidyl serine and nucleic acid were double stained and simultaneously measured by annexin V and propidium iodide. RESULTS: Lidocaine at a clinical dose (5-20 mM) induced morphological change (bulla and bleb) in the neuron and increased cell size in a concentration-dependent manner. Membrane potential was depolarized in a concentration-dependent manner. At perfusion of more than 5 mM lidocaine, the depolarized membrane potential was irreversible. Lidocaine decreased membrane resistance and increased membrane capacitance in a concentration-dependent manner. Both phosphatidyl serine and nucleic acid were stained under lidocaine exposure in a concentration-dependent manner. CONCLUSIONS: A clinical dose of lidocaine greater than 5 mM destroys the cell membrane and induces both necrosis and apoptosis in an identified Lymnaea neuron.