Figure 4.

Changes in motoneuron excitability induced by H₂O₂. (a) Examples of responses of hypoglossal motoneuron to bath-applied H₂O₂. Trace is a continuous, slow record (in current clamp configuration) of a cell with initial membrane potential of −65 mV (for methods, see Sharifullina et al. 2005; Lamanauskas & Nistri 2008). Segments of this trace are also shown on a faster time base to depict spike firing evoked by intracellular injection of 300 pA (500 ms). Note that, following the application of H₂O₂, there is gradual membrane depolarization (8 mV) associated with reduction in global synaptic events (decrease in baseline thickness and noise; see (d) for quantification of event frequency) and enhanced spike firing (when the membrane potential is repolarized back to rest). (b) Fast time base example of spike activity in control (blue) and during H₂O₂ application (pink). Note the larger number of spikes and the larger amplitude of the membrane voltage response to the same current injection pulse (300 pA). The box section shows (at higher gain) superimposed spike afterhyperpolarizations recorded in control or during H₂O₂ application. Despite the higher number of spikes, the afterhyperpolarization is decreased. (c) Change in cell input resistance (measured from voltage response to a hyperpolarizing current pulse of −50 pA) in the presence of H₂O₂. Data are averages from five motoneurons (*p < 0.01). (d) Reduction in global synaptic event frequency elicited by H₂O₂ (data are from five motoneurons voltage clamped at −70 mV; *p < 0.04) (F. Nani 2008, unpublished data).