Fig. 1.
A: measurement of spike-timing precision and reliability. The top trace displays membrane voltage (Vm) of a patch-clamped hypoglossal motoneuron (XIIMN) responding to the injected current profile seen in the bottom trace. Sinusoidal current injections were delivered at amplitudes of 25, 150, or 250 pA. The DC offset (shaded area, bottom trace) was determined before injection of sinusoidal current patterns and varied between cells, as explained in materials and methods. DC offset adjustment was made to position the cells firing threshold at the midpoint of the sinusoidal current amplitudes. The peak of the sinusoidal current injection cycle (point a) was defined as 0° for analysis. A pre-peak position is defined by the diagonal bar shading, and spikes falling here have negative phase angles. Spikes occurring after the peak (defined by the crosshatch shading) would have positive phase angles. The dashed line shows that the 1st spike in the 2nd burst falls before the peak of the sine wave and therefore has a negative phase angle. B: comparison of typical responses to sinusoidal current injection in control and developmental nicotine exposure (DNE) XIIMN. Ba: phase-locked XIIMN from a control animal (top trace), which generates action potentials at the peak of the injected sinusoidal current waveform (middle trace) or just after it (solid vertical lines connect action potential onset to the corresponding sine wave). Bb: phase-locked XIIMN from a DNE animal. Note that the action potentials occur well before the peak of the sine wave (vertical dashed lines), consistent with a negative phase angle.