Figure 8.
Synaptic currents in four types of swimmeret motor neurons during two complete cycles of the swimmeret motor pattern and power-stroke activity (PS) recorded simultaneously with one of the current recordings. A, Three recordings of membrane currents (Im) from a PSE motor neuron during two cycles of the motor pattern. These voltage-clamp recordings were each triggered off the start of a PS burst (top trace) but made at different clamp potentials: -51, -64, and -83 mV. Raw recordings were low-pass filtered [cutoff frequency (fc), 500 Hz] but not averaged. Leakage currents recorded at the same clamp potentials when the system was silent were subtracted from the -64 and -83 mV traces; the mean current of the trace was subtracted from the -51 mV trace. Resting potential was -64 mV. Clamp parameters were as follows: sampling rate 5 kHz, gain 20, anti-alias filter10.B, Three recordings of membrane currents from an RSE motor neuron made at different clamp potentials:-55, -70, and -85 mV. Each trace is the average of two or three raw traces that had been low-pass filtered (fc, 500 Hz), with leakage current corrected by subtracting the mean current of the averaged trace. Traces were aligned to the start of the first PS burst; the period of the -70 mV recording was longer than that of the other two, so the second cycle of the -70 mV current is somewhat delayed. Resting potential was -73 mV. Clamp parameters were as follows: sampling rate 5.7 kHz, gain >10, anti-alias filter 10. C, Three recordings of membrane currents from a PSI motor neuron, made at -50, -70, and -90 mV clamp potential. Resting potential was -53 mV. In this example, the outward inhibitory currents decreased with hyperpolarization but did not reverse. Each trace is a single sweep, low-pass filtered (fc, 500 Hz) but not averaged. Leakage current of each trace was corrected by subtracting the mean current. Clamp parameters were as follows: sampling rate 5 kHz, gain >50, anti-alias filter 5. D, Three recordings from an RSI motor neuron, made at -47, -52, and -75 mV clamp potential. Resting potential was -52 mV. Each trace is the average of between 7 and 10 single sweeps that were low-pass filtered (fc, 1 kHz). Leakage current of -75 trace was corrected by adding 0.5 nA. Clamp parameters were as follows: sampling rate 5.2 kHz, gain 25, anti-alias filter 20.