Analysis of Mechanisms of Spiking in Normally ‘Non-Spiking’ Motoneurone Somata in Crayfish

The soma membrane of the abdominal giant motor neurone (MoG) of the crayfish was studied by use of current injection and by measurements of total and local membrane current under voltage-clamp. Depolarization of the soma from the recorded resting potential (about −70 mV) did not produce a regenerative potential. Sodium and calcium currents were observed under voltage-clamp. It was shown that the sodium spike cannot develop at the usual resting potential since sodium channels are already partially inactivated; the spike can appear after the removal of inactivation by a hyperpolarizing prepulse. It was also shown that an early outward current prevents the Ca2+; regenerative potential; the potential can appear after inactivation of this outward current by a depolarizing prepulse.