Barium-induced bistability in rat ocular motoneurones in vitro.

Intracellular recordings were obtained from adult rat oculomotor neurones in an in vitro brainstem slice preparation. In motoneurones hyperpolarized to levels below -90 mV, depolarizing current injections induced voltage-dependent low-threshold plateau potentials. These potentials were triggered at rest when charge transfer through Ca2+ channels was increased by Ba2+ substitution. In such conditions, the membrane displayed voltage-dependent bistable properties similar to those described in other preparations and shown in vivo to be under neurotransmitter control. These results show that increasing inward currents in adult oculomotor neurones of the rat induce functionally different responses to slight shifts of membrane potential.