Intrinsic membrane properties causing a bistable behaviour of alpha-motoneurones.
In decerebrate cats a train of impulses in Ia afferents may lead to a sustained increase in excitability of alpha-motoneurones of homonymous and heteronymous muscles. It was previously suggested that this long-lasting excitability increase reflects a maintained synaptic input to the motoneurones from excitatory interneurones. With intracellular recording from motoneurones we here demonstrate that the sustained increase of alpha-motoneurone activity is due to an all-or-none plateau depolarization. This plateau can be induced by a short train of excitatory synaptic potentials or a brief, intracellularly injected depolarizing current pulse and is terminated by a short train of inhibitory synaptic potentials or a hyperpolarizing current pulse. It is concluded that maintained motor unit firing triggered by a brief train of impulses in Ia afferent reflects an intrinsic bistable behaviour of alpha-motoneurones.
D000818:Animals; D002415:Cats; D003655:Decerebrate State / Q000503:physiopathology; D007395:Interneurons / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology*; D012701:Serotonin / Q000502:physiology; D009435:Synaptic Transmission
D012701:Serotonin