Axon conduction failure under in vivo conditions in crayfish

Action potential discharge in an identified axon was recorded in 'intact' crayfish, and conduction block occurred during prolonged high-frequency activity. These in vivo recordings were also used to trigger stimulation of the same axon in vitro; conduction block occurred during high-frequency bursts in small terminal branches. Quantal release was distributed in a bimodal fashion, with numerous failures, due to these occurrences of conduction block. These results indicate that conduction block may occur in intact animals and that it may also cause selective recruitment of specific nerve terminals during normal behaviour.