Physiological Properties of Crustacean Motor Neurons and the Alteration of These Properties

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Crustacean phasic motor neurons, recruited for rapid movements, are generally silent, release relatively large amounts of transmitter onto their target muscle fibers and exhibit rapid synaptic depression with repeated activation. Tonic motor neurons, recruited for postural activities or slow movements, are more continuously active, generally produce small, facilitating synaptic potentials in target muscle fibers, and resist synaptic depression. In adult crustaceans, imposition of a tonic pattern of activity on phasic neurons in vivo leads to adaptive alterations of their synaptic physiology and morphology; such neurons assume a more tonic phenotype. Short-lasting inhibition of protein synthesis by cycloheximide, when timed to occur before a period of imposed tonic activity, effectively prevents the activity-dependent adaptive modification of synaptic transmission.