Lack of Specificity of Motoneurone Responses to Microiontophoretically Applied Phenolic Amines

Intracellular recordings from spinal motoneurones have revealed that iontophoresed noradrenaline (NA) causes a membrane hyperpolarization, sometimes leading to a block of spike generation (Curtis 1968, Phillis, Tebëcis and York 1968). Similar alterations of membrane activity were produced by serotonine and histamine. The hyperpolarization is possibly due to a reduction of the resting sodium permeability (P Na ) as the membrane conductance is decreased during NA application (Engberg and Marshall 1971, 1973)—a similar mechanism as in the slow synaptic inhibition in bullfrog sympathetic ganglion cells (Weight and Padjen 1973)—or it may be due to an activation of electrogenic ion transport as has been suggested for cerebellar Purkinje cells (Siggins et al. 1971).