Transcallosal evoked potentials: behavior-dependent modulation by muscarinic and serotonergic receptors

In chronically prepared rats, unilateral single pulse stimulation (35-80 microA) of the deep neocortex produced an evoked potential in the contralateral hemisphere. The evoked potential consisted of an initial negative component associated with multiunit discharge, and a subsequent positive component associated with multiunit suppression. Duration and amplitude of both evoked potential components were suppressed during movement relative to immobility. Scopolamine enhanced both evoked potential components, but the effect on the late component was apparent only during movement and not immobility. Ketanserin prolonged the duration of the late potential component during immobility but not movement. Methiothepin enhanced the duration and amplitude of both components, but these effects were largely dependent on the concurrent background neocortical slow wave activity. Urethane anesthesia enhanced the early and abolished the late potential components. Tail pinching reversed this effect of urethane. Muscarinic and serotonergic receptors may modulate both the excitatory and inhibitory responses of neocortical neurons to inputs from the contralateral neocortex.