Effects of noradrenaline applied iontophoretically on rat superior collicular neurons

In rats anesthetized with urethane effects of iontophoretically applied noradrenaline (ejection currents, less than 20 nA) were examined on spontaneous and/or photically evoked discharges of neurons in the superior colliculus (SC). In a given SC neuron NA acted either to facilitate or to inhibit both spontaneous and evoked discharges. Though the inhibition was more frequently observed than the facilitation in all layers of the SC, the ratio of the facilitated neurons to the inhibited ones increased as one advanced through the SC from superficial to deep. These findings are in line with those obtained when SC neurons were subject to repetitive electrical stimulation of the locus coeruleus.