The excitation of neurons by noradrenaline

Responses of single cortical neurons to microelectrophoretically applied noradrenaline at pH 3.1 and 5.0 and to hydrogen ions were compared in the halothane-anaesthetized cat. Of 16 neurons sensitive to noradrenaline, 13 were excited and 3 were depressed by noradrenaline at both pH values, whereas hydrogen ions released from an HCl solution did not affect the firing rate. Dose-response studies showed that noradrenaline at pH 3.1 was more potent than at pH 5.0. It is concluded that excitatory responses to noradrenaline are not artifacts and that the adjustment of the pH of noradrenaline solutions with NaOH should be avoided.