[Electroencephalographic effects of lopramine].

Electroencephalographic (EEG) effects of lopramine, a new antidepressant, were investigated in rabbits with chronic electrode implants, and compared with those of imipramine and amitriptyline. All drugs were administered i.v. Lopramine (10, 20 mg/kg) induced a drowsy pattern of spontaneous EEG consisted of high voltage slow waves in the cortex and amygdala, and desynchronization of hippocampal thetha waves. Imipramine and amitriptyline (1-5 mg/kg) also elicited similar EEG changes but were much more potent than lopramine in this effect. Lopramine (10, 20 mg/kg) failed to suppress the EEG arousal responses induced by not only auditory stimulation but also electrical stimulation of the mesencephalic reticular formation, centromedian thalamus and posterior hypothalamus, whereas imipramine and amitriptyline (1 approximately 5 mg/kg) markedly inhibited these responses. The EEG arousal response induced by i.v. injection of physostigmine 0.1 mg/kg showed no change after lopramine (20 mg/kg), while the response was significantly suppressed by imipramine (2, 5 mg/kg) and amitriptyline (1, 2 mg/kg). Lopramine showed no effect on the recruiting response induced by electrical stimulation (8 Hz) of the centromedian thalamus and slightly enhanced the limbic afterdischarges elicited by either hippocampal or amygdaloid stimulation, while imipramine (2, 5 mg/kg) and amitriptyline (1--5 mg/kg) caused an initial depression followed by sustained enhancement of these afterdischarges. These results demonstrate lopramine to be an antidepressant of a new type which has no effect on the ascending reticular activating system and no central anticholinergic action.