Effects of nicotine on eeg and evoked potentials and their interactions with autonomic drugs

Abstract

The effects of nicotine on behaviour, electrical activity and evoked potentials from the auditory cortex were studied in restrained conscious cats. Nicotine (12.5 μg/kg i.P.) produced biphasic effects consisting, of an initial stimulation followed by depression, whereas in higher doses (25. 50, 100 μg/kg intraperitoneally and 10 μg into the lateral ventricle) it caused only depression. The stimulant phase was characterized by behavioural arousal, EEG desynchronization, decrease in the duration of both high and low alpha bursts, alpha indices, electrogenesis and auditory evoked potentials. Depression was associated with EEG synchronization, and increases in the duration of both high and low alpha bursts, alpha indices, electrogenesis and auditory evoked potentials. Most of these responses in the initial stimulation phase could be blocked by scopolamine. whereas those in later depressant phase were blocked by phenoxybenzamine and phentolamine. Nicotine exerted a biphasic action with initial muscarinic stimulation followed by noradrenergic depression. It is suggested that nicotine induces concomitant muscarinic and noradrenergic stimulations that are reflected in the time-course of action with initial cholinergic and subsequent noradrenergic preponderence.