Changes in electric activity (EEG) of the telencephalon of conscious toads (Bufo paracnemis) caused by cholinergic stimulation of the mesencephalic tegmentum.

Studies were carried out to investigate the effect of microinjection of cholinergic agonist carbamylcholine (carbachol) into the mesencephalic tegmentum of conscious toads (Bufo paracnemis), subjected or not to section of the olfactory nerves, on the electrical activity (EEG) of the telencephalon. The response depended on the type of preexisting EEG activity. Marked desynchronization was observed both in animals with intact nerves and in animals with sectioned nerves, whose previous basal activity was already desynchronized (high frequency and low amplitude). In toads with synchronized basal activity and with intact nerves, an increase, a fall or even abolition of preexisting spindle-like activity occurred, whereas in animals with sectioned nerves the effect was reduction or abolition of spindle-like activity. The data show that stimulation of the mesencephalic tegmentum can alter the electrical activity of the telencephalon and that this effect is not only secondary to a change in nasal air flow alterations since it occurs in toads with sectioned olfactory nerves.