Abstract

A quantitative EEG study was made of the action of adrenergic stimulant and blocking drugs. It was found that:

At doses of 1 to 5 µg/kg, epinephrine or norepinephrine exerted an EEG stimulant action in only 20% of the animals. The same was true for methoxamine at 200 to 500 µg/kg.

This effect could be obtained in all the animals when epinephrine, norepinephrine and methoxamine were administered after a pretreatment with 4 mg/kg of DCI. The EEG effect appeared to be independent of the vascular action of epinephrine, norepinephrine and methoxamine.

Alpha-blocking drugs were found to belong to 2 groups: either they blocked entirely the EEG stimulant action of epinephrine, norepinephrine and methoxamine (phenoxybenzamine and chlorpromazine), or they did not change their effect in any way (dihydroergotamine, phentolamine and azapetine).

Isoproterenol exerted an EEG stimulant action which could be blocked by DCI, by all the alpha-blocking drugs used, and by denervation of the carotid sinuses.

When the indirectly determined stimulant EEG action of isoproterenol was suppressed one could demonstrate an EEG depressant effect with large doses of this catecholamine.

When alpha-blocking drugs capable of suppressing the stimulant effect of the amines on the EEG, such as phenoxybenzamine, were administered, one could obtain depressant EEG actions with epinephrine, but not with norepinephrine.

Assuming a direct central effect of the amines, these experimental findings are discussed. Two hypotheses are presented of which one involves the existence of adrenergic stimulant and depressant receptors in the brain.