On the role of catecholamines in the humoral modulation of the electrocortical activity in the cat.

By using the mescaline or the strychnine spikes as indicators of electrocortical activity it was found that they are increased in size by some catecholamines topically applied. These spikes showed late and long-lasting changes after somatic, as well as after autonomic afferent stimulation. The latter induced by cyanide, light asphyxia, intravenous injections of adrenaline or noradrenaline, and after a small dose of 6-hydroxydopamine. After a dose of this last substance, high enough to deplete the catecholamines of the brain, the late increase in amplitude of the cortical potentials observed following afferent stimulation disappeared leaving a long lasting reduction in that amplitude. The hypothesis is presented that the noradrenaline liberated by the adrenergic nerve fibers reaching the upper layers of the cortex acts on the nonsynaptic dendritic membranes modulating their activity in a humoral-like way. The pattern of this facilitating effect has a different temporal course and is longer lasting than that which is to be expectec only by the arrival of impulses at the cortex during the persistence of the neuronal activation induced by the information input to the CNS.