Physiological fractionation of the effect of serotonin on evoked potentials

¹ Laboratory of Neurophysiology, Worcester Foundation for Experimental Biology, Shrewsbury, Massachusetts

The effect of serotonin on the evoked potentials depends upon whether the drug is injected into a carotid artery with a normally innervated or a denervated carotid sinus, and also, whether the injection is given into the ipsi or the contralateral artery (with respect to recording). On the basis of these differences the working hypothesis is developed that serotonin exerts its effect upon the cortical potentials via at least three receptor systems: a) by stimulating receptors in the carotid sinus area and thus initiating modulatory impulses in the diffuse unspecific ascending systems b) by stimulating receptors in the brain stem and initiating ascending unspecific modulatory discharge and c) by a direct chemical effect upon the specific sensory pathways. Depending upon the experimental situation, one, two or all three of these factors combine to yield a particular effect on evoked potentials. Quantitative testing of our results indicates the validity of our hypothesis. Furthermore, the results are also indicative of homeostatic adjusting mechanisms. The significance of these findings and practical applicability of this ‘fractionation’ method are discussed.