Modulatory influence on cerebral cortical optic response from the carotid sinus area

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

We have previously shown that serotonin injected intracarotidly exerts its effect on the cerebral evoked response through at least three receptor fields: the carotid sinus (factor X), the brain stem (Y) and the specific sensory synapses (Z). To demonstrate factor X directly, Dial-anesthetized cats were prepared for recording of the cortical visual response. The normally innervated carotid sinus area was isolated from the circulation and cannulated for perfusion with Ringer's solution. Depending upon the dose, serotonin added to the perfusion fluid induced enhancement or reduction of the amplitude of the evoked response. With doses ranging from 0.019 to 10.0 µg a dose-response curve similar to the one calculated in the previous series was found. Also, the time course of the changes in potential amplitude was similar to the one in the previous series. In order to match in this way the results of the present and the previous series a correcting factor of approximately 32 had to be introduced; for example the effect produced by 10.0 µg in the previous series was similar to the one induced by 0.3125 µg in the present series. This divergence is plausibly explained on the basis of the different perfusion rate used in the two series.