VENTRAL MEDULLARY NEURONAL RESPONSES TO PERIPHERAL CHEMORECEPTOR STIMULATION

Recent findings suggest that carotid chemoreceptor input into the vent ral medullary surface intermediate area during hypoxia is inhibitory ( Gozal et al., (1994) Neurosci. Lett. 178, 73-76. However, systemic hyp oxia is a complex stimulus, and effects of carotid chemoreceptor stimu lation per se on intermediate ventral medullary surface neuronal activ ity are difficult to isolate. Therefore, we studied neural activation of the intermediate ventral medullary surface during peripheral chemor eceptor stimulation by intravenous sodium cyanide using optical proced ures in seven pentobarbital-anesthetized cats. Control recordings were also acquired in the suprasylvian cortex of three cats. Images of ref lected 660 nm light were collected at 1/s with a charge-coupled device camera, triggered by the cardiac R wave, after 0.0, 0.5, 2, 5, 10, 20 and 40 mu g/kg i.v. sodium cyanide administration before and followin g carotid sinus denervation. Sodium cyanide doses > 5 mu g/kg signific antly increased ventilation, an effect which was eliminated following carotid sinus denervation. A pronounced, dose-dependent activity decre ase within the intermediate ventral medullary surface occurred within seconds of sodium cyanide administration, with subsequent return to ba seline. Carotid sinus denervation eliminated rapid-onset neural respon ses to all sodium cyanide doses. However, at the 40 mu g/kg dose, a sm aller, slower onset (25 s), activity decrease occurred both pre- and p ostdenervation. In the neocortex, the sodium cyanide-induced fast resp onses were absent. Intravenous cyanide, acting via a carotid sinus ner ve pathway, results in a dose-dependent decrease in neural activity wi thin the intermediate ventral medullary surface of cats. High-dose sod ium cyanide also appears to decrease intermediate ventral medullary su rface neural activity directly. Copyright (C) 1996 IBRO.