Abstract

In spontaneously breathing, pentobarbitone anesthetized cats, we recorded simultaneously the impulses in the chemosensory fibers of both carotid (sinus) nerves, to analyze the correlations between the frequencies of chemosensory discharges (f(?)) and their activation ({df(?)/dt}(a)) and deactivation ({df(?)/dt}(d)) rates. We studied the chemosensory responses to brief exposures to hypoxia (100% N 2; 5-s and 10-s) and hyperoxia (100% O 2; 30-s), and intravenous injections of excitatory (NaCN 0.2-100 ?g/kg) and inhibitory (dopamine hydrochloride 0.02-20 ?g/kg) chemoreceptor agents. Hypoxia increased f(?) with a high temporal correlation between frequency levels in both nerves. Prolonging hypoxic stimulation increased {df(?)/dt}(d), with preservation of {df(?)/dt}(a). Hyperoxic exposure produced highly correlated decreases in f? in both nerves, but reduced correlation if df(?)/dt. Increasing doses of NaCN produced analogous increments in f(?), df(?)/dt and their correlations, the {df(?)/dt}(a)/{df(?)/dt](d) ratio remaining constant along all the experimental range, except in one animal in which the ratio increased in both nerves alike. Dopamine reduced f(?) bilaterally, with chemosensory silencing being reached with doses of about 0.2-0.5 ?g/kg, the correlations between f(?)'s of both nerves remaining constant within the range analyzed. Maximal {df(?)/dt}(d) was not affected along the range of dopamine doses, except in one animal in which it increased in both nerves. It is concluded that both carotid nerves constitute either cooperative inputs or redundant afferences contributing to a high safety factor.