INHIBITORY INFLUENCE OF FRONTAL-CORTEX ON LOCUS-COERULEUS NEURONS

The functional influence of the frontal cortex (FC) on the noradrenerg ic nucleus locus coeruleus (LC) was studied in the rat under ketamine anesthesia. The FC was inactivated by local infusion of lidocaine or i ce-cold Ringer's solution while recording neuronal activity simultaneo usly in FC and LC. Lidocaine produced a transient increase in activity in FC, accompanied by a decrease in LC unit and multiunit activity. T his was followed by a total inactivation of FC and a sustained increas e in firing rate of LC neurons. Subsequent experiments revealed antidr omic responses in the FC when stimulation was applied to the LC region . The antidromic responses in FC were found in a population of neurons (about 8%) restricted to the dorsomedial area, FR2. The results indic ate that there is a strong inhibitory influence of FC on the tonic act ivity of LC neurons. The antidromic responses in FC to stimulation of the LC region suggest that this influence is locally mediated, perhaps through interneurons within the nucleus or neighboring the LC,