SLOW OSCILLATIONS AS A PROBE OF THE DYNAMICS OF THE LOCUS COERULEUS-FRONTAL CORTEX INTERACTION IN ANESTHETIZED RATS

Multiunit or single unit activity recorded simultaneously from frontal cortex (FC) and locus coeruleus (LC) under ketamine anesthesia reveal ed that both regions show slow oscillatory activity, together or separ ately. Lf, however, both regions are engaged in this oscillatory activ ity, there is a systematic relationship between their phases with peak LC firing always following FC firing by 200-400 ms. This was confirme d by cross-correlational analyses, which indicated that the two struct ures temporarily form a resonant system. The FC-LC resonant state is, however, loose enough to remain open to other intrinsic or extrinsic i nfluences, keeping the measured frequencies of oscillations at each si te slightly different, as demonstrated by a detailed analysis of the a utocorrelograms. An injection of lidocaine at the frontal cortex site, while sharply reducing the prefrontal activity to essentially zero, l eads to an increase of the LC activity and to a modification of the sh ape of the LC autocorrelogram, but does not change appreciably the pha se relationship between the activity in the two structures during the diminishing activity in FC.