LOCUS COERULEUS-INDUCED MODULATION OF FOREBRAIN ELECTROENCEPHALOGRAPHIC (EEG) STATE IN HALOTHANE-ANESTHETIZED RAT

The effects of reversible enhancement or suppression of locus coeruleu s (LC) neuronal discharge activity on forebrain electroencephalographi c (EEG) activity have been previously examined in two series of experi ments in halothane-anesthetized rats. Unilateral enhancement of LC act ivity increased EEG measures of arousal in frontal cortex and hippocam pus. The EEG effects of LC activation were blocked by intracerebrovent ricular pretreatment with the noradrenergic beta-antagonist, propranol ol. Bilateral, but not unilateral, suppression of LC activity substant ially increased EEG measures of sedation/anesthesia in cortex and hipp ocampus. In all experiments: a) EEG responses were only observed follo wing changes in LC activity levels; b) onset of EEG responses closely followed changes in LC neuronal activity; c) recovery of EEG responses closely followed the recovery of LC neuronal activity. The present re port integrates these previous results and considers their implication s for the hypothesis that the LC may be an important modulator of beha vioral state and/or state-dependent processes. Together, the two serie s of experiments yield complementary observations that have implicatio ns for LC function that are not apparent when considering each series in isolation.