EFFECTS OF LOCUS-CERULEUS LESIONS ON VIGILANCE AND ATTENTIVE BEHAVIOR IN CAT

Previous data have suggested that in the cat, expectancy behaviour (waiting for a target to appear) and associated electrocortical, focal, synchronized activity ('mu' rhythms) are modulated by a noradrenergic system possibly originating from the locus coeruleus (LC). To test the latter hypothesis, we have examined the behavioural and ECoG changes induced after bilateral LC lesions. Our results demonstrated that destruction of the anterior 3/4th of the LC (A6 noradrenergic cell group) resulted in a considerable increase of mu rhythms and expectancy behaviour, without episodes of drowsiness that normally occur. Destruction of the posterior fourth of LC (A4 noradrenergic group) only increased the duration of slow sleep. Extending the A6 lesion to include the dorsal ascending noradrenergic bundle also increased the expectancy behaviour and mu rhythms. Finally, when the nucleus subcoeruleus was also involved, the duration of slow sleep and the frequency of paradoxical sleep episodes increased. These findings indicate that the LC exerts an inhibitory effect on structures involved in the induction and persistence of expectancy behaviour with accompanying mu rhythms.