Antikindling effects of locus coeruleus stimulation: mediation by ascending noradrenergic projections.

Electrical stimulation of the noradrenergic locus coeruleus (LC) delays the generalization of partial seizures during amygdaloid kindling by increasing the time spent in the earliest stages of seizure development. To determine whether noradrenergic axons projecting to the midbrain and forebrain are involved in this antikindling effect, we examined the effects of lesions of the dorsal noradrenergic bundle, induced by intracerebral infusions of 6-hydroxydopamine (6-OHDA), on kindling and the antikindling action of stimulation of the LC. Stimulation of the LC during amygdaloid kindling increased the number of afterdischarges (ADs) spent in the early stages of partial seizure and decreased the number of ADs spent in later stages of generalized seizure, as has been described previously. LC-stimulated rats also displayed longer durations of AD during early stages of kindling. The antikindling effect of LC stimulation was blocked by lesions of the dorsal bundle, whereas the facilitatory effects of LC stimulation on generalization and on the duration of AD were unaffected by the lesions. These results suggest that the antikindling action of LC stimulation is mediated by the ascending projections of noradrenergic neurons, presumably through enhanced release of noradrenaline. On the other hand, the facilitatory effects of LC stimulation on the development of later stages of seizure and on the duration of AD appear to be independent of the ascending dorsal bundle.