Massive activation of c-fos in forebrain after mechanical stimulation of the locus coeruleus.

Brief implantation of a 33-ga cannula in the locus coeruleus (LC) of the rat caused widespread and intense ipsilateral activation of c-fos throughout the forebrain. Areas showing heavy staining included the cingulate, piriform, parietal, frontal cortex, and the olfactory tubercle. Prior lesion of the LC with 6-hydroxydopamine (6-OHDA) abolished the response. It is concluded that the mechanical stimulation and/or trauma involved in the implantation of a cannula in the LC is sufficient to cause widespread activation of noradrenergic neurotransmission throughout the forebrain. The use of this procedure for drug delivery should therefore be reevaluated.