Intracranial self-stimulation in relation to the ascending noradrenergic fiber systems of the pontine tegmentum and caudal midbrain: a moveable electrode mapping study.

Chronically implanted moveable electrodes were used to map the pontine tegmentum and caudal midbrain for intracranial self-stimulation in relation to the ascending noradrenergic systems as revealed by fluorescence histochemistry. In no area tested was there a consistent correlation between the quality or the presence of self-stimulation and the degree of noradrenergic fiber density or cellular aggregation. Of particular importance was the failure to obtain self-stimulation from the locus coeruleus, despite repeated testing and extensive attempts at behavioral shaping. Those areas supporting self-stimulation included the dorsal raphe nucleus, the superior cerebellar peduncle and the mesencephalic and motor nuclei of the trigeminal nerve. These data appear to rule out activation of the ascending noradrenergic systems as an explanation of the rewarding effects of stimulation in these areas. A gustatory-visceral fiber system is suggested as an alternative possible substrate.