ASCENDING PROJECTIONS OF LOCUS COERULEUS IN RAT .1. AXONAL-TRANSPORT IN CENTRAL NORADRENALINE NEURONS

Axonal transport of protein and metabolites of L-[3H]dopa was studied in the central noradrenaline [norepinephrine] neurons of the pontine nucleus locus coeruleus and was correlated with regional alterations of noradrenaline content following destruction of the nucleus. Unilateral lesions of the locus coeruleus produced a partial depletion of noradrenaline in the ipsilateral hypothalamus and telencephalon, indicating that these neurons project widely to the ipsilateral forebrain. Following local injections of 50 .mu.Ci [3H]proline (24-48 h), locus coeruleus neurons took up labeled material and transported it, presumably as protein, to ipsilateral structures in the midbrain, diencephalon and telencephalon including the neocortex. Similarly 8 h after injection of 25 .mu.Ci [3H]dopa into the locus coeruleus, transport of material including catecholamines occurred to ipsilateral diencephalon and telencephalon. Axonal transport of proteins to telencephalic structures was greatly diminished by selective lesions of catecholamine terminals with 6-hydroxydopamine (6-OHDA) and following destruction of the medial forebrain bundle. Noradrenaline neurons of the locus coeruleus nucleus apparently project widely within the neuraxis to ipsilateral structures of the brain stem, diencephalon and telencephalon, including all cortical areas. Evidence was presented for a contralateral projection with a similar distribution. The rate of axonal transport of labeled protein and metabolites of [3H]dopa including [3H]catecholamines in central noradrenaline neurons was estimated to be 3-4 mm/h, similar to that reported for noradrenaline neurons of the peripheral sympathetic nervous system.