Adrenergic innervation of noradrenergic locus coeruleus neurons. A dual labeling immunocytochemical study in the rat.

By means of dual immunocytochemistry, synaptic associations between adrenergic terminals and noradrenergic neurons were directly demonstrated in the rat locus ceruleus (LC). It could be estimated that every adrenergic afferent contacts at least one noradrenergic dendrite in the nucleus. An adrenergic innervation of non-noradrenergic targets was also evidenced. These data add to our knowledge on the synaptic circuitry by which activation of the adrenergic input could affect central mechanisms known to be influenced by LC neurons.