Dopaminergic innervation of rat locus coeruleus: a light and electron microscopic immunohistochemical study

Dopaminergic innervation of the rat locus coeruleus (LC) was immunohistochemically studied by using monoclonal antibody directed against dopamine (DA) at the light- and electron-microscopic levels. A dense plexus of DA-immunoreactive (IR) varicose fibers was found not only in the cell body area of the LC but also in the dendritic area. Three hundred and forty DA-IR terminal boutons were observed. They were distributed in a wide range of diameters of 0.1-1.8 microns but most of them were large (mean value: 0.98 micron). Sixty-nine percent formed an asymmetric synapse. There were many axo-spinous connections. Small dendrites less than 0.3 micron in diameter displaying synaptic specialization were mostly dendritic spines (75%). Most of the target dendrites seemed to be noradrenergic in nature. It is suggested that dopaminergic innervation may play a powerful role in control mechanisms of activity of NA-containing neurons of the LC.