Ultrastructural localization of the kainate selective glutamate receptor in noradrenergic perikarya and dendrites of the nucleus locus coeruleus in the rat brain.

To determine the regional and cellular distribution of the kainate receptor subtype in the LC, we combined immunoperoxidase labeling of an antibody which recognized the three identified members of the kainate receptor subunit class, with immunogold-silver localization of tyrosine hydroxylase (TH). Light microscopy showed that kainate receptor-like (KAr-li) immunoreactivity was dense throughout the LC. Electron microscopy revealed that KAr-li immunoreactivity was mainly located at synaptic and extrasynaptic portions of the plasmalemma in dendrites and somata, many of which also contained gold-silver labeling for TH. Unlabeled axon terminals often formed asymmetric (excitatory-type) synaptic contacts with postsynaptic dendrites containing KAr-li immunolabeling. In perikarya, KAr-li immunoreactivity was often associated with subcellular organelles including the Golgi apparatus and endoplasmic reticulum. Axon terminals were infrequently immunolabeled for KAr-li in the LC. These results provide the first direct ultrastructural evidence that the excitatory amino acid, glutamate, may locally modulate noradrenergic neurons in the LC through kainate-type receptors located at postsynaptic and extrasynaptic cellular sites.