Some noradrenergic neurons of locus ceruleus-olfactory pathways contain neuropeptide-Y

We report a specific tracing technique for studying projections of noradrenergic neurons that contain other transmitters. Autoradiography after retrograde axonal transport of tritiatednoradrenaline ([³H]NA) was combined with immunocytochemical detection of endogeneous NA or neuropeptide Y (NPY). The specificity of [³H]NA retrograde labeling was dependent on the concentration of [³H]NA injected at the terminal region. At 2 x 10⁻³ M, the specificity of [³H]NA retrograde labeling was confirmed by immunodetection of endogenous NA in radiolabeled cell bodies of the locus ceruleus. Combination of autoradiography of [³H]NA retrograde labeling with immunodetection of NPY demonstrated that a some scattered locus ceruleus noradrenergic neurons (about 26%) projecting to the olfactory bulb do contain NPY.