Biochemical and autoradiographic investigations of the retrograde axonal transport of labeled material following [(3)H]norepinephrine injection in the olfactory bulb.

Biochemical and autoradiographic methods were used to investigate the retrograde transport of labeled material after injection of [(3)H]norepinephrine ([(3)H]NE) in the olfactory bulb (OB) of rat. Mechanical obstruction of the ventricular recess prevented intraventricular diffusion. At different time intervals following bilateral [(3)H]NE injections, total radioactivity was measured in the OB, locus caeruleus (LC), raphe dorsalis and periaqueductal gray. Preferential accumulation occurred in the LC, and an approximate rate of retrograde transport of 1-6 mm/h could be calculated. Previous administration of 6-hydroxydopamine in the OB reduced this accumulation by 60%. Sixteen hours after [(3)H]NE injection, the radioactivity in LC was equally distributed between an ethanol-soluble and -insoluble fraction. A small proportion of the soluble material was recovered as [(3)H]NE and/or [(3)H]normetanephrine. Following unilateral injections of [(3)H]NE, light microscopic autoradiograms demonstrated nerve cell body labeling mainly in the ipsilateral LC and of greater intensity after 16 than 4 and 8 h. These data lead to the conclusion that the movement of radioactive material was indeed representative of retrograde axonal transport rather than of other mechanisms such as diffusion. The observation of a preferential labeling of noradrenergic perikarya in LC supports the hypothesis of a process mediated by specific binding and/or uptake of [(3)H]NE into noradrenergic axon terminals.