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

Abstract

Biochemical and autoradiographic methods were used to investigate the retrograde transport of labeled material after injection of [ 3H]norepinephrine ([ 3H]NE) in the olfactory bulb (OB) of rat. Mechanical obstruction of the ventricular recess prevented intraventricular diffusion. At different time intervals following bilateral [ 3H]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 [ 3H]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 [ 3H]NE and/or [ 3H]normetanephrine. Following unilateral injections of [ 3H]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 [ 3H]NE into noradrenergic axon terminals.