Retrograde axonal transport after radioactive hydroxyindole injections into the olfactory bulb-an autoradiographic...

Light microscope autoradiography was used to study the retrograde transport of labelled material after injection of [(3)H]serotonin ([(3)H]5-HT), [(3)H]5-hydroxytryptophan ([(3)H]5-HTP) and [(14)C]5-hydroxyindoleacetic acid ([(14)C]5-HIAA) into the olfactory bulb (OB) of rat. A perikaryal labelling was clearly visualized in the Raphe Dorsalis (RD) and the Raphe Centralis (RC) 24 h after injection of [(3)H]5-HT (but not after injection of [(3)H]5-HTP or [(14)C]5-HIAA) into the OB of rats without monoamine-oxidase inhibitor (MAOI). In the OB, the labelled cells (mitral, granular, periglomerular and tufted cells) and the varicosities (dispersed in granular, plexiform and glomerular layers) were greater in number and intensity at 8 h than at 24 h after [(3)H]5-HT (10(?3) M) injection. Five hours after injection of [(14)C]5-HIAA (10(?3) M) some mitral, granular and tufted cells were labelled in the cytoplasm, nuclei and dendrites. A few varicosities were also observed. In contrast, after [(3)H]5-HTP injection no clear labelling was visualized in axonal processes. A net autoradiographic reaction was seen, however, in the capillary walls and some granular cells. After injection of [(3)H]5-HT at various concentrations (10(?2) M to 10(?5) M) into the OB of rats pretreated with MAOI, a selectivity in the pattern of labelling in the injection site and the afferent cell bodies was found at 10(?4) M and 10(?5) M. At these concentrations, the serotoninergic RD and RC neurons were clearly labelled, but the non-serotoninergic neurons such as those originating in the Locus Coeruleus, prepiriform cortex were devoid of label. In the OB, only varicosities and fiber-like structures were reactive. In the RD cell bodies, the intensity of labelling as well as the number of labelled cells were greater at higher concentrations of injected [(3)H]5-HT and when rats were pretreated with a MAOI.