Quantitative autoradiographic evidence for axonal transport of imipramine receptors in the central nervous system of the rat

Interruption of the ascending serotonin axons of the medial forebrain bundle (MFB) in the rat brain produced a progressive time-dependent accumulation of imipramine receptors (labeled for autoradiography with [³H]imipramine). The largest accumulation of receptors occurred during the first 12 h at the caudal aspect of the lesion. An electrolytic lesion of the nucleus raphe dorsalis, administered 24 h prior to interruption of the medial forebrain bundle, markedly reduced the number of imipramine receptors on the caudal side of the lesion, while a significant accumulation was still evident on the rostral aspect. These results suggest that imipramine receptors are undergoing the process of orthograde axonal transport to terminals in the forebrain from the neuronal perikarya found in the nucleus raphe dorsalis. These receptors may also be undergoing retrograde transport back to their cell bodies of origin.