EFFECT OF HYPOTHALAMIC 5,7-DIHYDROXYTRYPTAMINE LESION ON THE ANTEROGRADE TRANSPORT OF SEROTONIN AS MEASURED WITH LABELED ALPHA-METHYL SEROTONIN

The anterograde axonal transport of serotonin along the medial forebrain bundle (MFB) 5 days after unilateral dorsal hypothalamic 5,7-dihydroxytryptamine (5,7-DHT) lesion was examined in rat brain. Measurements were done using in vivo synthesized radioactively labeled alpha-methyl serotonin (used here as a serotonin tracer), from i.v. injected labeled alpha-methyl-L-tryptophan, a substitute neurotransmitter and analog of serotonin. Data indicated that after destruction of the presynaptic terminals with 5,7-DHT, the rate of axonal transport of serotonin and/or the rate of serotonin synthesis in the spared and/or damaged neurons was increased. The rate of serotonin anterograde transport on the lesioned side was above 25 mm/d compared to 12.31 +/- 0.49 mm/d on the contralateral side and 12.13 +/- 0.44 mm/d in control (sham injected) rats. The difference in rate between the lesioned and control rats was highly significant; P < 0.005 (two-tailed t-test). The amount of neurotransmitter anterogradely transported along the medial forebrain bundle and/or synthesized in the neurons was 18.8 +/- 4.1 times greater on the side of the 5,7-DHT hypothalamic lesion than that on the contralateral sides or that found in the saline-injected rats. There was no difference in the radioactivity found on the left or right side of the medial forebrain bundle in the rats 5 days after lesion in the rostal midbrain with 5,7-DHT. Five days after the lesion there was also no difference in the anterograde protein transport measured by stereotaxic injection of [H-3]proline into the dorsal raphe.