Differential actions of neurotrophic factors on lesion-induced damage of the serotonergic neurons projecting to the hippocampus

The changes induced by nerve growth factor (NGF) and by GM₁-ganglioside administration on serotonin (5-HT), 5-hydroxyin-doleacetic acid (5-HIAA) and tryptophan content and on choline acetyltransferase activity, were studied in the central nervous system of rats undergoing electrolytic damage of a mesencephalic area, located near the nucleus interpeduncularis. This lesion selectively reduced the content of 5-HT and 5-HIAA in the ipsilateral hippocampus. Daily intraperitoneal injection of GM₁-ganglioside (30 mg/kg/day for 6-14 days) significantly reduced the injury-induced loss of hippocampal 5-HT and 5-HIAA content. On the contrary NGF, administered at a dose (10 μg/rat i.c.v. twice a week for 2 weeks) which was able to increase, in the same animals, the cortical choline acetyltransferase activity, failed to affect the lesion-induced reduction of 5-HT and of 5-HIAA in the hippocampus.