Effects of colchicine treatment on the cholinergic septohippocampal system.

The influence of hippocampal target cells on the septohippocampal cholinergic system was studied using immunocytochemical and autoradiographic procedures. The destruction of dentate granular cells by colchicine injection promotes a significant increase in the density of acetylcholinesterase staining and cholinergic-muscarinic receptors in the zone denervated by the terminal axons of granular cells, which supports the hypothesis of a proliferation of cholinergic fibers in CA3. In the septal region the number of choline acetyl transferase positive cells was significantly lower (by 23%) ipsilaterally to the colchicine injection as compared to the contralateral side; when the hippocampus is almost completely destroyed by colchicine treatment this cell loss is more important (by over 50%). The present results agree with those of earlier studies and suggest that target-derived trophic factors are important for the maintenance of the basal forebrain cholinergic system and that the fascia dentata provides a significant source of such factors.