Immunofluorescence and immunoelectron microscopic evidence for differences in myelination of GABAergic and cholinergic septohippocampal fibres

It is known that the rat septohippocampal projection is realised at least by GABAergic, parvalbumin containing and cholinergic fibres. The GABAergic component originates from fast-firing and fast-conducting neurons, whereas the cholinergic component represents the slow-firing, slow-conducting type. The present immunofluorescence and immunoelectron microscopic study shows that the vast majority of parvalbumin-immunoreactive. GABAergic axons are surrounded by enormously thick myelin sheaths, but choline acetyltransferase immunoreactive axons were rarely found to be myelinated. In addition, cholinergic fibres show considerably smaller diameters. Accordingly, our results are correlated with the well-known differences in conduction velocities between the GABAergic and cholinergic fibres of the septohippocampal pathway, which depend on myelination and axon calibre. (C) 2001 ISDN. Published by Elsevier Science Ltd. All rights reserved.