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

It is known that the rat septohippocampal projection is realised at least b y GABAergic, parvalbumin containing and cholinergic fibres. The GABAergic c omponent originates from fast-firing and fast-conducting neurons, whereas t he cholinergic component represents the slow-firing, slow-conducting type. The present immunofluorescence and immunoelectron microscopic study shows t hat the vast majority of parvalbumin-immunoreactive. GABAergic axons are su rrounded by enormously thick myelin sheaths, but choline acetyltransferase immunoreactive axons were rarely found to be myelinated. In addition, choli nergic fibres show considerably smaller diameters. Accordingly, our results are correlated with the well-known differences in conduction velocities be tween 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.