Through projections to the cerebral cortex, the basal forebrain plays a critical role in cortical activation and attention, yet also in cortical slow wave activity and sleep. The basalocortical projections have recently been shown to be comprised by cholinergic, GABAergic and glutamatergic fibers (Henny et al, SFN, 2002), which could be differentially involved in these opposing roles. In the present study, we examined the relative contributions of each fiber system to innervation of the limbic prefrontal cortex in the rat. For this purpose, we employed anterograde transport of biotin dextran amine (BDA) from neurons in the magnocellular preoptic-substantia innominata region with dual staining for BDA and the vesicular transporter proteins for acetylcholine (VAChT), GABA (VGAT) or glutamate (VGluT2). Based upon strereological estimates, we found that the VAChT+, VGAT+ and VGluT2+ varicosities accounted respectively for ~50%, ~40% and <10% of the total number of BDA+ varicosities in the orbitofrontal cortex....