Neurons with neurokinin B mRNA in the rat magnocellular basal nucleus: distribution, projection and colocalization...

Mapping and cortical projections of neurons containing neurokinin B (NKB) mRNA in the rat basal forebrain were studied using hybridization histochemistry and retrograde labeling. Neurokinin B mRNA was found in a small proportion of the neurons present in the magnocellular basal nucleus that project to the cortex. Most of these neurons projected to the frontal and parietal cortices, whereas only few projected to the occipital cortex and almost none to allocortical areas, including the olfactory bulb. NKB mRNA colocalization with galanin or substance P mRNAs, both found within neurons of the magnocellular basal nucleus, was not detected there. These results demonstrate a novel diffuse neocortical tachykinin input from the basal forebrain, in addition to the well-known cholinergic one.