Neurons with galanin innervate cholinergic cells in the human basal forebrain and galanin and acetylcholine coexist

Immunocytochemistry with antibodies against cholinacetyltransferase (ChAT) and the novel peptide galanin (GA) were conducted as a single label or as double label experiments on the basal forebrain nuclei of brains from eleven human subjects without prior history of neurological disease. ChAT positive or cholinergic neurons form the major population of cells in the basal nucleus of Meynert. A minor portion of these ChAT positive neurons demonstrate a coexistence with GA positive immunoreactivity suggesting that they are cholinergic/GA neurons. Small fusiform neurons with long dendrites and complex local axonal networks are GA immunoreactive and are local circuit interneurons. The cholinergic cells in the basal nucleus are innervated by a fine network of GA immunoreactive axons and terminals which enwrap their perikarya and dendrites. It is suggested that GA in local circuit interneurons may provide a significant control or modulation of the cholinergic neurons and of cholinergic functions within the basal nucleus. In human diseases which feature a destruction of the basal forebrain cholinergic neurons, surviving GA neurons may inhibit most remaining cholinergic neurons and their function, with severe consequences.