A History of Neuroanatomical Mapping

Publisher Summary This chapter outlines the history of neuroanatomical mapping. The first useful stain for nervous tissue, carmine, significantly increased the contrast in histological sections so that neuronal cell bodies were more distinct when viewed under the microscope. With the gradual realization that neurotransmission is mediated chemically, and with the identification of the molecules involved, histological techniques were developed to determine the cellular distribution of neurotransmitters and their receptors. The development of histofluorescence methods for biogenic amines led to a series of classic brain mapping studies that defined a whole new class of unexpected neural systems—noradrenergic, adrenergic, dopaminergic, and serotonergic cell groups with very widespread, “diffuse” projections more reminiscent of the sympathetic system than the apparently simple sensory and motor pathways so familiar and comfortable to neuroanatomists. Even though histochemical methods for localizing acetylcholinesterase and the biogenic amines were very important and influential, they were not general in the sense that they could not be applied to a wide range of molecules. Their success was based instead on the specificity of chemical reactions taking place within tissue sections. The introduction of immunohistochemistry revolutionized chemoarchitectonics because in principle any antigenic molecule could now be localized at the cellular level by applying antibodies to tissue sections.