Processing and Analysis of Neuroanatomical Images

Today, neuroanatomists have an almost bewildering array of techniques that are being used to study the organization of the nervous system along dimensions that were not even conceived 10 to 15 years ago. Brain circuits are no longer viewed as wiring diagrams interlinking classical brain structures but rather as subpopulations of neurons differing along morphological and neurochemical lines having interconnections with other equally specific subpopulations of neurons in multiple other brain structures. No longer are neural circuits “excitatory” or “inhibitory.” Neurons may contain several transmitters/modulators, and the actions of modulators may depend on the moment-to-moment status of their target cells. The levels of these neuroac-tive molecules may vary with the animal’s functional, humoral, or developmental state. On the postsynaptic side, multiple receptor subtypes are well established for many transmitter systems; these link presynaptic inputs to a growing multitude of channel types and second messenger systems, which may or may not have direct actions on the genome or gene products of the target cell. Methods for studying these phenomena in brain sections are now available, and there are exciting possibilities to apply similar techniques to in vitro brain-slice preparations to study functioning neuroanatomy.