Developmental reorganization of acetylcholinesterase-rich inputs to somatosensory cortex of the mouse.

In this histochemical study, maturational changes in acetylcholinesterase-(AChE) staining in the barrel field of mouse somatosensory cortex were traced. Three distinct stages in the maturation of the AChE positive barrel innervation of mouse can be observed. In the first stage, individual AChE-positive fibers are initially detected in layer IV between 4-5 days postnatal (dpn). This lamina remains lightly stained for the next several days. At 11-12 dpn there is an abrupt increase in the intensity of AChE activity in the barrel hollows, that marks the beginning of the second stage. In the third stage between 17 and 21 dpn, this AChE-rich plexus of fibers is reorganized in the following manner. AChE fiber staining of the barrel hollows becomes limited to the superficial 75-100 microns of barrel depth, i.e. at the boundary between layers III and IV. At deeper levels in layer IV only the septae are AChE-positive. These observations differ from those previously reported for the rat, both in terms of the organization and development of the AChE-positive innervation to the barrels. The present work also provides the first indication that there is a stratification of inputs to the barrels.