Somatosensory cortex: acetylcholinesterase staining of barrel neuropil in the rat.

Acetylcholinesterase (AchE) staining of layer IV of rat somatosensory (SmI) cortex was studied. In the barrel field of SmI, there are periodic, intensely AchE staining foci in the pattern and with the dimensions of barrels. The onset of this staining, at age 3 days, corresponds with the arrival of thalamocortical input to the barrels. Undercutting of SmI prevents staining in layer IV. We conclude that there are AchE-rich zones in layer IV that coincide with the specific thalamocortical projection to SmI.