Development of Transient Acetylcholinesterase Staining in Cells and Permanent Staining in Fibers in Cortex of Rat Brain.

The development of the acetylcholinesterase (AChE) texture of the cortex of the rat brain was studied during the first three weeks of life. The Tago technique enables visualization of both AChE+ cells and fibers with both shown in exquisite detail making quantification possible. At each age--0 (birth), 7, 14, 21 and 60 days (adult)--four brain areas were studied (cingulate, dorsal neocortex, lateral neocortex and olfactory) at each of three coronal planes in the brain (anterior, intermediate, posterior). Fiber density reached adult levels by Day 21 in cingulate cortex in intermediate and posterior planes. In other areas fiber density reached adult levels by Day 14 indicating a high rate of fiber growth during the first two weeks of life since at birth rat cortex is innervated only by a sparse AChE+ fiber invasion into neocortex in the anterior plane. Fiber density did not regress after adult levels were reached, however, cell staining showed a different pattern. At birth many lightly stained cells were seen in the olfactory cortex in all three planes, but other areas were devoid of cells. In all areas there was a peak at Day 7 in number of cells stained and in intensity of cells staining with a gradual decline in cell staining until by Day 21 very few stained cells were seen in the cortex (typical adult pattern).