Light- and electron-microscopic studies on acetylcholinesterase activity in Auerbach's plexus of the developing rat colon.

The distal portions of rat colon from 14-, 16-, 18-, and 21-day fetuses, newborns, and adults were histochemically examined for acetylcholinesterase (AChE) activity by light and electron microscopy. The specificity of AChE activity in Auerbach's plexus was confirmed by specific and/or nonspecific cholinesterase inhibition tests. Enzyme activity was first detectable after 18 days of gestation and became stronger with age. The reaction product was demonstrated by electron microscopy in and between the plasma membranes of the nerve fibers and their terminals. Ganglion cells also showed positive activity in the plasma membrane, nuclear envelope, and rough endoplasmic reticulum. The distribution pattern of the reaction product in fetal and newborn rat colons was basically the same as in adult rat colon. Therefore, the localization of AChE activity is considered to be a good marker for identifying premature ganglion cells in Auerbach's plexus, and the degree of AChE staining is a good indication of the degree of maturation of the plexus.