Distribution of acetylcholinesterase in the nerve endings of chicken m. retractor phalli cranialis.

The distance of the neuromuscular gap was measured in a chicken smooth muscle, m. retractor phalli cranialis (MRPC). For the identification of active neuromuscular contacts, acetylcholinesterase (AChE) was stained according to Tago's modification of the Karnovsky and Roots' method. Thirty two out of 500 muscle cells were within 200 nm from the nerve endings. The MRPC was classified as Burnstock's Model C, which is characterised by the low frequency of directly innervated cells. The AChE-positive reaction was observed on both muscular and neural membranes only when the distance between the two was less than 170 nm. These results suggest that the smooth muscle cells may be innervated by axon varicosities within such a distance.