Histochemical and biochemical studies of cholinesterases in the carotid labyrinth of amphibians.

Acetylcholinesterase activity was detected in the carotid labyrinth of amphibians by both biochemical and histochemical methods. The histochemical tests showed enzyme activity in surfaces of afferent and efferent nerve terminals in contact with type I cells, but none within the type I cells. Acetylcholinesterase activity occurred on some, though not all, nerve fibers in the extra-cellular spaces. These fibers might be parasympathetic cholinergic fibers innervating blood vessels.