FINE STRUCTURAL LOCALIZATION OF CHOLINESTERASE ACTIVITY IN THE RAT SUBMANDIBULAR GLAND

Abstract

The innervation of the rat submandibular gland was investigated by means of electron microscopy and cytochemical techniques. Axonal swellings partially depleted of their Schwann cell investment were observed in relationship to myoepithelial cells, acinar cells, ducts, capillaries and smooth muscle cells of arterioles. No direct contacts were found to exist between these elements and the nerve fibers. Axonal swellings containing mitochondria and vesicles fell into two distinct types: those characterized by small agranular vesicles and larger vesicles with pale cores and those characterized by small agranular vesicles and small vesicles with dense cores. Reaction product due to acetylcholinesterase activity was observed to be associated with the axolemma and the Schwann cell membrane at the axon-Schwann cell interface of many unmyelinated nerves found in relationship to both the vascular and parenchymal elements of the gland. Activity was found in association with the surface pits and vesicles of myoepithelial cells and arteriolar smooth muscle cells and with the rough endoplasmic reticulum and the nuclear envelope of the myoepithelial cells. Axonal swellings devoid of activity were observed particularly in relationship to arterioles. Reaction product was found only at the axon-Schwann cell interface when sections were incubated in medium for the demonstration of butyrylcholinesterase activity, while no reaction product was found upon addition of eserine sulfate to any of the media. The possibility that the reaction product due to acetylcholinesterase activity observed in association with the axolemma and the surface vesicles and pits of the myoepithelial cells and the arteriolar smooth muscle cells may define the autonomic cholinergic junction in the rat submandibular gland was explored.