Acetylcholinesterase activity at the synapses of presynaptic boutons with presumed alpha-motoneurons in chicken ventral horn. Light- and electron-microscopic studies.

Acetylcholinesterase (AChE) activity at the synapses of presynaptic boutons on presumed α-motoneurons in the chicken ventral horn was studied histochemically at the light- and electron-microscope levels. At the light-microscope level, many dot-like AChE-active sites were observed on the soma and dendrites of presumed α-motoneurons. On electron microscopy, reaction products for AChE activity were observed mainly in the synaptic clefts of the four kinds of presynaptic boutons: (1) S type boutons, (2) boutons containing small, spherical, dense cored vesicles (diameter range, 60–105 nm) and spherical, clear vesicles, (3) boutons containing medium-sized, spherical, dense cored vesicles (65–115 nm) and spherical, clear vesicles, and (4) boutons containing large, spherical, dense cored vesicles (80–130 nm) and spherical, clear vesicles. In the light of previous physiological and biochemical studies, the present results suggest the possibility that each of these presynaptic boutons which are AChE-active in their synaptic clefts may contain acetylcholine, substance P, or enkephalins which acts as a neurotransmitter or modulator.