Vesicular glutamate transporter 1 immunoreactivity in motor endplates of striated esophageal but not skeletal muscles in the mouse.

Glutamate, the major excitatory transmitter in the central nervous system, has been speculated for years to influence mammalian motor endplates but trials to identify glutamatergic motor terminals failed because specific markers were not available. Recently, antibodies to vesicular glutamate transporters (VGLUTs) opened new possibilities for further morphological investigations. We detected VGLUT1 immunoreactivity (-ir), but not VGLUT2-ir and VGLUT3-ir, respectively, in many motor nerve terminals in motor endplates of the mouse esophagus as identified by alpha-bungarotoxin or colocalization of VGLUT1 with choline acetyltransferase. These findings suggest that glutamate is co-stored with acetylcholine in esophageal neuromuscular junctions. Surprisingly, we found neither VGLUT1-ir nor VGLUT2-ir or VGLUT3-ir in neuromuscular junctions of somitic and branchiogenic skeletal muscles. This may reflect differences in functional properties and the embryonic origin between skeletal and esophageal striated muscle fibers.