Vesicular glutamate transporter 2-immunoreactive afferent nerve terminals in rat carotid sinus baroreceptors

Sensory nerve endings respond to various stimuli and subsequently transmit afferent informations to central nervous system, but their responsibility has been suggested to be modulated by glutamate. In the present study, we examined the immunohistochemical localization of vesicular glutamate transporter 1 (vGLUT1) and vGLUT2 in baroreceptor nerve endings immunoreactive for P2X2 and P2X3 purinoceptors in the rat carotid sinus by immunohistochemistry of whole-mount preparations with confocal scanning laser microscopy. P2X3-immunoreactive flat leaf-like axon terminals were immunoreactive to vGLUT2, but not to vGLUT1. Among members of the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex, immunoreactivities for synaptosomal-associated protein, 25 kDa, Syntaxin1, and vesicle-associated membrane protein 2 (VAMP2) were localized in P2X2- and P2X3-immunoreactive axon terminals. Punctate immunoreactive products for VAMP2 and vGLUT2 were co-localized in axon terminals. These results suggest that vGLUT2 is localized in P2X3-immunoreactive baroreceptor terminals in the carotid sinus, and these terminals may release glutamate by exocytosis in order to modulate baroreceptor function in the carotid sinus.