No abstract

A second vesicular glutamate transporter (VGLUT2) has been reported to be expressed in neurosecretory neurons of the hypothalamic‐neurohypophysial system. To study its role in the neurosecretory neurons, we evaluated the expression of the VGLUT2 gene in the paraventricular (PVN) and supraoptic (SON) nuclei as well as the immunoreactivity in the neurohypophysis under euhydrated and chronic hyperosmotic conditions with in situ hybridization and immunohistochemistry. The intensity of hybridization signals in the PVN, SON and thalamus of rats subjected to water deprivation for 7 days, or drinking 2% NaCl for 4 or 7 days, was compared with that of euhydrated rats (control). The overall intensity in the entire PVN or SON, but not the thalamus, was higher in osmotically stimulated rats than in controls. Within the PVN, a significantly higher intensity of signals than that of controls was found only in the dorsolateral posterior magnocellular region in 4‐day salt‐loaded rats and in all subregions in water‐deprived or 7‐day salt‐loaded rats. The intensity in the SON was higher in the stimulated rats than in controls, regardless of subregions. In the neurohypophysis, VGLUT2 staining was frequently localized in vasopressin terminals of control rats and was apparently reduced in stimulated rats. These results indicate that VGLUT2 is principally expressed in magnocellular vasopressin neurons, suggesting some local effect of intrinsic glutamate on neurohypophysial hormone secretion.