Presence of vesicular glutamate transporter‐2 in hypophysiotropic somatostatin but not growth hormone‐releasing hormone neurons of the male rat

Abstract

Recent evidence indicates that hypophysiotropic gonadotropin-releasing hormone (GnRH), corticotropin-releasing hormone (CRH) and thyrotropin-releasing hormone (TRH) neurons of the adult male rat express mRNA and immunoreactivity for type-2 vesicular glutamate transporter (VGLUT2), a marker for glutamatergic neuronal phenotype. In the present study, we investigated the issue of whether these glutamatergic features are shared by growth hormone-releasing hormone (GHRH) neurons of the hypothalamic arcuate nucleus (ARH) and somatostatin (SS) neurons of the anterior periventricular nucleus (PVa), the two parvicellular neurosecretory systems that regulate anterior pituitary somatotrophs. Dual-label in situ hybridization studies revealed relatively few cells that expressed VGLUT2 mRNA in the ARH; the GHRH neurons were devoid of VGLUT2 hybridization signal. In contrast, VGLUT2 mRNA was expressed abundantly in the PVa; virtually all (97.5 +/- 0.4%) SS neurons showed labelling for VGLUT2 mRNA. In accordance with these hybridization results, dual-label immunofluorescent studies followed by confocal laser microscopic analysis of the median eminence established the absence of VGLUT2 immunoreactivity in GHRH terminals and its presence in many neurosecretory SS terminals. The GHRH terminals, in turn, were immunoreactive for the vesicular gamma-aminobutyric acid (GABA) transporter, used in these studies as a marker for GABA-ergic neuronal phenotype. Together, these results suggest the paradoxic cosecretion of the excitatory amino acid neurotransmitter glutamate with the inhibitory peptide SS and the cosecretion of the inhibitory amino acid neurotransmitter GABA with the stimulatory peptide GHRH. The mechanisms of action of intrinsic amino acids in hypophysiotropic neurosecretory systems require clarification.

Subcellular Dynamics of Somatostatin Receptor Subtype 1 in the Rat Arcuate Nucleus: Receptor Localization and Synaptic Connectivity Vary in Parallel with the Ultradian Rhythm of Growth Hormone Secretion

“…To elucidate the neurochemical identity of synaptic terminals in this region, we incubated parallel sections of mediobasal hypothalamus with antibodies recognizing VGluT2 and VGAT, respectively. In agreement with previous reports (Hrabovszky et al, 2005;Kiss et al, 2006), single labeling for VGluT2 revealed dense VGluT2-positive punctate staining, likely excitatory terminals, throughout the ARC (supplemental Fig. 1 B, available at www.jneurosci.org as supplemental material).…”

Coexpression of the mu‐opioid receptor splice variant MOR1C and the vesicular glutamate transporter 2 (VGLUT2) in rat central nervous system

“…In particular, the external layer of the median eminence (ME) provides direct access to the blood stream where hypophysiotropic hormones are released (Armstrong, 1995). The ME is densely innervated by fibers expressing MOR 1C as well as those expressing VGLUT2 (Abbadie et al, 2000a;Hrabovszky et al, 2005aHrabovszky et al, ,b, 2006, especially in the external layer. In the present study we have also shown considerable doublelabeling for MOR 1C and VGLUT2 in ME.…”

“…In the present study we have also shown considerable doublelabeling for MOR 1C and VGLUT2 in ME. It has been reported that hypophysiotropic peptides such as thyrotropin-releasing hormone, gonadotropin-releasing hormone, corticotrophin-releasing hormone, and somatostatin are coexpressed with VGLUT2 (Hrabovszky et al, Hrabovszky et al, 2005a,b, 2006. Thus, our data suggest that activation of MOR 1C may modulate the release of some hypophysiotropic hormones (Plotsky, 1986;Doi et al, 2001;Kutlu et al, 2004).…”

Galanin receptor 1 is expressed in a subpopulation of glutamatergic interneurons in the dorsal horn of the rat spinal cord

“…The specificity of the rabbit antiVGLUTs antibodies has previously been established in our preparation (Landry et al, 2004). The specificity of the AB5907 Chemicon anti-VGLUT2 antibody has been previously assessed in various studies (Montana et al, 2004;Hrabovszky et al, 2005;Wittmann et al, 2005;Fournier et al, 2005). The specificity of the MAB351R anti-GAD65 (Wang et al, 2003) and T-4334 anti-galanin (Geerling et al, 2005) antibodies was also previously assessed.…”