Glutamatergic innervation of the hypothalamic median eminence and posterior pituitary of the rat.
Recent studies have localized the glutamatergic cell marker type-2 vesicular glutamate transporter (VGLUT2) to distinct peptidergic neurosecretory systems that regulate hypophysial functions in rats. The present studies were aimed to map the neuronal sources of VGLUT2 in the median eminence and the posterior pituitary, the main terminal fields of hypothalamic neurosecretory neurons. Neurons innervating these regions were identified by the uptake of the retrograde tract-tracer Fluoro-Gold (FG) from the systemic circulation, whereas glutamatergic perikarya of the hypothalamus were visualized via the radioisotopic in situ hybridization detection of VGLUT2 mRNA. The results of dual-labeling studies established that the majority of neurons accumulating FG and also expressing VGLUT2 mRNA were located within the paraventricular, periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area. In contrast, only few FG-accumulating cells exhibited VGLUT2 mRNA signal in the arcuate nucleus. Dual-label immunofluorescent studies of the median eminence and posterior pituitary to determine the subcellular location of VGLUT2, revealed the association of VGLUT2 immunoreactivity with SV2 protein, a marker for small clear vesicles in neurosecretory endings. Electron microscopic studies using pre-embedding colloidal gold labeling confirmed the localization of VGLUT2 in small clear synaptic vesicles. These data suggest that neurosecretory neurons located mainly within the paraventricular, anterior periventricular and supraoptic nuclei and around the organum vasculosum of the lamina terminalis and the preoptic area secrete glutamate into the fenestrated vessels of the median eminence and posterior pituitary. The functional aspects of the putative neuropeptide/glutamate co-release from neuroendocrine terminals remain to be elucidated.
Hrabovszky
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Laboratory of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, P.O. Box 67, 1450 Budapest, Hungary.
Deli
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Turi
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GF
Kalló
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Liposits
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D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D007031:Hypothalamus / Q000378:metabolism* / Q000648:ultrastructure; D017403:In Situ Hybridization; D008297:Male; D008473:Median Eminence / Q000098:blood supply / Q000294:innervation* / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism; D008833:Microcirculation / Q000166:cytology / Q000502:physiology; D016253:Microscopy, Immunoelectron; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009434:Neural Pathways / Q000378:metabolism* / Q000648:ultrastructure; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D009490:Neurosecretory Systems / Q000378:metabolism / Q000648:ultrastructure; D010902:Pituitary Gland / Q000098:blood supply / Q000294:innervation / Q000502:physiology; D010904:Pituitary Gland, Posterior / Q000098:blood supply / Q000294:innervation* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013266:Stilbamidines; D013572:Synaptic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D050599:Vesicular Glutamate Transport Protein 2 / Q000235:genetics / Q000378:metabolism*
C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; D015415:Biomarkers; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; C493475:Slc17a6 protein, rat; D013266:Stilbamidines; C489618:Sv2a protein, rat; D050599:Vesicular Glutamate Transport Protein 2; D018698:Glutamic Acid