Variation of pro-vasopressin processing in parvocellular and magnocellular neurons in the paraventricular nucleus of the hypothalamus: Evidence from the vasopressin-related glycopeptide copeptin

Arginine vasopressin (AVP) is synthesized in parvocellular- and magnocellular neuroendocrine neurons in the paraventricular nucleus (PVN) of the hypothalamus. Whereas magnocellular AVP neurons project primarily to the posterior pituitary, parvocellular AVP neurons project to the median eminence (ME) and to extrahypothalamic areas. The AVP gene encodes pre-pro-AVP that comprises the signal peptide, AVP, neurophysin (NPII), and a copeptin glycopeptide. In the present study, we used an N-terminal copeptin antiserum to examine copeptin expression in magnocellular and parvocellular neurons in the hypothalamus in the mouse, rat, and macaque monkey. Although magnocellular NPII-expressing neurons exhibited strong N-terminal copeptin immunoreactivity in all three species, a great majority (~90%) of parvocellular neurons that expressed NPII was devoid of copeptin immunoreactivity in the mouse, and in approximately half (~53%) of them in the rat, whereas in monkey hypothalamus, virtually all NPII-immunoreactive parvocellular neurons contained strong copeptin immunoreactivity. Immunoelectron microscopy in the mouse clearly showed copeptin-immunoreactivity co-localized with NPII-immunoreactivity in neurosecretory vesicles in the internal layer of the ME and posterior pituitary, but not in the external layer of the ME. Intracerebroventricular administration of a prohormone convertase inhibitor, hexa-d-arginine amide resulted in a marked reduction of copeptin-immunoreactivity in the NPII-immunoreactive magnocellular PVN neurons in the mouse, suggesting that low protease activity and incomplete processing of pro-AVP could explain the disproportionally low levels of N-terminal copeptin expression in rodent AVP (NPII)-expressing parvocellular neurons. Physiologic and phylogenetic aspects of copeptin expression among neuroendocrine neurons require further exploration.

Vasopressin gene products are colocalised with corticotrophin-releasing factor within neurosecretory vesicles in the external zone of the median eminence of the Japanese macaque monkey (Macaca fuscata)

Arginine vasopressin (AVP), when released into portal capillaries with corticotrophin-releasing factor (CRF) from terminals of parvocellular neurones of the hypothalamic paraventricular nucleus (PVH), facilitates the secretion of adrenocorticotrophic hormone (ACTH) in stressed rodents. The AVP gene encodes a propeptide precursor containing AVP, AVP-associated neurophysin II (NPII), and a glycopeptide copeptin, although it is currently unclear whether copeptin is always cleaved from the neurophysin and whether the NPII and/or copeptin have any functional role in the pituitary. Furthermore, for primates, it is unknown whether CRF, AVP, NPII and copeptin are all colocalised in neurosecretory vesicles in the terminal region of the paraventricular CRF neurone axons. Therefore, we investigated, by fluorescence and immunogold immunocytochemistry, the cellular and subcellular relationships of these peptides in the CRF- and AVP-producing cells in unstressed Japanese macaque monkeys (Macaca fuscata). Reverse transcription-polymerase chain reaction analysis showed the expression of both CRF and AVP mRNAs in the monkey PVH. As expected, in the magnocellular neurones of the PVH and supraoptic nucleus, essentially no CRF immunoreactivity could be detected in NPII-immunoreactive (AVP-producing) neurones. Immunofluorescence showed that, in the parvocellular part of the PVH, NPII was detectable in a subpopulation (approximately 39%) of the numerous CRF-immunoreactive neuronal perikarya, whereas, in the outer median eminence, NPII was more prominent (approximately 52%) in the CRF varicosities. Triple immunoelectron microscopy in the median eminence demonstrated the presence of both NPII and copeptin immunoreactivity in dense-cored vesicles of CRF-containing axons. The results are consistent with an idea that the AVP propeptide is processed and NPII and copeptin are colocalised in hypothalamic-pituitary CRF axons in the median eminence of a primate. The CRF, AVP and copeptin are all co-packaged in neurosecretory vesicles in monkeys and are thus likely to be co-released into the portal capillary blood to amplify ACTH release from the primate anterior pituitary.

Detection and Characterization of Estrogen Receptor Beta Expression in the Brain with Newly Developed Transgenic Mice

Two types of nuclear estrogen receptors, ERα and ERβ, have been shown to be differentially involved in the regulation of various types of behaviors. Due to a lack of tools for identifying ERβ expression, detailed anatomical distribution and neurochemical characteristics of ERβ expressing cells and cellular co-expression with ERα remain unclear. We have generated transgenic mice ERβ-RFP^tg, in which RFP was inserted downstream of ERβ BAC promotor. We verified RFP signals as ERβ by confirming: (1) high ERβ mRNA levels in RFP-expressing cells collected by fluorescence-activated cell sorting; and (2) co-localization of ERβ mRNA and RFP proteins in the paraventricular nucleus (PVN). Strong ERβ-RFP signals were found in the PVN, medial preoptic area (MPOA), bed nucleus of the stria terminalis, medial amygdala (MeA), and dorsal raphe nucleus (DRN). In the MPOA and MeA, three types of cell populations were identified; those expressing both ERα and ERβ, and those expressing exclusively either ERα or ERβ. The majority of PVN and DRN cells expressed only ERβ-RFP. Further, ERβ-RFP positive cells co-expressed oxytocin in the PVN, and tryptophan hydroxylase 2 and progesterone receptors in the DRN. In the MeA, some ERβ-RFP positive cells co-expressed oxytocin receptors. These findings collectively suggest that ERβ-RFP^tg mice can be a powerful tool for future studies on ERβ function in the estrogenic regulation of social behaviors.