Localization of vasopressin mRNA and immunoreactivity in pituicytes of pituitary stalk-transected rats after osmotic stimulation.

Abstract

The presence of [arginine] vasopressin (AVP) mRNA and AVP immunoreactivity in pituicytes of the neural lobe (NL) of intact and pituitary stalk-transected rats, with and without osmotic stimulation, was examined. AVP mRNA was analyzed by Northern blotting, as well as by in situ hybridization in combination with immunocytochemistry using anti-glial fibrillary acidic protein (GFAP) as a marker for pituicytes. In intact rats, a poly(A) tail-truncated 0.62-kb AVP mRNA was detected in the NL and was found to increase 10-fold with 7 days of continuous salt loading. Morphological analysis of the NL of 7-day salt-loaded rats revealed the presence of AVP mRNA in a significant number of GFAPpositive pituicytes in the NL and in areas most probably containing nerve fibers. Eight days after pituitary stalk transection the NL AVP mRNA diminished in animals given water to drink, whereas in those given 2% saline for 18 h followed by 6 h of water, a treatment repeated on 6 successive days beginning 2 days after surgery, the 0.62-kb AVP mRNA was present. The AVP mRNA in the pituitary stalk-transected, salt-loaded rats showed an exclusive cellular distribution in the NL, indicative of localization in pituicytes. Immunoelectron microscopy showed the presence of AVP immunoreactivity in a subpopulation of pituicytes 7 and 10 days after pituitary stalk transection in salt-loaded animals, when almost all AVP fibers had disappeared from the NL. These data show that a subset of pituicytes in the NL is activated to synthesize AVP mRNA and AVP in response to osmotic stimulation.The [arginine] vasopressin (AVP) gene is abundantly expressed in magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) in the hypothalamus (1). However, recent studies have shown the presence of AVP mRNA in the neural lobe (NL) of the pituitary as well, where the axons of these neurons terminate. This NL mRNA is shorter than that present in the hypothalamus due to a truncated poly(A) tail and is up-regulated during osmotic stimulation (2-5). After disconnection of the hypothalamoneurohypophysial tract by electrically damaging the ventromedial hypothalamic area, the AVP mRNA disappeared from the NL (5). This latter observation, together with the detection of AVP mRNA at the electron microscopic level in a subset of axonal swellings in the median eminence and NL (6), has led investigators to propose that the NL AVP mRNA is derived from the hypothalamic magnocellular neurons and is axonally transported to the NL (5, 6). Furthermore, the poly(A) tail of this AVP mRNA appears to be truncated during axonal transport (7). The existing data, however, do not fully exclude the possibility that some of the NL AVP mRNA is expressed in pituicytes.In this study, we have carried out in situ hybridization histochemistry in combination with immunocytochemistry, using a glial fibrillary acidic protein (GFAP) antibody as a marker for the pituicytes (8, 9) to examine the expression of AVP mRNA in these astrocytes in the NL. Studies were conducte...

Neurohormones: oxytocin, vasopressin and related peptides – structure, genes, receptors, and evolution

“…Vasopressin mRNAs were identified in a subset of pituitary cells (Murphy et al, 1993), which is in concordance with the presence of their translation proteins in these cells (Boersma et al, 1993;Pu et al, 1995;Murphy and Wells, 2003).…”

Transgenic studies in rats and mice on the osmotic regulation of vasopressin gene expression

“…Vasopressin transcripts have been described in a sub-set of pituicytes (Pu et al 1995), consistent with the presence of their translation products in these cells (Boersma et al 1993;Pu et al 1995). However, it is unclear whether the vasopressin transcripts arise from transcription within the pituicyte, or whether they are transferred to pituicytes from axons.…”

“…The description of vasopressin RNAs in the neural lobe of the rat pituitary gland (Murphy et al 1989) has prompted much interest in their origin, regulation and function (Levy et al 1990;Jirikowski et al 1990;McCabe et al 1990;Mohr et al 1990Mohr et al , 1991Mohr et al , 1995Murphy et al 1993;Trembleau et al 1994Trembleau et al , 1996Pu et al 1995). Vasopressin RNA has also been detected in the mouse neural lobe (Murphy et al 1989) and in the bovine neurointermediate lobe (Murphy et al 1992).…”

Hypothalamic-pituitary-adrenal axis up-regulation in rats submitted to pituitary stalk compression

“…In the Brattleboro rat, an experimental model of inherited DI, a deficiency in magnocellular neurons has been described (Pickering & North 1982, Schmale & Richter 1984. Other experimental models of central DI have been created, some of them based on pituitary stalk transsection (Pu et al 1995, Huang & Dellmann 1996. However, this surgical procedure induces not only central DI but also anterior pituitary failure (Makara et al 1979), therefore studies involving the activity of the HPA axis cannot be performed.…”