ΔFosB in the supraoptic nucleus contributes to hyponatremia in rats with cirrhosis

Abstract

Bile duct ligation (BDL), a model of hepatic cirrhosis, is associated with dilutional hyponatremia and inappropriate vasopressin release. ΔFosB staining was significantly increased in vasopressin and oxytocin magnocellular neurosecretory cells in the supraoptic nucleus (SON) of BDL rats. We tested the role of SON ΔFosB in fluid retention following BDL by injecting the SON (n = 10) with 400 nl of an adeno-associated virus (AAV) vector expressing ΔJunD (a dominant negative construct for ΔFosB) plus green fluorescent protein (GFP) (AAV-GFP-ΔJunD). Controls were either noninjected or injected with an AAV vector expressing only GFP. Three weeks after BDL or sham ligation surgery, rats were individually housed in metabolism cages for 1 wk. Average daily water intake was significantly elevated in all BDL rats compared with sham ligated controls. Average daily urine output was significantly greater in AAV-GFP-ΔJunD-treated BDL rats compared with all other groups. Daily average urine sodium concentration was significantly lower in AAV-GFP-ΔJunD-treated BDL rats than the other groups, although average daily sodium excretion was not different among the groups. SON expression of ΔJunD produced a diuresis in BDL rats that may be related to decreased circulating levels of vasopressin or oxytocin. These findings support the view that ΔFosB expression in SON magnocellular secretory cells contribute to dilutional hyponatremia in BDL rats.

Fig. 1.

Representative digital images of ΔFosB/FosB staining (A and B), vasopressin immunofluorescence (C and D), and merged pseudocolored images (E and F) of the supraoptic nucleus from a bile duct-ligated (BDL) rat (left) and a sham ligated control (right). Scale bar is 50 μm for each image. ot, optic tract; SON, supraoptic nucleus. G: effects of BDL on the numbers of cells stained for ΔFosB, vasopressin (AVP), and ΔFosB and vasopressin in the supraoptic nucleus of sham ligated (Sham, n = 6) and BDL rats (n = 6). H: effects of BDL on ΔFosB mRNA (Sham n = 5; BDL n = 8) and vasopressin heterogeneous nuclear RNA (hnRNA) (Sham n = 6; BDL n = 8) expression from 7 to 10 laser microdissected vasopressin cells from the SON from each rat. The data depict means ± SE mRNA levels as calculated by the 2^−ΔΔCT method. *P < 0.05 compared with Sham.

Fig. 2.

Representative digital images of ΔFosB/FosB staining (A and B), oxytocin immunofluorescence (C and D), and merged pseudocolored images (E and F) of the supraoptic nucleus from a BDL rat (left) and a sham ligated control (right). Scale bar is 100 μm for each image. G: effects of BDL on the numbers of cells stained for ΔFosB, oxytocin (OXY), and ΔFosB and OXY in the supraoptic nucleus of sham ligated (Sham, n = 5) and BDL rats (n = 7). *P < 0.05 from sham.

Fig. 3.

Representative example of green fluorescent protein (GFP) fluorescence (A), vasopressin immunofluorescence (B), and a merged image (C) of the supraoptic nucleus from a BDL rat injected with adeno-associated virus (AAV)-GFP-ΔJunD. Scale bar is 100 μm for each image.

Fig. 4.

The effects of BDL and dominant negative inhibition of ΔFosB in the SON on average daily water intake and urine volume in noninjected sham ligated rats (Sham), sham ligated rats injected with the control AAV (Sham + GFP), sham ligated rats injected with the dominant negative construct for ΔFosB (Sham + ΔJunD), noninjected BDL rats, and BDL rats injected the control virus (BDL + GFP) or the dominant negative construct against ΔFosB (BDL + ΔJunD). The number of rats for each group is given in Table 2. **P < 0.05 from all sham groups. #P < 0.05 from all other groups.

Fig. 5.

Average daily urine sodium concentration (A) and average daily sodium excretion (B) in noninjected sham ligated rats (Sham), sham ligated rats injected with the control AAV (Sham + GFP), sham ligated rats injected with the dominant negative construct for ΔFosB (Sham + ΔJunD), noninjected BDL rats, and BDL rats injected the control virus (BDL + GFP) or the dominant negative construct against ΔFosB (BDL + ΔJunD). #P < 0.05 from all other groups.