Differential effects of water deprivation and rehydration on Fos and FosB/ΔFosB staining in the rat brainstem

Abstract

This study examined the effects of dehydration and rehydration with water on Fos and FosB staining in the brainstem of rats. Male rats were water deprived for 48 h (Dehyd, n = 7) or 46 h followed by 2 h access to water (Rehyd, n = 7). Controls had ad libitum access to water (Con, n = 9). Brainstems were stained for Fos and FosB/ΔFosB using commercially available antibodies. In the nucleus of the solitary tract (NTS), the number of Fos stained neurons was significantly increased by dehydration and increased further following rehydration (Con 5 ± 1; Dehyd 22 ± 1; Rehyd 48 ± 5). The average number of Fos-positive cells in the parabrachial nucleus (PBN) was significantly increased only by rehydration (Con 12 ± 2; Dehyd 6 ± 2; Rehyd 51 ± 4). The area postrema (AP) showed significant increases in Fos staining after dehydration and rehydration (Fos: Con 4 ± 1; Dehyd 28 ± 3; Rehyd 24 ± 3). In the rostral ventrolateral medulla (RVL), Fos staining significantly increased after dehydration and this effect was reduced by rehydration (Con 3 ± 1; Dehyd 21 ± 2; Rehyd 12 ± 1). In contrast, Fos staining in the caudal ventrolateral medulla (CVL) was not significantly influenced following either dehydration or rehydration with water (Con 4 ± 1; Dehyd 4 ± 1; Rehyd 5 ± 1). FosB/ΔFosB staining in the NTS, AP, and RVL was comparably increased by dehydration and rehydration. In the PBN and CVL, FosB/ΔFosB staining was not affected by the treatments. Dehydration and rehydration have regionally specific effects on Fos and FosB/ΔFosB staining in the brainstem.

Introduction

A number of studies have examined the effects of water deprivation on Fos staining in the rat forebrain and hypothalamus (De Luca et al., 2002, Ji et al., 2005, McKinley et al., 1994, Morien et al., 1999, Sly et al., 2001, Stocker et al., 2004a, Ueta et al., 1995). In contrast, only a few studies have tested the effects of water deprivation on Fos staining in the brainstem. These studies report that water deprivation increases Fos staining in the nucleus of the solitary tract (NTS) and the area postrema (AP) (De Luca et al., 2002, Ueta et al., 1995).

Water deprivation is associated with an increase in plasma osmolality, hypovolemia, and activation of the renin–angiotensin system. Each of these in isolation affects Fos staining in various regions of the brainstem (Curtis et al., 2002, Hochstenbach et al., 1993, Potts et al., 1999, Potts et al., 2000). For example, in the NTS and caudal ventrolateral medulla (CVL), hyperosmotic stimulation has been shown to increase Fos staining (Hochstenbach and Ciriello, 1995). Similar effects have been observed in these areas after hypovolemia (Curtis et al., 2002, Grove et al., 2003, Potts et al., 2000). Circulating angiotensin has also been shown to induce Fos staining in a number of brainstem regions including the NTS, AP, CVL, and the rostral ventrolateral medulla (RVL) (Potts et al., 1999). Therefore, since these brainstem regions are sensitive to changes in plasma osmolality, hypovolemia, and circulating angiotensin II, we hypothesized that they would also demonstrate increased Fos staining following water deprivation.

In addition, we also examined the effects of water deprivation on another Fos-related protein, FosB. FosB is a member of the AP-1 family of proteins that has a different time course than Fos. Staining for FosB and its splice variant ΔFosB in the central nervous system increases following a single exposure to cocaine or amphetamine, and this increase lasts for days or weeks (Nestler et al., 2001). Previous studies have shown that FosB/ΔFosB increases in the SON 6 to 8 h following an osmotic stimulus and that it persists for at least 24 h (Miyata et al., 2001, Penny et al., 2005). In contrast, Fos staining peaks at 2 h and returns to control levels at 6 h post-stimulation. These results demonstrate that Fos and FosB/ΔFosB staining are increased following an acute physiological challenge and that they have different time courses. FosB/ΔFosB staining can be detected in brain regions that are involved in body fluid homeostasis following an acute volume expansion (Howe et al., 2004) and in the forebrain following water deprivation and rehydration (Ji et al., 2005).

It has been hypothesized that a splice variant ΔFosB is a signal for long term adaptations in the CNS and may regulate the expression of glutamate receptor subunits, cytoskeletal proteins, and peptides (McClung et al., 2004). Since increased FosB/ΔFosB staining occurs following acute or progressive physiological challenges, it is possible that FosB/ΔFosB mediates adaptive changes in gene expression associated with these physiological stimuli. Therefore, we included FosB/ΔFosB staining in the current study in order to determine whether or not it is expressed in brainstem circuits activated in association with dehydration.

We also investigated the effects of rehydration following water deprivation on Fos staining in the brainstem. Previous studies have shown that 2–6 h of rehydration differentially affects Fos staining in the forebrain (De Luca et al., 2002, Herbert et al., 1992, Ji et al., 2005, Xu and Herbert, 1994). For example, 2 h of access to water blocks Fos staining in the SON after water deprivation but Fos staining persists in the subfornical organ, organum vasculosum of the lamina terminalis, and median preoptic nucleus (Gottlieb et al., 2006, Ji et al., 2005). In the same study, we observed that rehydration attenuated FosB staining in the SON but not in the other regions included in the study (Ji et al., 2005). Therefore, we examined the effects of rehydration on Fos and FosB/ΔFosB staining in the hindbrain. In addition, increased FosB/ΔFosB staining in the brainstem following water deprivation and rehydration could indicate that these regions participate in long term changes in neural function.