A comparison of physiological and transcriptome responses to water deprivation and salt loading in the rat supraoptic nucleus

Abstract

-Salt loading (SL) and water deprivation (WD) are experimental challenges that are often used to study the osmotic circuitry of the brain. Central to this circuit is the supraoptic nucleus (SON) of the hypothalamus, which is responsible for the biosynthesis of the hormones, arginine vasopressin (AVP) and oxytocin (OXT), and their transport to terminals that reside in the posterior lobe of the pituitary. On osmotic challenge evoked by a change in blood volume or osmolality, the SON undergoes a functionrelated plasticity that creates an environment that allows for an appropriate hormone response. Here, we have described the impact of SL and WD compared with euhydrated (EU) controls in terms of drinking and eating behavior, body weight, and recorded physiological data including circulating hormone data and plasma and urine osmolality. We have also used microarrays to profile the transcriptome of the SON following SL and remined data from the SON that describes the transcriptome response to WD. From a list of 2,783 commonly regulated transcripts, we selected 20 genes for validation by qPCR. All of the 9 genes that have already been described as expressed or regulated in the SON by osmotic stimuli were confirmed in our models. Of the 11 novel genes, 5 were successfully validated while 6 were false discoveries. transcriptome; supraoptic nucleus; water restriction; salt load; neuroendocrine TERRESTRIAL LIFE requires that the osmolality of the extracellular fluid (ECF) is strictly controlled. Increased ECF osmolality results in water leaving the cell, reducing intracellular fluid (ICF) volume, while increasing ICF osmolality, which will compromise the metabolic processes necessary for life. Chronic increases in ECF osmolality can be brought about experimentally by a high intake of salt (salt loading, SL) or by water deprivation (WD) (5). In the absence of drinking fluid (WD), extracellular and intracellular fluid volumes decrease, as water and sodium are inevitably lost in sweat and urine leading to hypovolemia and, as a consequence of dehydration-induced natriuresis, sodium depletion (14,35). This depletion of sodium means that WD animals also display enhanced salt appetite (14). In contrast, SL increases body sodium content, causing an increase in ECF volume, but a decrease in the volume of the ICF (35).Angiotensin II (ANG II), atrial natriuretic peptide (ANP), arginine vasopressin (AVP), and oxytocin (OXT) are the main hormones involved in the control of hydromineral homeostasis in mammals (5). ANP is synthesized and secreted into the bloodstream in response to stretching of the right atrial muscle cells by increased blood volume. Once in the bloodstream, ANP has a potent natriuretic effect, acting on the distal convoluted tubule of the nephron to inhibit sodium reabsorption (13,44). ANP is an important indicator of blood volume. AVP and OXT release are stimulated by hypovolemia, hypertonicity, and hypernatremia, among other stimuli (36). Circulating levels of AVP correlate with plasma osmolality (4) and thirst perce...

Unsupervised Network Analysis of the Plastic Supraoptic Nucleus Transcriptome Predicts Caprin2 Regulatory Interactions

“…We re-mined raw data taken from analysis of 29 Affymetrix 230 2.0 microarrays that represented animals in either the naïve state ( n = 4 female and n = 5 male) or the plastic state ( n = 5 dehydration-male, n = 5 lactation-female, n = 5 dehydrated-female, n = 5 salt-loaded-male; Hindmarch et al, 2006; Qiu et al, 2011; Greenwood et al, 2015). NCBI Accession numbers (incorporating controls): male dehydration, GSE3110; male salt loading, GSE65663; female dehydration and lactation, GSE30733.…”

“…We note that the biological importance of salt and water balance, especially after challenge, ensures small standard deviations (10%) in the data (Hindmarch et al, 2013). Validation using quantitative reverse transcription PCR (qRT-PCR; Hindmarch et al, 2006; Qiu et al, 2011; Greenwood et al, 2015; Fig. 3) has shown that the microarray data are very robust and reliable.…”

“…Twelve-week-old male SD Rats (Harlan) were given access to standard laboratory rat chow and water ad libitum for one week to acclimatize to laboratory conditions, following which half the animals were completely deprived of drinking water for 72 h (dehydration), which elicits a reliable and consistent increase in plasma osmolality with limited weight loss (Greenwood et al, 2015). Animals were killed by stunning and then decapitated with a small animal guillotine (Harvard Apparatus).…”

“…In addition, It has been demonstrated that the AVP mRNAs is subject to post-transcriptional modification in the form of an increase in the length of the 3’ poly(A) tail following dehydration (Carrazana et al, 1988; Zingg et al, 1988; Carter and Murphy, 1989; Murphy and Carter, 1990). Recently, microarrays have been used to document transcriptome-wide changes in gene expression in the SON of male rats subject to salt-loading and dehydration (Hindmarch et al, 2006; Greenwood et al, 2015), and in female rats in response to both dehydration and 11 d of lactation (Qiu et al, 2011), and it has been suggested that these changes are part of an organized response to maintaining homeostasis in a changing environment (Hindmarch et al, 2013). …”

AZ Street in Vasopressin Synthesis

“…These gene lists can be linked to the street index at the back of the A-Z Street Atlas (5). Some of these genes (streets) are clearly important, as illustrated by the identification of Creb311 (6) and Azin1 (2) as regulators of AVP gene expression.…”