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Salt appetite is reduced by a single experience of drinking hypertonic saline in the adult rat.

Greenwood MP, Greenwood M, Paton JF, Murphy D - PLoS ONE (2014)

Bottom Line: Inducing thirst by subcutaneous administration of angiotensin II did not overcome this salt aversion.We hypothesised that this behavior results from altered gene expression in brain structures important in thirst and salt appetite.These results indicate that a single experience of drinking HS is a memorable one, with long-term changes in gene expression accompanying this aversion to salty solutions.

View Article: PubMed Central - PubMed

Affiliation: School of Clinical Sciences, University of Bristol, Bristol, England.

ABSTRACT
Salt appetite, the primordial instinct to favorably ingest salty substances, represents a vital evolutionary important drive to successfully maintain body fluid and electrolyte homeostasis. This innate instinct was shown here in Sprague-Dawley rats by increased ingestion of isotonic saline (IS) over water in fluid intake tests. However, this appetitive stimulus was fundamentally transformed into a powerfully aversive one by increasing the salt content of drinking fluid from IS to hypertonic saline (2% w/v NaCl, HS) in intake tests. Rats ingested HS similar to IS when given no choice in one-bottle tests and previous studies have indicated that this may modify salt appetite. We thus investigated if a single 24 h experience of ingesting IS or HS, dehydration (DH) or 4% high salt food (HSD) altered salt preference. Here we show that 24 h of ingesting IS and HS solutions, but not DH or HSD, robustly transformed salt appetite in rats when tested 7 days and 35 days later. Using two-bottle tests rats previously exposed to IS preferred neither IS or water, whereas rats exposed to HS showed aversion to IS. Responses to sweet solutions (1% sucrose) were not different in two-bottle tests with water, suggesting that salt was the primary aversive taste pathway recruited in this model. Inducing thirst by subcutaneous administration of angiotensin II did not overcome this salt aversion. We hypothesised that this behavior results from altered gene expression in brain structures important in thirst and salt appetite. Thus we also report here lasting changes in mRNAs for markers of neuronal activity, peptide hormones and neuronal plasticity in supraoptic and paraventricular nuclei of the hypothalamus following rehydration after both DH and HS. These results indicate that a single experience of drinking HS is a memorable one, with long-term changes in gene expression accompanying this aversion to salty solutions.

No MeSH data available.


Related in: MedlinePlus

Gene expression changes in rat SON and PVN 1 d and 7 d after DHEx or HSEx compared to control animals.Relative mRNA expression of hnAVP, hnOT, AVP, OT, hnCRH, CRH, c-Fos, Nr4a1 and Arc was investigated by qPCR in the SON and PVN of rats RH (1 d and 7 d) after DHEx and HSEx. Values are means +SEM of n = 6 animals per group. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; DHEx dehydrated exposed; HS, hypertonic saline; HSEx, hypertonic saline exposed; RH, Rehydration.
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pone-0104802-g006: Gene expression changes in rat SON and PVN 1 d and 7 d after DHEx or HSEx compared to control animals.Relative mRNA expression of hnAVP, hnOT, AVP, OT, hnCRH, CRH, c-Fos, Nr4a1 and Arc was investigated by qPCR in the SON and PVN of rats RH (1 d and 7 d) after DHEx and HSEx. Values are means +SEM of n = 6 animals per group. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; DHEx dehydrated exposed; HS, hypertonic saline; HSEx, hypertonic saline exposed; RH, Rehydration.

Mentions: In a separate experiment, we analysed the expression of the same transcripts after 1 d and 7 d RH in 1 d DHEx or 1 d HSEx compared to control (euhydrated) animals (Fig. 6). There were no significant differences in hnAVP (Fig. 6A) or hnOT (Fig. 6B) RNA expression in either the SON or PVN following either 1 d or 7 d RH. However, the expression of mature AVP transcripts were significantly higher in PVN, but not SON, of 7 d RH following DHEx and 1 d and 7 d RH following HSEx compared to control animals, suggesting long-term alterations in the expression of this gene (Fig. 6C). OT mRNA expression was significantly higher in SON, but not PVN, of 1 d and 7 d RH following DHEx and 1 d following HSEx compared to control again supporting long-term changes in gene expression (Fig. 6D). As in 1 d DH and 1 d HS animals, no significant differences in hnCRH or mature CRH transcripts were detected in the PVN after 1 d or 7 d RH (Fig. 6E). In contrast, c-Fos mRNA expression was significantly lower in SON and PVN of DHEx and HSEx animals after 1 d RH (Fig. 6F) and in the PVN of 7 d DHEx animals. Nr4a1 mRNA levels were also significantly lower than controls at both RH time-points in both the SON and PVN (Fig. 6G). Interestingly, Arc mRNA expression was significantly lower at both time-points in SON but only for DHEx and not HSEx animals compared to control, with no significant changes in PVN (Fig. 6H).


Salt appetite is reduced by a single experience of drinking hypertonic saline in the adult rat.

Greenwood MP, Greenwood M, Paton JF, Murphy D - PLoS ONE (2014)

Gene expression changes in rat SON and PVN 1 d and 7 d after DHEx or HSEx compared to control animals.Relative mRNA expression of hnAVP, hnOT, AVP, OT, hnCRH, CRH, c-Fos, Nr4a1 and Arc was investigated by qPCR in the SON and PVN of rats RH (1 d and 7 d) after DHEx and HSEx. Values are means +SEM of n = 6 animals per group. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; DHEx dehydrated exposed; HS, hypertonic saline; HSEx, hypertonic saline exposed; RH, Rehydration.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4128734&req=5

pone-0104802-g006: Gene expression changes in rat SON and PVN 1 d and 7 d after DHEx or HSEx compared to control animals.Relative mRNA expression of hnAVP, hnOT, AVP, OT, hnCRH, CRH, c-Fos, Nr4a1 and Arc was investigated by qPCR in the SON and PVN of rats RH (1 d and 7 d) after DHEx and HSEx. Values are means +SEM of n = 6 animals per group. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; DHEx dehydrated exposed; HS, hypertonic saline; HSEx, hypertonic saline exposed; RH, Rehydration.
Mentions: In a separate experiment, we analysed the expression of the same transcripts after 1 d and 7 d RH in 1 d DHEx or 1 d HSEx compared to control (euhydrated) animals (Fig. 6). There were no significant differences in hnAVP (Fig. 6A) or hnOT (Fig. 6B) RNA expression in either the SON or PVN following either 1 d or 7 d RH. However, the expression of mature AVP transcripts were significantly higher in PVN, but not SON, of 7 d RH following DHEx and 1 d and 7 d RH following HSEx compared to control animals, suggesting long-term alterations in the expression of this gene (Fig. 6C). OT mRNA expression was significantly higher in SON, but not PVN, of 1 d and 7 d RH following DHEx and 1 d following HSEx compared to control again supporting long-term changes in gene expression (Fig. 6D). As in 1 d DH and 1 d HS animals, no significant differences in hnCRH or mature CRH transcripts were detected in the PVN after 1 d or 7 d RH (Fig. 6E). In contrast, c-Fos mRNA expression was significantly lower in SON and PVN of DHEx and HSEx animals after 1 d RH (Fig. 6F) and in the PVN of 7 d DHEx animals. Nr4a1 mRNA levels were also significantly lower than controls at both RH time-points in both the SON and PVN (Fig. 6G). Interestingly, Arc mRNA expression was significantly lower at both time-points in SON but only for DHEx and not HSEx animals compared to control, with no significant changes in PVN (Fig. 6H).

Bottom Line: Inducing thirst by subcutaneous administration of angiotensin II did not overcome this salt aversion.We hypothesised that this behavior results from altered gene expression in brain structures important in thirst and salt appetite.These results indicate that a single experience of drinking HS is a memorable one, with long-term changes in gene expression accompanying this aversion to salty solutions.

View Article: PubMed Central - PubMed

Affiliation: School of Clinical Sciences, University of Bristol, Bristol, England.

ABSTRACT
Salt appetite, the primordial instinct to favorably ingest salty substances, represents a vital evolutionary important drive to successfully maintain body fluid and electrolyte homeostasis. This innate instinct was shown here in Sprague-Dawley rats by increased ingestion of isotonic saline (IS) over water in fluid intake tests. However, this appetitive stimulus was fundamentally transformed into a powerfully aversive one by increasing the salt content of drinking fluid from IS to hypertonic saline (2% w/v NaCl, HS) in intake tests. Rats ingested HS similar to IS when given no choice in one-bottle tests and previous studies have indicated that this may modify salt appetite. We thus investigated if a single 24 h experience of ingesting IS or HS, dehydration (DH) or 4% high salt food (HSD) altered salt preference. Here we show that 24 h of ingesting IS and HS solutions, but not DH or HSD, robustly transformed salt appetite in rats when tested 7 days and 35 days later. Using two-bottle tests rats previously exposed to IS preferred neither IS or water, whereas rats exposed to HS showed aversion to IS. Responses to sweet solutions (1% sucrose) were not different in two-bottle tests with water, suggesting that salt was the primary aversive taste pathway recruited in this model. Inducing thirst by subcutaneous administration of angiotensin II did not overcome this salt aversion. We hypothesised that this behavior results from altered gene expression in brain structures important in thirst and salt appetite. Thus we also report here lasting changes in mRNAs for markers of neuronal activity, peptide hormones and neuronal plasticity in supraoptic and paraventricular nuclei of the hypothalamus following rehydration after both DH and HS. These results indicate that a single experience of drinking HS is a memorable one, with long-term changes in gene expression accompanying this aversion to salty solutions.

No MeSH data available.


Related in: MedlinePlus