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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

A significantly reduced appetite for salt solutions following a single 24 h one-bottle test with HS.A, Mean preference scores have been calculated from 24 h measures of water and salt intake at the percentage shown for WEx and HSEx rats. B, mean preference score for IS on day 9 (before tests) and day 30 (after tests). C, mean intakes of 1% sucrose solution compared to water in 24 h two-bottle choice test. D, mean intakes of 1% sucrose prepared in IS in 24 h two-bottle choice test with water. E, mean preference scores calculated from the fluid intake data in C and D. Values are means +SEM of n = 8 animals per group. *p<0.05, **p<0.01, ***p<0.001. HS, hypertonic saline. HSEx, hypertonic saline exposed; IS, isotonic saline; Suc, sucrose; WEx, water exposed.
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pone-0104802-g003: A significantly reduced appetite for salt solutions following a single 24 h one-bottle test with HS.A, Mean preference scores have been calculated from 24 h measures of water and salt intake at the percentage shown for WEx and HSEx rats. B, mean preference score for IS on day 9 (before tests) and day 30 (after tests). C, mean intakes of 1% sucrose solution compared to water in 24 h two-bottle choice test. D, mean intakes of 1% sucrose prepared in IS in 24 h two-bottle choice test with water. E, mean preference scores calculated from the fluid intake data in C and D. Values are means +SEM of n = 8 animals per group. *p<0.05, **p<0.01, ***p<0.001. HS, hypertonic saline. HSEx, hypertonic saline exposed; IS, isotonic saline; Suc, sucrose; WEx, water exposed.

Mentions: To determine the threshold of aversion to salt elicited by HS, rats were presented with a descending series of salt solutions (0.7%, 0.5%, 0.3%, 0.2%, 0.1%, 0.05%, 0.025%, 0.0125% and 0.00625%) in 24 h two-bottle choice tests with water (Fig. 3A). The control WEx rats preferred the salty solution at all salt percentages tested, as indicated by mean scores >0.5. The opposite behaviour was observed for the HSEx group, which preferred water over salt solutions, as indicated by preference scores <0.5. The paired comparisons of preference scores in HSEx and WEx rats showed that HSEx rats maintained a significantly lower preference for salt solutions as low as 0.0125%. A strong aversion to IS was still evident after 30 d in HSEx compared to WEx rats (Fig. 3B). Both the WEx and HSEx rats preferred 1% sucrose solution in the absence (Fig. 3C) or presence (Fig. 3D) of IS compared to water consumption. Interestingly, the preference score significantly dropped in HSEx compared to WEx rats after addition of salt to the sucrose solution (Fig. 3E).


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)

A significantly reduced appetite for salt solutions following a single 24 h one-bottle test with HS.A, Mean preference scores have been calculated from 24 h measures of water and salt intake at the percentage shown for WEx and HSEx rats. B, mean preference score for IS on day 9 (before tests) and day 30 (after tests). C, mean intakes of 1% sucrose solution compared to water in 24 h two-bottle choice test. D, mean intakes of 1% sucrose prepared in IS in 24 h two-bottle choice test with water. E, mean preference scores calculated from the fluid intake data in C and D. Values are means +SEM of n = 8 animals per group. *p<0.05, **p<0.01, ***p<0.001. HS, hypertonic saline. HSEx, hypertonic saline exposed; IS, isotonic saline; Suc, sucrose; WEx, water exposed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104802-g003: A significantly reduced appetite for salt solutions following a single 24 h one-bottle test with HS.A, Mean preference scores have been calculated from 24 h measures of water and salt intake at the percentage shown for WEx and HSEx rats. B, mean preference score for IS on day 9 (before tests) and day 30 (after tests). C, mean intakes of 1% sucrose solution compared to water in 24 h two-bottle choice test. D, mean intakes of 1% sucrose prepared in IS in 24 h two-bottle choice test with water. E, mean preference scores calculated from the fluid intake data in C and D. Values are means +SEM of n = 8 animals per group. *p<0.05, **p<0.01, ***p<0.001. HS, hypertonic saline. HSEx, hypertonic saline exposed; IS, isotonic saline; Suc, sucrose; WEx, water exposed.
Mentions: To determine the threshold of aversion to salt elicited by HS, rats were presented with a descending series of salt solutions (0.7%, 0.5%, 0.3%, 0.2%, 0.1%, 0.05%, 0.025%, 0.0125% and 0.00625%) in 24 h two-bottle choice tests with water (Fig. 3A). The control WEx rats preferred the salty solution at all salt percentages tested, as indicated by mean scores >0.5. The opposite behaviour was observed for the HSEx group, which preferred water over salt solutions, as indicated by preference scores <0.5. The paired comparisons of preference scores in HSEx and WEx rats showed that HSEx rats maintained a significantly lower preference for salt solutions as low as 0.0125%. A strong aversion to IS was still evident after 30 d in HSEx compared to WEx rats (Fig. 3B). Both the WEx and HSEx rats preferred 1% sucrose solution in the absence (Fig. 3C) or presence (Fig. 3D) of IS compared to water consumption. Interestingly, the preference score significantly dropped in HSEx compared to WEx rats after addition of salt to the sucrose solution (Fig. 3E).

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