Limits...
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 dramatic and lasting switch in salt preference after 24 h one-bottle tests with IS and HS solutions.Ai, Mean fluid intake following 5 different 24 h one-bottle treatments, control, IS, HS, DH and 4% HSD. Aii, water intake measures for the proceeding 24 h after treatment. B, mean intakes of water and IS solution in two-bottle choice tests performed 7 d after one-bottle tests. C, mean salt preference scores for all groups calculated from the total fluid intake data in B. D, the two-bottle choice tests were repeated 35 d after one-bottle tests for control WEx, ISEx and HSEx groups. Values are means +SEM of n = 6–10 animals per group. E, mean salt preference scores for all groups calculated from the total fluid intake data in D. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; HS, hypertonic saline; HSD, high salt diet; HSEx, hypertonic saline exposed; IS, isotonic saline ISEx isotonic saline exposed; W, water; WEx, water exposed.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4128734&req=5

pone-0104802-g002: A dramatic and lasting switch in salt preference after 24 h one-bottle tests with IS and HS solutions.Ai, Mean fluid intake following 5 different 24 h one-bottle treatments, control, IS, HS, DH and 4% HSD. Aii, water intake measures for the proceeding 24 h after treatment. B, mean intakes of water and IS solution in two-bottle choice tests performed 7 d after one-bottle tests. C, mean salt preference scores for all groups calculated from the total fluid intake data in B. D, the two-bottle choice tests were repeated 35 d after one-bottle tests for control WEx, ISEx and HSEx groups. Values are means +SEM of n = 6–10 animals per group. E, mean salt preference scores for all groups calculated from the total fluid intake data in D. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; HS, hypertonic saline; HSD, high salt diet; HSEx, hypertonic saline exposed; IS, isotonic saline ISEx isotonic saline exposed; W, water; WEx, water exposed.

Mentions: Fluid intake was first measured over a 24 h period in control WEx, ISEx, HSEx, DHx and HSDx groups (Fig. 2Ai). Compared to WEx rats, fluid intake was significantly higher in the ISEx and HSDEx animals. Water intake during the 24 h recovery period was significantly higher for all experimental groups (Fig. 2Aii), with the exception of the HSDEx group. The effects of these treatments on salt appetite were then investigated 7 d later using two-bottle IS vs. water choice tests (Fig. 2B). As before (Fig. 1A), WEx animals showed a strong preference for IS compared to water. There were no significant differences in IS preference in DHEx or HSDEx treated rats compared to WEx controls. Interestingly, prior exposure to 24 h ingestion of either IS or HS solutions in the ISEx and HSEx groups respectively resulted in significant alterations in drinking behaviour. The ISEx group displayed no preference for either water or IS. In contrast, the HSEx group showed a strong preference for water over IS. Both the ISEx and HSEx rats exhibited significantly lower salt preference scores compared to control WEx rats (Fig. 2C). After a further 28 d, the two-bottle test was repeated on these same animals (Fig. 2D). We were surprised to see that, 35 days after exposure, the ISEx and HSEx groups still showed no preference for the normally very palatable IS, rather, as at 7 d, the ISEx group showed no preference, whereas the HSEx group preferred water. However, only HSEx rats exhibited significantly lower salt preference scores compared to control WEx rats (Fig. 2E).


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 dramatic and lasting switch in salt preference after 24 h one-bottle tests with IS and HS solutions.Ai, Mean fluid intake following 5 different 24 h one-bottle treatments, control, IS, HS, DH and 4% HSD. Aii, water intake measures for the proceeding 24 h after treatment. B, mean intakes of water and IS solution in two-bottle choice tests performed 7 d after one-bottle tests. C, mean salt preference scores for all groups calculated from the total fluid intake data in B. D, the two-bottle choice tests were repeated 35 d after one-bottle tests for control WEx, ISEx and HSEx groups. Values are means +SEM of n = 6–10 animals per group. E, mean salt preference scores for all groups calculated from the total fluid intake data in D. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; HS, hypertonic saline; HSD, high salt diet; HSEx, hypertonic saline exposed; IS, isotonic saline ISEx isotonic saline exposed; W, water; WEx, water exposed.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104802-g002: A dramatic and lasting switch in salt preference after 24 h one-bottle tests with IS and HS solutions.Ai, Mean fluid intake following 5 different 24 h one-bottle treatments, control, IS, HS, DH and 4% HSD. Aii, water intake measures for the proceeding 24 h after treatment. B, mean intakes of water and IS solution in two-bottle choice tests performed 7 d after one-bottle tests. C, mean salt preference scores for all groups calculated from the total fluid intake data in B. D, the two-bottle choice tests were repeated 35 d after one-bottle tests for control WEx, ISEx and HSEx groups. Values are means +SEM of n = 6–10 animals per group. E, mean salt preference scores for all groups calculated from the total fluid intake data in D. *p<0.05, **p<0.01, ***p<0.001. DH, dehydrated; HS, hypertonic saline; HSD, high salt diet; HSEx, hypertonic saline exposed; IS, isotonic saline ISEx isotonic saline exposed; W, water; WEx, water exposed.
Mentions: Fluid intake was first measured over a 24 h period in control WEx, ISEx, HSEx, DHx and HSDx groups (Fig. 2Ai). Compared to WEx rats, fluid intake was significantly higher in the ISEx and HSDEx animals. Water intake during the 24 h recovery period was significantly higher for all experimental groups (Fig. 2Aii), with the exception of the HSDEx group. The effects of these treatments on salt appetite were then investigated 7 d later using two-bottle IS vs. water choice tests (Fig. 2B). As before (Fig. 1A), WEx animals showed a strong preference for IS compared to water. There were no significant differences in IS preference in DHEx or HSDEx treated rats compared to WEx controls. Interestingly, prior exposure to 24 h ingestion of either IS or HS solutions in the ISEx and HSEx groups respectively resulted in significant alterations in drinking behaviour. The ISEx group displayed no preference for either water or IS. In contrast, the HSEx group showed a strong preference for water over IS. Both the ISEx and HSEx rats exhibited significantly lower salt preference scores compared to control WEx rats (Fig. 2C). After a further 28 d, the two-bottle test was repeated on these same animals (Fig. 2D). We were surprised to see that, 35 days after exposure, the ISEx and HSEx groups still showed no preference for the normally very palatable IS, rather, as at 7 d, the ISEx group showed no preference, whereas the HSEx group preferred water. However, only HSEx rats exhibited significantly lower salt preference scores compared to control WEx rats (Fig. 2E).

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