The Perceptual Characteristics of Sodium Chloride to Sodium-Depleted Rats

Abstract

Three experiments assessed potential changes in the rat's perception of sodium chloride (NaCl) during a state of sodium appetite. In Experiment 1, sodium-sufficient rats licking a range of NaCl concentrations (0.028-0.89 M) in 15 s trials showed an inverted U-shaped concentration response function peaking at 0.281 M. Depleted rats (furosemide) showed an identical function, merely elevated, suggesting altered qualitative or hedonic perception but no change in perceived intensity. In Experiment 2, sodium-depleted rats were tested with NaCl, sodium gluconate, and potassium chloride (KCl; 0.028-0.89 M) similar to Experiment 1. KCl was licked at the same rate as water except for a slight elevation at 0.158; sodium gluconate and NaCl were treated similarly, but rats showed more licking for hypertonic sodium gluconate than hypertonic NaCl. Sodium-depleted rats were also tested with NaCl mixed in amiloride (10-300 μM). Amiloride reduced licking but did not alter the shape of the concentration-response function. Collectively, these results suggest that transduction of sodium by epithelial sodium channels (which are blocked by amiloride and are more dominant in sodium gluconate than NaCl transduction) is crucial for the perception of sodium during physiological sodium depletion. In Experiment 3, sodium-deplete rats were tested with NaCl as in Experiment 1 but after taste aversion conditioning to 0.3 M NaCl or sucrose. Rats conditioned to avoid NaCl but not sucrose failed to express a sodium appetite, strongly suggesting that NaCl does not undergo a change in taste quality during sodium appetite-rats show no confusion between sucrose and NaCl in this paradigm.

Sodium Imbalance in Mice Results Primarily in Compensatory Gene Regulatory Responses in Kidney and Colon, but Not in Taste Tissue

“…Indeed, sodium-depleted human subjects also displayed an increased preference for high salt diets [77]. Moreover, sodium-depleted rodents drink sodium-containing solutions even at concentrations they would normally reject [18]. Accordingly, sodium deficits seem to trigger an intake behavior towards concentrated sodium solutions.…”

“…Sodium appetite is the instinctive drive to seek salty substances or beverages for consumption [17] stimulated by sodium deficiency, hypovolemia, or mineralocorticoids. Accordingly, sodium-depleted rats ingest high sodium chloride solutions even at concentrations they would normally reject [18][19][20][21]. Already decades ago, studies revealed that amiloride not only affects the kidney but also acts as a potent blocker of salt taste in rodents [22][23][24][25].…”

Sex Differences in Salt Appetite: Perspectives from Animal Models and Human Studies

“…Although these two approaches suggest that the perception of sodium by a sodium deplete rat is blunted, such that high concentration saline that is normally disliked becomes liked, brief access tests using a Davis Rig [ 43 ] failed to support the hypothesis that there is a shift in the preference curve of sodium concentrations. Specifically, using this approach, sodium deplete rats were found to lick all solutions more, instead of showing a shift toward more licking of high concentration solutions [ 44 ]. Accordingly, it remains unclear how the shift in taste reactivity and nerve recordings can be reconciled with the lack of a shift in brief-access testing, but the avid consumption of sodium by the sodium deplete rat is undisputed.…”

A Pharmacological Perspective on the Study of Taste

“…Even in animal models where taste responses are operationally defined, measurements of overt behavior often are interpreted as a reflection of internal sensory experiences. Thus, changes in tastant concentration are said to be detectable as changes in taste "intensity" (Gautam et al, 2012), and "changes in an animal's perceptual experience of the taste of saline" are thought to occur from depletion of dietary sodium (St John, 2017). Such instances of the language used to describe taste-related behavior suggest a top-down view of sensory processing (Rauss and Pourtois, 2013).…”