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A special issue of Nutrients (ISSN 2072-6643). This special issue belongs to the section "Micronutrients and Human Health".

Deadline for manuscript submissions: closed (25 November 2022) | Viewed by 21215

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Special Issue Editor

Prof. Dr. Micah Leshem

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Guest Editor

School of Psychological Sciences, University of Haifa, Haifa, Israel
Interests: Salt Appetite; ingestive behavior; transgenerational effects of stress

Special Issue Information

Dear colleagues,

This Special Issue addresses how and why salt appetite affects salt intake, selection, restriction, reduction, policies, and health. It is not about the effects of salt.

For many animals, salt appetite, or rather sodium appetite and sodium hunger, are life-preserving behaviors aimed at ingesting sodium to preserve or restore health.

Humans differ from animals in salt intake behaviours—we seem incapable of seeking it when in need, almost never eat it, invariably take it with food, rarely with drink, and ingest only NaCl, whereas for animals, any source of sodium will do. Hence, for humans, “salt appetite” is the predilection only for NaCl, and only as a flavor.

What are the origins of the appetite, its adaptive value, what causes us to overeat salt, and why is it the dominant seasoning of our diet? Do its taste-enhancing effects really account for its extraordinary and extant use, and if so, how is it adaptive? Why, of the five senses serving the infinite variety of tastes, is one exclusively devoted to the sodium ion? Beyond the little and sufficient sodium an omnivore diet supplies, evidence is scarce for the benefits of a salt appetite. However, it is a powerful incentive which we have little ability to regulate.

Manuscripts describing original research, reviews, or theory related to salt appetite as it relates to the above issues are welcome.

Prof. Dr. Micah Leshem
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Keywords

animal
causes of salt appetite
flavor
human
regulation
sodium appetite
taste

Published Papers (7 papers)

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Editorial

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6 pages, 824 KiB

Open AccessEditorial

The Hunger for Salt: A Tribute to Derek Denton and Jay Schulkin with an Updated Collection of Papers on Salt Appetite

by Michael McKinley, Neil Rowland and Micah Leshem

Nutrients 2023, 15(10), 2313; https://doi.org/10.3390/nu15102313 - 15 May 2023

Viewed by 1562

Abstract

This collection of outstanding papers is a trove for all concerned with salt intake [...] Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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Research

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22 pages, 2995 KiB

Open AccessArticle

Homeostatic Reinforcement Theory Accounts for Sodium Appetitive State- and Taste-Dependent Dopamine Responding

by Alexia Duriez, Clémence Bergerot, Jackson J. Cone, Mitchell F. Roitman and Boris Gutkin

Nutrients 2023, 15(4), 1015; https://doi.org/10.3390/nu15041015 - 17 Feb 2023

Cited by 2 | Viewed by 1837

Abstract

Seeking and consuming nutrients is essential to survival and the maintenance of life. Dynamic and volatile environments require that animals learn complex behavioral strategies to obtain the necessary nutritive substances. While this has been classically viewed in terms of homeostatic regulation, recent theoretical work proposed that such strategies result from reinforcement learning processes. This theory proposed that phasic dopamine (DA) signals play a key role in signaling potentially need-fulfilling outcomes. To examine links between homeostatic and reinforcement learning processes, we focus on sodium appetite as sodium depletion triggers state- and taste-dependent changes in behavior and DA signaling evoked by sodium-related stimuli. We find that both the behavior and the dynamics of DA signaling underlying sodium appetite can be accounted for by a homeostatically regulated reinforcement learning framework (HRRL). We first optimized HRRL-based agents to sodium-seeking behavior measured in rodents. Agents successfully reproduced the state and the taste dependence of behavioral responding for sodium as well as for lithium and potassium salts. We then showed that these same agents account for the regulation of DA signals evoked by sodium tastants in a taste- and state-dependent manner. Our models quantitatively describe how DA signals evoked by sodium decrease with satiety and increase with deprivation. Lastly, our HRRL agents assigned equal preference for sodium versus the lithium containing salts, accounting for similar behavioral and neurophysiological observations in rodents. We propose that animals use orosensory signals as predictors of the internal impact of the consumed good and our results pose clear targets for future experiments. In sum, this work suggests that appetite-driven behavior may be driven by reinforcement learning mechanisms that are dynamically tuned by homeostatic need. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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15 pages, 2845 KiB

Open AccessArticle

Effects of Voluntary Sodium Consumption during the Perinatal Period on Renal Mechanisms, Blood Pressure, and Vasopressin Responses after an Osmotic Challenge in Rats

by Cintia Y. Porcari, Agustina Macagno, André S. Mecawi, Agustín Anastasía, Ximena E. Caeiro and Andrea Godino

Nutrients 2023, 15(2), 254; https://doi.org/10.3390/nu15020254 - 4 Jan 2023

Cited by 1 | Viewed by 2023

Abstract

Cardiovascular control is vulnerable to forced high sodium consumption during the per-inatal period, inducing programming effects, with anatomical and molecular changes at the kidney, brain, and vascular levels that increase basal and induce blood pressure. However, the program- ming effects of the natriophilia proper of the perinatal period on blood pressure control have not yet been elucidated. In order to evaluate this, we studied the effect of a sodium overload challenge (SO) on blood pressure response and kidney and brain gene expression in adult offspring exposed to voluntary hypertonic sodium consumption during the perinatal period (PM-NaCl group). Male PM-NaCl rats showed a more sustained increase in blood pressure after SO than controls (PM-Ctrol). They also presented a reduced number of glomeruli, decreased expression of TRPV1, and increased expression of At1a in the kidney cortex. The relative expression of heteronuclear vaso- pressin (AVP hnRNA) and AVP in the supraoptic nucleus was unchanged after SO in PM-NaCl in contrast to the increase observed in PM-Ctrol. The data indicate that the availability of a rich source of sodium during the perinatal period induces a long-term effect modifying renal, cardiovascular, and neuroendocrine responses implicated in the control of hydroelectrolyte homeostasis. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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19 pages, 1849 KiB

Open AccessArticle

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

by Jessica Santollo, Derek Daniels, Micah Leshem and Jay Schulkin

Nutrients 2023, 15(1), 208; https://doi.org/10.3390/nu15010208 - 1 Jan 2023

Cited by 7 | Viewed by 3305

Abstract

Salt ingestion by animals and humans has been noted from prehistory. The search for salt is largely driven by a physiological need for sodium. There is a large body of literature on sodium intake in laboratory rats, but the vast majority of this work has used male rats. The limited work conducted in both male and female rats, however, reveals sex differences in sodium intake. Importantly, while humans ingest salt every day, with every meal and with many foods, we do not know how many of these findings from rodent studies can be generalized to men and women. This review provides a synthesis of the literature that examines sex differences in sodium intake and highlights open questions. Sodium serves many important physiological functions and is inextricably linked to the maintenance of body fluid homeostasis. Indeed, from a motivated behavior perspective, the drive to consume sodium has largely been studied in conjunction with the study of thirst. This review will describe the neuroendocrine controls of fluid balance, mechanisms underlying sex differences, sex differences in sodium intake, changes in sodium intake during pregnancy, and the possible neuronal mechanisms underlying these differences in behavior. Having reviewed the mechanisms that can only be studied in animal experiments, we address sex differences in human dietary sodium intake in reproduction, and with age. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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Review

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12 pages, 260 KiB

Open AccessReview

Neurobehavioral Mechanisms of Sodium Appetite

by Neil E. Rowland

Nutrients 2023, 15(3), 620; https://doi.org/10.3390/nu15030620 - 25 Jan 2023

Cited by 1 | Viewed by 1899

Abstract

The objectives of this paper are to first present physiological and ecological aspects of the unique motivational state of sodium appetite, then to focus on systemic physiology and brain mechanisms. I describe how laboratory protocols have been developed to allow the study of sodium appetite under controlled conditions, and focus on two such conditions specifically. The first of these is the presentation a sodium-deficient diet (SDD) for at least one week, and the second is accelerated sodium loss using SDD for 1–2 days coupled with the diuretic furosemide. The modality of consumption is also considered, ranging from a free intake of high concentration of sodium solution, to sodium-rich food or gels, and to operant protocols. I describe the pivotal role of angiotensin and aldosterone in these appetites and discuss whether the intakes or appetite are matched to the physiological need state. Several brain systems have been identified, most recently and microscopically using molecular biological methods. These include clusters in both the hindbrain and the forebrain. Satiation of sodium appetite is often studied using concentrated sodium solutions, but these can be consumed in apparent excess, and I suggest that future studies of satiation might emulate natural conditions in which excess consumption does not occur, using either SDD only as a stimulus, offering a sodium-rich food for the assessment of appetite, or a simple operant task. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

33 pages, 7851 KiB

Open AccessFeature PaperReview

Sodium Intake and Disease: Another Relationship to Consider

by Caitlin Baumer-Harrison, Joseph M. Breza, Colin Sumners, Eric G. Krause and Annette D. de Kloet

Nutrients 2023, 15(3), 535; https://doi.org/10.3390/nu15030535 - 19 Jan 2023

Cited by 4 | Viewed by 3660

Abstract

Sodium (Na⁺) is crucial for numerous homeostatic processes in the body and, consequentially, its levels are tightly regulated by multiple organ systems. Sodium is acquired from the diet, commonly in the form of NaCl (table salt), and substances that contain sodium taste salty and are innately palatable at concentrations that are advantageous to physiological homeostasis. The importance of sodium homeostasis is reflected by sodium appetite, an “all-hands-on-deck” response involving the brain, multiple peripheral organ systems, and endocrine factors, to increase sodium intake and replenish sodium levels in times of depletion. Visceral sensory information and endocrine signals are integrated by the brain to regulate sodium intake. Dysregulation of the systems involved can lead to sodium overconsumption, which numerous studies have considered causal for the development of diseases, such as hypertension. The purpose here is to consider the inverse—how disease impacts sodium intake, with a focus on stress-related and cardiometabolic diseases. Our proposition is that such diseases contribute to an increase in sodium intake, potentially eliciting a vicious cycle toward disease exacerbation. First, we describe the mechanism(s) that regulate each of these processes independently. Then, we highlight the points of overlap and integration of these processes. We propose that the analogous neural circuitry involved in regulating sodium intake and blood pressure, at least in part, underlies the reciprocal relationship between neural control of these functions. Finally, we conclude with a discussion on how stress-related and cardiometabolic diseases influence these circuitries to alter the consumption of sodium. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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23 pages, 2206 KiB

Open AccessEditor’s ChoiceReview

Sodium Homeostasis, a Balance Necessary for Life

by Antonio Bernal, María A. Zafra, María J. Simón and Javier Mahía

Nutrients 2023, 15(2), 395; https://doi.org/10.3390/nu15020395 - 12 Jan 2023

Cited by 12 | Viewed by 5942

Abstract

Body sodium (Na) levels must be maintained within a narrow range for the correct functioning of the organism (Na homeostasis). Na disorders include not only elevated levels of this solute (hypernatremia), as in diabetes insipidus, but also reduced levels (hyponatremia), as in cerebral salt wasting syndrome. The balance in body Na levels therefore requires a delicate equilibrium to be maintained between the ingestion and excretion of Na. Salt (NaCl) intake is processed by receptors in the tongue and digestive system, which transmit the information to the nucleus of the solitary tract via a neural pathway (chorda tympani/vagus nerves) and to circumventricular organs, including the subfornical organ and area postrema, via a humoral pathway (blood/cerebrospinal fluid). Circuits are formed that stimulate or inhibit homeostatic Na intake involving participation of the parabrachial nucleus, pre-locus coeruleus, medial tuberomammillary nuclei, median eminence, paraventricular and supraoptic nuclei, and other structures with reward properties such as the bed nucleus of the stria terminalis, central amygdala, and ventral tegmental area. Finally, the kidney uses neural signals (e.g., renal sympathetic nerves) and vascular (e.g., renal perfusion pressure) and humoral (e.g., renin–angiotensin–aldosterone system, cardiac natriuretic peptides, antidiuretic hormone, and oxytocin) factors to promote Na excretion or retention and thereby maintain extracellular fluid volume. All these intake and excretion processes are modulated by chemical messengers, many of which (e.g., aldosterone, angiotensin II, and oxytocin) have effects that are coordinated at peripheral and central level to ensure Na homeostasis. Full article

(This article belongs to the Special Issue Salt Appetite and Diet)

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