Hydration state controls stress responsiveness and social behavior

Chronic corticosterone administration alters synaptic mitochondrial function within the hippocampus of C57Bl/6NTac mice

Chronic activation of the hypothalamic-pituitary-adrenal axis increases circulating corticosterone levels, causing a host of downstream behavioral, molecular, and metabolic changes. Here, we assess the effects of chronic exogenous CORT administration on changes in behavior and mitochondrial respiration in hippocampal synaptosomes of male and female mice. Adult male (n = 15) and female (n = 17) C57Bl/6NTac mice were given 35ug/mL CORT or vehicle dissolved in their drinking water for 21 consecutive days. Chronic CORT increased piloerection in males only. Although volume of CORT-containing water consumed was similar between males and females, circulating plasma and fecal corticosterone levels were only elevated in CORT-exposed males. Behavioral effects of CORT were evident in the Y-maze such that CORT caused a decrease in direct revisits in both sexes. There was no observed presentation of anxiety-like behavior following chronic CORT administration. Functional hippocampal synaptosomes were analyzed for mitochondrial respiration using Agilent's Cell Mito Stress test. Chronic CORT caused a decrease in synaptic mitochondria basal respiration, maximal respiration, proton leak, and ATP production in both sexes. Despite only observing an effect of chronic CORT on corticosterone concentrations in fecal and blood samples of males, chronic CORT induced marked changes in hippocampal synaptic mitochondrial function of both sexes. These data highlight the importance of considering effects of stress hormone exposure on neural function even in the absence of measurable peripheral elevations in females.

A high salt intake in early life affects stress-coping response in males but not in female rats

Eating diets high in salt has been associated with alterations in the immune system and the potential development of neuropsychiatric disorders. This area of research shows promise, but there is currently a limited amount of research on this topic. The present study investigated whether a high salt diet (HSD) affects anhedonia and stress-coping response behaviors in young male and female Wistar rats. In this study, male and female Wistar rats were fed an HSD (8 % NaCl w/w) from weaning to post-natal day (PND) 64. From PND 60 to 64, the rats underwent a spontaneous locomotor activity test (SLA), sucrose splash test (SST), sucrose preference test (SPT), and forced swim test (FST), followed by euthanasia at PND 65. Male and female rats consuming the HSD exhibited an increase in water intake compared to the corresponding control diet (CD) groups. Male rats had lower body weight despite having similar food intakes compared to the CD group. Male rats displayed an active stress-coping behavior in the FST, characterized by increased mobility. Additionally, HSD-fed males exhibited a greater preference for sucrose solution in the SPT. However, no effect of diet and sex were detected in the SST and the SLA, and hypothalamic levels of leptin and ghrelin receptors. On the other hand, female rats were less susceptible to the experimental conditions applied in this protocol than males.

Establishing the relationship between wildfire smoke and performance metrics on finished beef cattle in Western Rangelands

Identifying causal relationships is complicated. Researchers usually overlook causality behind relationships which can generate misleading associations. Herein, we carefully examine the parametric relationship and causality between wildfire smoke exposure and animal performance and behavior metrics over a period of 2 yr in Reno, Nevada. The animals in the 2020 smoke season were grain-finished (n = 12) and grass-finished (n = 12), whereas the animals during the 2021 season were fed under the same diet but finished with either a hormonal implant (n = 9), or without (n = 9). The dataset included daily records of feed intake (FI), body weight (BW), water intake (WI), average daily gain (ADG), and WI behavior (time spent drinking [TSD]; water intake events [WIE]; no-WIE [NWIE]). Variable tree length Bayesian additive regression trees (BART) were utilized to investigate the relationships between air quality index (AQI), particulate matter 2.5 μm (PM2.5) and 10 μm (PM10), NO2, SO2, Ozone, and CO levels in the air (sensors < 1.6 km from animals) with the animal data. Additionally, linear mixed models with a 7-d lag were used to evaluate parametric relationships among the same variables. All statistical analyses were performed on R Statistical Software (R Core Team 2023). Under the linear mixed model with a 7-d lag, significant positive and negative associations were found for all parameters examined (P < 0.05). Negative associations were found between FI, WI, ADG, BW, WIE, NWIE, TSD, and PM2.5 (P < 0.05) for at least one animal group. Positive linear associations between wildfire smoke parameters and the metrics evaluated were more variable and dependent on year, treatment, and smoke parameters. When examining the credible intervals and the variable importance in the BART, relationships were more difficult to identify. However, some associations were found for Ozone, AQI, NO2, CO, and PM10 (P < 0.05). Overall, our results carefully examine the relationship between smoke parameters and cattle performance and present interesting pathways previously unexplored that could guide early culling/finishing of animals to avoid economic losses associated with performance decrease in response to wildfire smoke exposure. Though interesting associations are found under linear mixed models, causality is difficult to establish, which highlights the need for controlled exposure experiments.

Thyroid hormone biosynthesis and its role in brain development and maintenance

Thyroid hormones are critical modulators in the physiological processes necessary to virtually all tissues, with exceptionally fundamental roles in brain development and maintenance. These hormones regulate essential neurodevelopment events, including neuronal migration, synaptogenesis, and myelination. Additionally, thyroid hormones are crucial for maintaining brain homeostasis and cognitive function in adulthood. This chapter aims to offer a comprehensive understanding of thyroid hormone biosynthesis and its intricate role in brain physiology. Here, we described the mechanisms underlying the biosynthesis of thyroid hormones, their influence on various aspects of brain development and ongoing maintenance, and the proteins in the brain that are responsive to these hormones. This chapter was geared towards broadening our understanding of thyroid hormone action in the brain, shedding light on potential therapeutic targets for neurodevelopmental and neurodegenerative disorders.

Nucleus of the lateral olfactory tract: A hub linking the water homeostasis-associated supraoptic nucleus-arginine vasopressin circuit and neocortical regions to promote social behavior under osmotic challenge

Homeostatic challenges may alter the drive for social interaction. The neural activity that prompts this motivation remains poorly understood. In the present study, we identify direct projections from the hypothalamic supraoptic nucleus to the cortico-amygdalar nucleus of the lateral olfactory tract (NLOT). Dual in situ hybridization with probes for pituitary adenylate cyclase-activating polypeptide (PACAP), as well as vesicular glutamate transporter (VGLUT)1, VGLUT2, V1a and V1b, revealed a population of vasopressin-receptive PACAPergic neurons in NLOT layer 2 (NLOT2). Water deprivation (48 h, WD48) increased sociability compared to euhydrated subjects, as assessed with the three-chamber social interaction test (3CST). Fos expression immunohistochemistry showed NLOT and its main efferent regions had further increases in rats subjected to WD48 + 3CST. These regions strongly expressed PAC1 mRNA. Microinjections of arginine vasopressin (AVP) into the NLOT produced similar changes in sociability to water deprivation, and these were reduced by co-injection of V1a or V1b antagonists along with AVP. We conclude that, during challenge to water homeostasis, there is a recruitment of a glutamatergic-multi-peptidergic cooperative circuit that promotes social behavior.

Sodium Intake and Disease: Another Relationship to Consider

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.

Water deprivation induces hypoactivity in rats independently of oxytocin receptor signaling at the central amygdala

INTRODUCTION

Vasopressin (AVP) and oxytocin (OXT) are neuropeptides produced by magnocellular neurons (MCNs) of the hypothalamus and secreted through neurohypophysis to defend mammals against dehydration. It was recently demonstrated that MCNs also project to limbic structures, modulating several behavioral responses.

METHODS AND RESULTS

We found that 24 h of water deprivation (WD) or salt loading (SL) did not change exploration or anxiety-like behaviors in the elevated plus maze (EPM) test. However, rats deprived of water for 48 h showed reduced exploration of open field and the closed arms of EPM, indicating hypoactivity during night time. We evaluated mRNA expression of glutamate decarboxylase 1 (Gad1), vesicular glutamate transporter 2 (Slc17a6), AVP (Avpr1a) and OXT (Oxtr) receptors in the lateral habenula (LHb), basolateral (BLA) and central (CeA) amygdala after 48 h of WD or SL. WD, but not SL, increased Oxtr mRNA expression in the CeA. Bilateral pharmacological inhibition of OXTR function in the CeA with the OXTR antagonist L-371,257 was performed to evaluate its possible role in regulating the EPM exploration or water intake induced by WD. The blockade of OXTR in the CeA did not reverse the hypoactivity response in the EPM, nor did it change water intake induced in 48-h water-deprived rats.

DISCUSSION

We found that WD modulates exploratory activity in rats, but this response is not mediated by oxytocin receptor signaling to the CeA, despite the upregulated Oxtr mRNA expression in that structure after WD for 48 h.

Intrahypothalamic effects of oxytocin on PVN CRH neurons in response to acute stress

Much of the centrally available oxytocin (OT) is synthesized in magnocellular neurons located in the paraventricular nucleus of the hypothalamus. This same area is home to parvocellular corticotropin-releasing hormone (CRH) synthesizing neurons that regulate activation of the hypothalamic-pituitary-adrenal (HPA) axis. A large body of data indicates that complex interactions between these systems inextricably link central OT signaling with the neuroendocrine response to stress. This review focuses on a small but diverse set of cellular and synaptic mechanisms that have been proposed to underlie intrahypothalamic OT/CRF interactions during the response to acute stress.

Oxytocin and cardiometabolic interoception: Knowing oneself affects ingestive and social behaviors

Maintaining homeostasis while navigating one's environment involves accurately assessing and interacting with external stimuli while remaining consciously in tune with internal signals such as hunger and thirst. Both atypical social interactions and unhealthy eating patterns emerge as a result of dysregulation in factors that mediate the prioritization and attention to salient stimuli. Oxytocin is an evolutionarily conserved peptide that regulates attention to exteroceptive and interoceptive stimuli in a social environment by functioning in the brain as a modulatory neuropeptide to control social behavior, but also in the periphery as a hormone acting at oxytocin receptors (Oxtr) expressed in the heart, gut, and peripheral ganglia. Specialized sensory afferent nerve endings of Oxtr-expressing nodose ganglia cells transmit cardiometabolic signals via the Vagus nerve to integrative regions in the brain that also express Oxtr(s). These brain regions are influenced by vagal sensory pathways and coordinate with external events such as those demanding attention to social stimuli, thus the sensations related to cardiometabolic function and social interactions are influenced by oxytocin signaling. This review investigates the literature supporting the idea that oxytocin mediates the interoception of cardiovascular and gastrointestinal systems, and that the modulation of this awareness likewise influences social cognition. These concepts are then considered in relation to Autism Spectrum Disorder, exploring how atypical social behavior is comorbid with cardiometabolic dysfunction.

Early Stepdown Weaning of Dairy Calves with Glutamine and Branched-Chain Amino Acid Supplementations

Simple Summary

We demonstrated previously that supplementation of glutamine (Gln) at 2.0% of dry matter intake (DMI) increased the rate at which dairy calves achieved ≥1.0 kg/d starter feed intake (SFI) during weaning. Because Gln supplements at <1.0% of DMI or branched-chain amino acid (BCAA) supplements have been shown to improve the performance of weaning piglets, we examined the effects of a lower dose of Gln (8.0 g/d equivalent to 1% of DMI) alone or in combination with BCAA supplementations on SFI and average daily gain (ADG) in this study. Amino acids did not affect SFI or ADG during the supplementations but decreased post-weaning SFI in an additive manner even though the ADG was not affected. The blood analysis on the last day of supplementations revealed a possibility for the Gln and BCAA supplementations to suppress SFI through leptin and serotonin secreted by the gastrointestinal tract.

Abstract

The study objective was to examine the effects of supplementing Gln and BCAA on the SFI and ADG of weaning dairy calves. Holstein heifer calves (11 calves /treatment) at 35 d of age were assigned to: (1) no amino acids (CTL), (2) Gln (8.0 g/d) alone (GLN), or (3) Gln (8.0 g/d) and BCAA (GLNB; 17.0, 10.0, and 11.0 g/d leucine, isoleucine, and valine, respectively) supplementations in whole milk during a stepdown weaning scheme. Calves were weaned completely once they achieved ≥1.0 kg/d SFI. Neither GLN nor GLNB affected SFI or ADG in the first week during weaning. The GLNB decreased SFI compared to CTL, but the SFI was similar between CTL and GLN in the remainder of the weaning scheme. All calves were weaned at 50 d of age. The SFI of GLNB was lower than that of GLN, and the SFI of both GLN and GLNB were lower than CTL post-weaning. The decreased SFI did not alter ADG during weaning or post-weaning. The GLNB tended to have higher plasma leptin and lower plasma serotonin concentrations compared to CTL. Glutamine and BCAA seem to affect the SFI of calves by modulating the secretions of endocrine cells in the gastrointestinal tract.

Suppression of ventral hippocampal CA1 pyramidal neuronal activities enhances water intake

Thirst is an important interoceptive response and drives water consumption. The hippocampus actively modulates food intake and energy metabolism, but direct evidence for the exact role of the hippocampus in modulating drinking behaviors is lacking. We observed decreased number of c-Fos-positive neurons in the ventral hippocampal CA1 (vCA1) after water restriction or hypertonic saline injection in rats. Suppressed vCA1 neuronal activities under the hypertonic state were further confirmed with in vivo electrophysiological recording and the level of suppression paralleled both the duration and the total amount of water consumption. Chemogenetic inhibition of vCA1 pyramidal neurons increased water consumption in rats injected with both normal and hypertonic saline. These findings suggest that suppression of vCA1 pyramidal neuronal activities enhances water intake.

Centrally acting antihypertensives change the psychogenic cardiovascular reactivity

Clonidine (CL) and Rilmenidine (RI) are among the most frequently prescribed centrally acting antihypertensives. Here, we compared CL and RI effects on psychogenic cardiovascular reactivity to sonant, luminous, motosensory, and vibrotactile stimuli during neurogenic hypertension. The femoral artery and vein of Wistar (WT - normotensive) and spontaneously hypertensive rats (SHR) were catheterized before (24 h interval) i.p. injection of vehicle (NaCl 0.9%, control - CT group), CL (10 µg/kg), or RI (10 µg/kg) and acute exposure to luminous (5000 lm), sonant (75 dB sudden tap), motor (180° cage twist), and air-jet (10 L/min - restraint and vibrotactile). Findings showed that: (i) CL or RI reduced the arterial pressure of SHR, without affecting basal heart rate in WT and SHR; (ii) different stimuli evoked pressor and tachycardic responses; (iii) CL and RI reduced pressor response to sound; (iv) CL or RI reduced pressor responses to luminous stimulus without a change in peak tachycardia in SHR; (v) cage twist increased blood pressure in SHR, which was attenuated by CL or RI; (vi) air-jet increased pressure and heart rate; (vii) CL or RI attenuated the pressor responses to air-jet in SHR while RI reduced the chronotropic reactivity in both strains. Altogether, both antihypertensives relieved the psychogenic cardiovascular responses to different stimuli. The RI elicited higher cardioprotective effects through a reduction in air-jet-induced tachycardia.

Oxytocin reverses ethanol consumption and neuroinflammation induced by social defeat in male mice

Oxytocin (OXT) modulates social interactions, attenuates stressful responses and can decrease drug-seeking and taking behaviors. In previous studies, we observed that social defeat (SD) induced a long-lasting increase in ethanol intake and neuroinflammation in male mice. We also know that OXT blocks the increase in cocaine reward induced by SD. Therefore, in the present study we aimed to evaluate the effect of 1 mg/kg of OXT administered 30 min before each episode of SD on ethanol consumption and the neuroinflammatory response in adult male mice. Three weeks after the last SD, mice underwent oral ethanol self-administration (SA) procedure, and striatal levels of the two chemokines CX3CL1 and CXCL12 were measured after the last SD and at the end of the ethanol SA. OXT administration blocked the increase in voluntary ethanol consumption observed in defeated mice, although it did not affect motivation for ethanol. An increase in the striatal levels of CX3CL1 and CXCL12 was observed in defeated animals immediately after the last defeat and after the ethanol SA. However, defeated mice treated with OXT did not show this increase in the neuroinflammatory response. In conclusion, OXT treatment can be a powerful therapeutic target to reduce the negative effects of social stress on ethanol consumption and the neuroinflammatory process.

The Biology of Physiological Health

The ability to maintain health, or recover to a healthy state after disease, is an active process involving distinct adaptation mechanisms coordinating interactions between all physiological systems of an organism. Studies over the past several decades have assumed the mechanisms of health and disease are essentially inter-changeable, focusing on the elucidation of the mechanisms of disease pathogenesis to enhance health, treat disease, and increase healthspan. Here, I propose that the evolved mechanisms of health are distinct from disease pathogenesis mechanisms and suggest that we develop an understanding of the biology of physiological health. In this Perspective, I provide a definition of, a conceptual framework for, and proposed mechanisms of physiological health to complement our understanding of disease and its treatment.

Thyroid hormone, gene expression, and Central Nervous System: Where we are

Thyroid hormones (TH; T3 and T4) play a fundamental role in the fetal stage to the adult phase, controlling gene and protein expression in virtually all tissues. The endocrine and CNS systems have relevant interaction, and the TH are pivotal for the proper functioning of the CNS. A slight failure to regulate TH availability during pregnancy and/or childhood can lead to neurological disorders, for example, autism and cognitive impairment, or depression. In this review, we highlight how TH acts in controlling gene expression, its role in the CNS, and what substances widely found in the environment can cause in this tissue. We highlight the role of Endocrine Disruptors used on an everyday basis in the processing of mRNAs responsible for neurodevelopment. We conclude that TH, more precisely T3, acts mainly throughout its nuclear receptors, that the deficiency of this hormone, either due to the lack of its main substrate iodine, or by to incorrect organification of T4 and T3 in the gland, or by a mutation in transporters, receptors and deiodinases may cause mild (dysregulated mood in adulthood) to severe neurological impairment (Allan-Herndon-Dudley syndrome, presented as early as childhood); T3 is responsible for the expression of numerous CNS genes related to oxygen transport, growth factors, myelination, cell maturation. Substances present in the environment and widely used can interfere with the functioning of the thyroid gland, the action of TH, and the functioning of the CNS.

Restricted Water Intake Adversely Affects Rat Vocal Fold Biology

OBJECTIVES

A holistic understanding of the many ways that systemic dehydration affects vocal fold biology is still evolving. There are also myriad physiologically relevant methodologies to induce systemic dehydration. To untangle the effects of systemic dehydration on vocal fold biology, we need to utilize realistic, clinically translatable paradigms of systemic dehydration in lab animals. Restricted access to water accommodates clinical translation. We investigated whether systemic dehydration via reduced water intake would negatively affect vocal fold biology.

STUDY DESIGN

Prospective, in vivo study design.

METHODS

Male Sprague Dawley rats (N = 13) were provided 4 mL/100 g of water/day for 5 days, whereas male control rats (N = 8) were given ad lib access to water. Following euthanasia, tissues were processed for histological staining, gene expression, and protein assays.

RESULTS

Renin gene expression level in kidneys increased significantly (P ≤ .05), validating dehydration. Dehydration induced by restricted water access downregulated the gene expression of interleukin-1α and desmoglein-1 (P ≤ .05). Hyaluronidase-2 gene expression increased after dehydration (P ≤ .05). The protein level of desmoglein-1 decreased after dehydration (P ≤ .05). Histological analyses suggested decreased hyaluronan (P ≤ .05) in the water-restricted rat vocal fold.

CONCLUSION

Reduced daily water intake for just 5 days impairs vocal fold biology by disrupting inflammatory cytokine release, reducing plasma membrane integrity, and disrupting the hyaluronan network. This is the first study investigating the dehydrating effects of restricted water intake on vocal fold tissue in an in vivo model.

LEVEL OF EVIDENCE

NA (prospective animal study). Laryngoscope, 131:839-845, 2021.

Salt need needs investigation

Expensive and extensive studies on the epidemiology of excessive Na intake and its pathology have been conducted over four decades. The resultant consensus that dietary Na is toxic, as well as the contention that it is less so, ignores the root cause of the attractiveness of salted food. The extant hypotheses are that most Na is infiltrated into our bodies via heavily salted industrialised food without our knowledge and that mere exposure early in life determines lifelong intake. However, these hypotheses are poorly evidenced and are meagre explanations for the comparable salt intake of people worldwide despite their markedly different diets. The love of salt begins at birth for some, vacillates in infancy, climaxes during adolescent growth, settles into separate patterns for men and women in adulthood and, with age, fades for some and persists for others. Salt adds flavour to food. It sustains and protects humans in exertion, may modulate their mood and contributes to their ailments. It may have as yet unknown benefits that may promote its delectability, and it generates controversy. An understanding of the predilection for salt should allow a more evidence-based and effective reduction of the health risks associated with Na surfeit and deficiency. The purpose of this brief review is to show the need for research into the determinants of salt intake by summarising the little we know.

Evaluating the potential role of tryptophan in calf milk replacers to facilitate weaning

Tryptophan is a precursor of serotonin, a neurotransmitter that participates in the control of the affective state of an animal. We hypothesized that Trp supplementation could help dairy calves to cope with weaning stress. Twenty-seven Holstein male calves (48 ± 0.8 d old; 82 ± 2.6 kg of body weight) were used to evaluate the effects of Trp supplementation at a rate of 4.5 g/d via milk replacer (MR) on performance and behavioral parameters around weaning. All calves received the same feeding program (6 L/d at 15% dry matter from d 1 to 7, 4 L/d at 15% dry matter from d 8 to 14, and 2 L/d at 15% dry matter in one feeding until d 21 of study) and were completely weaned 22 d after the beginning of the study (around 70 d of life). Calves were fed a starter feed (19.3% crude protein and 16.2% neutral detergent fiber, on a dry matter basis) and chopped straw ad libitum. Animals were weighed weekly, dry matter intakes were recorded daily, lying behavior was recorded using accelerometers throughout the study, and scan sampling was performed twice a week, 1 h after the morning feeding, to record behavioral activity (nonnutritive oral behaviors, suckling a neighbor calf, standing, resting, rumination, vocalizations, eating, and drinking). Tryptophan supplementation did not affect calf performance or concentrate and MR intake, but straw intake tended to be greater in nonsupplemented compared with Trp-supplemented calves (153 vs. 129 ± 9.0 g/d, respectively). Lying time, lying bouts, and lying duration decreased when changes in the MR feeding program occurred, independent of treatment. Similarly, differences in behavioral observations occurred along days of study, with no effect of Trp supplementation. The main changes observed in calf behavior were an increase in vocalizations and standing time 1 h after the morning feeding at weaning, but again these changes were independent of treatment. Parameters measured in serum and plasma indicated an increase in Trp, kynurenine, and the kynurenine/Trp ratio after feeding in the Trp calves. A tendency for lower plasma glucose concentration after feeding was observed in the Trp group. No changes in stress markers such as cortisol and haptoglobin in serum were detected. In conclusion, supplementing 4.5 g/d of Trp via MR between 48 and 62 d of life had no effect on performance or behavior in calves around weaning.

Vasopressin & Oxytocin in Control of the Cardiovascular System: An Updated Review

Since the discovery of vasopressin (VP) and oxytocin (OT) in 1953, considerable knowledge has been gathered about their roles in cardiovascular homeostasis. Unraveling VP vasoconstrictor properties and V1a receptors in blood vessels generated powerful hemostatic drugs and drugs effective in the treatment of certain forms of circulatory collapse (shock). Recognition of the key role of VP in water balance via renal V2 receptors gave birth to aquaretic drugs found to be useful in advanced stages of congestive heart failure. There are still unexplored actions of VP and OT on the cardiovascular system, both at the periphery and in the brain that may open new venues in treatment of cardiovascular diseases. After a brief overview on VP, OT and their peripheral action on the cardiovascular system, this review focuses on newly discovered hypothalamic mechanisms involved in neurogenic control of the circulation in stress and disease.

Oxytocin treatment for alcoholism: Potential neurocircuitry targets

Oxytocin (OT) has gained considerable interest in recent years as a potential treatment for alcoholism and other substance use disorders. Evidence continues to mount that OT administered either centrally, peripherally or intranasally can decrease ethanol intake in both humans and animal models. The potential mechanisms for the ability of OT to decrease ethanol reward, and importantly, cue- and stress-induced ethanol relapse, are explored by reviewing the specific neuronal circuits involved in mediating these actions and their sensitivity to OT. In addition to dopamine neurons that project from ventral tegmental area (VTA) to nucleus accumbens (NAc) to signal positively reinforcing events, OT receptors (OxTR) are also expressed by dopamine neurons that project from VTA to brain regions that can convey aversive properties of a stimulus. Moreover, OxTR are expressed by non-dopaminergic neurons in the VTA, such as GABA and glutamate neurons, which can both modulate the activity of dopamine VTA neurons locally (in opposite directions) or can project to other brain regions, including the NAc, where it can alter either positive reinforcement or aversion caused by ethanol. The ability of OT to regulate limbic circuitry and the hypothalamic-pituitary-adrenal axis is discussed as a potential mechanism for the ability of OT to inhibit ethanol-induced negative reinforcement. Together, understanding the diversity and complexity of OT regulation of ethanol reward may contribute to more effective use of OT as pharmacotherapy for alcohol use disorder. This article is part of the special issue on Neuropeptides.

Transcription factor Creb3l1 regulates the synthesis of prohormone convertase enzyme PC1/3 in endocrine cells

Transcription factor cAMP responsive element-binding protein 3 like 1 (Creb3l1) is a non-classical endoplasmic reticulum stress molecule that is emerging as an important component for cellular homeostasis, particularly within cell types with high peptide secretory capabilities. We have previously shown that Creb3l1 serves an important role in body fluid homeostasis through its transcriptional control of the gene coding for antidiuretic hormone arginine vasopressin in the neuropeptide-rich magnocellular neurones of the supraoptic nucleus. In response to osmotic stimuli such as dehydration, vasopressin magnocellular neurones undergo remarkable transcriptome changes, including increased Creb3l1 expression, to ensure that the supply of vasopressin meets demand. To determine where else Creb3l1 fits into the secretory cell supply chain, we performed RNA-sequencing of Creb3l1 knockdown anterior pituitary mouse corticotroph cell line AtT20. The target chosen for further investigation was Pcsk1, which encodes proprotein convertase enzyme 1 (PC1/3). PC1/3 is crucial for processing of neuropeptides and peptide hormones such as pro-opiomelanocortin (POMC), proinsulin, proglucagon, vasopressin and oxytocin. Viral manipulations in supraoptic nuclei by over-expression of Creb3l1 increased Pcsk1, whereas Creb3l1 knockdown decreased Pcsk1 expression. In vitro promoter activity and binding studies showed that Creb3l1 was a transcription factor of the Pcsk1 gene binding directly to a G-box motif in the promoter. In the dehydrated rat anterior pituitary, Creb3l1 and Pcsk1 expression decreased in parallel compared to control, supporting our findings from manipulations in AtT20 cells and the supraoptic nucleus. No relationship was observed between Creb3l1 and Pcsk1 expression in the neurointermediate lobe of the pituitary, indicating a different mechanism of PC1/3 synthesis by these POMC-synthesising cells. Therefore, Creb3l1, by regulating the expression of Pcsk1, does not control the processing of POMC peptides in the intermediate lobe.

Endogenous oxytocin inhibits hypothalamic corticotrophin-releasing hormone neurones following acute hypernatraemia

Significant prior evidence indicates that centrally acting oxytocin robustly modulates stress responsiveness and anxiety-like behaviour, although the neural mechanisms behind these effects are not entirely understood. A plausible neural basis for oxytocin-mediated stress reduction is via inhibition of corticotrophin-releasing hormone (CRH) neurones in the paraventricular nucleus of the hypothalamus (PVN) that regulate activation of the hypothalamic-pituitary-adrenal axis. Previously, we have shown that, following s.c. injection of 2.0 mol L^-1 NaCl, oxytocin synthesising neurones are activated in the rat PVN, an oxytocin receptor (Oxtr)-dependent inhibitory tone develops on a subset of parvocellular neurones and stress-mediated increases in plasma corticosterone levels are blunted. In the present study, we utilised transgenic male CRH-reporter mice to selectively target PVN CRH neurones for whole-cell recordings. These experiments reveal that acute salt loading produces tonic inhibition of PVN CRH neurones through a mechanism that is largely independent of synaptic activity. Further studies reveal that a subset of CRH neurones within the PVN synthesise mRNA for Oxtr(s). Salt induced Oxtr-dependent inhibitory tone was eliminated in individual PVN CRH neurones filled with GDP-β-S. Additional electrophysiological studies suggest that reduced excitability of PVN CRH neurones in salt-loaded animals is associated with increased activation of inwardly rectifying potassium channels. Nevertheless, substantial effort to recapitulate the core effects of salt loading by activating Oxtr(s) with an exogenous agonist produced mixed results. Collectively, these results enhance our understanding of how oxytocin receptor-mediated signalling modulates the function of CRH neurones in the PVN.

Mechanisms involved in the cardiovascular effects caused by acute osmotic stimulation in conscious rats

Both the autonomic nervous system and the neuroendocrine system are activated by osmotic stimulation (OS) evoking cardiovascular effects. The current study investigated the mechanisms involved in the cardiovascular responses evoked by an acute osmotic stimulus with intraperitoneal (i.p.) injection of either isotonic (0.15 M NaCl) or hypertonic saline (0.6 M NaCl) in conscious rats. Hypertonic saline increased mean arterial pressure (MAP) and heart rate (HR) for 30 min, as well as plasma osmolality and sodium content. Urinary sodium and urinary volume were also increased. Pretreatment with the ganglion blocker pentolinium (i.v.) did not affect the pressor response, but significantly decreased the tachycardic response caused by OS. Pretreatment with the V₁-vasopressin receptor antagonist dTyr(CH₂)₅(Me)AVP (i.v.) reduced the pressor response, without affecting the tachycardic response evoked by the hypertonic OS. Neither the pressor nor the tachycardic response to OS was affected by pretreatment with either the oxytocin receptor antagonist atosiban or the α1-antagonist prazosin. Pretreatment with the β1-antagonist atenolol had no effect on the pressor response, but markedly decreased the tachycardic response evoked by OS. Results indicate that i.p. hypertonic OS-evoked pressor response is mediated by the release of vasopressin, with a minor influence of the vascular sympathetic input.LAY SUMMARYIncreased plasma osmolality, such as that observed during dehydration or salt intake, is a potent stimulus yielding to marked cardiovascular and neuroendocrine responses. The intraperitoneal (i.p.) injection of hypertonic saline solution is a commonly used animal model to cause a sustained increase in plasma osmolality, leading to a cardiovascular response characterized by sustained blood pressure and heart increases, whose systemic mechanisms were presently studied. Our findings indicate that the pressor response to the i.p. osmotic stimulus (OS) is mediated mainly by the release of vasopressin into the blood circulation with a minor or even the noninvolvement of the vascular sympathetic nervous system, whereas activation of the sympathetic-cardiac system mediates the tachycardic response to OS.

Anterior cingulate cortex modulates the affective-motivative dimension of hyperosmolality-induced thirst

Neuroimaging studies have shown that the anterior cingulate cortex (ACC) is consistently activated by thirst and may underlie the affective motivation of drinking behaviour demanded by thirst. But direct evidence for this hypothesis is lacking. The present study evaluated potential correlations between ACC neuronal activity and drinking behaviour in rats injected with different concentrations of saline. We observed an increased number of c-Fos-positive neurons in the ACC after injection of hypertonic saline, indicating strong ACC neuronal activation under hyperosmotic thirst. Increased firing rates of putative ACC pyramidal neurons preceded drinking behaviour and positively correlated with both the total duration of drinking and the total amount of water consumed. Chemogenetic inhibition of ACC pyramidal neurons changed drinking behaviour from an explosive and short-lasting pattern to a gradual but more persistent pattern, without affecting either the total duration of drinking or the total amount of water consumed. Together, these findings support a role of the ACC in modulating the affective-motivative dimension of hyperosmolality-induced thirst.

Ethology, physiological, and ingestive responses of sheep subjected to different temperatures and salinity levels of water

The objective of this study was to evaluate the physiological responses, ethology, and ingestive behavior of female Morada Nova sheep kept in a thermoneutral environment, after thermal stress and after consuming water with different levels of salinity. Thirty-six Morada Nova females with a mean age of 10.0 ± 2.0 months and a mean weight of 25.0 ± 3.0 kg were evaluated and distributed in a climatic chamber. The experimental design was completely randomized, with a factorial scheme of 2 (air temperature (AT)) × 3 (salinity levels (SLs)) and six replications. The sheep's physiological responses, ethology (day/night), and ingestive behavior were evaluated while they were subjected to ATs of 26.0 and 32.0 °C and SLs of 3.0, 6.0, and 9.0 dS/m. With elevation in AT, the animals experienced increased (P < 0.05) rectal temperatures (RTs), respiratory rates (RFs), and surface temperatures (STs) and exhibited reduced (P < 0.05) heart rates (HRs). When consuming water with an SL of 9.0 dS/m, a HR reduction (P < 0.05) was observed. Sleep behavior increased (P < 0.05) with the increase in SL during the day. Sleeping and drinking behaviors increased (P < 0.05), and the time of inactivity was reduced (P < 0.05) during the nocturnal period with increased SLs. With increased SLs, sheep consumed more water (P < 0.05) and reduced (P < 0.05) the number of regurgitated ruminal boluses per day (NRBD). Under the conditions of thermal stress (32.0 °C), sheep need to make physiological adjustments to maintain homeothermy. Water consumption of SLs up to 9.0 dS/m causes a higher state of dormancy in female Morada Nova sheep.

Neural mechanisms of social homeostasis

Social connections are vital to survival throughout the animal kingdom and are dynamic across the life span. There are debilitating consequences of social isolation and loneliness, and social support is increasingly a primary consideration in health care, disease prevention, and recovery. Considering social connection as an "innate need," it is hypothesized that evolutionarily conserved neural systems underlie the maintenance of social connections: alerting the individual to their absence and coordinating effector mechanisms to restore social contact. This is reminiscent of a homeostatic system designed to maintain social connection. Here, we explore the identity of neural systems regulating "social homeostasis." We review findings from rodent studies evaluating the rapid response to social deficit (in the form of acute social isolation) and propose that parallel, overlapping circuits are engaged to adapt to the vulnerabilities of isolation and restore social connection. By considering the neural systems regulating other homeostatic needs, such as energy and fluid balance, we discuss the potential attributes of social homeostatic circuitry. We reason that uncovering the identity of these circuits/mechanisms will facilitate our understanding of how loneliness perpetuates long-term disease states, which we speculate may result from sustained recruitment of social homeostatic circuits.

Markers of mineralocorticoid receptor function: changes over time and relationship to response in patients with major depression

The renin-angiotensin-aldosterone system and its hormone receptors, i.e. the angiotensin and mineralocorticoid receptor (MR), have emerged as important targets for central nervous system disorders and in particular for major depression. We have recently characterized baseline MR function as a predictor for treatment outcome with standard antidepressants. The aims of this study are (i) to characterize how strongly an early biomarker change (after 2 weeks) is related to outcome and (ii) whether these biomarker changes are related to the final outcome, that is, could serve as surrogate markers for response. Twenty-four of 30 patients with unipolar major depression completed the observational trial. MR-related biomarkers were assessed at baseline, 2 weeks, and 6 weeks of standard antidepressant treatment. These biomarkers included slow wave sleep (SWS), salivary cortisol and aldosterone after awakening, heart rate variability measured as respiratory sinus arrhythmia (RSA), systolic blood pressure, salt taste intensity (STI), salt pleasantness (SP), and plasma electrolytes. The Hamilton depression rating scale with 21 items was primarily used to determine depression severity. In the overall sample, STI increased and SP decreased significantly with treatment without a clear relationship with treatment outcome. No other significant changes were observed. Reductions in cortisol and aldosterone after 2 weeks of treatment were significantly related to improvement after 6 weeks (P<0.05). SWS increase after 2 and 6 weeks was by trend (P<0.08) correlated to clinical improvement after 6 weeks. Systolic blood pressure differentiated responders and nonresponders at baseline (P<0.05), but did not change significantly during treatment. We earlier identified a relationship between clinical outcome and baseline values of STI, SP, and RSA only in male patients; therefore, changes in this subgroup were analyzed separately: in male treatment responders, a trend toward an increase in SWS occurred after 2 (P<0.07) and 6 (P<0.07) weeks. Further, a trend toward RSA reduction (P<0.07) was observed. Changes in STI and SP were similar to the total group, but did not reach levels of significance. Early changes in central MR-related biomarkers appear to influence the outcome of standard antidepressant treatment: reduced salivary cortisol, increased SWS, and reduced RSA are linked to a better treatment outcome. These features point to a mechanism involving increased central MR activation in responders to standard antidepressants, but not in nonresponders.

Prefrontal-Bed Nucleus Circuit Modulation of a Passive Coping Response Set

One of the challenges facing neuroscience entails localization of circuits and mechanisms accounting for how multiple features of stress responses are organized to promote survival during adverse experiences. The rodent medial prefrontal cortex (mPFC) is generally regarded as a key site for cognitive and affective information processing, and the anteroventral bed nuclei of the stria terminalis (avBST) integrates homeostatic information from a variety of sources, including the mPFC. Thus, we proposed that the mPFC is capable of generating multiple features (endocrine, behavioral) of adaptive responses via its influence over the avBST. To address this possibility, we first optogenetically inhibited input to avBST from the rostral prelimbic cortical region of mPFC and observed concurrent increases in immobility and hypothalamo-pituitary-adrenal (HPA) output in male rats during tail suspension, whereas photostimulation of this pathway decreased immobility during the same challenge. Anatomical tracing experiments confirmed projections from the rostral prelimbic subfield to separate populations of avBST neurons, and from these to HPA effector neurons in the paraventricular hypothalamic nucleus, and to aspects of the midbrain periaqueductal gray that coordinate passive defensive behaviors. Finally, stimulation and inhibition of the prelimbic-avBST pathway, respectively, decreased and increased passive coping in the shock-probe defensive burying test, without having any direct effect on active coping (burying) behavior. These results define a new neural substrate in the coordination of a response set that involves the gating of passive, rather than active, coping behaviors while restraining neuroendocrine activation to optimize adaptation during threat exposure.SIGNIFICANCE STATEMENT The circuits and mechanisms accounting for how multiple features of responses are organized to promote adaptation have yet to be elucidated. Our report identifies a prefrontal-bed nucleus pathway that organizes a response set capable of gating passive coping behaviors while concurrently restraining neuroendocrine activation during exposure to inescapable stressors. These data provide insight into the central organization of how multiple features of responses are integrated to promote adaptation during adverse experiences, and how disruption in one neural pathway may underlie a broad array of maladaptive responses in stress-related psychiatric disorders.

Neural responses to familiar conspecifics are modulated by a nonapeptide receptor in a winter flocking sparrow

The social behavior network, a collection of reciprocally connected areas within the basal forebrain and midbrain, plays a conserved role in the regulation of vertebrate social behavior. Specific behaviors are associated with patterns of activity across the network, and these activity profiles vary with species and context. We investigated how the social behavior network responds to familiar social stimuli in a seasonally flocking songbird. Further, we explored how socially-induced neural responses are modulated by endogenous nonapeptide receptor blockade. Winter flocking dark-eyed juncos were exposed to either familiar conspecifics or a familiar empty aviary following a peripheral injection of either saline or [desGly-NH₂,d(CH₂)₅, Tyr(Me)²,Thr⁴]-ornithine vasotocin, an VT3 receptor antagonist. Socially-exposed animals exhibited greater Fos induction across the social behavior network. Sex and drug effects were site-specific, with females tending to exhibit greater Fos responses to social stimuli and a greater sensitivity to VT3 antagonism. We suggest that in flocking animals, VT3 activation during social interaction may shift the pattern of neural activity towards the dorsocaudal lateral septum and rostral arcopallium and away from the extended amygdala, anterior and ventromedial hypothalamus, and the caudal ventral/ventrolateral lateral septum.

Intermittent living; the use of ancient challenges as a vaccine against the deleterious effects of modern life - A hypothesis

Chronic non-communicable diseases (CNCD) are the leading cause of mortality in developed countries. They ensue from the sum of modern anthropogenic risk factors, including high calorie nutrition, malnutrition, sedentary lifestyle, social stress, environmental toxins, politics and economic factors. Many of these factors are beyond the span of control of individuals, suggesting that CNCD are inevitable. However, various studies, ours included, show that the use of intermittent challenges with hormetic effects improve subjective and objective wellbeing of individuals with CNCD, while having favourable effects on immunological, metabolic and behavioural indices. Intermittent cold, heat, fasting and hypoxia, together with phytochemicals in multiple food products, have widespread influence on many pathways related with overall health. Until recently, most of the employed challenges with hormetic effects belonged to the usual transient live experiences of our ancestors. Our hypothesis; we conclude that, whereas the total inflammatory load of multi-metabolic and psychological risk factors causes low grade inflammation and aging, the use of intermittent challenges, united in a 7-10 days lasting hormetic intervention, might serve as a vaccine against the deleterious effects of chronic low grade inflammation and it's metabolic and (premature) aging consequences.

High salt intake enhances swim stress-induced PVN vasopressin cell activation and active stress coping

PURPOSE

Stress contributes to many psychiatric disorders; however, responsivity to stressors can vary depending on previous or current stress exposure. Relatively innocuous heterotypic (differing in type) stressors can summate to result in exaggerated neuronal and behavioral responses. Here we investigated the ability of prior high dietary sodium chloride (salt) intake, a dehydrating osmotic stressor, to enhance neuronal and behavioral responses of mice to an acute psychogenic swim stress (SS). Further, we evaluated the contribution of the osmo-regulatory stress-related neuropeptide arginine vasopressin (VP) in the hypothalamic paraventricular nucleus (PVN), one of only a few brain regions that synthesize VP. The purpose of this study was to determine the impact of high dietary salt intake on responsivity to heterotypic stress and the potential contribution of VPergic-mediated neuronal activity on high salt-induced stress modulation, thereby providing insight into how dietary (homeostatic) and environmental (psychogenic) stressors might interact to facilitate psychiatric disorder vulnerability.

APPROACH

Salt loading (SL) with 4% saline for 7 days was used to dehydrate and osmotically stress mice prior to exposure to an acute SS. Fluid intake and hematological measurements were taken to quantify osmotic dehydration, and serum corticosterone levels were measured to index stress axis activation. Immunohistochemistry (IHC) was used to stain for the immediate early gene product c-Fos to quantify effects of SL on SS-induced activation of neurons in the PVN and extended amygdala - brain regions that are synaptically connected and implicated in responding to osmotic stress and in modulation of SS behavior, respectively. Lastly, the role of VPergic PVN neurons and VP type 1 receptor (V1R) activity in the amygdala in mediating effects of SL on SS behavior was evaluated by quantifying c-Fos activation of VPergic PVN neurons and, in functional experiments, by nano-injecting the V1R selective antagonist dGly[Phaa1,d-tyr(et), Lys, Arg]-VP bilaterally into the amygdala prior to the SS.

FINDINGS

SL increased serum osmolality (P < 0.01), which positively correlated with time spent mobile during, and time spent grooming after a SS (P < 0.01, P < 0.01), and SL increased serum corticosterone levels (P < 0.01). SL alone increased c-Fos immunoreactivity among PVN neurons (P = .02), including VP positive neurons (P < 0.01). SL increased SS-induced c-Fos activation of PVN neurons as well (P < 0.01). In addition, SL and SS each increased the total number of PVN neurons that were immunoreactive for VP (P < 0.01). An enhancing effect of SL and SS was observed on c-Fos positive cell counts in the central (P = .02) and basolateral (P < 0.01) nuclei of the amygdala and bilateral nano-injections of V1R antagonist into the amygdala reduced time spent mobile both in salt loaded and control mice during SS (P < 0.05, P < 0.05).

SUMMARY

Taken together, these data indicate that neuronal and behavioral responsivity to an acute psychogenic stressor is potentiated by prior exposure to high salt intake. This synergistic effect was associated with activation of PVN VP neurons and depended, in part, on activity of V1 receptors in the amygdala. Findings provide novel insight into neural mechanisms whereby prior exposure to a homeostatic stressor such as osmotic dehydration by excessive salt intake increases responsivity to a perceived stress. These experiments show that high dietary salt can influence stress responsivity and raise the possibility that excessive salt intake could be a contributing factor in the development of stress-related psychiatric disorders.

Using the cerebrospinal fluid to understand ingestive behavior

The cerebrospinal fluid (CSF) offers a window into the workings of the brain and blood-brain barrier (BBB). Molecules that enter into the central nervous system (CNS) by passive diffusion or receptor-mediated transport through the choroid plexus often appear in the CSF prior to acting within the brain. Other molecules enter the CNS by passing through the BBB into the brain's interstitial fluid prior to appearing in the CSF. This pattern is also often observed for molecules synthesized by neurons or glia within the CNS. The CSF is therefore an important conduit for the entry and clearance of molecules into/from the CNS and thereby constitutes an important window onto brain activity and barrier function. Assessing the CSF basally, under experimental conditions, or in the context of challenges or metabolic diseases can provide powerful insights about brain function. Here, we review important findings made by our labs, as influenced by the late Randall Sakai, by interrogating the CSF.

A Single Angiotensin II Hypertensive Stimulus Is Associated with Prolonged Neuronal and Immune System Activation in Wistar-Kyoto Rats

Activation of autonomic neural pathways by chronic hypertensive stimuli plays a significant role in pathogenesis of hypertension. Here, we proposed that even a single acute hypertensive stimulus will activate neural and immune pathways that may be important in initiation of memory imprinting seen in chronic hypertension. We investigated the effects of acute angiotensin II (Ang II) administration on blood pressure, neural activation in cardioregulatory brain regions, and central and systemic immune responses, at 1 and 24 h post-injection. Administration of a single bolus intra-peritoneal (I.P.) injection of Ang II (36 μg/kg) resulted in a transient increase in the mean arterial pressure (MAP) (by 22 ± 4 mmHg vs saline), which returned to baseline within 1 h. However, in contrast to MAP, neuronal activity, as measured by manganese-enhanced magnetic resonance (MEMRI), remained elevated in several cardioregulatory brain regions over 24 h. The increase was predominant in autonomic regions, such as the subfornical organ (SFO; ~20%), paraventricular nucleus of the hypothalamus (PVN; ~20%) and rostral ventrolateral medulla (RVLM; ~900%), among others. Similarly, systemic and central immune responses, as evidenced by circulating levels of CD4⁺/IL17⁺ T cells, and increased IL17 levels and activation of microglia in the PVN, respectively, remained elevated at 24 h following Ang II challenge. Elevated Fos expression in the PVN was also present at 24 h (by 73 ± 11%) following Ang II compared to control saline injections, confirming persistent activation of PVN. Thus, even a single Ang II hypertensive stimulus will initiate changes in neuronal and immune cells that play a role in the developing hypertensive phenotype.

Chronic salt-loading reduces basal excitatory input to CRH neurons in the paraventricular nucleus and accelerates recovery from restraint stress in male mice

Neurons synthesizing corticotrophin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN) are activated during acute stress and act via the hypothalamic-pituitary-adrenal (HPA) axis to increase systemic levels of corticosterone (CORT). Recent data indicates that CRH neurons in the PVN are inhibited by acute salt-loading, and that this inhibition blunts the response to restraint stress as measured by increases in plasma CORT. The current study evaluates the effects of chronic rather than acute salt-loading on stress-induced activation of the HPA axis. Relative to euhydrated controls, chronic salt-loading over a 5-day period elevated plasma sodium and fluid intake without eliciting hypovolemia or substantial alterations in food intake or body weight. Chronic salt-loading also decreased expression of CRH mRNA in the anterior but not posterior portion of the PVN. Similarly, whole cell patch clamp recordings revealed that salt-loading effectively decreases spontaneous excitatory input to CRH neurons in the PVN without altering spontaneous inhibitory input. Generally consistent with these observations, chronic salt attenuated HPA axis activation as indicated by a significant reduction of plasma CORT during recovery from restraint stress.

Testing a Model of Sodium Reduction in Hypertensive Older Thai Adults

Hypertensive older adults will benefit if there is a clear understanding of the factors related to sodium reduction. That would raise awareness of the causes, consequently reducing many health risks, lowering health care costs, and diminishing economic and social burden from high blood pressure. This study explored predictors of urinary sodium excretion. A cross-sectional, correlational study was conducted in 312 hypertensive older Thai adults. Questionnaires related to knowledge, self-care agency, self-care behavior of sodium reduction, and 24-hour urinary sodium analyses were used, followed by the application of structural equation modeling and the Analysis of Moment Structures program. Self-care agency, knowledge, self-care behavior, rural/urban location, and education accounted for 61% of urinary sodium excretion. Self-care agency, knowledge, and self-care behavior were the main predictors in the urinary sodium excretion model. This study suggests establishing supportive educative sodium reduction-related programs that improve knowledge and enhance self-care agency, as well as a comparison of the changes of sodium reduction self-care behavior and urinary sodium excretion over time after the intervention.

Postprandial sleep mechanics in Drosophila

Food consumption is thought to induce sleepiness. However, little is known about how postprandial sleep is regulated. Here, we simultaneously measured sleep and food intake of individual flies and found a transient rise in sleep following meals. Depending on the amount consumed, the effect ranged from slightly arousing to strongly sleep inducing. Postprandial sleep was positively correlated with ingested volume, protein, and salt—but not sucrose—revealing meal property-specific regulation. Silencing of leucokinin receptor (Lkr) neurons specifically reduced sleep induced by protein consumption. Thermogenetic stimulation of leucokinin (Lk) neurons decreased whereas Lk downregulation by RNAi increased postprandial sleep, suggestive of an inhibitory connection in the Lk-Lkr circuit. We further identified a subset of non-leucokininergic cells proximal to Lkr neurons that rhythmically increased postprandial sleep when silenced, suggesting that these cells are cyclically gated inhibitory inputs to Lkr neurons. Together, these findings reveal the dynamic nature of postprandial sleep.

DOI:http://dx.doi.org/10.7554/eLife.19334.001

Many of us have experienced feelings of sleepiness after a large meal. However, there is little scientific evidence that this “food coma” effect is real. If it is, it may vary between individuals, or depend on the type of food consumed. This variability makes it difficult to study the causes of post-meal sleepiness.

Murphy et al. have now developed a system that can measure fruit fly sleep and feeding behavior at the same time. Recordings using this system reveal that after a meal, flies sleep more for a short period before returning to a normal state of wakefulness. The sleep period lasts around 20-40 minutes, with flies that ate more generally sleeping more.

Further investigation revealed that salty or protein-rich foods promote sleep, whereas sugary foods do not. By using genetic tools to turn on and off neurons in the fly brain, Murphy et al. identified a number of brain circuits that play a role in controlling post-meal sleepiness. Some of these respond specifically to the consumption of protein. Others are sensitive to the fruit fly’s internal clock, reducing post-meal sleepiness only around dusk. Thus, post-meal sleepiness can be regulated in a number of different ways.

Future experiments are now needed to explore the genes and circuits that enable meal size and the protein or salt content of food to drive sleep. In nature, sleep is likely a vulnerable state for animals. Thus, another challenge will be to uncover why post-meal sleep is important. Does sleeping after a meal boost digestion? Or might it help animals to form memories about a food source, making it easier to find similar food in the future?

DOI:http://dx.doi.org/10.7554/eLife.19334.002

Angiotensin type 1a receptors in the paraventricular nucleus of the hypothalamus control cardiovascular reactivity and anxiety-like behavior in male mice

This study tested the hypothesis that deletion of angiotensin type 1a receptors (AT1a) from the paraventricular nucleus of hypothalamus (PVN) attenuates anxiety-like behavior, hypothalamic-pituitary-adrenal (HPA) axis activity, and cardiovascular reactivity. We used the Cre/LoxP system to generate male mice with AT1a specifically deleted from the PVN. Deletion of the AT1a from the PVN reduced anxiety-like behavior as indicated by increased time spent in the open arms of the elevated plus maze. In contrast, PVN AT1a deletion had no effect on HPA axis activation subsequent to an acute restraint challenge but did reduce hypothalamic mRNA expression for corticotropin-releasing hormone (CRH). To determine whether PVN AT1a deletion inhibits cardiovascular reactivity, we measured systolic blood pressure, heart rate, and heart rate variability (HRV) using telemetry and found that PVN AT1a deletion attenuated restraint-induced elevations in systolic blood pressure and elicited changes in HRV indicative of reduced sympathetic nervous activity. Consistent with the decreased HRV, PVN AT1a deletion also decreased adrenal weight, suggestive of decreased adrenal sympathetic outflow. Interestingly, the altered stress responsivity of mice with AT1a deleted from the PVN was associated with decreased hypothalamic microglia and proinflammatory cytokine expression. Collectively, these results suggest that deletion of AT1a from the PVN attenuates anxiety, CRH gene transcription, and cardiovascular reactivity and reduced brain inflammation may contribute to these effects.

Angiotensin Type-2 Receptors Influence the Activity of Vasopressin Neurons in the Paraventricular Nucleus of the Hypothalamus in Male Mice

It is known that angiotensin-II acts at its type-1 receptor to stimulate vasopressin (AVP) secretion, which may contribute to angiotensin-II-induced hypertension. Less well known is the impact of angiotensin type-2 receptor (AT2R) activation on these processes. Studies conducted in a transgenic AT2R enhanced green fluorescent protein reporter mouse revealed that although AT2R are not themselves localized to AVP neurons within the paraventricular nucleus of the hypothalamus (PVN), they are localized to neurons that extend processes into the PVN. In the present set of studies, we set out to characterize the origin, phenotype, and function of nerve terminals within the PVN that arise from AT2R-enhanced green fluorescent protein-positive neurons and synapse onto AVP neurons. Initial experiments combined genetic and neuroanatomical techniques to determine that γ-aminobutyric acid (GABA)ergic neurons derived from the peri-PVN area containing AT2R make appositions onto AVP neurons within the PVN, thereby positioning AT2R to negatively regulate neuroendocrine secretion. Subsequent patch-clamp electrophysiological experiments revealed that selective activation of AT2R in the peri-PVN area using compound 21 facilitates inhibitory (ie, GABAergic) neurotransmission and leads to reduced activity of AVP neurons within the PVN. Final experiments determined the functional impact of AT2R activation by testing the effects of compound 21 on plasma AVP levels. Collectively, these experiments revealed that AT2R expressing neurons make GABAergic synapses onto AVP neurons that inhibit AVP neuronal activity and suppress baseline systemic AVP levels. These findings have direct implications in the targeting of AT2R for disorders of AVP secretion and also for the alleviation of high blood pressure.

Conditioned stress prevents cue-primed cocaine reinstatement only in stress-responsive rats

Neurobiological mechanisms underlying comorbid posttraumatic stress disorder (PTSD) and cocaine use disorder (CUD) are unknown. We aimed to develop an animal model of PTSD + CUD to examine the neurobiology underlying cocaine-seeking in the presence of PTSD comorbidity. Rats were exposed to cat urine once for 10-minutes and tested for anxiety-like behaviors one week later. Subsequently, rats underwent long-access (LgA) cocaine self-administration and extinction training. Rats were re-exposed to the trauma context and then immediately tested for cue-primed reinstatement of cocaine-seeking. Plasma and brains were collected afterwards for corticosterone assays and real-time qPCR analysis. Urine-exposed (UE; n = 23) and controls not exposed to urine (Ctrl; n = 11) did not differ in elevated plus maze behavior, but UE rats displayed significantly reduced habituation of the acoustic startle response (ASR) relative to Ctrl rats. A median split of ASR habituation scores was used to classify stress-responsive rats. UE rats (n = 10) self-administered more cocaine on Day 1 of LgA than control rats (Ctrl + Coc; n = 8). Re-exposure to the trauma context prevented cocaine reinstatement only in stress-responsive rats. Ctrl + Coc rats had lower plasma corticosterone concentrations than Ctrls, and decreased gene expression of corticotropin releasing hormone (CRH) and Glcci1 in the hippocampus. Rats that self-administered cocaine displayed greater CRH expression in the amygdala that was independent of urine exposure. While we did not find that cat urine exposure induced a PTSD-like phenotype in our rats, the present study underscores the need to separate stressed rats into cohorts based on anxiety-like behavior in order to study individual vulnerability to PTSD + CUD.

Emotional Stress and Cardiovascular Complications in Animal Models: A Review of the Influence of Stress Type

Emotional stress has been recognized as a modifiable risk factor for cardiovascular diseases. The impact of stress on physiological and psychological processes is determined by characteristics of the stress stimulus. For example, distinct responses are induced by acute vs. chronic aversive stimuli. Additionally, the magnitude of stress responses has been reported to be inversely related to the degree of predictability of the aversive stimulus. Therefore, the purpose of the present review was to discuss experimental research in animal models describing the influence of stressor stimulus characteristics, such as chronicity and predictability, in cardiovascular dysfunctions induced by emotional stress. Regarding chronicity, the importance of cardiovascular and autonomic adjustments during acute stress sessions and cardiovascular consequences of frequent stress response activation during repeated exposure to aversive threats (i.e., chronic stress) is discussed. Evidence of the cardiovascular and autonomic changes induced by chronic stressors involving daily exposure to the same stressor (predictable) vs. different stressors (unpredictable) is reviewed and discussed in terms of the impact of predictability in cardiovascular dysfunctions induced by stress.

Influence of a 10-Day Mimic of Our Ancient Lifestyle on Anthropometrics and Parameters of Metabolism and Inflammation: The "Study of Origin"

Chronic low-grade inflammation and insulin resistance are intimately related entities that are common to most, if not all, chronic diseases of affluence. We hypothesized that a short-term intervention based on “ancient stress factors” may improve anthropometrics and clinical chemical indices. We executed a pilot study of whether a 10-day mimic of a hunter-gatherer lifestyle favorably affects anthropometrics and clinical chemical indices. Fifty-five apparently healthy subjects, in 5 groups, engaged in a 10-day trip through the Pyrenees. They walked 14 km/day on average, carrying an 8-kilo backpack. Raw food was provided and self-prepared and water was obtained from waterholes. They slept outside in sleeping bags and were exposed to temperatures ranging from 12 to 42°C. Anthropometric data and fasting blood samples were collected at baseline and the study end. We found important significant changes in most outcomes favoring better metabolic functioning and improved anthropometrics. Coping with “ancient mild stress factors,” including physical exercise, thirst, hunger, and climate, may influence immune status and improve anthropometrics and metabolic indices in healthy subjects and possibly patients suffering from metabolic and immunological disorders.

GABAergic Signaling within a Limbic-Hypothalamic Circuit Integrates Social and Anxiety-Like Behavior with Stress Reactivity

The posterior hypothalamic nucleus (PH) stimulates autonomic stress responses. However, the role of the PH in behavioral correlates of psychiatric illness, such as social and anxiety-like behavior, is largely unexplored, as is the neurochemistry of PH connectivity with limbic and neuroendocrine systems. Thus, the current study tested the hypothesis that GABAergic signaling within the PH is a critical link between forebrain behavior-regulatory nuclei and the neuroendocrine hypothalamus, integrating social and anxiety-related behaviors with physiological stress reactivity. To address this hypothesis, GABAA receptor pharmacology was used to locally inhibit or disinhibit the PH immediately before behavioral measures of social and anxiety-like behavior in rats. Limbic connectivity of the PH was then established by simultaneous co-injection of anterograde and retrograde tracers. Further, the role of PH GABAergic signaling in neuroendocrine stress responses was tested via inhibition/disinhibition of the PH. These studies determined a prominent role for the PH in the expression of anxiety-related behaviors and social withdrawal. Histological analyses revealed divergent stress-activated limbic input to the PH, emanating predominantly from the prefrontal cortex, lateral septum, and amygdala. PH projections also targeted both parvicellular and magnocellular peptidergic neurons in the paraventricular and supraoptic hypothalamus. Further, GABAA receptor pharmacology determined an excitatory effect of the PH on neuroendocrine responses to stress. These data indicate that the PH represents an important stress-integrative center, regulating behavioral processes and connecting the limbic forebrain with neuroendocrine systems. Moreover, the PH appears to be uniquely situated to have a role in stress-related pathologies associated with limbic-hypothalamic dysfunction.

Hemodynamic responses to mental stress during salt loading

PURPOSE

The purpose was to examine whether prolonged moderate stress associated with a student exam would increase the blood pressure response to a salt load in young healthy normotensive individuals.

METHODS

Ten healthy young subjects were examined at two different occasions in random order (i) during preparation for a medical exam (prolonged stress) and (ii) outside the exam period (low stress). All subjects consumed a controlled diet for 3 days with low- or high-salt content in randomized order. The subjective stress was measured by Spielberger's State-Trait Anxiety Inventory-Scale, SCL Symptom Checklist for stress and the Visual Analogue Scale. On each level of stress, 24-h ambulatory blood pressure and cardiac output (CO) were measured. Furthermore, plasma norepinephrine (NE), epinephrine (E) and plasma renin activity (PRA) were measured.

RESULTS

Twenty-four-hour ABP, 24-h heart rate, CO as well as plasma levels of NE, E and PRA remained unchanged by changes in stress level. Day-night reduction in SAP was significantly larger during moderate stress and high-salt intake; however, no significant difference was observed during daytime and night-time. Individual increase in mental stress correlated significantly with an individual decrease in PRA (SCL-17, r = -0·80, P<0·05, STAIr = -0·64 P<0·05) during high-salt intake.

CONCLUSION

Moderate stress over a period of time in young healthy normotensive individuals does not lead to changes in 24-h ABP. However, the augmented reduction in day-to-night systolic blood pressure during high-salt intake and moderate stress may indicate that stress affects blood pressure regulation.

Thirst Is Associated with Suppression of Habenula Output and Active Stress Coping: Is there a Role for a Non-canonical Vasopressin-Glutamate Pathway?

Water-homeostasis is a fundamental physiological process for terrestrial life. In vertebrates, thirst drives water intake, but the neuronal circuits that connect the physiology of water regulation with emotional context are poorly understood. Vasopressin (VP) is a prominent messenger in this circuit, as well as L-glutamate. We have investigated the role of a VP circuit and interaction between thirst and motivational behaviors evoked by life-threatening stimuli in rats. We demonstrate a direct pathway from hypothalamic paraventricular VP-expressing, glutamatergic magnocellular neurons to the medial division of lateral habenula (LHbM), a region containing GABAergic neurons. In vivo recording and juxtacellular labeling revealed that GABAergic neurons in the LHbM had locally branching axons, and received VP-positive axon terminal contacts on their dendrites. Water deprivation significantly reduced freezing and immobility behaviors evoked by innate fear and behavioral despair, respectively, accompanied by decreased Fos expression in the lateral habenula. Our results reveal a novel VP-expressing hypothalamus to the LHbM circuit that is likely to evoke GABA-mediated inhibition in the LHbM, which promotes escape behavior during stress coping.

Increasing brain angiotensin converting enzyme 2 activity decreases anxiety-like behavior in male mice by activating central Mas receptors

Over-activation of the brain renin-angiotensin system (RAS) has been implicated in the etiology of anxiety disorders. Angiotensin converting enzyme 2 (ACE2) inhibits RAS activity by converting angiotensin-II, the effector peptide of RAS, to angiotensin-(1-7), which activates the Mas receptor (MasR). Whether increasing brain ACE2 activity reduces anxiety by stimulating central MasR is unknown. To test the hypothesis that increasing brain ACE2 activity reduces anxiety-like behavior via central MasR stimulation, we generated male mice overexpressing ACE2 (ACE2 KI mice) and wild type littermate controls (WT). ACE2 KI mice explored the open arms of the elevated plus maze (EPM) significantly more than WT, suggesting increasing ACE2 activity is anxiolytic. Central delivery of diminazene aceturate, an ACE2 activator, to C57BL/6 mice also reduced anxiety-like behavior in the EPM, but centrally administering ACE2 KI mice A-779, a MasR antagonist, abolished their anxiolytic phenotype, suggesting that ACE2 reduces anxiety-like behavior by activating central MasR. To identify the brain circuits mediating these effects, we measured Fos, a marker of neuronal activation, subsequent to EPM exposure and found that ACE2 KI mice had decreased Fos in the bed nucleus of stria terminalis but had increased Fos in the basolateral amygdala (BLA). Within the BLA, we determined that ∼62% of GABAergic neurons contained MasR mRNA and expression of MasR mRNA was upregulated by ACE2 overexpression, suggesting that ACE2 may influence GABA neurotransmission within the BLA via MasR activation. Indeed, ACE2 overexpression was associated with increased frequency of spontaneous inhibitory postsynaptic currents (indicative of presynaptic release of GABA) onto BLA pyramidal neurons and central infusion of A-779 eliminated this effect. Collectively, these results suggest that ACE2 may reduce anxiety-like behavior by activating central MasR that facilitate GABA release onto pyramidal neurons within the BLA.

Methyl donor supplementation in rats reverses the deleterious effect of maternal separation on depression-like behaviour

Adverse early life events are associated with altered stress responsiveness and metabolic disturbances in the adult life. Dietary methyl donor supplementation could be able to reverse the negative effects of maternal separation by affecting DNA methylation in the brain. In this study, maternal separation during lactation reduced body weight gain in the female adult offspring without affecting food intake, and altered total and HDL-cholesterol levels. Also, maternal separation induced a cognitive deficit as measured by NORT and an increase in the immobility time in the Porsolt forced swimming test, consistent with increased depression-like behaviour. An 18-week dietary supplementation with methyl donors (choline, betaine, folate and vitamin B12) from postnatal day 60 also reduced body weight without affecting food intake. Some of the deleterious effects induced by maternal separation, such as the abnormal levels of total and HDL-cholesterol, but especially the depression-like behaviour as measured by the Porsolt test, were reversed by methyl donor supplementation. Also, the administration of methyl donors increased total DNA methylation (measured by immunohistochemistry) and affected the expression of insulin receptor in the hippocampus of the adult offspring. However, no changes were observed in the DNA methylation status of insulin receptor and corticotropin-releasing hormone (CRH) promoter regions in the hypothalamus. In summary, methyl donor supplementation reversed some of the deleterious effects of an early life-induced model of depression in rats and altered the DNA methylation profile in the brain.

Target-based biomarker selection - Mineralocorticoid receptor-related biomarkers and treatment outcome in major depression

Aldosterone and mineralocorticoid receptor (MR)-function have been related to depression. We examined central and peripheral parameters of MR-function in order to characterize their relationship to clinical treatment outcome after six weeks in patients with acute depression. 30 patients with a diagnosis of major depression were examined 3 times over a 6 week period. Aldosterone and cortisol salvia samples were taken at 7.00 a.m. before patients got out of bed. Easy to use e-devices were used to measure markers of central MR function, i.e. slow wave sleep (SWS) and heart-rate variability (HRV). Salt-taste intensity (STI) and salt pleasantness (SP) of a 0.9% salt solution were determined by a newly developed scale. In addition, systolic blood pressure (SBP) and plasma electrolytes were determined as markers for peripheral MR activity. The relationship between the levels of these biomarkers at baseline and the change in clinical outcome parameters (Hamilton depression rating scale (HDRS)-21, anxiety, QIDS and BDI) after 6 weeks of treatment was investigated. A higher aldosterone/cortisol ratio (Aldo/Cort) (n = 17 due to missing values; p < 0.05) and lower SBP (n = 24; p < 0.05) at baseline predicted poor outcome, as measured with the HDRS, independent of gender. Only in male patients higher STI, lower SP, lower SWS (all n = 13) and higher HRV (n = 11) at baseline predicted good outcome p < 0.05). Likewise, in male patients low baseline sodium appears to be predictive for a poor outcome (n = 12; p = 0.05; based on HDRS-6). In conclusion, correlates of higher central MR-activation are associated with poorer clinical improvement, particularly in men. This contrasts with the finding of a peripheral MR-desensitization in more refractory patients. As one potential mechanism to consider, sodium loss on the basis of dysfunctional peripheral MR function and additional environmental factors may trigger increased aldosterone secretion and consequently worse outcome. These markers deserve further study as potential biological correlates for therapy refractory depression.

The influence of early life sexual abuse on oxytocin concentrations and premenstrual symptomatology in women with a menstrually related mood disorder

Oxytocin (OT), associated with affiliation and social bonding, social salience, and stress/pain regulation, may play a role in the pathophysiology of stress-related disorders, including menstrually-related mood disorders (MRMD's). Adverse impacts of early life sexual abuse (ESA) on adult attachment, affective regulation, and pain sensitivity suggest ESA-related OT dysregulation in MRMD pathophysiology. We investigated the influence of ESA on plasma OT, and the relationship of OT to the clinical phenomenology of MRMD's. Compared to MRMD women without ESA (n=40), those with ESA (n=20) displayed significantly greater OT [5.39pg/mL (SD, 2.4) vs. 4.36pg/mL (SD, 1.1); t (58)=-2.26, p=0.03]. In women with ESA, OT was significantly, inversely correlated with premenstrual psychological and somatic symptoms (r's=-0.45 to -0.64, p's<0.05). The relationship between OT and premenstrual symptomatology was uniformly low and non-significant in women without ESA. In women with ESA, OT may positively modulate MRMD symptomatology.