Food and the circadian activity of the hypothalamic-pituitary-adrenal axis

Advancing the Assessment and Treatment of Comorbid Pediatric Chronic Functional Abdominal Pain (CFAP) and Restrictive Eating Disorders

The aim of this review is to heighten awareness of the association between chronic functional abdominal pain (CFAP) and restrictive eating disorders (ED) in adolescents. We describe current diagnostic practices and propose future research efforts to improve the assessment and treatment of comorbid CFAP and restrictive EDs. A narrative review of the literature on CFAP and EDs was performed using PubMed, JSTOR, ScienceDirect, and PsycINFO and the following search terms: 'restrictive eating disorders', 'chronic functional abdominal pain', 'chronic pain' 'treatment' 'diagnosis' and 'adolescents'. Published studies on restrictive EDs and CFAP from May 2008 to March 2023 were included. Ascribable to the overlap in etiology and symptom presentation, adolescents with chronic pain are significantly less likely to have their ED pathology promptly identified by providers compared to adolescents without comorbid chronic pain. This highlights the importance of the time sensitive and accurate identification of EDs in adolescents with CFAP. Overall, assessment methods are limited and EDs take longer to be identified in adolescents with comorbid CFAP. Future efforts should address diagnostic practices in pediatric settings and improve the communication among medical and mental health providers in order to promote the rapid and effective diagnosis and treatment of comorbid CFAP and EDs.

New Insights into the Role of Insulin and Hypothalamic-Pituitary-Adrenal (HPA) Axis in the Metabolic Syndrome

Recent data suggests that (pre)diabetes onset is preceded by a period of hyperinsulinemia. Consumption of the "modern" Western diet, over-nutrition, genetic background, decreased hepatic insulin clearance, and fetal/metabolic programming may increase insulin secretion, thereby causing chronic hyperinsulinemia. Hyperinsulinemia is an important etiological factor in the development of metabolic syndrome, type 2 diabetes, cardiovascular disease, polycystic ovarian syndrome, and Alzheimer's disease. Recent data suggests that the onset of prediabetes and diabetes are preceded by a variable period of hyperinsulinemia. Emerging data suggest that chromic hyperinsulinemia is also a driving force for increased activation of the hypothalamic-adrenal-pituitary (HPA) axis in subjects with the metabolic syndrome, leading to a state of "functional hypercortisolism". This "functional hypercortisolism" by antagonizing insulin actions may prevent hypoglycemia. It also disturbs energy balance by shifting energy fluxes away from muscles toward abdominal fat stores. Synergistic effects of hyperinsulinemia and "functional hypercortisolism" promote abdominal visceral obesity and insulin resistance which are core pathophysiological components of the metabolic syndrome. It is hypothesized that hyperinsulinemia-induced increased activation of the HPA axis plays an important etiological role in the development of the metabolic syndrome and its consequences. Numerous studies have demonstrated reversibility of hyperinsulinemia with lifestyle, surgical, and pharmaceutical-based therapies. Longitudinal studies should be performed to investigate whether strategies that reduce hyperinsulinemia at an early stage are successfully in preventing increased activation of the HPA axis and the metabolic syndrome.

Cardiorenal Metabolic Consequences of Nighttime Snacking: Is it an Innocent Eating Behavior?

PURPOSE OF REVIEW

Health consequences of nighttime eating, as a publicly discussed eating behavior type, have been speculated lately. Nighttime eating has been linked to various metabolic outcomes including hyperlipidemia, hypertriglyceridemia, hyperglycemia, weight gain, elevated blood pressure, obesity, and metabolic syndrome, and cardiorenal outcomes such as atherosclerosis, a decline in eGFR, and proteinuria.

RECENT FINDINGS

Although the exact underlying pathophysiological mechanism is not yet clear, multiple hypotheses including disrupted circadian rhythm, altered hormonal levels, and decline in cellular regeneration have been proposed. In this review, we aim to evaluate the growing literature on nighttime eating behavior in terms of metabolic and cardiorenal outcomes, pathophysiological basis, and potential therapeutic alternatives.

A proposed role for glucocorticoids in mediating dopamine-dependent cue-reward learning

Learning to respond appropriately to one's surrounding environment is fundamental to survival. Importantly, however, individuals vary in how they respond to cues in the environment and this variation may be a key determinant of psychopathology. The ability of seemingly neutral cues to promote maladaptive behavior is a hallmark of several psychiatric disorders including, substance use disorder, post-traumatic stress disorder, eating disorders and obsessive-compulsive disorder. Thus, it is important to uncover the neural mechanisms by which such cues are able to attain inordinate control and promote psychopathological behavior. Here, we suggest that glucocorticoids play a critical role in this process. Glucocorticoids are primarily recognized as the main hormone secreted in response to stress but are known to exert their effects across the body and the brain, and to affect learning and memory, cognition and reward-related behaviors, among other things. Here we speculate that glucocorticoids act to facilitate a dopamine-dependent form of cue-reward learning that appears to be relevant to a number of psychiatric conditions. Specifically, we propose to utilize the sign-tracker/goal-tracker animal model as a means to capture individual variation in stimulus-reward learning and to isolate the role of glucocorticoid-dopamine interactions in mediating these individual differences. It is hoped that this framework will lead to the discovery of novel mechanisms that contribute to complex neuropsychiatric disorders and their comorbidity.

Assessing for Eating Disorders: A Primer for Gastroenterologists

Eating disorders involve irregularities in eating behavior that may cause gastrointestinal (GI) symptoms. Consequently, many patients with eating disorders seek gastroenterological healthcare at some point in their illness, with many seeking this care even before they seek treatment for and/or diagnosed with their eating disorder. As such, the gastroenterology provider is in a unique position to identify, manage, and facilitate treatment for an eating disorder early in the course of the illness. Although assessing eating disorders is already a difficult task, the identification of eating disorders in patients with GI disease represents an even greater challenge. In particular, common GI symptoms, such as nausea, vomiting, and bloating, may disguise an eating disorder because these symptoms are often viewed as a sufficient impetus for dietary restriction and subsequent weight loss. In addition, the focus on identifying an organic etiology for the GI symptoms can distract providers from considering an eating disorder. During this prolonged diagnostic evaluation, the eating disorder can progress in severity and become more difficult to treat. Unfortunately, a misconception that hinders eating disorder detection is the notion that the rate or method of weight loss is associated with an eating disorder. Regardless of whether weight loss is slow or rapid, purposeful or accidental, eating disorder behaviors and thought patterns may be present. Unidentified eating disorders are not only dangerous in their own right but also can interfere with effective management of GI disease and its symptoms. As such, it is imperative for the GI provider to remain well versed in the identification of these diseases.

Diurnal rhythms of blood glucose, serum ghrelin, faecal IgA and faecal corticosterone in rats subjected to restricted feeding using the diet board

Laboratory rats are generally fed ad libitum, although this method is associated with obesity and an increased frequency of spontaneous tumours. It has been challenging looking for ways to limit feed consumption in group-housed rats without any setbacks to animal welfare and scientific results. The diet board, as a method of dietary restriction, was used in the present study. Diet board feeding allows group housing and should result in enhanced welfare compared with traditional methods of dietary restriction. With respect to animal model robustness and translatability of results it is important that the feeding regime does not affect diurnal rhythmicity of biological parameters. In the present study the effects of diet board feeding on diurnal rhythms of blood glucose, serum ghrelin, faecal immunoglobulin A (IgA) and faecal corticosterone were assessed. The diet board did not alter diurnal rhythms, and adds weight to the use of this method for dietary restriction which should benefit animal health and the validity of scientific results generated from the animals.

Postnatal Ontogeny of the Circadian Expression of the Adrenal Clock Genes and Corticosterone Rhythm in Male Rats

The postnatal synchronization of the circadian variation of the adrenal clock genes in mammals remains unknown. We evaluated the postnatal ontogeny of daily variation of clock genes (Clock/Bmal1/Per1/Per2/Per3/Cry1/Cry2/Rorα/Rev-Erbα) and steroidogenesis-related genes (Star and Mc2r) in rat adrenals and its relationship with the emergence of plasma corticosterone rhythm using cosinor analysis. Plasma corticosterone circadian rhythm was detected from postnatal day (P)1, with morning acrophase, between zeitgeber time (ZT)0 and ZT2. From P14, there was a nocturnal acrophase of corticosterone at ZT20, which was associated with pups' eye opening. From P3 there was a circadian variation of the mRNA expression of Bmal1, Per2, Per3, and Cry1 genes with morning acrophase, whereas Rev-Erbα had nocturnal acrophase. From P14, Bmal1, Per2, Per3, and Cry1 acrophases advanced by approximately 10 hours, as compared with early neonatal days, becoming vespertine-nocturnal. In all postnatal ages, Per2 and Cry1 circadian profiles were synchronized in phase with the circadian rhythm of plasma corticosterone, whereas Bmal1 was in antiphase. An adult-like Star circadian rhythm profile was observed only from P21. In conclusion, our original data demonstrated a progressive postnatal maturation of the circadian variation of the adrenal clock genes in synchrony with the development of the corticosterone circadian rhythm in rats.

Environmental Enrichment Effect on Fecal Glucocorticoid Metabolites and Captive Maned Wolf (Chrysocyon brachyurus) Behavior

Environmental enrichment is a technique that may reduce the stress of nonhuman animals in captivity. Stress may interfere with normal behavioral expression and affect cognitive decision making. Noninvasive hormonal studies can provide important information about the stress statuses of animals. This study evaluated the effectiveness of different environmental enrichment treatments in the diminution of fecal glucocorticoid metabolites (stress indicators) of three captive maned wolves (Chrysocyon brachyurus). Correlations of the fecal glucocorticoid metabolite levels with expressed behaviors were also determined. Results showed that environmental enrichment reduced fecal glucocorticoid metabolite levels. Furthermore, interspecific and foraging enrichment items were most effective in reducing stress in two of the three wolves. No definite pattern was found between behavioral and physiological responses to stress. In conclusion, these behavioral and physiological data showed that maned wolves responded positively from an animal well being perspective to the enrichment items presented.

Regulation of the Hypothalamic-Pituitary-Adrenocortical Stress Response

The hypothalamo-pituitary-adrenocortical (HPA) axis is required for stress adaptation. Activation of the HPA axis causes secretion of glucocorticoids, which act on multiple organ systems to redirect energy resources to meet real or anticipated demand. The HPA stress response is driven primarily by neural mechanisms, invoking corticotrophin releasing hormone (CRH) release from hypothalamic paraventricular nucleus (PVN) neurons. Pathways activating CRH release are stressor dependent: reactive responses to homeostatic disruption frequently involve direct noradrenergic or peptidergic drive of PVN neurons by sensory relays, whereas anticipatory responses use oligosynaptic pathways originating in upstream limbic structures. Anticipatory responses are driven largely by disinhibition, mediated by trans-synaptic silencing of tonic PVN inhibition via GABAergic neurons in the amygdala. Stress responses are inhibited by negative feedback mechanisms, whereby glucocorticoids act to diminish drive (brainstem) and promote transsynaptic inhibition by limbic structures (e.g., hippocampus). Glucocorticoids also act at the PVN to rapidly inhibit CRH neuronal activity via membrane glucocorticoid receptors. Chronic stress-induced activation of the HPA axis takes many forms (chronic basal hypersecretion, sensitized stress responses, and even adrenal exhaustion), with manifestation dependent upon factors such as stressor chronicity, intensity, frequency, and modality. Neural mechanisms driving chronic stress responses can be distinct from those controlling acute reactions, including recruitment of novel limbic, hypothalamic, and brainstem circuits. Importantly, an individual's response to acute or chronic stress is determined by numerous factors, including genetics, early life experience, environmental conditions, sex, and age. The context in which stressors occur will determine whether an individual's acute or chronic stress responses are adaptive or maladaptive (pathological).

Theory of Inpatient Circadian Care (TICC): A Proposal for a Middle-Range Theory

The circadian system controls the daily rhythms of a variety of physiological processes. Most organisms show physiological, metabolic and behavioral rhythms that are coupled to environmental signals. In humans, the main synchronizer is the light/dark cycle, although non-photic cues such as food availability, noise, and work schedules are also involved. In a continuously operating hospital, the lack of rhythmicity in these elements can alter the patient’s biological rhythms and resilience. This paper presents a Theory of Inpatient Circadian Care (TICC) grounded in circadian principles. We conducted a literature search on biological rhythms, chronobiology, nursing care, and middle-range theories in the databases PubMed, SciELO Public Health, and Google Scholar. The search was performed considering a period of 6 decades from 1950 to 2013. Information was analyzed to look for links between chronobiology concepts and characteristics of inpatient care. TICC aims to integrate multidisciplinary knowledge of biomedical sciences and apply it to clinical practice in a formal way. The conceptual points of this theory are supported by abundant literature related to disease and altered biological rhythms. Our theory will be able to enrich current and future professional practice.

Integrated circuits and molecular components for stress and feeding: implications for eating disorders

Eating disorders are complex brain disorders that afflict millions of individuals worldwide. The etiology of these diseases is not fully understood, but a growing body of literature suggests that stress and anxiety may play a critical role in their development. As our understanding of the genetic and environmental factors that contribute to disease in clinical populations like anorexia nervosa, bulimia nervosa and binge eating disorder continue to grow, neuroscientists are using animal models to understand the neurobiology of stress and feeding. We hypothesize that eating disorder clinical phenotypes may result from stress-induced maladaptive alterations in neural circuits that regulate feeding, and that these circuits can be neurochemically isolated using animal model of eating disorders.

Novel aspects of glucocorticoid actions

Normal hypothalamic-pituitary-adrenal (HPA) axis activity leading to the rhythmic and episodic release of adrenal glucocorticoids (GCs) is essential for body homeostasis and survival during stress. Acting through specific intracellular receptors in the brain and periphery, GCs regulate behaviour, as well as metabolic, cardiovascular, immune and neuroendocrine activities. By contrast to chronic elevated levels, circadian and acute stress-induced increases in GCs are necessary for hippocampal neuronal survival and memory acquisition and consolidation, as a result of the inhibition of apoptosis, the facilitation of glutamatergic neurotransmission and the formation of excitatory synapses, and the induction of immediate early genes and dendritic spine formation. In addition to metabolic actions leading to increased energy availability, GCs have profound effects on feeding behaviour, mainly via the modulation of orexigenic and anorixegenic neuropeptides. Evidence is also emerging that, in addition to the recognised immune suppressive actions of GCs by counteracting adrenergic pro-inflammatory actions, circadian elevations have priming effects in the immune system, potentiating acute defensive responses. In addition, negative-feedback by GCs involves multiple mechanisms leading to limited HPA axis activation and prevention of the deleterious effects of excessive GC production. Adequate GC secretion to meet body demands is tightly regulated by a complex neural circuitry controlling hypothalamic corticotrophin-releasing hormone (CRH) and vasopressin secretion, which are the main regulators of pituitary adrenocorticotrophic hormone (ACTH). Rapid feedback mechanisms, likely involving nongenomic actions of GCs, mediate the immediate inhibition of hypothalamic CRH and ACTH secretion, whereas intermediate and delayed mechanisms mediated by genomic actions involve the modulation of limbic circuitry and peripheral metabolic messengers. Consistent with their key adaptive roles, HPA axis components are evolutionarily conserved, being present in the earliest vertebrates. An understanding of these basic mechanisms may lead to novel approaches for the development of diagnostic and therapeutic tools for disorders related to stress and alterations of GC secretion.

GFAP Expression in Astrocytes of Suprachiasmatic Nucleus and Medial Preoptic Area are Differentially Affected by Malnutrition during Rat Brain Development

The aim of the present study was investigate, in young rats, the effects of malnutrition on astrocyte distribution of two hypothalamic regions, the circadian pacemaker suprachiasmatic nucleus (SCN) and the medial preoptic area (MPA). Control rats were born from mothers fed on commercial diet since gestation and malnourished rats from mothers fed on multideficient diet, from the beginning of gestation (GLA group) or from the onset of lactation (LA group). After weaning, pups received ad libitum the same diet as their mothers, and were maintained under a 12/12 h light/dark cycle. The animals were analyzed either at 30-33, or 60-63 days of life. Brain coronal sections (50 microm) were processed to visualize glial fibrillary acidic protein (GFAP) immunoreactivity. Compared to control rats, both malnourished groups of 30 and 60 days exhibited a reduced number of GFAP-immunoreactive astrocytes in the SCN. The total GFAP-immunoreactive area in the SCN of the GLA group differed from the control group at both age ranges analyzed. The GFAP expression as measured by the relative optical density (ROD) exhibited a 50-60% reduction in the MPA in both malnourished groups, compared to controls. The results suggest that malnutrition early in life leads to alterations in gliogenesis or glial cell proliferation in both nuclei, being these alterations greater in the MPA. Compensatory plasticity mechanisms in the GFAP-expression seem to be developed in the astrocyte differentiation process in the SCN, especially when the malnutrition is installed from the lactation.

Argyrophil cell density in the oxyntic mucosa is higher in female than in male morbidly obese patients

Obesity is a multifactorial disorder often associated with many important diseases such as diabetes, hypertension and other metabolic syndrome conditions. Argyrophil cells represent almost the total population of endocrine cells of the human gastric mucosa and some reports have described changes of specific types of these cells in patients with obesity and metabolic syndrome. The present study was designed to evaluate the global population of argyrophil cells of the gastric mucosa of morbidly obese and dyspeptic non-obese patients. Gastric biopsies of antropyloric and oxyntic mucosa were obtained from 50 morbidly obese patients (BMI >40) and 50 non-obese patients (17 dyspeptic overweight and 33 lean individuals) and processed for histology and Grimelius staining for argyrophil cell demonstration. Argyrophil cell density in the oxyntic mucosa of morbidly obese patients was higher in female (238.68 ± 83.71 cells/mm²) than in male patients (179.31 ± 85.96 cells/mm²) and also higher in female (214.20 ± 50.38 cells/mm²) than in male (141.90 ± 61.22 cells/mm²) morbidly obese patients with metabolic syndrome (P = 0.01 and P = 0.02, respectively). In antropyloric mucosa, the main difference in argyrophil cell density was observed between female morbidly obese patients with (167.00 ± 69.30 cells/mm²) and without (234.00 ± 69.54 cells/mm²) metabolic syndrome (P = 0.001). In conclusion, the present results show that the number of gastric argyrophil cells could be under gender influence in patients with morbid obesity. In addition, gastric argyrophil cells seem to behave differently among female morbidly obese patients with and without metabolic syndrome.

Decreased plasma nesfatin-1 levels in patients with generalized anxiety disorder

Nesfatin-1, a recently discovered satiety molecule, is localized in neurons of the hypothalamus and brain stem and colocalized with stress-related substances. However, the relation between nesfatin-1 and stressor related behaviors like anxiety and/or fear has not yet been investigated in human subjects. In the present study, our aim was to investigate whether there was a relationship between plasma nesfatin-1 levels and generalized anxiety disorder. The study group consisted of 40 patients (BMI, 22.98 ± 0.56) with generalized anxiety disorder and 34 age-matched healthy male control subjects (23.05 ± 0.4). Patients fully met the fourth Diagnostic and Statistical Manual of Mental Disorders, text revision. Blood samples for nesfatin-1 were drawn at the end of an overnight fasting period at least 10h. Plasma nesfatin-1 levels were measured and found significantly lower in anxiety disorder group than in control group (0.35 ± 0.037 ng/ml vs. 0.63 ± 0.080 ng/ml, respectively, p<0.05). Low nesfatin-1 levels may be related with generalized anxiety disorder.

Cortisol and the polycystic ovary syndrome

Adrenal steroidogenesis is under the control of the hypothalamic-pituitary-adrenal (HPA) axis. Furthermore, metabolic factors including insulin and obesity-related signals may play a role in the regulation of both enzymes involved in the steroidogenetic pathways, as well as in the regulation of the HPA axis. In women with the polycystic ovary syndrome (PCOS), cortisol production rate is probably normal, although adrenal androgens can be overproduced in a subset of affected women. Cortisol metabolism and regeneration from inactive glucocorticoids can also be disrupted in PCOS, thereby contributing to determining an adrenal hyperandrogenic state. Finally, overactivity of the HPA axis may be related to the high prevalence of psychopathological and eating disorders in women with PCOS, implying a maladaptive allostatic load in the adaptive mechanisms to chronic stress exposure.

High plasma nesfatin-1 level in patients with major depressive disorder

AIM

In the present study, our aim was to determine the changes in the plasma concentrations of a recently discovered peptide hormone nesfatin-1 in patients with major depressive disorder and then to make a comparison with the control group.

METHOD

Subjects in the patient group were randomly selected from Mustafa Kemal University, Medical School, Research and Training Hospital, Psychiatry Department, Outpatient Clinic and subjects in the control group were selected from healthy volunteers. Healthy control subjects were matched in terms of weight and body mass index. Hamilton Depression Rating Scale (HAM-D) was applied to both groups. ELISA method was used for measurement of plasma nesfatin-1 levels.

RESULTS

The average nesfatin-1 level was statistically higher in patients with major depressive disorder than in the control group (p<0.001). A positive correlation was observed between plasma nesfatin-1 levels and HAM-D scores both in the patient group (r=0.59, p<0.001) and in the control group (r=0.58, p<0.001).

CONCLUSION

Our findings suggest a possible relationship between major depressive disorder and high plasma nesfatin-1 level.

Glucocorticoid regulation of the circadian clock modulates glucose homeostasis

Circadian clock genes are regulated by glucocorticoids; however, whether this regulation is a direct or secondary effect and the physiological consequences of this regulation were unknown. Here, we identified glucocorticoid response elements (GREs) at multiple clock genes and showed that 3 were directly regulated by the glucocorticoid receptor. We determined that a GRE within the core clock gene Per2 was continuously occupied during rhythmic expression and essential for glucocorticoid regulation of that gene in vivo. We further demonstrated that mice with a genomic deletion spanning this GRE expressed elevated leptin levels and were protected from glucose intolerance and insulin resistance on glucocorticoid treatment but not from muscle wasting. We conclude that Per2 is an integral component of a particular glucocorticoid regulatory pathway and that glucocorticoid regulation of the peripheral clock is selectively required for some actions of glucocorticoids.

Diurnal expression of functional and clock-related genes throughout the rat HPA axis: system-wide shifts in response to a restricted feeding schedule

The diurnal rhythm of glucocorticoid secretion depends on the suprachiasmatic (SCN) and dorsomedial (putative food-entrainable oscillator; FEO) nuclei of the hypothalamus, two brain regions critical for coordination of physiological responses to photoperiod and feeding cues, respectively. In both cases, time keeping relies upon diurnal oscillations in clock gene (per1, per2, and bmal) expression. Glucocorticoids may play a key role in synchronization of the rest of the body to photoperiod and food availability. Thus glucocorticoid secretion may be both a target and an important effector of SCN and FEO output. Remarkably little, however, is known about the functional diurnal rhythms of the individual components of the hypothalamic-pituitary-adrenal (HPA) axis. We examined the 24-h pattern of hormonal secretion (ACTH and corticosterone), functional gene expression (c-fos, crh, pomc, star), and clock gene expression (per1, per2 and bmal) in each compartment of the HPA axis under a 12:12-h light-dark cycle and compared with relevant SCN gene expression. We found that each anatomic component of the HPA axis has a unique circadian signature of functional and clock gene expression. We then tested the susceptibility of these measures to nonphotic entrainment cues by restricting food availability to only a portion of the light phase of a 12:12-h light-dark cycle. Restricted feeding is a strong zeitgeber that can dramatically alter functional and clock gene expression at all levels of the HPA axis, despite ongoing photoperiod cues and only minor changes in SCN clock gene expression. Thus the HPA axis may be an important mediator of the body entrainment to the FEO.

Nesfatin-1 increases anxiety- and fear-related behaviors in the rat

RATIONALE

Nesfatin-1, derived from the protein NEFA/nucleobindin2 (NUCB2), is a newly identified peptide that acts as a potent satiety agent. It has been reported that peptides involved in the regulation of ingestive behavior are also involved in the regulation of the stress response. However, the relation between nesfatin-1 and stressor-related behaviors like anxiety and/or fear has not yet been investigated.

OBJECTIVE

The effects of intracerebroventricular (ICV) injection of nesfatin-1 (0, 5, and 25 pmol/3 microl) were assessed in several paradigms that are thought to reflect anxiety and/or fear in rats.

RESULTS

Consistent with an anxiogenic effect, nesfatin-1 dose-dependently decreased the percentage of time spent on the open arms of the elevated plus maze, increased latency to approach, and decreased consumption of a palatable snack in an anxiogenic (unfamiliar) environment. Moreover, ICV nesfatin-1 increased the fear-potentiated startle response and the time spent freezing to both context and conditioned cues in a conditioned emotional response test.

CONCLUSIONS

These findings suggest that in addition to its role as a satiety peptide, nesfatin-1 may also be involved in the mediation of anxiety- and/or fear-related responses.

Nesfatin-1 increases anxiety- and fear-related behaviors in the rat

RATIONALE

Nesfatin-1, derived from the protein NEFA/nucleobindin2 (NUCB2), is a newly identified peptide that acts as a potent satiety agent. It has been reported that peptides involved in the regulation of ingestive behavior are also involved in the regulation of the stress response. However, the relation between nesfatin-1 and stressor-related behaviors like anxiety and/or fear has not yet been investigated.

OBJECTIVE

The effects of intracerebroventricular (ICV) injection of nesfatin-1 (0, 5, and 25 pmol/3 microl) were assessed in several paradigms that are thought to reflect anxiety and/or fear in rats.

RESULTS

Consistent with an anxiogenic effect, nesfatin-1 dose-dependently decreased the percentage of time spent on the open arms of the elevated plus maze, increased latency to approach, and decreased consumption of a palatable snack in an anxiogenic (unfamiliar) environment. Moreover, ICV nesfatin-1 increased the fear-potentiated startle response and the time spent freezing to both context and conditioned cues in a conditioned emotional response test.

CONCLUSIONS

These findings suggest that in addition to its role as a satiety peptide, nesfatin-1 may also be involved in the mediation of anxiety- and/or fear-related responses.

Patterns of fos activation in rat raphe nuclei during feeding behavior

To analyze the differential recruitment of the raphe nuclei during different phases of feeding behavior, rats were subjected to a food restriction schedule (food for 2 h/day, during 15 days). The animals were submitted to different feeding conditions, constituting the experimental groups: search for food (MFS), food ingestion (MFI), satiety (MFSa) and food restriction control (MFC). A baseline condition (BC) group was included as further control. The MFI and MFC groups, which presented greater autonomic and somatic activation, had more FOS-immunoreactive (FOS-IR) neurons. The MFI group presented more labeled cells in the linear (LRN) and dorsal (DRN) nuclei; the MFC group showed more labeling in the median (MRN), pontine (PRN), magnus (NRM) and obscurus (NRO) nuclei; and the MFSa group had more labeled cells in the pallidus (NRP). The BC exhibited the lowest number of reactive cells. The PRN presented the highest percentage of activation in the raphe while the DRN the lowest. Additional experiments revealed few double-labeled (FOS-IR+5-HT-IR) cells within the raphe nuclei in the MFI group, suggesting little serotonergic activation in the raphe during food ingestion. These findings suggest a differential recruitment of raphe nuclei during various phases of feeding behavior. Such findings may reflect changes in behavioral state (e.g., food-induced arousal versus sleep) that lead to greater motor activation, and consequently increased FOS expression. While these data are consistent with the idea that the raphe system acts as gain setter for autonomic and somatic activities, the functional complexity of the raphe is not completely understood.

Influence of meal time on salivary circadian cortisol rhythms and weight loss in obese women

OBJECTIVE

We aimed to determine the influence of meal time on salivary circadian cortisol rhythms and weight loss in obese women.

METHODS

Twelve obese subjects (body mass index >40 kg/m(2)) were hospitalized for 64 d and then randomly assigned to one of three 18-d stages with a 5-d interval between stages. In stage 1, the subjects received a hypocaloric diet (1000 kcal/d) portioned into five meals per day. In stage 2, the subjects received the same diet between 0900 and 1100 h. In stage 3, they received the same diet between 1800 and 2000 h. Between admissions, the subjects were discharged from the hospital and consumed their usual diet at home. Salivary cortisol rhythm (in six samples collected over a 24-h period) was determined during each stage, and anthropometric, bioimpedance, indirect calorimetric, and urinary nitrogen excretion variables were measured.

RESULTS

Salivary cortisol circadian rhythms were similar during all stages when measured on day 1 or 18 of treatment. Despite significant reductions in all anthropometric measurements except waist/hip ratio, no significant changes were observed in salivary cortisol rhythm after alteration of the eating hours. Starting on day 4 of treatment, nitrogen ingestion and excretion levels decreased significantly; on day 10, nitrogen balance was negative in all study stages.

CONCLUSION

Administration of a hypocaloric diet led to changes in weight, body composition, resting metabolic rate, and nitrogen balance but did not significantly alter salivary circadian cortisol rhythms.

The emergence of the cortisol circadian rhythm in monozygotic and dizygotic twin infants: the twin-pair synchrony

OBJECTIVE

Studies on the influence of genetic factors on the ontogeny of cortisol circadian rhythm in infants are lacking. This study evaluated the influence of twinning and the heritability on the age of emergence of salivary cortisol rhythm.

DESIGN AND SUBJECTS

A longitudinal study was performed using salivary samples obtained during morning and night, at 2, 4, 8, 12, 16, 20 and 24 weeks of postnatal life in 34 infants, 10 monozygotic (MZ) and 7 dizygotic (DZ) twin pairs. Salivary cortisol was determined by radioimmunoassay (RIA). Zigosity was verified by DNA analysis of at least 13 short tandem repeat polymorphisms. Difference of the emergence of cortisol circadian rhythm, within each twin pair, the intraclass correlation coefficient and the heritability index (h(2)) were calculated.

RESULTS

The mean (+/- SEM) age of emergence of salivary cortisol circadian rhythm was similar in MZ and DZ (7.8 +/- 1.0 vs 7.4 +/- 1.3 weeks). Seven pairs showed coincidence of the emergence of cortisol rhythm. Ten pairs were not coincident; among them the within-pair difference of emergence of salivary circadian rhythm was similar in both MZ and DZ groups. The intraclass correlation coefficients were rMZ = 0.60, P = 0.02; and rDZ = 0.65, P = 0.03, respectively. The heritability index (h(2)) was 0.21 (ns).

CONCLUSIONS

Salivary circadian rhythm appeared at the same postnatal age in MZ and DZ twin infants. Although several physiological aspects might be involved, the heritability index, obtained in the present study, suggests less genetic than environmental impact on the age of the onset of the cortisol circadian rhythm. Our data also indicated that each twin-pair show synchrony because they probably shared prenatal and postnatal environmental synchronizers.

The Hypothalamic-Pituitary-Adrenal Axis Activity in Obesity and the Metabolic Syndrome

A hypothetical role of glucocorticoids in human obesity has been suggested since the abdominal obesity phenotype and syndromes of endogenous or exogenous hypercortisolism share several clinical, metabolic, and cardiovascular similarities. An emerging body of evidence indicates that both neuroendocrine dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as well as peripheral alterations of cortisol metabolism may play a role in the pathophysiology of abdominal obesity. Major alterations of the HPA axis in vivo may be identified in different ways. They include evaluation of hormone concentrations: (a) in basal conditions, in blood, urine, or saliva samples; (b) during dynamic studies following stimulation with different neuropeptides or psychological stress challenges, or suppression with inhibiting agents of the HPA axis at different levels; and (c) after mixed meals or meals containing different nutrient compositions. In addition, alteration of peripheral cortisol metabolism can be detected by direct measurement of cortisol metabolites in urine, although this is a matter of more complex investigation. Alterations of the HPA axis in abdominal obesity are associated with insulin resistance, which suggests a direct responsibility of these hormonal alterations in the susceptibility of affected patients to develop both metabolic and cardiovascular diseases. According to available data, no single marker probably has the power to detect subtle alterations of the HPA axis in conditions, such as the abdominal obesity and the metabolic syndrome. On the contrary, they indicate the need for multiple parameters. At present, evaluation of urinary free cortisol, particularly during the night-time, and salivary-free cortisol appear to be promising for these purposes, whereas dynamic tests should be reserved for specific clinical settings, involving well-characterized patients.

Circadian rhythm of corticosterone secretion in the neonatal rabbit

Maternal care in the rabbit is restricted to a single 3- to 5-min period of nursing each day. One to three hours prior to the arrival of the mother, pups exhibit anticipatory behavioral arousal and elevation of core body temperature. In rodents, the hypothalamic-pituitary-adrenal axis is quiescent and levels of the adrenal hormone, corticosterone (CORT), are stable and extremely low during the first days of life, which are known collectively as the stress-hyporesponsive period (SHRP). It has been proposed that the rabbit also has an SHRP. However, we decided to examine CORT changes associated with the daily nursing bout, since behavioral arousal, core body temperature, and CORT are elevated prior to the onset of feeding in many other species. We scheduled the nursing bout at 1000 h and analyzed CORT concentration using RIA in pups sampled at various intervals after suckling. CORT levels showed a circadian variation that peaked at the time of the daily nursing bout. After nursing, values steadily decreased to a nadir at 2200 h and then rose again in advance of the next scheduled nursing. The three-fold difference between the highest (1000 h) and the lowest (2200 h) CORT values suggests that either the SHRP does not exist in rabbit pups or else it has properties that differ from those described for rodents. Unlike rodents, rabbit pups show a circadian secretion of CORT synchronized to the scheduled nursing bout.

Differential vulnerability of the rat retina, suprachiasmatic nucleus and intergeniculate leaflet to malnutrition induced during brain development

We investigated in young rats the effects of malnutrition on the main structures of the circadian timing system: retina, hypothalamic suprachiasmatic nuclei (SCN), thalamic intergeniculate leaflet, retinohypothalamic- and geniculohypothalamic tracts. Control rats were born from mothers fed a commercial diet since gestation, and malnourished rats from mothers fed a multideficient diet since gestation (GLA group) or lactation (LA group). After weaning, pups received the same diet as their mothers, and were analysed at postnatal days 27, 30-33 and 60-63. Brain sections were processed to visualise in the SCN neuropeptide Y immunoreactivity and terminal labeling after intraocular tracer injections. Nissl staining was used to assess cytoarchitectonic boundaries of the SCN and cell features in retinal whole mounts. Cell counts, morphometric and densitometric analysis were performed. Compared with controls, the total retinal surface was reduced and the topographical distribution of retinal ganglion cells was altered in malnourished rats, with changes in their density. Alterations were also detected in the SCN dimensions in the GLA and LA groups at one and two postnatal months, as well as in the SCN portion occupied by the retinal input in the GLA group at days 30-33, but not in the NPY-containing geniculohypothalamic tract. The present data point to subtle changes, with a low and differential vulnerability to early malnutrition, of structures involved in circadian timing regulation. Furthermore, the present findings suggest that the altered circadian rhythmicity previously documented in malnourished rats cannot be ascribed to impaired development of the retino- and geniculohypothalamic projections to the SCN.

Influence of Nutrition on Responses to Resistance Training

A variety of dietary practices designed to enhance acute responses and chronic adaptations to resistance training have been examined with little consensus on the optimal nutritional approach for maximizing muscle and strength gains. From a scientific and practical perspective, the quantity, quality, and timing of nutrient ingestion around a workout are important factors to consider. Manipulation of exercise and nutritional variables can alter events that impact adaptations to training by a variety of mechanisms related to nutrient availability and uptake into tissues, hormonal secretion and interactions with receptors on target tissues, and gene transcription and translation of proteins that eventually impact protein, carbohydrate, and lipid metabolism. If the nutrition-mediated postresistance exercise change in any of these processes is of sufficient magnitude and duration, then over time an effect of muscle size, strength, and body composition is possible. To date, the majority of research has concentrated on providing carbohydrate alone or combined with protein before or after resistance exercise. Carbohydrate and protein intake significantly alters circulating metabolites and the hormonal milieu (i.e., insulin, testosterone, growth hormone, and cortisol), as well as the response of muscle protein and glycogen balance. The pathway of adaptation is proposed as a model to assist in integrating research findings from the current body of literature and future studies examining various diet and resistance exercise configurations.

Palatable solutions during paradoxical sleep deprivation: reduction of hypothalamic-pituitary-adrenal axis activity and lack of effect on energy imbalance

Paradoxical sleep deprivation (PSD) induces increased energy expenditure in rats, insofar as rats eat more but loose weight throughout the deprivation period. In the present study, rats were offered water, saccharin or sucrose to drink during the deprivation period, since it has been proposed that carbohydrates reduce the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Rats were submitted to the flower pot technique for 96 h. During the PSD period, they were weighed daily and food and fluid intake was assessed twice a day. At the end of the PSD period, rats were killed and plasma concentrations of glucose, adrenocorticotropic hormone (ACTH) and corticosterone were assayed. Compared to their control counterparts, all paradoxical sleep-deprived rats consumed more food, but lost weight. Paradoxical sleep-deprived rats given sucrose drank more than their control counterparts (especially in the light phase of the light/dark cycle). Paradoxical sleep-deprived rats showed increased food intake during all periods throughout the experiment, with peak intake during the dark phase and nadir during the light phase of the light/dark cycle. All paradoxical sleep-deprived rats showed lower glucose plasma levels than control rats and increased relative adrenal weight. However, when given saccharin or sucrose, paradoxical sleep-deprived rats showed lower concentrations of ACTH and corticosterone than their water-provided counterparts, indicating that palatable fluids were capable of lowering HPA axis activation produced by PSD. The fact that PSD induced energy imbalance regardless of the relative attenuation of the HPA axis activity produced by saccharin or sucrose suggests that the HPA axis may play only a secondary role in this phenomenon, and that other mechanisms may account for this effect. The data also suggest that supply of palatable fluids can be an additional modification to reduce the stress of the flower pot method.

Effect of tidal cycle and food intake on the baseline plasma corticosterone rhythm in intertidally foraging marine iguanas

In most species, plasma levels of baseline glucocorticoids such as corticosterone (B) have a circadian rhythm. This rhythm can be entrained by both photoperiod and food intake and is related to aspects of energy intake and metabolism. Marine iguanas (Amblyrhynchus cristatus) offer a unique opportunity to better understand the relative importance of the light:dark cycle versus food intake in influencing the rhythm in baseline B in a natural system. Compared to other species, food intake is not as strictly determined by the phase of the light:dark cycle. Animals feed in the intertidal zone so feeding activity is heavily influenced by the tidal cycle. We measured baseline plasma B levels in free-living iguanas over several 24-h periods that varied in the timing of low tide/foraging activity. We found that baseline B levels were higher during the day relative to night. However, when low tide occurred during the day, baseline B levels dropped coincident with the timing of low tide. Whether the baseline B rhythm (including the drop during foraging) is an endogenous rhythm with a circatidal component, or is simply a result of feeding and associated physiological changes needs to be tested. Together, these data suggest that the baseline B rhythm in marine iguanas is influenced by the tidal cycle/food intake as well as the light:dark cycle.

Comment: response of the hypothalamic-pituitary-adrenocortical axis to high-protein/fat and high-carbohydrate meals in women with different obesity phenotypes

Subjects with abdominal obesity are characterized by hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis. Food intake, particularly at noon, is a well-known inducer of HPA axis activation. Whether obese subjects present an abnormal response to meals containing different macronutrient proportions is at present unknown. Therefore, this study was carried out to investigate the effect of a high-lipid/protein meal (HLP-meal) and a high-carbohydrate meal (HCHO-meal) on the HPA axis activity in women with different obesity phenotypes. Nondepressed, noncomplicated obese (body mass index greater than 28 kg/m(2)) women with abdominal (A-BFD) (n = 10) and peripheral body fat distribution (P-BFD) (n = 9) and a group of 11 normal-weight controls were investigated in the follicular phase of the menstrual cycle. They were randomly given an 800-kcal HCHO-meal (containing 89% carbohydrates, 11% proteins, 0% lipids), and an 800-kcal HLP-meal (containing 53% lipids, 43% proteins, 4% carbohydrates), which were eaten within 15 min at noon, with an interval of 2 d between each meal. Blood samples for ACTH, cortisol, glucose, and insulin were obtained at 15-min intervals before and after each meal. Baseline hormone and glucose concentrations in the three groups were similar. After the HLP-meal, ACTH tended to similarly but insignificantly increase in all groups, whereas cortisol increased significantly (P < 0.05) in the P-BFD group and insignificantly in the other groups. Conversely, both ACTH and cortisol significantly (P < 0.05) increased only in the A-BFD group, without any significant changes in both controls and P-BFD women. The analysis of the interaction between meals and groups clearly indicated that the cortisol response to the HLP-meal and the HCHO-meal was significantly different (P < 0.025) between the two obese groups, the A-BFD group being characterized by a significantly lower response to the HLP-meal and a significantly higher response to the HCHO-meal, compared with the P-BFD group. Considering all groups together and after adjusting for body mass index, a highly significant relationship was found between cortisol-area under the curve and ACTH-area under the curve after each meal test. However, no relationships were found between changes in ACTH and cortisol and those of glucose, insulin, and the glucose:insulin ratio after each meal. Therefore, our data demonstrate that the response of the HPA axis to meals containing different macronutrient proportions may depend on the pattern of body fat distribution. We also suggest that the activation of the HPA axis following the ingestion of large amounts of carbohydrates may have some pathophysiological relevance, specifically in women with the abdominal obesity phenotype.

Effect of obesity and starvation on thyroid hormone, growth hormone, and cortisol secretion

Obesity and starvation have opposing affects on normal physiology and are associated with adaptive changes in hormone secretion. The effects of obesity and starvation on thyroid hormone, GH, and cortisol secretion are summarized in Table 1. Although hypothyroidism is associated with some weight gain, surveys of obese individuals show that less than 10% are hypothyroid. Discrepancies have been reported in some studies, but in untreated obesity, total and free T4, total and free T3, TSH levels, and the TSH response to TRH are normal. Some reports suggest an increase in total T3 and decrease in rT3 induced by overfeeding. Treatment of obesity with hypocaloric diets causes changes in thyroid function that resemble sick euthyroid syndrome. Changes consist of a decrease in total T4 and total and free T3 with a corresponding increase in rT3. untreated obesity is also associated with low GH levels; however, levels of IGF-1 are normal. GH-binding protein levels are increased and the GH response to GHRH is decreased. These changes are reversed by drastic weight reduction. Cortisol levels are abnormal in people with abdominal obesity who exhibit an increase in urinary free cortisol but exhibit normal or decreased serum cortisol and normal ACTH levels. These changes are explained by an increase in cortisol clearance. There is also an increased response to CRH. Treatment of obesity with very low calorie diets causes a decrease in serum cortisol explained by a decrease in cortisol-binding proteins. The increase in cortisol secretion seen in patients with abdominal obesity may contribute to the metabolic syndrome (insulin resistance, glucose intolerance, dyslipidemia, and hypertension). States of chronic starvation such as seen in anorexia nervosa are also associated with changes in thyroid hormone, GH, and cortisol secretion. There is a decrease in total and free T4 and T3, and an increase in rT3 similar to findings in sick euthyroid syndrome. The TSH response to TRH is diminished and, in severe cases, thyroid-binding protein levels are decreased. In regards to GH, there is an increase in GH secretion with a decrease in IGF-1 levels. GH responses to GHRH are increased. The [table: see text] changes in cortisol secretion in patients with anorexia nervosa resemble depression. They present with increased urinary free cortisol and serum cortisol levels but without changes in ACTH levels. In contrast to the findings observed in obesity, the ACTH response to CRH is suppressed, suggesting an increased secretion of CRH. The endocrine changes observed in obesity and starvation may complicate the diagnosis of primary endocrine diseases. The increase in cortisol secretion in obesity needs to be distinguished from Cushing's syndrome, the decrease in thyroid hormone levels in anorexia nervosa needs to be distinguished from secondary hypothyroidism, and the increase in cortisol secretion observed in anorexia nervosa requires a differential diagnosis with primary depressive disorder.

Effect of a meal feeding schedule on hepatic glycogen synthesis and gluconeogenesis in rats

We investigated the effect of a meal feeding schedule (MFS) on food intake, hepatic glycogen synthesis, hepatic capacity to produce glucose and glycemia in rats. The MFS comprised free access to food for a 2-hour period daily at a fixed mealtime (8.00-10.00 a.m.) for 13 days. The control group was composed of rats with free access to food from day 1 to 12, which were then starved for 22 h, refed with a single meal at 8.00-10.00 a.m. and starved again for another 22 h. All experiments were performed at the meal time (i.e. 8.00 a.m.). The MFS group exhibited increased food intake and higher glycogen synthase activity. Since gluconeogenesis from L-glutamine or L-alanine was not affected by MFS, we conclude that the increased food intake and higher glycogen synthase activity contributed to the better glucose maintenance showed by MFS rats at the fixed meal time.

Plasma oxytocin and cortisol concentrations in dairy cows in relation to feeding duration and rumen fill

The aim of this study was to investigate if the release of oxytocin and cortisol were different depending on levels of oral manipulation with feed or rumen fill in dairy cows. Blood samples and behavior of 12 rumen-fistulated cows were analyzed in 2 consecutive years during morning and afternoon periods when the cows were subjected to either (A) long duration of oral manipulation of feed with low rumen fill or (B) short duration of oral manipulation of feed but with filled rumen. The response areas under the curve for oxytocin in both years were larger in A than in B in the afternoons. There were peaks in oxytocin release at milking in the afternoon in both treatments. In B, the oxytocin concentration was higher after than before feeding, higher in B than in A after the non-oral rumen filling, and higher in B after than before the non-oral rumen filling in Year 1. The level of cortisol was higher in B than in A in the morning, lower in both treatments before than after milking in the afternoon, and there was a tendency for the cortisol level to be higher in A than in B after oral feeding. The B cows spent a shorter time eating and the A cows spent a shorter time ruminating. This study indicates that a long duration of oral manipulation of feed in cows, may, per se be linked to higher oxytocin but lower cortisol levels, compared with shorter oral feeding time and filled rumen.

Salivary cortisol as a tool for physiological studies and diagnostic strategies

Salivary cortisol is an index of plasma free cortisol and is obtained by a noninvasive procedure. We have been using salivary cortisol as a tool for physiological and diagnostic studies, among them the emergence of circadian rhythm in preterm and term infants. The salivary cortisol circadian rhythm in term and premature infants was established between 8 and 12 postnatal weeks. In the preterm infants the emergence of circadian rhythm was parallel to the onset of sleep rhythm. We also studied the use of salivary cortisol for screening for Cushing's syndrome (CS) in control and obese outpatients based on circadian rhythm and the overnight 1 mg dexamethasone (DEX) suppression test. Salivary cortisol was suppressed to less than 100 ng/dl after 1 mg DEX in control and obese patients. A single salivary cortisol measurement at 23:00 h and again after 1 mg DEX above the 90th percentile of the obese group values had sensitivity and specificity of 93 and 93% (23:00 h), and 91 and 94% (after DEX), respectively. The sensitivity improved to 100% when we combined both parameters. We also studied 11 CS children and 21 age-matched primary obese children for whom salivary cortisol sensitivity and specificity were 100/95% (23:00 h), and 100/95% (1 mg DEX), respectively. Similar to adults, sensitivity and specificity of 100% were obtained by combining 23:00 h and 1 mg DEX. The measurement of salivary cortisol is a useful tool for physiological studies and for the diagnosis of CS in children and adults on an outpatient basis.

Meal-feeding scheme: twenty years of research in Brazil

Naomi Shinomiya Hell was the first researcher to investigate the physiological adaptations to a meal-feeding scheme (MFS) in Brazil. Over a period of 20 years, from 1979 to 1999, Naomi's group determined the physiological and metabolic adaptations induced by this feeding scheme in rats. The group showed the persistence of such adaptations even when MFS is associated with moderate exercise training and the performance to a session of intense physical effort. The metabolic changes induced by the feeding training were discriminated from those caused by the effective fasting period. Naomi made an important contribution to the understanding of the MFS but a lot still has to be done. One crucial question still remains to be satisfactorily answered: what is the ideal control for the MFS?

Involvement of the caudal raphe nuclei in the feeding behavior of rats

Involvement of the caudal raphe nuclei (raphe pallidus, RPa; raphe magnus, RMg, and raphe obscurus, ROb) in feeding behavior of adult rats was studied by measuring c-Fos protein expression, in animals submitted to the "meal-feeding" model of food restriction in which the rats were fed ad libitum only from 7:00 to 9:00 h, for 15 days. The experimental groups submitted to chronic fasting, named 'search for food' (SF), 'ingestion of food' (IF) and 'satiety of food' (SaF) were scheduled after a previous study in which the body weight and the general and feeding behaviors were evaluated by daily monitoring. Acute, 48-h fasting (AF) was used as control. In the chronic group, the animals presented a 16% reduction in body weight in the first week, followed by a continuous, slow rise in weight over the subsequent days. Entrainment of the sleep-wake cycle to the schedule of food presentation was also observed. The RPa was the most Fos immunopositive nucleus in the chronic fasting group, followed by the RMg. The ANOVA and Tukey test (P<0.05) confirmed these results. The IF group was significantly different from the other three groups, as also was the number of labeled cells in the RPa in SF and IF groups. Nevertheless, no significant difference was observed between RMg and RPa, or RMg and ROb in the SaF and AF. However, it is interesting to observe that the groups in which the animals were more active, searching for or ingesting food, presented a larger number of labeled cells. These results suggest a different involvement of the caudal raphe nuclei in the somatic and autonomic events of feeding behavior, corroborating the functions reported for them earlier.

Feeding-entrained circadian rhythms in hypophysectomized rats with suprachiasmatic nucleus lesions

Several pituitary hormones are important in the regulation of metabolism, and their release appears to be controlled by a circadian clock. Consequently, they may be involved in feeding-entrained circadian rhythms. Hypophysectomized (Hypox) and sham-operated male Sprague-Dawley rats had access to food for 4 h each day. Food-anticipatory activity (FAA) and core body temperature (T(b)) were monitored. Both groups entrained to the daily meal with an increase in activity in the 4 h preceding meal access and quickly reentrained after an 8-h phase advance of food access. FAA was not disrupted in either group after suprachiasmatic lesions were added. Core T(b) increased in the sham-operated subjects before mealtime, but Hypox rats failed to show this effect. Rather, T(b) declined during anticipation and throughout the food access period. Respiratory quotient (RQ), an indirect measure of metabolic rate, was measured for 24 h in some subjects. Sham-operated rats showed a dramatic downturn in RQ 1 h before mealtime, whereas Hypox rats showed a steadily decreasing RQ throughout the day. The results show that the pituitary hormones are not necessary for FAA and that in Hypox rats the anticipatory rise in T(b) and changes in RQ become dissociated from anticipatory behavior, indicating that these functions are separate outputs of the food-entrainable circadian oscillator.