24-hour changes in ACTH, corticosterone, growth hormone, and leptin levels in young male rats subjected to calorie restriction

Fasting and prolonged food restriction differentially affect GH secretion independently of GH receptor signaling in AgRP neurons

Growth hormone (GH) receptor (GHR) is abundantly expressed in neurons that co-release the agouti-related protein (AgRP) and neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus (ARH). Since ARHAgRP/NPY neurons regulate several hypothalamic-pituitary-endocrine axes, this neuronal population possibly modulates GH secretion via a negative feedback loop, particularly during food restriction, when ARHAgRP/NPY neurons are highly active. The present study aims to determine the importance of GHR signaling in ARHAgRP/NPY neurons on the pattern of GH secretion in fed and food-deprived male mice. Additionally, we compared the effect of two distinct situations of food deprivation: 16 h of fasting or four days of food restriction (40% of usual food intake). Overnight fasting strongly suppressed both basal and pulsatile GH secretion. Animals lacking GHR in ARHAgRP/NPY neurons (AgRP∆GHR mice) did not exhibit differences in GH secretion either in the fed or fasted state, compared to control mice. In contrast, four days of food restriction increased GH pulse frequency, basal GH secretion, and pulse irregularity/complexity (measured by sample entropy), whereas pulsatile GH secretion was not affected in both control and AgRP∆GHR mice. Hypothalamic Ghrh mRNA levels were unaffected by fasting or food restriction, but Sst expression increased in acutely fasted mice, but decreased after prolonged food restriction in both control and AgRP∆GHR mice. Our findings indicate that short-term fasting and prolonged food restriction differentially affect the pattern of GH secretion, independently of GHR signaling in ARHAgRP/NPY neurons.

Circadian rhythms modulate the effect of eccentric exercise on rat soleus muscles

We investigated whether time-of-day dependent changes in the rat soleus (SOL) muscle size, after eccentric exercises, operate via the mechanistic target of rapamycin (mTOR) signaling pathway. For our first experiment, we assigned 9-week-old male Wistar rats randomly into four groups: light phase (zeitgeber time; ZT6) non-trained control, dark phase (ZT18) non-trained control, light phase-trained, and dark phase-trained. Trained animals performed 90 min of downhill running once every 3 d for 8 weeks. The second experiment involved dividing 9-week-old male Wistar rats to control and exercise groups. The latter were subjected to 15 min of downhill running at ZT6 and ZT18. The absolute (+12.8%) and relative (+9.4%) SOL muscle weights were higher in the light phase-trained group. p70S6K phosphorylation ratio was 42.6% higher in the SOL muscle of rats that had exercised only in light (non-trained ZT6). Collectively, the degree of muscle hypertrophy in SOL is time-of-day dependent, perhaps via the mTOR/p70S6K signaling.

Glucagon-Like Peptide-1 (GLP-1) in the Integration of Neural and Endocrine Responses to Stress

Glucagon like-peptide 1 (GLP-1) within the brain is produced by a population of preproglucagon neurons located in the caudal nucleus of the solitary tract. These neurons project to the hypothalamus and another forebrain, hindbrain, and mesolimbic brain areas control the autonomic function, feeding, and the motivation to feed or regulate the stress response and the hypothalamic-pituitary-adrenal axis. GLP-1 receptor (GLP-1R) controls both food intake and feeding behavior (hunger-driven feeding, the hedonic value of food, and food motivation). The activation of GLP-1 receptors involves second messenger pathways and ionic events in the autonomic nervous system, which are very relevant to explain the essential central actions of GLP-1 as neuromodulator coordinating food intake in response to a physiological and stress-related stimulus to maintain homeostasis. Alterations in GLP-1 signaling associated with obesity or chronic stress induce the dysregulation of eating behavior. This review summarized the experimental shreds of evidence from studies using GLP-1R agonists to describe the neural and endocrine integration of stress responses and feeding behavior.

Rhythmicity matters: Circadian and ultradian patterns of HPA axis activity

Oscillations are a fundamental feature of neural and endocrine systems. The hypothalamic-pituitary-adrenal (HPA) axis dynamically controls corticosteroid secretion in basal conditions and in response to stress. Across the 24-h day, HPA axis activity oscillates with both an ultradian and circadian rhythm. These rhythms have been shown to be important for regulating metabolism, inflammation, mood, cognition and stress responsiveness. Here we will discuss the neural and endocrine mechanisms driving these rhythms, the physiological importance of these rhythms and health consequences when they are disrupted.

The role of glucocorticoids in the vertebrate response to weather

Changes in the environment related to inclement weather can threaten survival and reproductive success both through direct adverse exposure and indirectly by decreasing food availability. Glucocorticoids, released during activation of the hypothalamic-pituitary-adrenal axis as part of the stress response, are an important candidate for linking vertebrate coping mechanisms to weather. This review attempts to determine if there is a consensus response of glucocorticoids to exposure to weather-related stimuli, including food availability, precipitation, temperature and barometric pressure. The included studies cover field and laboratory studies for all vertebrate taxa, and are separated into four exposure periods, e.g., hours, days, weeks and months. Each reported result was assigned a score based on the glucocorticoid response, e.g., increased, no change, or decreased. Short-term exposure to weather-related stimuli, of up to 24 h, is generally associated with increased glucocorticoids (79% of studies), suggesting that these stimuli are perceived as stressors by most animals. In contrast, the pattern for exposures longer than 24 h shows more variation, even though a majority of studies still report an increase (64%). Lack of glucocorticoid increases appeared to result from instances where: (1) prolonged exposure was a predictable part of the life history of an animal; (2) environmental context was important for the ultimate effect of a stimulus (e.g., precipitation limited food availability in one environment, but increased food in another); (3) prolonged exposure induced chronic stress; and (4) long-term responses appeared to reflect adaptations to seasonal shifts, instead of to short-term weather. However, there is a strong bias towards studies in domesticated laboratory species and wild animals held in captivity, indicating a need for field studies, especially in reptiles and amphibians. In conclusion, the accumulated literature supports the hypothesis that glucocorticoids can serve as the physiological mechanism promoting fitness during inclement weather.

Rat Strain and Housing Conditions Alter Oxidative Stress and Hormone Responses to Chronic Intermittent Hypoxia

Sleep apnea has been associated with elevated risk for metabolic, cognitive, and cardiovascular disorders. Further, the role of hypothalamic–pituitary–adrenal (HPA) activation in sleep apnea has been controversial in human studies. Chronic intermittent hypoxia (CIH) is a rodent model, which mimics the hypoxemia experienced by patients with sleep apnea. Most studies of CIH in rats have been conducted in the Sprague Dawley rat strain. Previously published literature suggests different strains of rats exhibit various responses to disease models, and these effects can be further modulated by the housing conditions experienced by each strain. This variability in response is similar to what has been observed in clinical populations, especially with respect to the HPA system. To investigate if strain or housing (individual or pair-housed) can affect the results of CIH (AHI 8 or 10) treatment, we exposed individual and pair-housed Sprague Dawley and Long-Evans male rats to 7 days of CIH treatment. This was followed by biochemical analysis of circulating hormones, oxidative stress, and neurodegenerative markers. Both strain and housing conditions altered oxidative stress generation, hyperphosphorylated tau protein (tau tangles), circulating corticosterone and adrenocorticotropic hormone (ACTH), and weight metrics. Specifically, pair-housed Long-Evans rats were the most sensitive to CIH, which showed a significant association between oxidative stress generation and HPA activation under conditions of AHI of 8. These results suggest both strain and housing conditions can affect the outcomes of CIH.

Caloric Restriction Dramatically Stalls Lesion Growth in Mice With Induced Endometriosis

Caloric restriction (CR) has been demonstrated to have many health-beneficial effects in many species, but whether CR can impede the development of endometriosis is unknown. To test the hypothesis that CR can impede the growth of endometriotic lesions and fibrogenesis, we conducted 2 experiments. In experiment 1, 20 female Balb/C mice were randomly assigned to either ad libitum (AL) group that was fed AL or to CR group that was fed 30% less calories than that of AL mice. Two weeks after the implementation of the dietary intervention, endometriosis was induced by intraperitoneal injection of endometrial fragments. Two weeks after the induction, all mice were sacrificed and their lesion samples were evaluated. In experiment 2, another 20 mice were used and CR was implemented 2 weeks after induction of endometriosis and lasted for 4 weeks. Caloric restriction instituted before the induction of endometriosis reduced the lesion weight by 88.5%, whereas CR implemented well after lesions were established reduced the lesion weight by 93.0%. In both cases, CR significantly increased staining levels of markers of autophagy but reduced proliferation, angiogenesis, steroidogenesis, and fibrosis in lesions as compared with the AL group. Consequently, CR, instituted either before or after the induction of endometriosis, dramatically curbs the growth of endometriotic lesions and fibrogenesis through multiple mechanisms. Caloric restriction and CR mimetics, a family of compounds mimicking the beneficial effect of CR, even when instituted well after lesions are established, may stall the development of endometriosis. Given the scarcity in research on how lifestyle can impact on the development of endometriosis, our study should hopefully stimulate more research in this area.

Testosterone and Corticosterone in the Mesocorticolimbic System of Male Rats: Effects of Gonadectomy and Caloric Restriction

Steroid hormones can modulate motivated behaviors through the mesocorticolimbic system. Gonadectomy (GDX) is a common method to determine how steroids influence the mesocorticolimbic system, and caloric restriction (CR) is often used to invigorate motivated behaviors. A common assumption is that the effects of these manipulations on brain steroid levels reflects circulating steroid levels. We now know that the brain regulates local steroid levels in a region-specific manner; however, previous studies have low spatial resolution. Using ultrasensitive liquid chromatography tandem mass spectrometry, we examined steroids in microdissected regions of the mesocorticolimbic system (ventral tegmental area, nucleus accumbens, medial prefrontal cortex). We examined whether GDX or CR influences systemic and local steroids, particularly testosterone (T) and steroidogenic enzyme transcripts. Adult male rats underwent a GDX surgery and/or CR for either 2 or 6 weeks. Levels of T, the primary steroid of interest, were higher in all brain regions than in the blood, whereas corticosterone (CORT) was lower in the brain than in the blood. Importantly, GDX completely eliminated T in the blood and lowered T in the brain. Yet, T remained present in the brain, even 6 weeks after GDX. CR decreased both T and CORT in the blood and brain. Steroidogenic enzyme (Cyp17a1, 3β-hydroxysteroid dehydrogenase, aromatase) transcripts and androgen receptor transcripts were expressed in the mesocorticolimbic system and differentially affected by GDX and CR. Together, these results suggest that T is synthesized within the mesocorticolimbic system. These results provide a foundation for future studies examining how neurosteroids influence behaviors mediated by the mesocorticolimbic system.

Interoceptive modulation of neuroendocrine, emotional, and hypophagic responses to stress

Periods of caloric deficit substantially attenuate many centrally mediated responses to acute stress, including neural drive to the hypothalamic-pituitary-adrenal (HPA) axis, anxiety-like behavior, and stress-induced suppression of food intake (i.e., stress hypophagia). It is posited that this stress response plasticity supports food foraging and promotes intake during periods of negative energy balance, even in the face of other internal or external threats, thereby increasing the likelihood that energy stores are repleted. The mechanisms by which caloric deficit alters central stress responses, however, remain unclear. The caudal brainstem contains two distinct populations of stress-recruited neurons [i.e., noradrenergic neurons of the A2 cell group that co-express prolactin-releasing peptide (PrRP+ A2 neurons), and glucagon-like peptide 1 (GLP-1) neurons] that also are responsive to interoceptive feedback about feeding and metabolic status. A2/PrRP and GLP-1 neurons have been implicated anatomically and functionally in the central control of the HPA axis, anxiety-like behavior, and stress hypophagia. The current review summarizes a growing body of evidence that caloric deficits attenuate physiological and behavioral responses to acute stress as a consequence of reduced recruitment of PrRP+ A2 and hindbrain GLP-1 neurons, accompanied by reduced signaling to their brainstem, hypothalamic, and limbic forebrain targets.

Negative Energy Balance Blocks Neural and Behavioral Responses to Acute Stress by "Silencing" Central Glucagon-Like Peptide 1 Signaling in Rats

Previous reports indicate that caloric restriction attenuates anxiety and other behavioral responses to acute stress, and blunts the ability of stress to increase anterior pituitary release of adrenocorticotropic hormone. Since hindbrain glucagon-like peptide-1 (GLP-1) neurons and noradrenergic prolactin-releasing peptide (PrRP) neurons participate in behavioral and endocrine stress responses, and are sensitive to the metabolic state, we examined whether overnight food deprivation blunts stress-induced recruitment of these neurons and their downstream hypothalamic and limbic forebrain targets. A single overnight fast reduced anxiety-like behavior assessed in the elevated-plus maze and acoustic startle test, including marked attenuation of light-enhanced startle. Acute stress [i.e., 30 min restraint (RES) or 5 min elevated platform exposure] robustly activated c-Fos in GLP-1 and PrRP neurons in fed rats, but not in fasted rats. Fasting also significantly blunted the ability of acute stress to activate c-Fos expression within the anterior ventrolateral bed nucleus of the stria terminalis (vlBST). Acute RES stress suppressed dark-onset food intake in rats that were fed ad libitum, whereas central infusion of a GLP-1 receptor antagonist blocked RES-induced hypophagia, and reduced the ability of RES to activate PrRP and anterior vlBST neurons in ad libitum-fed rats. Thus, an overnight fast "silences" GLP-1 and PrRP neurons, and reduces both anxiety-like and hypophagic responses to acute stress. The partial mimicking of these fasting-induced effects in ad libitum-fed rats after GLP-1 receptor antagonism suggests a potential mechanism by which short-term negative energy balance attenuates neuroendocrine and behavioral responses to acute stress.

SIGNIFICANCE STATEMENT

The results from this study reveal a potential central mechanism for the "metabolic tuning" of stress responsiveness. A single overnight fast, which markedly reduces anxiety-like behavior in rats, reduces or blocks the ability of acute stress to activate hindbrain neurons that are immunoreactive for either prolactin-releasing peptide or glucagon-like peptide 1, and attenuates the activation of their stress-sensitive projection targets in the limbic forebrain. In nonfasted rats, central antagonism of glucagon-like peptide 1 receptors partially mimics the effect of an overnight fast by blocking the ability of acute stress to inhibit food intake, and by attenuating stress-induced activation of hindbrain and limbic forebrain neurons. We propose that caloric restriction attenuates behavioral and physiological responses to acute stress by "silencing" central glucagon-like peptide 1 signaling pathways.

Animal husbandry and experimental design

If the scientist needs to contact the animal facility after any study to inquire about husbandry details, this represents a lost opportunity, which can ultimately interfere with the study results and their interpretation. There is a clear tendency for authors to describe methodological procedures down to the smallest detail, but at the same time to provide minimal information on animals and their husbandry. Controlling all major variables as far as possible is the key issue when establishing an experimental design. The other common mechanism affecting study results is a change in the variation. Factors causing bias or variation changes are also detectable within husbandry. Our lives and the lives of animals are governed by cycles: the seasons, the reproductive cycle, the weekend-working days, the cage change/room sanitation cycle, and the diurnal rhythm. Some of these may be attributable to routine husbandry, and the rest are cycles, which may be affected by husbandry procedures. Other issues to be considered are consequences of in-house transport, restrictions caused by caging, randomization of cage location, the physical environment inside the cage, the acoustic environment audible to animals, olfactory environment, materials in the cage, cage complexity, feeding regimens, kinship, and humans. Laboratory animal husbandry issues are an integral but underappreciated part of investigators' experimental design, which if ignored can cause major interference with the results. All researchers should familiarize themselves with the current routine animal care of the facility serving them, including their capabilities for the monitoring of biological and physicochemical environment.

Rapid intra-adrenal feedback regulation of glucocorticoid synthesis

The hypothalamic–pituitary–adrenal axis is a vital neuroendocrine system that regulates the secretion of glucocorticoid hormones from the adrenal glands. This system is characterized by a dynamic ultradian hormonal oscillation, and in addition is highly responsive to stressful stimuli. We have recently shown that a primary mechanism generating this ultradian rhythm is a systems-level interaction where adrenocorticotrophin hormone (ACTH) released from the pituitary stimulates the secretion of adrenal glucocorticoids, which in turn feedback at the level of the pituitary to rapidly inhibit ACTH secretion. In this study, we combine experimental physiology and mathematical modelling to investigate intra-adrenal mechanisms regulating glucocorticoid synthesis. Our modelling results suggest that glucocorticoids can inhibit their own synthesis through a very rapid (within minutes), presumably non-genomic, intra-adrenal pathway. We present further evidence for the existence of a short time delay in this intra-adrenal inhibition, and also that at the initiation of each ACTH stimulus, this local feedback mechanism is rapidly antagonized, presumably via activation of the specific ACTH receptor (MC2R) signalling pathway. This mechanism of intra-adrenal inhibition enables the gland to rapidly release glucocorticoids while at the same time preventing uncontrolled release of glucocorticoids in response to large surges in ACTH associated with stress.

The Effects of Calorie Restriction in Depression and Potential Mechanisms

Depression, also called major depressive disorder, is a neuropsychiatric disorder jeopardizing an increasing number of the population worldwide. To date, a large number of studies have devoted great attention to this problematic condition and raised several hypotheses of depression. Based on these theories, many antidepressant drugs were developed for the treatment of depression. Yet, the depressed patients are often refractory to the antidepressant therapies. Recently, increasing experimental evidences demonstrated the effects of calorie restriction in neuroendocrine system and in depression. Both basic and clinical investigations indicated that short-term calorie restriction might induce an antidepressant efficacy in depression, providing a novel avenue for treatment. Molecular basis underlying the antidepressant actions of calorie restriction might involve multiple physiological processes, primarily including orexin signaling activation, increased CREB phosphorylation and neurotrophic effects, release of endorphin and ketone production. However, the effects of chronic calorie restriction were quite controversial, in the cases that it often resulted in the long-term detrimental effects via inhibiting the function of 5-HT system and decreasing leptin levels. Here we review such dual effects of calorie restriction in depression and potential molecular basis behind these effects, especially focusing on antidepressant effects.

Effects of crude kerosene on testosterone levels, aggression and toxicity in rat

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Kerosene supplementation increases serum testosterone levels in rat.

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Increased testosterone levels were associated with increased aggression.

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Kerosene supplementation had varied effects on blood parameters, notably, increased WBC counts.

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Supplementation resulted in active/chronic gastritis in the stomach of our rat model.

The use of crude kerosene as a dietary supplement in boarding schools has been a common practice in east Africa and other countries for many years, with the belief of it reducing the sex drive (libido) at the pubertal stage. There is however no scientific basis for this belief. The present study aimed at using a rat animal model to investigate the effects of crude kerosene on serum testosterone levels, aggression and its possible toxic effects. Fifteen male albino rats of approximately similar age and average weights were put into three groups of five animals each; the control group (placebo), low kerosene dose (10 μl/day) group and high kerosene dose (300 μl/day) group. ELISA was used to determine the serum testosterone levels. During treatment, changes in aggression were observed and noted. Liver toxicity was determined using enzyme assays, total protein and albumin while renal toxicity was monitored using serum creatinine levels. A full hemogram was conducted to determine hematological effects. Various tissue biopsies were obtained and examined using histopathological techniques for evidence of toxicity. Contrary to the common belief, our findings showed an overall increase of serum testosterone levels of up to 66% in the low dose and 75% in the high dose groups, with an increasing trend by the end of the study. The high dose group showed significantly increased levels of white blood cells (WBC) (p = 0.036), red blood cells (RBC) (p = 0.025), hematocrit (HCT) (p = 0.03), red cell distribution width (p = 0.028) and platelets (p = 0.017). The histological results of the stomach indicated chronic gastritis.

Fibroblast growth factor 21 is not required for the reductions in circulating insulin-like growth factor-1 or global cell proliferation rates in response to moderate calorie restriction in adult mice

Calorie restriction (CR) delays aging and extends lifespan in numerous organisms, including mice. Down-regulation of the somatotropic axis, including a reduction in insulin-like growth factor-1 (IGF-1), likely plays an important role in CR-induced lifespan extension, possibly by reducing cell proliferation rates, thereby delaying replicative senescence and inhibiting tumor promotion. Accordingly, elucidating the mechanism(s) by which IGF-1 is reduced in response to CR holds therapeutic potential in the fight against age-related diseases. Up-regulation of fibroblast growth factor 21 (FGF21) is one possible mechanism given that FGF21 expression is induced in response to nutritional deprivation and has been implicated as a negative regulator of IGF-1 expression. Here we investigated alterations in hepatic growth hormone (GH)-mediated IGF-1 production and signaling as well as the role of FGF21 in the regulation of IGF-1 levels and cell proliferation rates in response to moderate CR in adult mice. We found that in response to moderate CR, circulating GH and hepatic janus kinase 2 (JAK2) phosphorylation levels are unchanged but that hepatic signal transducer and activator of transcription 5 (STAT5) phosphorylation levels are reduced, identifying STAT5 phosphorylation as a potential key site of CR action within the somatotropic axis. Circadian measurements revealed that the relative level of FGF21 expression is both higher and lower in CR vs. ad libitum (AL)-fed mice, depending on the time of measurement. Employing FGF21-knockout mice, we determined that FGF21 is not required for the reduction in IGF-1 levels or cell proliferation rates in response to moderate CR. However, compared to AL-fed WT mice, AL-fed FGF21-knockout mice exhibited higher basal rates of cell proliferation, suggesting anti-mitotic effects of FGF21. This work provides insights into both GH-mediated IGF-1 production in the context of CR and the complex network that regulates FGF21 and IGF-1 expression and cell proliferation rates in response to nutritional status.

Effects of mild calorie restriction on anxiety and hypothalamic-pituitary-adrenal axis responses to stress in the male rat

Chronic calorie restriction (CR) is one of the few interventions to improve longevity and quality of life in a variety of species. It also reduces behavioral indices of anxiety and influences some stress hormones under basal conditions. However, it is not known how CR influences hypothalamic–pituitary–adrenal (HPA) axis function or if those on a CR diet have heightened HPA axis responses to stress. We hypothesized elevated basal glucocorticoid levels induced by CR would lead to exacerbated HPA axis responses to the psychological stress, restraint, in the male rat. We first confirmed rats fed 75% of their normal calorie intake for 3 weeks were less anxious than ad libitum‐fed (AD) rats in the elevated plus maze test for anxiety. The anxiolytic effect was mild, with only grooming significantly attenuated in the open field and no measured behavior affected in the light/dark box. Despite elevated basal glucocorticoids, CR rats had very similar hormonal and central responses to 15‐min restraint to the AD rats. Both CR and AD rats responded to restraint stress with a robust increase in glucocorticoids that was resolved by 60 min. Both groups also showed robust neuronal activation in the paraventricular nucleus of the hypothalamus and in other stress‐ and feeding‐sensitive brain regions that was not substantially affected by calorie intake. Our findings thus demonstrate chronic mild CR is subtly anxiolytic and is not likely to affect HPA axis responses to psychological stress. These findings support research suggesting a beneficial effect of mild CR.

Additive antidepressant-like effects of fasting with imipramine via modulation of 5-HT2 receptors in the mice

Recently, studies show that intermittent fasting and caloric restriction may improve symptoms of depression. However, there is little scientific evidence regarding the literature on the antidepressant-like effects of acute fasting. The present study aims to investigate the antidepressant-like effects and its influence on brain levels of the transcription factor cAMP response element-binding protein (CREB) and its phosphorylated form (p-CREB) in different time periods of fasting mice. Furthermore, the additive antidepressant-like effects of fasting with imipramine and the possible involvement of the 5-HT2 receptors were examined. In the present study 9h, but not 3h and 18h of fasting significantly reduced immobility time in the forced swimming test (FST) without alteration in locomotor activity in the open field test. 9h fasting also enhanced the ratio of p-CREB/CREB in the frontal cortex and hippocampus. Co-administration of 9h of fasting and imipramine (30mg/kg, i.p) produced the additive antidepressant-like effects in the FST and increased the ratio of p-CREB/CREB. Meanwhile, the additive effects were partially reversed by treatment with a 5-HT2A/2C receptor agonist, (±)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI) (5mg/kg, s.c). Furthermore, the antidepressant-like effects of 9h fasting was also blocked by DOI compared to the non-fasting control group. Serum corticosterone level, but not 5-HT and noradrenaline, was significantly increased in a time-dependent manner following different time periods of fasting. Taken together, these results suggest that acute fasting produces antidepressant-like effects via enhancement of the p-CREB/CREB ratio, and additive antidepressant-like effects of fasting with imipramine may be related to modulating 5-HT2 receptors.

Short-term calorie restriction feminizes the mRNA profiles of drug metabolizing enzymes and transporters in livers of mice

Calorie restriction (CR) is one of the most effective anti-aging interventions in mammals. A modern theory suggests that aging results from a decline in detoxification capabilities and thus accumulation of damaged macromolecules. The present study aimed to determine how short-term CR alters mRNA profiles of genes that encode metabolism and detoxification machinery in the liver. Male C57BL/6 mice were fed CR (0, 15, 30, or 40%) diets for one month, followed by mRNA quantification of 98 xenobiotic processing genes (XPGs) in the liver, including 7 uptake transporters, 39 phase-I enzymes, 37 phase-II enzymes, 10 efflux transporters, and 5 transcription factors. In general, 15% CR did not alter mRNAs of most XPGs, whereas 30 and 40% CR altered over half of the XPGs (32 increased and 29 decreased). CR up-regulated some phase-I enzymes (fold increase), such as Cyp4a14 (12), Por (2.3), Nqo1 (1.4), Fmo2 (5.4), and Fmo3 (346), and numerous number of phase-II enzymes, such as Sult1a1 (1.2), Sult1d1 (2.0), Sult1e1 (33), Sult3a1 (2.2), Gsta4 (1.3), Gstm2 (1.3), Gstm3 (1.7), and Mgst3 (2.2). CR feminized the mRNA profiles of 32 XPGs in livers of male mice. For instance, CR decreased the male-predominantly expressed Oatp1a1 (97%) and increased the female-predominantly expressed Oatp1a4 (11). In conclusion, short-term CR alters the mRNA levels of over half of the 98 XPGs quantified in livers of male mice, and over half of these alterations appear to be due to feminization of the liver.

Being suckled in a large litter mitigates the effects of early-life stress on hypothalamic-pituitary-adrenal axis function in the male rat

The perinatal environment influences stress responses in the long-term, as does body composition. Male rats suckled in large litters, where they have reduced access to milk and attention from the dam, are less anxious and have attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to stress compared to rats from control litters. In the present study, we investigated whether this early-life environment can also ameliorate anxiety and HPA axis function in rats prone to be stress-sensitive. We conducted these experiments in male rats from control litters (n = 12) or large litters (n = 20). Half were given 24 h of maternal separation on postnatal day 10 to induce HPA axis hyperactivity; the remainder staying undisturbed with their dam. When the rats reached adulthood, we examined behavioural indices of anxiety (elevated plus maze) and depression (Porsolt's forced swim test) under basal conditions and after 15 min of restraint stress. We also examined neuronal activation in the paraventricular nucleus of the hypothalamus (PVN) as an index of HPA axis function. Being suckled in a large litter led to a significantly attenuated PVN response to stress in adulthood. Maternal separation strongly exacerbated the stress-induced increase in PVN neuronal activation in control rats but did not affect the PVN response in large-litter rats. Immobility in the forced swim after restraint was also exacerbated in neonatally maternally separated control rats but not in those from large litters. Our findings show that being suckled in large litters mitigates the effects of early-life stress on HPA axis function and indices of depression in the rat.

Weight control and cancer preventive mechanisms: role of insulin growth factor-1-mediated signaling pathways

Overweight and obese not only increase the risk of cardiovascular disease and type-2 diabetes mellitus, but are also now known risk factors for a variety of cancers. Weight control, via dietary calorie restriction and/or exercise, has been demonstrated to be beneficial for cancer prevention in various experimental models, but the underlying mechanisms are still not well defined. Recent studies conducted in a mouse skin carcinogenesis model show that weight loss induced a significant reduction of the circulating levels of insulin growth factor (IGF)-1 and other hormones, including insulin and leptin, resulting in reduced IGF-1-dependent signaling pathways, i.e. Ras-MAPK proliferation and protein kinase B-phosphoinositide 3-kinase (Akt-PI3K) antiapoptosis. Selective targeting IGF-1 to Akt/mammalian target of rapamycin and AMP-activated protein kinase pathways, via negative energy balance, might inactivate cell cycle progression and ultimately suppress tumor development. This review highlights the current studies focused on the major role of reducing IGF-1-activated signaling via weight control as a potential cancer preventive mechanism.

Effect of stress on fasting-induced ghrelin, orexin and galanin secretion in male rats fed different levels of their energy requirement

OBJECTIVE

Ghrelin, orexin, and galanin are orexigenic factors in rodents and humans which participate in adaptive response to weight loss. On the other hand, weight loss and fasting is accompanied by increased levels of epinephrine (Ep) and cortisol (Cor). In this study, we investigated the effects of Ep and Cor on fasting-induced ghrelin, orexin, and galanin secretion in rats fed different levels of their energy requirements.

DESIGN

Forty five male Wistar rats (300-350 g, 15 per group) were fed a diet containing 100, 50, and 25% of their energy requirement for 10 days followed by 2 days of fasting. Animals were then anesthetized for carotid artery cannulation for injections and blood samplings.

METHODS

Rats received either 3 µg Ep/kg body weight (BW), 3 µg Cor/kg BW, or a combination of those two (0.1 mg in 1 ml of phosphate-buffered saline). Blood samples were collected before, 30, 60, and 120 min after injection.

RESULTS

In normal and 50% food restricted groups, fasting ghrelin levels fell after Ep and combination of Ep and Cor injection (P ≤ 0.05), whereas, orexin were decreased by combination of Ep and Cor injection in rats fed 100% of their needs and Ep alone in rats fed 50%. Galanin just fell after combination of Ep and Cor injection in both starved (50%) and normal rats. In contrast, all groups whit 25% fed ad libitum did not response to any injections (P > 0.05).

CONCLUSIONS

These results indicate that Ep suppresses starvation-induced secretion of ghrelin, orexin, and galanin in normal (100%) and starved (50%) rats and their response to Ep might be affected by weight loss.

Anxiety and hypothalamic-pituitary-adrenal axis responses to psychological stress are attenuated in male rats made lean by large litter rearing

An excellent strategy to treat overactive responses to stress is to exploit the body's inherent stress-inhibitory mechanisms. Stress responses are known to differ between individuals depending upon their level and distribution of adiposity and their experiences in early life. For instance, we have recently shown that female rats made obese by overfeeding during the neonatal period have exacerbated responses to psychological stress. The converse may be true for those that are underfed during this period. In this investigation we hypothesized that rats made lean by neonatal underfeeding would have reduced anxiety and attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress. Our findings show that male (but not female) rats, made smaller by being suckled in a large litter, show reduced anxiety-related behaviour compared with those from normal litters when tested in the elevated plus maze. These smaller males also have attenuated activation of the paraventricular nucleus of the hypothalamus in response to the psychological stress, restraint, and corticosterone responses to restraint that return more quickly to baseline than controls. These findings are exciting from the perspective of understanding and potentially exploiting the body's inherent stress-inhibitory mechanisms to treat overactive responses to stress. They also provide an indication that being lean may be able to ameliorate overactive stress responses. Understanding the mechanisms by which these stress responses are attenuated in lean animals will be important for future strategies to treat diseases associated with overactive HPA axes in humans.

A highly saturated fat-rich diet is more obesogenic than diets with lower saturated fat content

The present study tested the hypothesis that a saturated fatty acid (SFA)-rich diet is more obesogenic than diets with lower SFA content. In 8 female Sprague-Dawley rats fed a low-SFA canola or a moderate-SFA lard-rich diets at 67% of energy for 26 days, body weight gain, final body weight, obesity index, and food and energy intake were comparable. Twenty-nine rats were fed canola or high-SFA butter-rich diets (67% of energy) or chow for 50 days; then high-fat feeding was followed by ad libitum low-fat feeding (27% of energy) for 28 days and by a food-restricted low-fat diet for 32 days. High-fat feeding resulted in a greater body weight gain (P < .04), final body weight (P < .04), and energy intake (P < .008) in butter-fed rats than in canola- and chow-fed controls, after 26 or 50 days. Ad libitum canola and butter low-fat diets or chow feeding resulted in similar weight change, whereas food-restricted low-fat diets led to comparable weight loss and final weight. Canola-fed animals adjusted their intake based on diet energy density, whereas lard and butter-fed animals failed to do so. Abdominal fat (P = .012) and plasma leptin (P = .005) were higher in chow-fed controls than in canola-fed rats, but comparable with those of butter-fed rats. Prone and resistant phenotypes were detected with high-fat feeding. In conclusion, only feeding the high-SFA butter-rich diet led to obesity development and failure to adjust intake based on the energy density and preserving body fat even after weight loss. The high availability of SFA-rich foods in today's obesogenic environment could contribute to develop and maintain obesity.

High-fat diet-induced obesity in animal models

Epidemiological studies have shown a positive relationship between dietary fat intake and obesity. Since rats and mice show a similar relationship, they are considered an appropriate model for studying dietary obesity. The present paper describes the history of using high-fat diets to induce obesity in animals, aims to clarify the consequences of changing the amount and type of dietary fats on weight gain, body composition and adipose tissue cellularity, and explores the contribution of genetics and sex, as well as the biochemical basis and the roles of hormones such as leptin, insulin and ghrelin in animal models of dietary obesity. The major factors that contribute to dietary obesity - hyperphagia, energy density and post-ingestive effects of the dietary fat - are discussed. Other factors that affect dietary obesity including feeding rhythmicity, social factors and stress are highlighted. Finally, we comment on the reversibility of high-fat diet-induced obesity.

Calorie restriction at increasing levels leads to augmented concentrations of corticosterone and decreasing concentrations of testosterone in rats

The influence of calorie restriction (CR) on increasing life span, enhancing immunocompetence, and reducing the incidence of age-related diseases is well established. Evidence points to the involvement of neuroendocrine alterations in these beneficial effects. Accordingly, we hypothesized that CR will result in significant alterations to the hormones investigated. Little attention has been directed toward ascertaining the doses of CR required to obtain such alterations and, indeed, whether a dose-response exists. Adult rats were subjected to 1 of 5 dietary regimens: control, CR12.5%, CR25%, CR37.5%, or CR50%. Rats were decapitated 3 weeks following the onset of restriction; and trunk blood was collected and assayed for concentrations of serum adrenocorticotropic hormone, corticosterone, and testosterone, as well as plasma concentrations of noradrenalin and adrenalin. No effect was found as a result of dietary manipulation for serum concentrations of adrenocorticotropic hormone. However, all doses of CR resulted in increased serum corticosterone in a dose-response trend. A dose-response was also observed for serum testosterone, with higher doses of CR associated with lower testosterone. Concentrations of noradrenalin were not found to be altered by any CR dose, although a trend toward a down-regulation at CR50% was observed. Plasma adrenalin displayed a biphasic distribution with reductions observed at CR25% and CR50%, although the down-regulations only attained statistical significance relative to the CR37.5% and not the control group. As well as reporting the effect of CR on multiple hormones within individual animals, these results go some way in determining the optimal levels of CR needed to induce neuroendocrinologic alterations.

Differential effects of photophase irradiance on metabolic and urinary stress hormone concentrations in blind and sighted rodents

The effects of different photophase irradiance levels on the daily rhythms of energy expenditure (DEE, calculated from oxygen consumption, VO(2)) and urinary metabolites of stress hormones in sighted (Microtus socialis) and blind (Spalax ehrenbergi) rodents were compared. Five groups of each species were exposed to different irradiance levels (73, 147, 293, 366, and 498 microW/cm(2)) under short photoperiod (8L:16D) condition with constant ambient temperature 25 +/- 2 degrees C for 21 days before assessments. As light intensity increased from 73 microW/cm(2), both species reduced DEE, especially among M. socialis. Cosinor analysis revealed significant ultradian rhythms in VO(2) of M. socialis with period length being inversely related to irradiance level. Conversely, in S. ehrenbergi, robust 24 h VO(2) rhythms were detected at all irradiances. In M. socialis, significant 24 h rhythms in urinary output of adrenaline were detected only at 293 microW/cm(2), whereas for cortisol, unambiguous rhythms were detected at 73 and 147 microW/cm(2). Distinct adrenaline daily rhythms of S. ehrenbergi were observed at 73 and 293 microW/cm(2), whereas this species exhibited significant rhythms in cortisol at 147 and 293 microW/cm(2). Changes in photophase irradiance levels affected stress hormone concentrations in a dose-dependent manner. There were significant negative and positive correlations of M. socialis and S. ehrenbergi stress hormones, respectively, with increasing irradiance. Our results indicate photophase light intensity is another environmental factor that can significantly affect entrainment of mammalian daily rhythms. Both low and high irradiance conditions can trigger stress responses, depending on the species' natural habitat.

Interactions between light, mealtime and calorie restriction to control daily timing in mammals

Daily variations in behaviour and physiology are controlled by a circadian timing system consisting of a network of oscillatory structures. In mammals, a master clock, located in the suprachiasmatic nuclei (SCN) of the hypothalamus, adjusts timing of other self-sustained oscillators in the brain and peripheral organs. Synchronisation to external cues is mainly achieved by ambient light, which resets the SCN clock. Other environmental factors, in particular food availability and time of feeding, also influence internal timing. Timed feeding can reset the phase of the peripheral oscillators whilst having almost no effect in shifting the phase of the SCN clockwork when animals are exposed (synchronised) to a light-dark cycle. Food deprivation and calorie restriction lead not only to loss of body mass (>15%) and increased motor activity, but also affect the timing of daily activity, nocturnal animals becoming partially diurnal (i.e. they are active during their usual sleep period). This change in behavioural timing is due in part to the fact that metabolic cues associated with calorie restriction affect the SCN clock and its synchronisation to light.

The diet board: welfare impacts of a novel method of dietary restriction in laboratory rats

Laboratory rats are commonly fed ad libitum (AL). Moderate dietary restriction (DR) decreases mortality and morbidity when compared with AL feeding, but there are several obstacles to the implementation of DR. Traditional methods of restricted feeding disrupt normal diurnal eating rhythms and are not compatible with group housing. We have designed a novel method, the diet board, to restrict the feeding of group-housed rats. Animals fed from the diet board had 15% lower body weight than the AL-fed animals at the age of 17 weeks. The welfare effects of diet board feeding were assessed by comparing the stress physiology of diet board fed animals with that of AL-fed animals. Diet board feeding was associated with higher serum corticosterone levels and lower faecal secretion of IgA, suggesting the diet board causes a stress reaction. However, the AL-fed group had larger adrenal glands with higher adrenaline and noradrenaline content than the diet board animals. No gastric ulcers were found in any of the animals at necropsy. The diet board thus appears to cause a stress reaction when compared with AL-fed rats, but no apparent pathology was associated with this reaction. The diet board could help to solve the health problems associated with AL feeding, while allowing the rats to be group-housed and to maintain their normal diurnal eating rhythms. The diet board can also be seen as a functional cage furniture item, dividing the cage into compartments and thus increasing the structural complexity of the environment. In conclusion, the diet board appears to possess refinement potential compared with traditional methods of DR.

A novel dietary restriction method for group-housed rats: weight gain and clinical chemistry characterization

Laboratory rodents are usually fed ad libitum. Moderate dietary restriction decreases mortality and morbidity compared with ad libitum feeding. There are, however, problems in achieving dietary restriction. Traditional methods of restricted feeding may interfere with the diurnal rhythms of the animals and are not compatible with group-housing of rodents. We have invented a novel method, the diet board, for restricting the feed intake of laboratory rats. The use of the diet board moderately decreased weight gain of rats when compared with ad libitum-fed animals. The diet board retarded skeletal growth only minimally, whereas major differences were found in body fat depositions. Serum free fatty acid, triglyceride and cholesterol values were lower in diet-restricted rats, while the opposite was true for serum creatine kinase. There were no differences in total protein, albumin or alanine aminotransferase. Moreover, differences in interindividual variances in parameters were not detected between the groups; hence this study could not combine the diet board with reduction potential. The diet board provides mild to moderate dietary restriction for group-housed rats and is unlikely to interfere with the diurnal eating rhythm. The diet board can also be seen as a cage furniture item, dividing the open cage space and increasing the structural complexity of the environment. In conclusion, the diet board appears to possess refinement potential when compared with traditional methods of dietary restriction.

Chronic calorie restriction attenuates experimental autoimmune encephalomyelitis

Calorie restriction (CR) prevents many age-associated diseases and prolongs the lifespan. CR induces multiple metabolic and physiologic modifications, including anti-inflammatory, antioxidant, and neuroprotective effects that may be beneficial in multiple sclerosis (MS). The present studies sought to determine whether CR or increased calorie intake alters the course of experimental autoimmune encephalomyelitis (EAE), the leading animal model for MS. SJL and C57BL/6 mice were subjected to 40% CR beginning at 5 weeks of age. After 5 weeks of CR, EAE was induced by immunizing with proteolipid protein in SJL mice and with myelin oligodendrocyte glycoprotein in C57BL/6 mice. Clinical, histologic, and immunologic features of EAE were compared with mice fed ad libitum and to SJL mice fed a high-fat, high-calorie diet. CR ameliorated clinical EAE in both mouse strains with less severe inflammation, demyelination, and axon injury. No suppression of immune function was observed. A high-calorie diet did not alter the EAE course. CR was associated with increased plasma levels of corticosterone and adiponectin and reduced concentrations of IL-6 and leptin. The CR-induced hormonal, metabolic, and cytokine changes observed in our studies suggest a combined anti-inflammatory and neuroprotective effect. CR with adequate nutrition and careful medical monitoring should be explored as a potential treatment for MS.

Food restriction induces long-lasting recovery of spatial memory deficits following global ischemia in delayed matching and non-matching-to-sample radial arm maze tasks

Food restriction has been shown to be beneficial for a number of brain processes. In the current study, we characterized the impact of food restriction on hippocampal damage 70 days following ischemia. We assessed memory and cognitive flexibility of ad libitum fed (AL) and food-restricted (FR) animals using complex delayed non-matching- and matching-to-sample tasks in the radial arm maze. Our findings demonstrate that food restriction led to significant improvement of ischemia-induced memory impairments. FR ischemic animals rapidly reached comparable performance as both AL and FR sham animals in delayed-non-matching (win-shift) and matching (win-stay) radial arm maze tasks. They also made considerably fewer microchoices in the retention trials than AL ischemic animals. In contrast, AL ischemic rats showed persistent spatial memory impairments in the same paradigms. Assessment of basal and stress-induced corticosterone (CORT) secretion revealed no significant differences in baseline levels in AL and FR rats prior to or following global ischemia. However, FR animals showed a more pronounced attenuation of CORT secretion 45 min following restraint. Both FR and AL ischemic rats had comparable cell loss within CA1 and CA3 subfields of Ammon's horn (CA1 and CA3) at 70 days following reperfusion, although a trend toward increased CA3 cell survival was observed in FR ischemic rats. The functional sparing in the FR ischemic animals in the face of equivalent hippocampal cell loss suggests that food restriction somehow enhanced the efficacy of remaining hippocampal or extrahippocampal neurons following ischemia. In the current study, this phenomenon was not associated with diet- and or ischemia-related alterations of vesicular glutamate transporter 1 expression in various hippocampal regions although lower vesicular GABA transporter immunostaining was present in the CA1 stratum oriens and the CA3 stratum radiatum in FR sham and ischemic rats.

Effect of aging on 24-hour pattern of stress hormones and leptin in rats

This work analyzes the 24-hour changes of hypothalamic-pituitary-adrenal (HPA) axis activity and leptin release in aged rats. Three- and 22-month-old male Wistar rats were killed at 6 time intervals during a 24-hour cycle (n=8-10 rats/group). Aging augmented plasma ACTH while it decreased plasma and adrenal gland corticosterone levels. Plasma and adrenal corticosterone levels attained high levels during all the scotophase, concomitantly with the maxima in ACTH levels, whereas in aged rats only a brief plasma corticosterone peak at the early scotophase and no time of day variations of adrenal corticosterone were observed. Aging augmented circulating leptin, with a significant interaction "agextime" in the factorial ANOVA, i.e. only in young rats time of day changes were significant, with the lowest values of leptin at the middle of the light period and higher values at night. When plasma leptin was expressed on body weight basis, the age-related differences became not significant but the daily pattern of plasma leptin found in young rats persisted. Plasma and adrenal corticosterone levels correlated significantly with plasma ACTH only in young rats. Likewise, plasma leptin correlated with plasma corticosterone only in young rats. These changes can be attributed to a disrupting effect of aging on the homeostatic mechanisms modulating HPA activity and leptin release.

Leptin extends the anorectic effects of chronic PYY(3-36) administration in ad libitum-fed rats

Acute administration of peptide YY(3-36) [PYY(3-36)] results in a reduction in food intake in several different vertebrates. However, long-term continuous administration of PYY(3-36) causes only a transient reduction in food intake, thus potentially limiting its therapeutic efficacy. We hypothesized that a fall in leptin levels associated with reduced food intake could contribute to the transient anorectic effects of continuous PYY(3-36) infusion and thus that leptin replacement might prolong the anorectic effects of PYY(3-36). Seven-day administration of 100 microg x kg body wt(-1) x day(-1) PYY(3-36) using osmotic minipumps caused a significant reduction in food intake of ad libitum-fed rats, but only for the first 2 days postimplantation. Circulating levels of leptin were reduced 1 day following continuous infusion of PYY(3-36), and combined leptin infusion at a dose of leptin that had no anorectic effects on its own (100 microg x kg body wt(-1) x day(-1)) prolonged the anorectic actions of PYY(3-36) in ad libitum-fed rats for up to 6 days postimplantation and yielded reduced weight gain compared with either peptide alone. The inhibitory effects of 100 microg x kg body wt(-1) x day(-1) PYY(3-36) on food intake were absent in rats refed after a 24-h fast and substantially reduced at a dose of 1,000 microg x kg body wt(-1) x day(-1) PYY(3-36). Leptin replacement was unable to recover the anorectic effects of PYY(3-36) in fasted rats. Our results suggest that an acute fall in leptin levels is not solely responsible for limiting duration of action of chronic PYY(3-36) infusion, yet chronic coadministration of a subanorectic dose of leptin can extend the anorectic effects of PYY(3-36).

Effects of Every-Other-Day Feeding on Prolactin Regulatory Mechanism in Transgenic Human Growth Hormone Mice

Transgenic mice overexpressing human growth hormone (hGH) exhibit accelerated aging with functional hyperprolactinemia and greatly depressed endogenous prolactin. Calorie restriction (CR) is widely recognized as the most effective experimental intervention to delay aging. The aim of the present work was to analyze the effects of lifelong overexpression of hGH on prolactin-gene expression as well as the dopamine production at the pituitary level and discern whether this mechanism changes as a function of feeding patterns. Ten-month-old mice fed every other day (EOD) were killed after one day of fasting. The results confirmed typical phenotypic features of these transgenic mice: an increase in body weight, very high hGH plasma concentrations, and hyperinsulinemia. There was a marked inhibition of the expression of the prolactin gene, together with an increased tyrosine hydroxylase (TH) and the long isoform of dopamine receptor type 2 (D2LR) gene expression at the pituitary level. These parameters were not affected by the EOD feeding pattern. These data may suggest an autocrine or paracrine effect of dopamine at the hypophyseal level on prolactin secretion that is independent of the feeding pattern.

Energy restriction and exercise differentially enhance components of systemic and mucosal immunity in mice

The prevalence of obesity, an established risk factor for several chronic diseases, including cancer, has risen dramatically over the past 4 decades. Dietary change and/or increased physical activity are the most commonly recommended lifestyle-based strategies for preventing or reversing obesity. One of several physiological systems that may be enhanced by dietary change and exercise is the immune system. In this study, we examined the effects of energy restriction (ER; 30% reduction relative to control energy intake) and/or exercise (EX; voluntary wheel running) on systemic and mucosal immune function. Female C57BL/6 mice were randomized into 4 treatment conditions: 1) controls consumed ad libitum (AL); 2) AL with access to running wheels (AL + EX); 3) 30% ER; and 4) 30% ER with access to running wheels (ER + EX). Both ER and EX reduced spleen weight and the number of splenic T and B lymphocytes (P < 0.05). ER enhanced natural killer (NK) cell function, but reduced concanavalin A (Con A)-induced T-cell proliferation (P < 0.05). In contrast, EX enhanced Con A-induced proliferation and cytokine production from Peyer's patch cells (P < 0.05). These data suggest that ER and EX enhance some, but not all, components of the immune system and are likely working via different biological mechanisms to regulate NK and T-cell function.

Neuroendocrine-immune correlates of circadian physiology: studies in experimental models of arthritis, ethanol feeding, aging, social isolation, and calorie restriction

Virtually all neuroendocrine and immunological variables investigated in animals and humans display biological periodicity. Circadian rhythmicity is revealed for every hormone in circulation as well as for circulating immune cells, lymphocyte metabolism and transformability, cytokines, receptors, and adhesion molecules. Clock genes, notably the three Period (Per1/Per2/Per3) genes and two Cryptochrome (Cry1/Cry2) genes, are present in immune and endocrine cells and are expressed in a circadian manner in human cells. This review discusses the circadian disruption of hormone release and immune-related mechanisms in several animal models in which circulating cytokines are modified including rat adjuvant arthritis, social isolation in rats and rabbits and alcoholism, the aging process and calorie restriction in rats. In every case the experimental manipulation used perturbed the temporal organization by affecting the shape and amplitude of a rhythm or by modifying the intrinsic oscillatory mechanism itself.

Chronic intermittent ethanol exposure during adolescence blocks ethanol-induced inhibition of spontaneously active hippocampal pyramidal neurons

BACKGROUND

Binge alcohol drinking among adolescents has been a serious public health problem. A model of binge alcohol, chronic intermittent ethanol exposure (CIEE), during adolescence significantly attenuates ethanol-induced spatial memory deficits in rats. However, the attenuation was absent following a 12-day ethanol-free period. Since spatial memory is hippocampal dependent, a reduction in ethanol-induced spatial memory impairments may be due to a reduction in the ability of ethanol to inhibit the firing rate of single hippocampal pyramidal neurons following CIEE.

METHODS

Beginning on postnatal day 30 (P30), male adolescent Sprague-Dawley rats (Harlan) were administered 5.0 g/kg ethanol (n = 10, CIEE-treated group) or an equivolume saline (n = 10, CISE-treated group) every 48 hours for 20 days. Single hippocampal pyramidal neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded on the day following completion of the chronic intermittent exposure procedure (animals now P50). Additionally, neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded 12 days after the completion of the chronic intermittent exposure procedure (animals now P62).

RESULTS

Ethanol exposure during adolescence completely blocked ethanol-induced inhibition of hippocampal pyramidal neurons in rats that were CIEE exposed. However, the effect of CIEE on hippocampal neurophysiology was time dependent. Specifically, neurons recorded from CIEE-treated rats after a 12-day ethanol-free period had similar maximal inhibition as neurons from CISE-treated animals, although the time to reach inhibition was significantly greater in neurons from CIEE-treated rats.

CONCLUSION

Chronic ethanol exposure during adolescence produces a reduction, or tolerance, to ethanol-induced inhibition of hippocampal pyramidal neural activity. Although the tolerance was greatly reversed after a 12-day ethanol-free period, neurons from CIEE animals inhibited slower than neurons from CISE animals. Since the hippocampus is known to be involved not only in spatial memory, but also in many other types of memory formation, the altered hippocampal functions because of CIEE during adolescence should be taken as a serious warning for society.

Faecal corticosterone concentrations indicate that separately housed male mice are not more stressed than group housed males

Mice account for over 80% of all animals used in experimentation. This study investigated how different housing conditions affected stress levels by measuring both corticosterone levels, using non-invasive faecal collection, and behaviour. Sixty outbred MF1 male mice were used which were separated into five different housing conditions at the beginning of the study, (A) individually housed, floor area 490 cm(2) per individual, (B) groups of three mice, floor area 163 cm(2) per individual, (C) groups of three mice, floor area 320 cm(2) per individual, (D) groups of six mice, floor area 160 cm(2) per individual, (E) groups of six mice, floor area 230 cm(2) with extra height per individual to allow visual contact. Mice in all housing conditions were provided with a basic enrichment of paper bedding and a plastic house. The results from this study showed that singly housed mice reduced their corticosterone levels over time after separation reaching a minimum from 14 days onwards. Groups of 6 mice housed together showed no difference over time. Also there was no significant difference in corticosterone levels between the different housing densities, with no differences for aggression or stereotypical behaviour suggesting that there is no ideal group density for this strain and sex of mouse. Providing additional enrichment to the cages caused a significant decrease in corticosterone levels for group housed mice, but individually housed mice remained unaffected by increasing their enrichment level. They spent significantly more time sleeping in the enhanced cage but without any reduction in stereotypical behaviour. For group housed mice, additional enrichment should be mandatory to reduce stress levels and therefore increase their welfare standards, while singly housed mice required only basic levels of enrichment and should be separated from their group for a minimum of 2 weeks before measurements are taken.