Glucocorticoids in the nonobese diabetic (NOD) mouse: basal serum levels, effect of endocrine manipulation and immobilization stress

Polysaccharide-Rich Extract of Phragmites rhizome Attenuates Water Immersion Stress and Forced Swimming Fatigue in Rodent Animal Model

Our study aimed to investigate the effects of the polysaccharide-rich extract of Phragmites rhizoma (PEP) against water immersion restraint (WIR) stress and forced swimming-induced fatigue. Exposure to WIR stress significantly increased the ulcer index, bleeding score, the weight of the adrenal gland, blood glucose concentrations, total cholesterol, cortisol, and creatine kinase (CK). The weight of the spleen decreased significantly. In addition, myeloperoxidase (MPO) and thiobarbituric acid-reactive substance (TBARS) were significantly upregulated by WIR stress. The antioxidative factors such as glutathione (GSH) and superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in the stomach were decreased by WIR stress. Alterations induced by WIR stress were effectively reversed by pretreatment with PEP. The swimming endurance capacity of mice was significantly prolonged by the oral administration of PEP. Swimming-induced fatigue significantly reduced the body weight; however, the injection of PEP inhibited the decrease of body weight. The PEP-treated group had significantly lower CK levels in plasma, an indicator of muscle damage. These results indicated that PEP has anti-stress and anti-fatigue effects, which are mediated by suppressing the hyperactivation of the hypothalamus-pituitary-adrenal axis, and antagonism of the oxidative damages induced by WIR stress and prolonged swimming times.

Comparison of blood sampling methods for plasma corticosterone measurements in mice associated with minimal stress-related artefacts

Accurate measurement of circulating glucocorticoid concentrations in rodents is often hampered by the stress-related activation of the hypothalamic-pituitaryadrenal axis during animal handling. The present study aims to identify methods of blood collection associated with minimal stress and thus artificial increases in plasma glucocorticoid levels. Using two strains of mice, we evaluated common laboratory methods of non-terminal (tail blood sampling with or without restraint; retro-orbital puncture) and terminal blood collection (cardiac puncture) and their immediate and prolonged effect on plasma corticosterone levels. Compared to retro-orbital and cardiac puncture, mice from both the unrestrained and restrained tail snip collection groups displayed the lowest plasma corticosterone levels in both mouse strains. Plasma corticosterone levels in samples obtained from retro-orbital and cardiac puncture collection were up to twenty times higher than those measured in mice undergoing blood collection via tail snip. Repeat tail snip collections (every 30 min for 120 min, or once after 120 min) revealed sustained hypercortisolaemia, compared to the initial collection. We conclude that blood sampling via tail snip without restraint remains the gold-standard method of collection that is associated with minimal stress-related artefacts and hence feasible for single time point corticosterone analyses.

Evaluation of the neutrophil:lymphocyte ratio as an indicator of chronic distress in the laboratory mouse

When evaluating the effect of husbandry and biomethodologies on the well-being of laboratory mice, it is critical to utilize measurements that allow the distinguishing of acute stress from chronic stress. One of the most common measurements of stress in laboratory animals is the corticosterone assessment. However, while this measurement provides a highly accurate reflection of the animal's response to acute stressors, its interpretation is more prone to error when evaluating the effect of chronic stress. This study evaluated the use of the neutrophil:lymphocyte (NE:LY) ratio as an assessment of chronic stress in male and female C57Bl/6N mice as compared to serum corticosterone. One group of mice was exposed to mild daily stressors for 7 days, while the control group was handled with normal husbandry. The NE:LY ratio and serum corticosterone levels were significantly elevated in the chronically stressed mice, though a significant increase in corticosterone was only significant in males when compared by sex. The chronically stressed mice also demonstrated significantly fewer entries into the open arms and less time spent in the open arms of the elevated plus maze, suggesting that the mild daily stressors had induced a state of distress. The findings of this study confirm that the NE:LY ratio is a valid measurement for chronic stress in the laboratory mouse. However, these assays do not distinguish between distress or eustress, so behavioral and physiological assessments should always be included to determine a complete assessment of the well-being of the mouse.

Adaptogenic potential of Oxitard in experimental chronic stress and chronic unpredictable stress induced dysfunctional homeostasis in rodents

Background

Oxitard, a polyherbal formulation comprising the extracts of Withania somnifera, Mangifera indica, Glycyrrhiza glabra, Daucus carota, Vitis vinifera, powders of Syzygium aromaticum, Yashada bhasma and Emblica officinalis; and oils of Triticum sativum.

Objective

Current study deals with the assessment of Oxitard (a marketed polyherbal formulation) for its adaptogenic potential in chronic unpredictable stress (CUS) and chronic stress (CS) induced dysfunctional homeostasis in rodents.

Materials & methods

Animals were immobilized for 2 h every day for ten days to induce CS. In order to induce CUS, animals were employed in a battery of stressors of variable value and duration for ten days. Following administration of Oxitard, stress was induced in the animals. Stress-induced efficient changes were evaluated by assessing organ (adrenal gland) weights, ulcer index, hematological parameters and biochemical levels of reduced glutathione (GSH), thiobarbituric acid reactive substances (TBARS) and catalase (CAT).

Results

CS and CUS significantly modified the oxidative stress parameters (increased MDA and decreased GSH). Furthermore, CS and CUS lead to weight reduction, adrenal hypertrophy and gastric ulceration. Pre-treatment with Oxitard (200 and 400 mg/kg, p.o.) significantly modified CS and CUS induced hematological changes, oxidative stress parameters and pathological effects.

Conclusion

In conclusion, Oxitard-intervened antioxidant actions are accountable for its adaptogenic effects in stress-induced dysfunctional homeostasis.

Diabetes as a chronic metabolic stressor: causes, consequences and clinical complications

Diabetes mellitus is an endocrine disorder resulting from inadequate insulin release and/or reduced insulin sensitivity. The complications of diabetes are well characterized in peripheral tissues, but there is a growing appreciation that the complications of diabetes extend to the central nervous system (CNS). One of the potential neurological complications of diabetes is cognitive deficits. Interestingly, the structural, electrophysiological, neurochemical and anatomical underpinnings responsible for cognitive deficits in diabetes are strikingly similar to those observed in animals subjected to chronic stress, as well as in patients with stress-related psychiatric illnesses such as major depressive disorder. Since diabetes is a chronic metabolic stressor, this has led to the suggestion that common mechanistic mediators are responsible for neuroplasticity deficits in both diabetes and depression. Moreover, these common mechanistic mediators may be responsible for the increase in the risk of depressive illness in diabetes patients. In view of these observations, the aims of this review are (1) to describe the neuroplasticity deficits observed in diabetic rodents and patients; (2) to summarize the similarities in the clinical and preclinical studies of depression and diabetes; and (3) to highlight the diabetes-induced neuroplasticity deficits in those brain regions that have been implicated as important pathological centers in depressive illness, namely, the hippocampus, the amygdala and the prefrontal cortex.

Glucocorticoid receptor blockade normalizes hippocampal alterations and cognitive impairment in streptozotocin-induced type 1 diabetes mice

Type 1 diabetes is a common metabolic disorder accompanied by an increased secretion of glucocorticoids and cognitive deficits. Chronic excess of glucocorticoids per se can evoke similar neuropathological signals linked to its major target in the brain, the hippocampus. This deleterious action exerted by excess adrenal stress hormone is mediated by glucocorticoid receptors (GRs). The aim of the present study was to assess whether excessive stimulation of GR is causal to compromised neuronal viability and cognitive performance associated with the hippocampal function of the diabetic mice. For this purpose, mice had type 1 diabetes induced by streptozotocin (STZ) administration (170 mg/kg, i.p.). After 11 days, these STZ-diabetic mice showed increased glucocorticoid secretion and hippocampal alterations characterized by: (1) increased glial fibrillary acidic protein-positive astrocytes as a marker reacting to neurodegeneration, (2) increased c-Jun expression marking neuronal activation, (3) reduced Ki-67 immunostaining indicating decreased cell proliferation. At the same time, mild cognitive deficits became obvious in the novel object-placement recognition task. After 6 days of diabetes the GR antagonist mifepristone (RU486) was administered twice daily for 4 days (200 mg/kg, p.o.). Blockade of GR during early type 1 diabetes attenuated the morphological signs of hippocampal aberrations and rescued the diabetic mice from the cognitive deficits. We conclude that hippocampal disruption and cognitive impairment at the early stage of diabetes are caused by excessive GR activation due to hypercorticism. These signs of neurodegeneration can be prevented and/or reversed by GR blockade with mifepristone.

Steroid hormones control circadian Elovl3 expression in mouse liver

The Elovl3 gene belongs to the Elovl gene family, which encodes for enzymes involved in the elongation of very long chain fatty acids. The recognized role for the enzyme is to control the elongation of saturated and monounsaturated fatty acids up to 24 carbons in length. Elovl3 was originally identified as a highly expressed gene in brown adipose tissue on cold exposure. Here we show that hepatic Elovl3 mRNA expression follows a distinct diurnal rhythm exclusively in mature male mice, with a sharp increase early in the morning Zeitgeber time (ZT) 20, peaks around ZT2, and is back to basal level at the end of the light period at ZT10. In female mice and sexually immature male mice, the Elovl3 expression was constantly low. Fasting and refeeding mice with chow or high-fat diet did not alter the Elovl3 mRNA levels. However, animals that were exclusively fed during the day for 9 d displayed an inverted expression profile. In addition, we show that Elovl3 expression is transcriptionally controlled and significantly induced by the exposure of the synthetic glucocorticoid dexamethasone. Taken together, these data suggest that Elovl3 expression in mouse liver is under strict diurnal control by circulating steroid hormones such as glucocorticoids and androgens. Finally, Elovl3 expression was found to be elevated in peroxisomal transporter ATP-binding cassette, subfamily D(ALD), member 2 ablated mice and suppressed in ATP-binding cassette subfamily D(ALD) member 2 overexpressing mice, implying a tight cross talk between very long chain fatty acid synthesis and peroxisomal fatty acid oxidation.

Anti-stress constituents of Evolvulus alsinoides: an ayurvedic crude drug

Bioactivity-guided purification of n-BuOH soluble fraction from the ethanol extract of Evolvulus alsinoides resulted in the isolation of two new compounds, 2,3,4-trihydroxy-3-methylbutyl 3-[3-hydroxy-4-(2,3,4-trihydroxy-2-methylbutoxy)-phenyl]-2-propenoate (1) and 1,3-di-O-caffeoyl quinic acid methyl ester (2) along with six known compounds, caffeic acid (3), 6-methoxy-7-O-beta-glucopyranoside coumarin (4), 2-C-methyl erythritol (5), kaempferol-7-O-beta-glucopyranoside (6), kaempferol-3-O-beta-glucopyranoside (7) and quecetine-3-O-beta-glucopyranoside (8). The structure of new compounds 1 and 2 were elucidated by spectroscopic analysis, while known compounds were confirmed by direct comparison of their NMR data with those reported in literature. This is the first report of the presence of phenolic constituents in Evolvulus alsinoides. The isolated compounds 1-5 and 8 were screened for anti-stress activity in acute stress induced biochemical changes in adult male Sprague-Dawley rats. Stress exposure has resulted in significant increase of plasma glucose, adrenal gland weight, plasma creatine kinase (CK), and corticosterone levels. Compound 1 displayed most promising antistress effect by normalizing hyperglycemia, plasma corticosterone, CK and adrenal hypertrophy, while compounds 2 and 3 were also effective in normalizing most of these stress parameters, however compounds 4, 5 and 8 were ineffective in normalizing these parameters.

The role of vasopressin in diabetes mellitus-induced hypothalamo-pituitary-adrenal axis activation: studies in Brattleboro rats

Chronic diabetes mellitus (DM) induces hyperactivity of the hypothalamo-pituitary-adrenal axis (HPA). Our present study addresses the role of vasopressin (AVP) in maintaining adrenocortical responsiveness during DM. AVP-deficient mutant Brattleboro rats were used with heterozygous controls and the V2 agonist, desmopressin was infused to replace peripheral AVP. To induce DM the rats were injected by streptozotocin (STZ, 60 mg/ml/kg i.v.) and studied 2 weeks later. The acute stress stimulus was 60 min restraint. The signs of DM (the increase in water consumption and in blood glucose levels) were discovered in all rats. The diuretic effect of the lack of AVP was additional to the DM-induced osmotic diuresis. DM induced significant, chronic stress-like somatic changes on which AVP-deficiency had no effect and although desmopressin infusion normalized the water consumption and the body weight gain in AVP-deficient rats, it had no effect on DM-induced changes. The acute stress-induced plasma ACTH elevation was smaller in AVP-deficient or DM rats but these effects were not additive. Desmopressin did not normalize the decreased ACTH-elevation of AVP-deficient animals. The resting morning plasma corticosterone level was elevated both in DM and AVP-deficient rats without interaction. The restraint-induced corticosterone rise was influenced neither by the lack of AVP nor by DM and the basal and stress-induced prolactin levels were smaller in DM rats without any effect of AVP-deficiency. In conclusion, our data suggest that AVP does not play a crucial role in HPA axis regulation during DM-induced chronic stress. In contrast, the role of AVP seems to be more important during acute stress, however, it is restricted to the ACTH regulation. According to the water consumption data diabetes insipidus seems to be an additional risk factor for DM.

Comparative study of perturbations of peripheral markers in different stressors in rats

Stress has been implicated in the etiopathogenesis of several diseases. In the present study, the effects of acute (AS), chronic (CS), and chronic unpredictable stress (CUS) were studied on the ulcer index, adrenal gland mass, and biochemical and hormonal changes in rats. The stress was provided in the form of immobilization-immobilization for 150 min, once only, and for 10 consecutive days in CS and CUS. In CUS, animals received variable unpredictable stressors. Immediately after stress, animals were decapitated, blood was collected, and plasma was separated for the estimation of plasma glucose, triglyceride, cholesterol, creatine kinase (CK), corticosterone, and insulin. The adrenal gland and stomach were also dissected for mass and ulcer scoring, respectively. AS significantly increased the ulcer index, plasma glucose, CK, corticosterone, and insulin. CS and CUS significantly increased the ulcer index, adrenal gland mass, and corticosterone. In CS, a significant decrease in plasma triglyceride and cholesterol levels was found, but in CUS only cholesterol was decreased significantly. High CK activity and hyperglycemia maintain the energy demands of metabolism, and elevated corticosterone desensitizes the insulin receptor in AS. In CS and CUS, prolonged elevation of corticosterone shifts metabolism to utilization of lipids as a secondary substrate by gluconeogenesis. From our experiment, it is clear that AS causes maximum activation of energy metabolism, which becomes specific after habituation in prolonged CS. These biochemical manipulations in the body by using different types of stressors are good markers that can be of great use to understand, target, and manage stress-induced etiologies.

Neuroendocrine Immuno-ontogeny of the Pathogenesis of Autoimmune Diabetes in the Nonobese Diabetic (NOD) Mouse

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which insulin-producing beta cells of the pancreatic islets of Langerhans are destroyed. The nonobese diabetic (NOD) mouse is one of the rare spontaneous models that enable the study of prediabetic pancreatic events. The etiology of the autoimmune attack in human and animal T1D is still unknown, but genetic and environmental factors are involved in both cases. Although several autoantigens have been identified and defective immune-system regulation is implicated, this information does not satisfactorily explain the generally accepted beta-cell specificity of the disease or how so many and diverse environmental factors intervene in its pathogenesis. Based on data obtained from evaluating glucose homeostasis in a variety of situations, particularly stress and cytokine administration, in young prediabetic NOD mice, the author hypothesizes that the islet of Langerhans is a major actor, and its altered regulation through environmentally induced insulin resistance might reveal latent T1D. It is also postulated that T1D pathogenesis might be linked to abnormal pancreas development, probably due to disturbances of glutamic acid decarboxylase (GAD)+ innervation phagocytosis by defective macrophages during the early postnatal period. Also discussed is the role of defective presentation of pancreatic hormones and GAD in the thymus, and its potential repercussion on T-cell tolerance. Observations have demonstrated that the diabetogenic process in the NOD mouse is extremely complex, involving neuroendocrine immune interaction from fetal life onward.

Perturbations of arginine vasopressin secretion during inflammatory stress. Pathophysiologic implications

Pro-inflammatory cytokines, such as interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF alpha), released from inflammatory foci, can activate the hypothalamus to produce corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP). These hypothalamic peptides in synergy increase ACTH production by the pituitary gland and hence corticosteroid (CS) secretion by the adrenal cortices. CS dampens inflammation. The pituitary also produces prolactin (PRL), which is pro-inflammatory, and macrophage inhibitory factor (MIF), which by counteracting the anti-inflammatory and immunosuppressive effects of CS, is pro-inflammatory. Lewis rats develop a variety of induced-autoimmune inflammatory conditions, such as streptococcal cell wall arthritis, whereas the histocompatible F344 Fisher rats are resistant to this condition. Lewis rats have a defective hypothalamic-pituitary adrenal (HPA) response to a variety of hypothalamic stimuli, but have augmented systemic secretion of AVP. Patients with rheumatoid arthritis (RA) have deficient CS with exaggerated PRL responses to inflammatory stimuli. Within inflammatory foci, CRH is pro-inflammatory. AVP, which augments autologous mixed lymphocyte reactions, can replace the IL-2 requirement for gamma IFN production by T cells via V1a receptors, and potentiates primary antibody responses, is also pro-inflammatory. Lewis rats have significantly high plasma levels, hypothalamic content, and in vitro release of AVP in comparison to the inflammatory disease-resistant Fischer rats. Immunoneutralization of AVP attenuates inflammatory responses. In Sprague-Dawley rats, AVP potentiates PRL secretion. Preliminary studies in patients with RA have shown that the circulating levels of AVP are significantly increased, which might be a compensatory response to low CS levels or a result of elevated levels of IL-6 in these patients but could nevertheless contribute to rheumatoid inflammation. A similar observation has been made in patients with ankylosing spondylitis.

The influence of the hormonal system on pediatric rheumatic diseases

The role of NEI interactions in children with chronic inflammatory rheumatic disorders has not been systematically studied to the same extent as in adults. The data that are currently available suggest that NEI mechanisms are involved in the pathophysiology of some of the diseases. These include JRA, JSLE, and JAS. Prolactin has been most extensively investigated, showing interesting parallels with findings in adult rheumatologic diseases. Limited data on cortisol suggest a deficiency of production in JRA, a situation similar to that in adult RA. These findings suggest that there is a proinflammatory hormonal bias in children with JRA and JSLE. The data in children with chronic autoimmune inflammatory disorders seem to be identical to those seen in adults with RA and SLE, but a clear delineation of the role of the neuroendocrine-immune system in disease pathophysiology is still required. The neuroendocrine aspects of pediatric rheumatologic disease observed to date suggest a number of avenues for further research in the field of neuroendocrine immunology, which may open up novel therapeutic options.

Sex of affected sibpairs and genetic linkage to type 1 diabetes

A mouse model of diabetes shows gender dimorphism in the cumulative incidence of diabetes. Based on this, evidence for genetic linkage to IDDM13 on chromosome arm 2q was reported to be greater in type 1 diabetes families where there was a predominance of affected female offspring compared with families with a predominance of affected male offspring. Our objective was to investigate whether the sex of affected offspring affects evidence for linkage to susceptibility loci. Data from a genome scan of 356 affected sibpair families with type 1 diabetes were analysed to determine if there is differential evidence for linkage in families with affected children of a particular sex. At markers on chromosomes 3, 5, 7, 9, 11, and 19, we found a number of regions where the evidence for linkage is greater in families with affected sibpairs of a particular sex. Thus, evidence for linkage in families with affected sibpairs of the same gender suggests the presence of additional susceptibility loci. Several biological explanations are possible for these findings, including X and Y linkage, effects of sex hormones on gene expression, and quasi-linkage between sex chromosomes and autosomes.

Early neonatal events and the disease incidence in nonobese diabetic mice

Epidemiologic studies have shown that perinatal events are associated with an increased risk for type 1 (insulin-dependent) diabetes in childhood. We used nonobese diabetic mice to examine whether neonatal separation from the mother with or without phototherapy would affect the incidence of diabetes in this genetically susceptible mouse model. The newborn pups were taken from their mothers for two 4-h periods during each of five successive days. One group of animals was just taken from their mothers and were left lying in daylight in the cage, whereas another group was exposed to identical light as used for treatment of neonatal jaundice in infants. Treatment resulted in a 30% death rate. For animals surviving more than 3 mo the incidence of diabetes was significantly higher in both treatment groups compared with control animals, allowed to stay with their mother. The odds ratio for treatment versus control, stratifying for sex, was 3.42 (95% confidence interval, 1.57-7.74). Histologic insulitis did not differ between treated and untreated animals when examined either at clinical diabetes onset or at 8 mo of age. Blood glucose values at 8 mo of age (in animals without clinical diabetes) did not differ between-treated and untreated animals. It is concluded that neonatal separation of the nonobese diabetic mice from their mothers will lead to a significantly increased risk for diabetes. This increase in risk seems to be associated with the induction of metabolic alterations leading to increased peripheral insulin need rather than with an increased rate of beta cell destruction.

Autoimmunity and the highway to diabetes

Insulin-dependent diabetes mellitus (IDDM) is an immunopathological condition involving loss of beta cell function, but views of how this arises are confusing and contradictory. For example, studies with non-obese diabetic mice implicate abnormal cytokine production in disease pathogenesis, but give little insight into how this arises. Many genetic and environmental risk factors have been described, but no single factor predicts the development of disease. Moreover, the prevalence of auto-antibodies suggests an autoimmune aetiology, but no antigen is recognized by all individuals. As an aid to understanding how IDDM develops, this review considers the risk factors as distinct starting points on a journey, and reviews current literature in search of the point where the roads from each origin merge into a highway to diabetes.

The lymphocyte and macrophage profile in the pancreas and spleen of NOD mice: percentage of interleukin-2 and prolactin receptors on immunocompetent cell subsets

The NOD mouse is a model for autoimmune diabetes that develops symptoms similar to Type I diabetes. The incidence of diabetes is greater in females but the degree of insulitis is comparable in both sexes. The purpose of this study was to assess the populations of lymphocytes and macrophages in the pancreas and spleen of NOD mice. Comparisons were made between male and female; young (32-40 days old) and old (197-297 days old); diabetic and non-diabetic mice. Using analytical fluorescent cell cytometry we quantitated the percentages of CD4, and CD8 T-cells, B-cells and macrophages and the percentages of these subsets expressing interleukin-2 (IL-2R), prolactin (PRLR) and Hi-intensity PRL (Hi-PRLR) receptors. Evaluation of T-splenocytes indicated a 2:1 ratio of CD4 to CD8 T-lymphocytes in the spleen. The pancreas had higher percentages of all of the subsets in the old male and female groups compared to their young counterparts. Pancreatic immunocompetent cell subsets expressed lower percentages of IL-2R, PRLR and Hi-PRLR compared to splenocytes. The results did not demonstrate any dramatic differences in the immunocompetent cell populations of the spleen or pancreas between male and female animals, however we were able to establish the percentage of immunocompetent cells with IL-2R, PRLR and Hi-PRLR as a reference for future studies.

Neuroendocrine immune responses to inflammation: the concept of the neuroendocrine immune loop

The neuroendocrine and immune responses to inflammatory stress represents an integrated circuit whose basis is reviewed in this chapter. Pro-inflammatory cytokines such as IL-1 beta, TNF-alpha and IL-6 released from inflammatory foci initiate local anti-inflammatory mechanisms and travel via the blood stream to the brain where they trigger a variety of neuroendocrine counter-regulatory mechanisms. There is therefore an important neuroendocrine-immune loop in which stimulatory signals are received by the neural systems from inflammatory foci. These signals are transduced by the hypothalamus which initiates a complex hormonal cascade reaction aimed at modulating inflammation and returning the organism to normal physiological homeostasis once the trigger has been neutralized. Abnormalities in this cross-talk can profoundly influence the susceptibility to developing chronic inflammatory disease. Thus, in conclusion, the neuroendocrine-immune loop has important pathophysiological implications for disease processes.

The neuroendocrine immunology of rheumatoid arthritis

Rheumatoid arthritis patients have defective neuroendocrine-immune responses to the stress of inflammation, and currently available data shows that this contributes to the pathophysiology of the disease. The advances in neuroendocrine immunology have improved our understanding of the pathophysiological mechanisms involved in RA. These observations raise important therapeutic questions which are certainly worth further investigation as they may open up novel avenues for the management of the disease.

Contribution of stress and gender to exploratory preferences for familiar versus unfamiliar conspecifics

An apparatus for measuring the exploratory preferences of rats for familiar and unfamiliar conspecifics in a novel environment was designed. The exploratory behavior of males and females was compared and contrasted to that elicited in response to an acute aversive event. Sprague-Dawley male and female rats were exposed to restraint and 60, 1 s, 1 mA tailshocks and returned to their home cage. Either 2 or 24 h later, they were placed in a novel environment with a familiar cage-mate and an unfamiliar conspecific of the same sex. Relative to unstressed controls and females, males stressed 2 h previously decreased the exploration of the unfamiliar conspecific, exhibiting a rapid decrease over the course of the trial. In response to the stressor, however both sexes, however, decreased the exploration of the familiar conspecific, decreased their overall activity, and returned preferentially to their starting quadrant. None of these stress-induced effects were evident 24 h later upon the first or second exposure to the apparatus. Thus, exposure to the stressor transiently increased perseveration and decreased activity in males and females, but only decreased the exploration of novel conspecifics in males. These results indicate that a number of behavioral responses to stressors are conserved across gender, but those relating to novelty are more pronounced in males.

Free fatty acid profiles in the non-obese diabetic (NOD) mouse: basal serum levels and effects of endocrine manipulation

The non-obese diabetic mouse (NOD) is one of the few available models of spontaneous autoimmune insulin-dependent diabetes mellitus (IDDM). The authors determined the free fatty acid (FFA) levels and the concentrations and relative percentages of the various classes of FFA before the onset of diabetes in both sexes at 2 and 4 months of age and in diabetic females. A circadian rhythm of FFA concentrations was found in prediabetic mice, with lower values in the evening. Moreover, there was a sex difference in FFA concentrations in the morning, with 2-month-old females having higher concentrations than males. Sex and age-related differences were also observed in the concentrations of the various classes of FFA, with higher polyunsaturated fatty acid concentrations in 2-month-old females and increases in di- and tri-unsaturated fatty acids concentrations in both sexes with age. Hormonal manipulation such as adrenalectomy and/or castration modulated total FFA and the concentrations of the various classes of FFA in 2-month-old mice. These FFA differences between males and females should be taken into account in the onset of type I diabetes.

Glucose, insulin, and open field responses to immobilization in nonobese diabetic (NOD) mice

Numerous studies have suggested that stress precipitates type I diabetes. Because stress-elicited hyperglycemia may play a role in this effect, we measured the influence of acute immobilization (90 min) upon plasma glucose and insulin levels in nonobese diabetic (NOD) mice, a spontaneous model of type I diabetes. To this end, prediabetic 8-week-old mice of both sexes were compared to age- and sex-matched C57BL/6 control mice. Baseline plasma glucose levels and immobilization-elicited hyperglycemia were both lower in male and female NOD mice compared to their C57BL/6 counterparts. However, the maximal effects of immobilization upon plasma insulin (and corticosterone) levels were not different between NOD and C57BL/6 mice. When subjected to a metabolic stressor, such as 2-deoxyglucose-induced neuroglucopenia, both strains responded with similar increases in plasma glucose levels. This change was associated with hyperinsulinemia, whose amplitude was lower in NOD than in C57BL/6 females. Lastly, administration of the alpha 2-adrenergic agonist, clonidine, elicited a marked increase in plasma glucose levels, whose amplitude was independent of the strain. The results from this study indicate that the two strains differed in their glycemic response to a psychological, but not to a metabolic, stressor. Because NOD mice were found to exhibit increased locomotion when placed for the first time in an open field, it is suggested that behavioral differences contribute to this differential effect of immobilization upon circulating glucose levels in NOD and C57BL/6 mice.