Corticosterone release is heightened in food or water deprived oxytocin deficient male mice

Refinements to rodent head fixation and fluid/food control for neuroscience

The use of head fixation in mice is increasingly common in research, its use having initially been restricted to the field of sensory neuroscience. Head restraint has often been combined with fluid control, rather than food restriction, to motivate behaviour, but this too is now in use for both restrained and non-restrained animals. Despite this, there is little guidance on how best to employ these techniques to optimise both scientific outcomes and animal welfare. This article summarises current practices and provides recommendations to improve animal wellbeing and data quality, based on a survey of the community, literature reviews, and the expert opinion and practical experience of an international working group convened by the UK's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). Topics covered include head fixation surgery and post-operative care, habituation to restraint, and the use of fluid/food control to motivate performance. We also discuss some recent developments that may offer alternative ways to collect data from large numbers of behavioural trials without the need for restraint. The aim is to provide support for researchers at all levels, animal care staff, and ethics committees to refine procedures and practices in line with the refinement principle of the 3Rs.

Androgens and Their Role in Regulating Sex Differences in the Hypothalamic/Pituitary/Adrenal Axis Stress Response and Stress-Related Behaviors

Androgens play a pivotal role during development. These gonadal hormones and their receptors exert organizational actions that shape brain morphology in regions controlling the stress regulatory systems in a male-specific manner. Specifically, androgens drive sex differences in the hypothalamic/pituitary/adrenal (HPA) axis and corresponding hypothalamic neuropeptides. While studies have examined the role of estradiol and its receptors in sex differences in the HPA axis and associated behaviors, the role of androgens remains far less studied. Androgens are generally thought to modulate the HPA axis through the activation of androgen receptors (ARs). They can also impact the HPA axis through reduction to estrogenic metabolites that can bind estrogen receptors in the brain and periphery. Such regulation of the HPA axis stress response by androgens can often result in sex-biased risk factors for stress-related disorders, such as anxiety and depression. This review focuses on the biosynthesis pathways and molecular actions of androgens and their nuclear receptors. The impact of androgens on hypothalamic neuropeptide systems (corticotropin-releasing hormone, arginine vasopressin, oxytocin, dopamine, and serotonin) that control the stress response and stress-related disorders is discussed. Finally, this review discusses potential therapeutics involving androgens (androgen replacement therapies, selective AR modulator therapies) and ongoing clinical trials.

Establishment of a biomarker of peripheral stress in opioid addicts based on the hypothalamic-pituitary-adrenal axis-The improvement effect of exercise

PURPOSE

This study aims to investigate the relationship between peripheral blood oxytocin (OT), vasopressin (AVP), and subjectively perceived stress and cortisol in male opioid addicts based on the hypothalamic-pituitary-adrenal (HPA) axis. We also investigate the impact of exercise on reducing subjectively perceived stress, craving level, negative reinforcement, anxiety, sleep quality, plasma OT, AVP, and cortisol levels.

METHODS

Participants were divided into 28 subjects in the low-stress control group (LSC group), 29 subjects in the medium-high stress control group (MTHSC group), and 28 subjects in the moderate-high-stress exercise group (MTHSE group), based on their subjectively perceived stress levels. Subjects in the MTHSE group performed 12 weeks of combined aerobic resistance training (60 min per day, 5 days per week). Plasma OT, AVP, and cortisol concentrations were analyzed via Elisa. PSQI was used to assess the subjective perceived stress, craving, negative reinforcement, anxiety, and sleep quality level, respectively. Mixed-effects ANOVA and Pearson correlation analysis were employed to explore the impact and correlation between different parameters.

RESULT

Plasma OT levels significantly increased (95% CI: -7.48, -2.26), while plasma AVP (95% CI: 2.90, 4.10), and cortisol (95% CI: 19.76, 28.17) levels significantly decreased in the MTHSE group after exercise. The PSS (95% CI: 1.756, 4.815), "Desire and Intention" (95% CI: 1.60, 2.71), and "Negative reinforcement" (95% CI: 0.85, 1.90) (DDQ), SAS (95% CI: 17.51, 26.06), and PSQI (95% CI: 1.18, 3.25) scores of the MTHSE group were significantly decreased after exercise. Plasma OT, plasma cortisol, craving, negative reinforcement and anxiety were negatively correlated. Plasma AVP was positively correlated with craving.

CONCLUSION

As an auxiliary treatment, exercise improves the plasma OT, AVP, and cortisol levels of opioid addicts, and reduces their subjective perceived stress level, desire, negative reinforcement level, anxiety level, and sleep quality. In addition, peripheral plasma OT, AVP, and cortisol may play a role as potential peripheral biomarkers to predict stress in male opioid addicts.

Roles for androgens in mediating the sex differences of neuroendocrine and behavioral stress responses

Estradiol and testosterone are powerful steroid hormones that impact brain function in numerous ways. During development, these hormones can act to program the adult brain in a male or female direction. During adulthood, gonadal steroid hormones can activate or inhibit brain regions to modulate adult functions. Sex differences in behavioral and neuroendocrine (i.e., hypothalamic pituitary adrenal (HPA) axis) responses to stress arise as a result of these organizational and activational actions. The sex differences that are present in the HPA and behavioral responses to stress are particularly important considering their role in maintaining homeostasis. Furthermore, dysregulation of these systems can underlie the sex biases in risk for complex, stress-related diseases that are found in humans. Although many studies have explored the role of estrogen and estrogen receptors in mediating sex differences in stress-related behaviors and HPA function, much less consideration has been given to the role of androgens. While circulating androgens can act by binding and activating androgen receptors, they can also act by metabolism to estrogenic molecules to impact estrogen signaling in the brain and periphery. This review focuses on androgens as an important hormone for modulating the HPA axis and behaviors throughout life and for setting up sex differences in key stress regulatory systems that could impact risk for disease in adulthood. In particular, impacts of androgens on neuropeptide systems known to play key roles in HPA and behavioral responses to stress (corticotropin-releasing factor, vasopressin, and oxytocin) are discussed. A greater knowledge of androgen action in the brain is key to understanding the neurobiology of stress in both sexes.

Additive antidepressant-like effects of fasting with β-estradiol in mice

Our recent study has shown that acute fasting produces antidepressant‐like effects in male mice. However, there is little evidence regarding the antidepressant‐like effects of acute fasting in female mice. Moreover, it is not yet clear whether estrogen produces additive effects with acute fasting. Therefore, this study aims to investigate the antidepressant‐like effects of acute fasting plus estrogen treatment. In this study, the acute fasting produced antidepressant‐like effects in female mice and the antidepressant‐like effects of 9 hours fasting with those of β‐estradiol (E2) were additive. Activity of the cyclic adenosine monophosphate (cAMP) response element‐binding protein (CREB)‐brain‐derived neurotrophic factor (BDNF) pathway in the prefrontal cortex (PFC) and hippocampus (HP) was increased, as well as neurogenesis in the subgranular zone of the hippocampus. Serum ghrelin and estrogen were also increased by fasting plus E2. Furthermore, RNA‐seq analysis indicated that fasting and E2 co‐regulate similar gene expression pathways, underlying similar neurological functions. Taken together, these data suggest that E2 produces additive antidepressant‐like effects with fasting by activating the CREB‐BDNF pathway in the PFC and HP. Genome‐wide transcriptome mapping suggests that fasting may be used as an adjunct to estrogen replacement therapy for the treatment of depression associated with reduced estrogen function.

Oxytocin and Rodent Models of Addiction

Interest for the use of oxytocin as a treatment for addiction began over 40years ago. Better known for its roles in parturition, lactation and pair bonding, oxytocin also has anxiolytic properties, reduces immune and inflammatory responses, and has a role in learning and memory. In this chapter, oxytocin effects on addiction processes are described by highlighting research findings that have used oxytocin within current preclinical animal models of addiction, relapse, or craving. First, we provide a brief background of the endogenous oxytocin system followed by descriptions of the behavioral models used to study addiction, including models of drug taking and seeking. Then we review recent preclinical studies that have used oxytocin as a therapeutic intervention throughout multiple stages of the addiction cycle from a behavioral and neurobiological perspective. These models encompass the entire range of the addiction cycle including acquisition and maintenance of drug taking, withdrawal and craving during periods of drug abstinence, and ultimately relapse. We then posit several theories about how oxytocin interacts with both drug and social reward, as well as presenting a mechanistic account of how specific oxytocin receptor localization may contribute to oxytocin's efficacy as an addiction therapeutic.

DUAL ACTION OF ARECOLINE ON ADRENAL FUNCTION AND GLUCOSE-GLYCOGEN HOMEOSTASIS IN METABOLIC STRESS IN MICE

Background

People chew betel nut (Areca catechu) for physical work and stress reduction, but it contains arecoline, which has both therapeutic value and untoward effects on endocrine and gonadal functions.

Objective

Aim of the present study is to investigate its role on adrenal with its target in metabolic stress in mice.

Materials and methods

Mice were deprived of water / food, each for 5 days / treated with arecoline (10 mg / kg body wt daily for 5 days) / arecoline after water or food deprivation, for 5 days each.

Results

Water or food-deprivation caused adrenocortical hyperactivity, evident from abundance of enlarged mitochondria and smooth endoplasmic reticulum (SER) with elevation of corticosterone level (C: 68.31 ± 2.30, WD: 159.31 ± 4.10 / FD: 194.12 ± 3.40 μg/ mL). Arecoline treatment alone or in water deprivation (C: 68.31 ± 2.30, AR: 144.50 ± 4.33, AR+WD: 194.42 ± 3.35 μg/ mL) / food deprivation (AR + FD: 180.89 ± 4.51 μg/ mL) stress also stimulated adrenocortical activity as recorded in metabolic stress. In contrast, adrenomedullary activity was not altered following water/ food deprivation. Arecoline treatment alone or in metabolic stress suppressed adrenomedullary activity by showing depletion of chromaffin granules (E/NE?), epinephrine (E) and norepinephrine (NE) concentrations. Both the stress decreased blood glucose and liver glycogen levels. Arecoline treatment decreased blood glucose level, with a rise in liver glycogen level, but elevated blood glucose level in water deprivation unlike in starvation.

Conclusion

Arecoline alone or in metabolic stress involves adrenal and probably other endocrine glands (pancreas, posterior pituitary and rennin-angiotensin system) to maintain homeostasis in metabolic stress in mice.

Autism-Like Behaviours and Memory Deficits Result from a Western Diet in Mice

Nonalcoholic fatty liver disease, induced by a Western diet (WD), evokes central and peripheral inflammation that is accompanied by altered emotionality. These changes can be associated with abnormalities in social behaviour, hippocampus-dependent cognitive functions, and metabolism. Female C57BL/6J mice were fed with a regular chow or with a WD containing 0.2% of cholesterol and 21% of saturated fat for three weeks. WD-treated mice exhibited increased social avoidance, crawl-over and digging behaviours, decreased body-body contacts, and hyperlocomotion. The WD-fed group also displayed deficits in hippocampal-dependent performance such as contextual memory in a fear conditioning and pellet displacement paradigms. A reduction in glucose tolerance and elevated levels of serum cholesterol and leptin were also associated with the WD. The peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1a) mRNA, a marker of mitochondrial activity, was decreased in the prefrontal cortex, hippocampus, hypothalamus, and dorsal raphe, suggesting suppressed brain mitochondrial functions, but not in the liver. This is the first report to show that a WD can profoundly suppress social interactions and induce dominant-like behaviours in naïve adult mice. The spectrum of behaviours that were found to be induced are reminiscent of symptoms associated with autism, and, if paralleled in humans, suggest that a WD might exacerbate autism spectrum disorder.

The selective dopamine D₃ receptor antagonist SB-277011A attenuates drug- or food-deprivation reactivation of expression of conditioned place preference for cocaine in male Sprague-Dawley rats

We determined the effect of the selective dopamine D3 receptor antagonist SB-277011A on reactivation of conditioned place preference (CPP) to cocaine elicited by priming injections of cocaine or exposure to food deprivation stress (21 h) in male Sprague-Dawley rats. Animals paired with the cocaine-associated chamber displayed a robust and consistent CPP response. This CPP was extinguished after repeated pairings of the conditioned stimuli (cocaine-paired chamber contextual cues) in the absence of the unconditioned stimulus (cocaine). Twenty-four hours later, the administration of 5 mg kg(-1) i.p. of cocaine (immediately before the test) or exposure to 21 h of food deprivation reactivated the expression of the cocaine-induced CPP. In contrast, administration of 1 ml kg(-1) i.p. of vehicle did not reactivate the CPP response. Administration of the selective dopamine D3 receptor antagonist SB-277011A (3-24 mg kg(-1) i.p.) 30 min before cocaine administration on the test day produced a significant attenuation of CPP reactivation. Reactivation of the CPP response produced by food deprivation was also significantly attenuated by SB-277011A (6 or 12 mg kg(-1) i.p.) given 30 min before the test session. SB-277011A (12 or 24 mg kg(-1) i.p.) did not itself produce reactivation of the CPP response. Overall, these results suggest that the reactivation of the incentive value of drug-associated cues by cocaine or food deprivation is attenuated by selective antagonism of D3 receptors.

Synergistic effects of diet and exercise on hippocampal function in chronically stressed mice

Severe chronic stress can have a profoundly negative impact on the brain, affecting plasticity, neurogenesis, memory and mood. On the other hand, there are factors that upregulate neurogenesis, which include dietary antioxidants and physical activity. These factors are associated with biochemical processes that are also altered in age-related cognitive decline and dementia, such as neurotrophin expression, oxidative stress and inflammation. We exposed mice to an unpredictable series of stressors or left them undisturbed (controls). Subsets of stressed and control mice were concurrently given (1) no additional treatment, (2) a complex dietary supplement (CDS) designed to ameliorate inflammation, oxidative stress, mitochondrial dysfunction, insulin resistance and membrane integrity, (3) a running wheel in each of their home cages that permitted them to exercise, or (4) both the CDS and the running wheel for exercise. Four weeks of unpredictable stress reduced the animals' preference for saccharin, increased their adrenal weights and abolished the exercise-induced upregulation of neurogenesis that was observed in non-stressed animals. Unexpectedly, stress did not reduce hippocampal size, brain-derived neurotrophic factor (BDNF), or neurogenesis. The combination of dietary supplementation and exercise had multiple beneficial effects, as reflected in the number of doublecortin (DCX)-positive immature neurons in the dentate gyrus (DG), the sectional area of the DG and hippocampal CA1, as well as increased hippocampal BDNF messenger ribonucleic acid (mRNA) and serum vascular endothelial growth factor (VEGF) levels. In contrast, these benefits were not observed in chronically stressed animals exposed to either dietary supplementation or exercise alone. These findings could have important clinical implications for those suffering from chronic stress-related disorders such as major depression.

Mouse handling limits the impact of stress on metabolic endpoints

Studies focused on end-points that are confounded by stress are best performed under minimally stressful conditions. The objective of this study was to demonstrate the impact of handling designed to reduce animal stress on measurements of glucose tolerance. A cohort of mice (CD1.C57BL/6) naïve to any specific handling was subjected to either a previously described "cup" handling method, or a "tail-picked" method in which the animals were picked up by the tail (as is common for metabolic studies). Following training, an elevated plus maze (EPM) test was performed followed by measurement of blood glucose and plasma corticosterone. A second cohort (CD1.C57BL/6) was rendered obese by exposure to a high fat diet, handled with either the tail-picked or cup method and subjected to an intraperitoneal glucose tolerance test. A third cohort of C57BL/6 mice was exposed to a cup regimen that included a component of massage and was subjected to tests of anxiety-like behavior, glucose homeostasis, and corticosterone secretion. We found that the cup mice showed reduced anxiety-like behaviors in the EPM coupled with a reduction in blood glucose levels compared to mice handled by the tail-picked method. Additionally, cup mice on the high fat diet exhibited improved glucose tolerance compared to tail-picked controls. Finally, we found that the cup/massage group showed lower glucose levels following an overnight fast, and decreased anxiety-like behaviors associated with lower stress-induced plasma corticosterone concentration compared to tail-picked controls. These data demonstrate that application of handling methods that reduce anxiety-like behaviors in mice mitigates the confounding contribution of stress to interpretation of metabolic endpoints (such as glucose tolerance).

Acute hypernatremia exerts an inhibitory oxytocinergic tone that is associated with anxiolytic mood in male rats

Anxiety disorders are the most common psychiatric illnesses and are associated with heightened stress responsiveness. The neuropeptide oxytocin (OT) has garnered significant attention for its potential as a treatment for anxiety disorders; however, the mechanism mediating its effects on stress responses and anxiety is not well understood. Here we used acute hypernatremia, a stimulus that elevates brain levels of OT, to discern the central oxytocinergic pathways mediating stress responsiveness and anxiety-like behavior. Rats were rendered hypernatremic by acute administration of 2.0 M NaCl and had increased plasma sodium concentration, plasma osmolality, and Fos induction in OT-containing neurons relative to 0.15 M NaCl-treated controls. Acute hypernatremia decreased restraint-induced elevations in corticosterone and created an inhibitory oxytocinergic tone on parvocellular neurosecretory neurons within the paraventricular nucleus of the hypothalamus. In contrast, evaluation of Fos immunohistochemistry determined that acute hypernatremia followed by restraint increased neuronal activation in brain regions receiving OT afferents that are also implicated in the expression of anxiety-like behavior. To determine whether these effects were predictive of altered anxiety-like behavior, rats were subjected to acute hypernatremia and then tested in the elevated plus maze. Relative to controls given 0.15 M NaCl, rats given 2.0 M NaCl spent more time in the open arms of the elevated plus maze, suggesting that acute hypernatremia is anxiolytic. Collectively the results suggest that acute elevations in plasma sodium concentration increase central levels of OT, which decreases anxiety by altering neuronal activity in hypothalamic and limbic nuclei.

Time-dependent effects of corticosterone on reward-based decision-making in a rodent model of the Iowa Gambling Task

Corticosteroid hormones, released after stress, are known to change neuronal activity in two time-domains: within minutes via non-genomic pathways and with a delay of >1 h through pathways involving transcriptional regulation. Recent evidence in rodents and humans indicates that these two modes of corticosteroid action differently affect cognitive tasks. Here, we investigated whether reward-based decision-making, in a rat model of the Iowa Gambling Task (rIGT), is also differently altered by rapid versus delayed actions of corticosterone. We targeted the rapid and delayed time domain by injecting corticosterone (CORT, 1 mg/kg, s.c.) at 30 min (rapid) or 180 min (delayed) respectively prior to behavioural testing, during the final 3 days of the behavioural paradigm. In saline treated rats, the number of visits to the disadvantageous arm decreased over trial blocks, whilst this was attenuated when CORT was administered 30 min before testing. This attenuation was associated with a significantly increased c-Fos expression in the lateral orbitofrontal cortex and insular cortex, and a trend for an increase in the infralimbic cortex. The rapid corticosteroid effect contrasted with treatment 180 min before testing, where the number of visits to the disadvantageous arm as well as c-Fos labelling was not affected. These findings indicate that rapid corticosteroid actions impair reward-based decision-making.

Neonatal tactile stimulation alleviates the negative effects of neonatal isolation on novel object recognition, sociability and neuroendocrine levels in male adult mandarin voles (Microtus mandarinus)

Neonatal isolation results in long-lasting negative alterations to the brain and behavior. Some of these changes include effects on non-spatial learning and memory, sociability and neuroendocrine levels. Theoretically, neonatal tactile stimulation should reverse the impacts of neonatal isolation; however, this remains unknown for changes relating to learning, memory, sociability and hormones in social animals. Using socially monogamous mandarin voles (Microtus mandarinus), the long-lasting effects of these early manipulations on anxiety-like behavior, novel object recognition, sociability, and neuroendocrine levels were investigated. Compared with neonatal-isolated males, males subjected to the same manipulation but accompanied with tactile stimulation had heavier body weights across PND4-18 and displayed significantly less anxiety-like behavior in an open field test. In addition, tactile stimulation increased the preference index for novel object recognition reduced by neonatal isolation. Compared with control males, neonatal-isolated males engaged in less body contact with unfamiliar same-sex individuals and this effect was reversed by neonatal tactile stimulation. Tactile stimulation enhanced aggressive behavior in neonatal-isolated males and increased the levels of AVP and OT in the paraventricular nucleus (PVN) which were decreased by neonatal isolation. This early manipulation also reduced serum CORT levels that were significantly up-regulated by neonatal isolation in both neonatal and adult offspring. These results indicate that adequate tactile stimulation in early life plays an important role in the prevention of behavioral disturbances induced by neonatal isolation, possibly through the alteration of central OT, AVP and the serum corticosterone levels.

FXR agonist GW4064 increases plasma glucocorticoid levels in C57BL/6 mice

Since high expression of farnesoid X receptor (FXR) has been detected in glucocorticoid-producing adrenocortical cells, we evaluated the potential role of FXR in adrenal glucocorticoid production. FXR agonist GW4064 increased fasting plasma corticosterone levels (+45%; P<0.01) in C57BL/6 mice, indicative of enhanced adrenal steroidogenesis. GW4064 treatment did not affect plasma ACTH levels, adrenal weight, or adrenal expression of steroidogenic genes. Scavenger receptor BI (SR-BI) mRNA and protein expression, respectively, increased 1.9-fold (P<0.01) and 1.5-fold, which suggests a stimulated lipoprotein-associated cholesterol uptake into the adrenals upon GW4064 treatment. In line with an enhanced flux of cellular cholesterol into the steroidogenic pathway, adrenal unesterified and esterified cholesterol stores were 21-41% decreased (P<0.01) upon GW4064 treatment. In conclusion, we have shown that the FXR agonist GW4064 stimulates plasma corticosterone levels in C57BL/6 mice. Our findings suggest a novel role for FXR in the modulation of adrenal cholesterol metabolism and glucocorticoid synthesis in mice.

Negative correlation between cerebrospinal fluid oxytocin levels and negative symptoms of male patients with schizophrenia

BACKGROUND

Accumulating evidence indicates that oxytocin plays an important role in social interactions. Previous studies also suggest altered oxytocin function in patients with schizophrenia and depression. However, few studies have examined the central oxytocin levels in these disorders.

METHODS

Cerebrospinal fluid (CSF) oxytocin levels were measured by ELISA in male participants consisting of 27 patients with schizophrenia, 17 with major depressive disorder (MDD), and 21 healthy controls.

RESULTS

CSF oxytocin levels of patients with schizophrenia or MDD did not differ significantly with healthy controls. The antidepressant dose or the Hamilton depression rating scale score did not significantly correlate with the oxytocin levels in MDD patients. CSF oxytocin levels in schizophrenic patients significantly negatively correlated with second generation antipsychotic dose (r=-0.49, P=0.010) but not with first generation antipsychotic dose (r=-0.13, P=0.50). A significant correlation was observed between oxytocin levels and negative subscale of PANSS (r=-0.38, P=0.050). This correlation remained significant even after controlling for second generation antipsychotic dose (r=-0.47, P=0.016).

CONCLUSIONS

We obtained no evidence of altered CSF oxytocin levels in patients with schizophrenia or those with MDD. However, lower oxytocin levels may be related to higher second generation antipsychotic dose and more severe negative symptoms in schizophrenia.

Neuroanatomical evidence for reciprocal regulation of the corticotrophin-releasing factor and oxytocin systems in the hypothalamus and the bed nucleus of the stria terminalis of the rat: Implications for balancing stress and affect

Activation of corticotrophin releasing factor (CRF) neurons in the paraventricular nucleus of the hypothalamus (PVN) is necessary for establishing the classic endocrine response to stress, while activation of forebrain CRF neurons mediates affective components of the stress response. Previous studies have reported that mRNA for CRF2 receptor (CRFR2) is expressed in the bed nucleus of the stria terminalis (BNST) as well as hypothalamic nuclei, but little is known about the localization and cellular distribution of CRFR2 in these regions. Using immunofluorescence with confocal microscopy, as well as electron microscopy, we demonstrate that in the BNST CRFR2-immunoreactive fibers represent moderate to strong labeling on axons terminals. Dual-immunofluorescence demonstrated that CRFR2-fibers co-localize oxytocin (OT), but not arginine-vasopressin (AVP), and make perisomatic contacts with CRF neurons. Dual-immunofluorescence and single cell RT-PCR demonstrate that in the hypothalamus, CRFR2 immunoreactivity and mRNA are found in OT, but not in CRF or AVP-neurons. Furthermore, CRF neurons of the PVN and BNST express mRNA for the oxytocin receptor, while the majority of OT/CRFR2 neurons in the hypothalamus do not. Finally, using adenoviral-based anterograde tracing of PVN neurons, we show that OT/CRFR2-immunoreactive fibers observed in the BNST originate in the PVN. Our results strongly suggest that CRFR2 located on oxytocinergic neurons and axon terminals might regulate the release of this neuropeptide and hence might be a crucial part of potential feedback loop between the hypothalamic oxytocin system and the forebrain CRF system that could significantly impact affective and social behaviors, in particular during times of stress.

Sustained delayed gastric emptying during repeated restraint stress in oxytocin knockout mice

We have recently shown that impaired gastric motility observed in acute restraint stress was restored following repeated restraint stress in mice. Repeated restraint stress up-regulates oxytocin mRNA expression and down-regulates corticotrophin-releasing factor (CRF) mRNA expression at the hypothalamus. Oxytocin knockout mice (OXT-KO) have been widely used to study the central oxytocin signalling pathways in response to various stressors. We studied the effects of acute and repeated restraint stress on solid gastric emptying and hypothalamic CRF mRNA expression in wild-type (WT) and OXT-KO mice. Heterozygous (HZ) parents (B6; 129S-Oxt(tm1Wsy)/J mice) were bred in our animal facility. Male OXT-KO, WT and HZ littermates were used for the study. Solid gastric emptying was measured following acute restraint stress (for 90 min) or repeated restraint stress (for five consecutive days). Expression of CRF mRNA in the paraventricular nucleus (PVN) was measured by real-time reverse transcriptase-polymerase chain reaction. There were no significant differences of gastric emptying in WT (68.4 ± 4.1%, n = 6), HZ (71.8 ± 3.1%, n = 6) and OXT-KO (70.6 ± 3.1%, n = 6) mice in nonstressed conditions. Acute stress significantly delayed gastric emptying in OXT-KO mice (33.10 ± 2.5%, n = 6) WT (39.1 ± 1.1%, n = 6) and HZ mice (35.8 ± 1.2%, n = 6). Following repeated restraint stress loading, gastric emptying was significantly restored in WT (68.3 ± 4.5%, n = 6) and HZ mice (63.1 ± 2.6%, n = 6). By contrast, gastric emptying was still delayed in OXT-KO mice (34.7 ± 1.3%, n = 6) following repeated restraint stress. The increase in CRF mRNA expression at the PVN was much pronounced in OXT-KO mice compared to WT or HZ mice following repeated restraint stress. These findings suggest that central oxytocin plays a pivotal role in mediating the adaptation mechanism following repeated restraint stress in mice.

Effects of chronic and intermittent cocaine treatment on dominance, aggression, and oxytocin levels in post-lactational rats

RATIONALE

Little is known about mechanisms underlying female rodent aggression during the late postpartum period with no pups present. Studies of aggression, dominance, and oxytocin (OT) response in cocaine-treated females are sparse.

OBJECTIVES

This study was designed to examine dominance (drinking success) and aggression in a limited-access drinking model of water competition. Acute OT level measures were made on postpartum day (PPD) 36 in several brain regions of interest. Chronic and intermittent cocaine- and saline-treated and untreated rats 10 days post-weaning were tested (without pups) over PPDs 31-35 following cessation of cocaine treatment 10-30 days before testing.

METHODS

Subjects were water-deprived overnight, and triads consisting of an untreated control (UN), a chronic continuous saline-treated (CS), and chronic continuous cocaine-treated (CC; 30 mg/kg/day throughout gestation) or a UN, an intermittent saline-treated (IS), and an intermittent cocaine-treated (IC; 30 mg/kg two consecutive days every 4 days throughout gestation until PPD 20) female were tested for aggression and drinking behavior during 5 min sessions on five consecutive days. The amygdala, medial preoptic area (MPOA), and ventral tegmental area were assayed for OT levels.

RESULTS

CC and IC females were more aggressive than controls, but only IC females drank more often than controls. OT levels were lower in the MPOA of IC and CC females than in controls.

CONCLUSIONS

Findings demonstrate that long after cessation of treatment, CC- and IC-treated non-lactating females (no pups present) had higher rates of aggression, altered drinking behavior, and acutely lower MPOA OT levels.

Corticosterone release in oxytocin gene deletion mice following exposure to psychogenic versus non-psychogenic stress

Both anxiety-related behavior [J.A. Amico, R.C. Mantella, R.R. Vollmer, X. Li, Anxiety and stress responses in female oxytocin deficient mice, J. Neuroendocrinol. 16 (2004) 1-6; R.C. Mantella, R.R. Vollmer, X. Li, J.A. Amico, Female oxytocin-deficient mice display enhanced anxiety-related behavior, Endocrinology 144 (2003) 2291-2296] and the release of corticosterone following a psychogenic stress such as exposure to platform shaker was greater in female [J.A. Amico, R.C. Mantella, R.R. Vollmer, X. Li, Anxiety and stress responses in female oxytocin deficient mice, J. Neuroendocrinol. 16 (2004) 1-6; R.C. Mantella, R.R. Vollmer, L. Rinaman, X. Li, J.A. Amico, Enhanced corticosterone concentrations and attenuated Fos expression in the medial amygdala of female oxytocin knockout mice exposed to psychogenic stress, Am. J. Physiol. Regul. Integr. Comp. Physiol. 287 (2004) R1494-R1504], but not male [R.C. Mantella, R.R. Vollmer, J.A. Amico, Corticosterone release is heightened in food or water deprived oxytocin deficient male mice, Brain Res. 1058 (2005) 56-61], oxytocin gene deletion (OTKO) mice compared to wild type (WT) cohorts. In the present study we exposed OTKO and WT female mice to another psychogenic stress, inserting a rectal probe to record body temperature followed by brief confinement in a metabolic cage, and measured plasma corticosterone following the stress. OTKO mice released more corticosterone than WT mice (P<0.03) following exposure to this stress. In contrast, if OTKO and WT female and male mice were administered insulin-induced hypoglycemia, an acute physical stress, corticosterone release was not different between genotypes. The absence of central OT signaling pathways in female mice heightens the neuroendocrine (e.g., corticosterone) response to psychogenic stress, but not to the physical stress of insulin-induced hypoglycemia.

Is the CCK2 receptor essential for normal regulation of body weight and adiposity?

Cholecystokinin (CCK) is a gastrointestinal satiety signal released from the duodenum to terminate feeding, via CCK1 receptors. CCK2 receptors are considered to be involved in anxiety. CCK2 receptor knockout mice have increased body weight and food intake. Little is known regarding the effects of CCK2 receptor deficiency on adipose distribution and hypothalamic feeding regulators such as neuropeptide Y (NPY), a powerful stimulator of feeding. Adult (10 week) CCK2 receptor knockout and wild-type mice were anaesthetized and killed by decapitation. Brain sections, organs and fat tissue were dissected. Plasma leptin, insulin and brain NPY content were measured by radioimmunoassay. Female CCK2 receptor knockout mice weighed more than control mice (22.0 +/- 0.2 vs. 19.9 +/- 0.4 g, P < 0.05), with this difference being less marked in male mice (26.4 +/- 0.4 vs. 25.6 +/- 0.6 g). Fat masses in all locations sampled were significantly smaller in CCK2 receptor knockout mice of both genders (P < 0.05), resulting in lower plasma leptin and insulin levels. NPY concentrations were significantly increased in arcuate nucleus and anterior hypothalamus in both male and female CCK2 receptor knockout mice, and total hypothalamic NPY content was increased by 7 and 9% in males and females, respectively (P < 0.05). CCK2 receptor deletion was associated with increased body weight and hypothalamic NPY content, but reduced fat masses and plasma leptin and insulin. Increased NPY might contribute to increased food intake in CCK2 receptor knockout mice. Further work needs to focus on the metabolic changes.

Oxytocin null mice ingest enhanced amounts of sweet solutions during light and dark cycles and during repeated shaker stress

Central oxytocin (OT) pathways appear to limit consumption of sweet solutions. Male and female C57BL/6 mice that lack the gene for oxytocin (OT KO mice) displayed an initial and sustained enhanced intake of sucrose solution over water compared to wild type (WT) mice when the solutions were presented as a two-bottle choice [Amico JA, Vollmer RR, Cai HM, Miedlar JA, Rinaman R. Enhanced initial and sustained intake of sucrose solution in mice with an oxytocin gene deletion. Am J Physiol: Regul Integr Comp Physiol 2005;289:R1798-806]. In this study we examined the ingestion of a non-nutritive sweetener, 0.2% saccharin in sucrose-experienced OT KO and WT mice given a two-bottle choice between saccharin solution and water available ad libitum for 4 days. Compared to WT mice, OT KO mice consumed significantly greater volumes of saccharin solution during the dark and light photoperiods on the first day and subsequent days of the study. The results were replicated when the experiment was repeated in the same animals. In another experiment, we determined that daily exposure to platform shaker stress did not alter the marked sucrose consumption in OT KO mice. OT KO mice drank significantly more sucrose than WT mice during periods of stress and non-stress. We conclude that the avid consumption of sweetened solutions by OT KO mice is not restricted to a single photoperiod, occurs independent of caloric content of the sweetened solution, and is not altered by exposure to the daily stress of platform shaker. The cumulative results from our studies of sucrose and saccharin ingestion in OT KO and WT male and female mice suggest a special role for sweet taste in the recruitment of OT neurons.

Oxytocin receptors in the nucleus accumbens facilitate “spontaneous” maternal behavior in adult female prairie voles

Oxytocin and the nucleus accumbens have been extensively implicated in the regulation of maternal behavior, and the processing of pup-related stimuli relevant for this behavior. Oxytocin receptor density in the nucleus accumbens is highly variable in virgin female prairie voles, as is their behavioral response to pups, ranging from neglecting and infanticidal to full maternal behavior. We hypothesized that oxytocin receptor in the nucleus accumbens facilitates the expression of "spontaneous" maternal behavior in prairie voles. Forty sexually-naive adult females were exposed to pups for the first time and tested for maternal behavior. Oxytocin receptor binding in the nucleus accumbens and other brain regions was later determined using autoradiography. Females that showed maternal behavior (lick and groom the pups and hover over them for at least 30 s, n=24) had higher oxytocin receptor density in the nucleus accumbens (shell subregion) (P<0.05) than females that did not show maternal behavior or attacked the pups (n=16). No differences were found in other brain regions (medial preoptic area, septum, prelimbic cortex). In a second experiment, we tested whether infusions of the oxytocin receptor antagonist (d(CH2)5(1),Tyr(Me)2,Orn8)-AVT into the nucleus accumbens would block "spontaneous" maternal behavior. As a control region, oxytocin receptor antagonist was also infused into the caudate putamen. Ten females were infused bilaterally into the nucleus accumbens or caudate putamen with either 2 ng/0.5 microl of oxytocin receptor antagonist or CSF (vehicle). While five of 10 nucleus accumbens CSF-infused animals showed maternal behavior, none of the nucleus accumbens oxytocin receptor antagonist-infused subjects did (0/10; chi2, P<0.01). Nucleus accumbens oxytocin receptor antagonist-infused females recovered the next day and were not different from controls. Animals infused with CSF or oxytocin receptor antagonist into the caudate putamen did not differ (four/10, four/10). This is the first study to show that the nucleus accumbens is involved in the regulation of "spontaneous" maternal behavior and that oxytocin receptor in this brain region facilitates maternal responses.