Pharmacological evidence for the role of nitric oxide in the modulation of stress-induced anxiety by morphine in rats

Moxie begets MOXI: The journey to a novel hypothesis about Mu-opioid and OXytocin system Interactions

This narrative review summarizes the early life of the author, Khalin E. Nisbett, and highlights the factors that led to her career in research and her development of two novel research hypotheses: the Mu-opioid and OXytocin system Interaction (MOXI) hypothesis and Mu-Opioid receptor antagonist and OXytocin receptor Agonist In Combination (MOXAIC) treatment hypothesis. Notably, Nisbett's career began in the era after countless studies demonstrated that oxytocin is not just a female neurotransmitter and not just a female reproductive hormone, an era in which researchers are exploring the role of oxytocin in emotion regulation, social interaction, and cognitive processing across both sexes. As such, the previously held perspective that oxytocin is "just a female hormone" did not impede Nisbett's ideas. Intrigued by science, emotion regulation, and social interaction, she began to explore the role of oxytocin and opioids in emotion regulation. On the heels of earlier theories, such as the Tend-and-Befriend theory and Opioid Theory of Social Attachment, she began to develop the MOXI hypothesis, which postulates that the μ-opioid receptor and oxytocin systems interact to mediate social interaction and emotion regulation. In this narrative review, Nisbett summarizes two studies that explored (i) the role of oxytocin in anxiety- and depression-like behavior and (ii) the effect of opioid receptor blockade on the anxiolytic-like effect of oxytocin, which led to a revision of the MOXI hypothesis and postulation of the Mu-Opioid receptor antagonist and OXytocin receptor Agonist In Combination (MOXAIC) treatment hypothesis. Nisbett also discusses several limitations of these hypotheses and her current research interests and aspirations.

Naloxone increases conditioned fear responses during social buffering in male rats

Social buffering is the phenomenon in which the presence of an affiliative conspecific mitigates stress responses. We previously demonstrated that social buffering completely ameliorates conditioned fear responses in rats. However, the neuromodulators involved in social buffering are poorly understood. Given that opioids, dopamine, oxytocin and vasopressin play an important role in affiliative behaviour, here, we assessed the effects of the most well-known antagonists, naloxone (opioid receptor antagonist), haloperidol (dopamine D2 receptor antagonist), atosiban (oxytocin receptor antagonist) and SR49059 (vasopressin V1a receptor antagonist), on social buffering. In Experiment 1, fear-conditioned male subjects were intraperitoneally administered one of the four antagonists 25 min prior to exposure to a conditioned stimulus with an unfamiliar non-conditioned rat. Naloxone, but not the other three antagonists, increased freezing and decreased walking and investigation as compared with saline administration. In Experiment 2, identical naloxone administration did not affect locomotor activity, anxiety-like behaviour or freezing in an open-field test. In Experiment 3, after confirming that the same naloxone administration again increased conditioned fear responses, as done in Experiment 1, we measured Fos expression in 16 brain regions. Compared with saline, naloxone increased Fos expression in the paraventricular nucleus of the hypothalamus and decreased Fos expression in the nucleus accumbens shell, anterior cingulate cortex and insular cortex and tended to decrease Fos expression in the nucleus accumbens core. Based on these results, we suggest that naloxone blocks social buffering of conditioned fear responses in male rats.

µ-Opioid receptor antagonism facilitates the anxiolytic-like effect of oxytocin in mice

Mood and anxiety disorders are leading causes of disability worldwide and are major contributors to the global burden of diseases. Neuropeptides, such as oxytocin and opioid peptides, are important for emotion regulation. Previous studies have demonstrated that oxytocin reduced depression- and anxiety-like behavior in male and female mice, and opioid receptor activation reduced depression-like behavior. However, it remains unclear whether the endogenous opioid system interacts with the oxytocin system to facilitate emotion regulation in male and female mice. We hypothesized that opioid receptor blockade would inhibit the anxiolytic- and antidepressant-like effects of oxytocin. In this study, we systemically administered naloxone, a preferential μ-opioid receptor antagonist, and then intracerebroventricularly administered oxytocin. We then tested mice on the elevated zero maze and the tail suspension tests, respective tests of anxiety- and depression-like behavior. Contrary to our initial hypothesis, naloxone potentiated the anxiolytic-like, but not the antidepressant-like, effect of oxytocin. Using a selective μ-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2, and a selective κ-opioid receptor antagonist, norbinaltorphimine, we demonstrate that μ-opioid receptor blockade potentiated the anxiolytic-like effect of oxytocin, whereas κ-opioid receptor blockade inhibited the oxytocin-induced anxiolytic-like effects. The present results suggest that endogenous opioids can regulate the oxytocin system to modulate anxiety-like behavior. Potential clinical implications of these findings are discussed.

Perinatal N(G)-Nitro-L-arginine methyl ester administration decreases anxiety- and depression-like behaviors in adult mice

OBJECTIVE

We hypothesized that perinatal manipulations of the nitrergic system would affect adult animal behaviors.

METHODS

We tested this hypothesis by perinatally administering N(G)-Nitro-L-arginine methyl ester (L-NAME), a non-specific antagonist of nitric oxide synthase for 15 days and assessed anxiety- and depression-like behaviors in adult mice. At 70 days of age, the mice were subjected to a battery of tests consisting of the open-field, light/dark box, forced swim, and tail-flick tests. The tests were performed at two-day intervals, and the order of the tests within the battery was determined according to the progressive invasiveness degree.

RESULTS

L-NAME-treated animals exhibited decreased anxiety-like behavior in the light/dark box and open field tests, with no change in locomotor activity. Additionally, they demonstrated decreased depression-like behavior in the forced swim test and no change in pain perception in the tail-flick test.

CONCLUSION

The nitrergic system is possibly involved in neural circuitry development that regulates behaviors since blocking perinatal nitric oxide production decreases anxiety- and depression-like behaviors in adult mice.

Zebrafish as a Useful Tool in the Research of Natural Products With Potential Anxiolytic Effects

Zebrafish (Danio rerio) is a popular and valuable species used in many different biomedical research areas. The complex behavior that fish exhibit in response to different stimuli allows researchers to explore the biological and pharmacological basis of affective and mood disorders. In this sense, anxiety is commonly studied in preclinical research with animal models in rodents. During the last decade, those models have been successfully adapted to zebrafish. Stressful stimuli, such as novel environments, chemical substances, light conditions, and predator images, can trigger defensive behaviors considered indicators of an anxiety-like state. In the first stage, models were adapted and validated with different stressors and anxiolytic drugs with promising results and are now successfully used to generate scientific knowledge. In that sense, zebrafish allows several routes of administration and other methodological advantages to explore the anxiolytic effects of natural products in behavioral tests as novel tank, light-dark chamber, and black/white maze, among others. The present work will review the main findings on preclinical research using adult zebrafish to explore anxiolytics effects of natural products as plant secondary metabolites such as flavonoids, alkaloids and terpenes or standardized extracts of plants, among others. Scientific literature confirms the utility of zebrafish tests to explore anxiety-like states and anxiolytic-like effects of plant secondary metabolites, which represent a useful and ethical tool in the first stages of behavioral.

Synergistic effect between quinpirole and L-NAME as well as sulpiride and L-arginine on the modulation of anxiety and memory processes in the 6-OHDA mouse model of Parkinson's disease: An isobologram analysis

We evaluated interactions between dopamine D2 receptor and nitric oxide (NO) actions on the regulation of anxiety and memory in the 6-hydroxydopamine (6-OHDA) mouse model of Parkinson's disease (PD). A unilateral guide cannula was stereotaxically implanted over the right striatum. Elevated plus-maze test (EPM) test-retest protocol was employed to evaluate anxiety and memory in mice. The results revealed that injection of L-NAME (9 mg/kg) induced anxiolytic and amnesic effects, while L-arginine (9 mg/kg) produced anxiogenic and memory-improvement effects in the 6-OHDA mouse model of PD. Administration of sulpiride (20 mg/kg) induced anxiogenic and memory-improvement effects, whereas quinpirole (20 mg/kg) caused anxiolytic and amnesic effects in PD mice. Co-injection of sulpiride (5, 10, and 20 mg/kg) plus L-NAME (3 mg/kg) induced anxiolytic and amnesic effects. Co-injection of sulpiride (20 mg/kg) plus L-arginine (3 mg/kg) induced anxiogenic and memory-improvement effects. Co-administrations of quinpirole (20 mg/kg) and L-NAME (3 mg/kg) induced anxiolytic effect, but co-administration of quinpirole (20 mg/kg) plus L-arginine (3 mg/kg) caused anxiogenic and memory-improvement effects. The isobologram analysis revealed that there is a synergistic effect between sulpiride and L-arginine as well as quinpirole and L-NAME upon induction of anxiogenic and anxiolytic effects, respectively in PD mice. Our results suggested: (1) NO and dopamine D2 receptor mechanisms affect anxiety and memory in PD mice; (2) L-NAME reversed anxiogenic and memory-improvement effect induced by sulpiride; (3) Anxiolytic and amnesic effects induced by quinpirole reversed by L-arginine; (4) There is a synergistic effect between dopamine D2 receptor and NO systems on the modulation of anxiety and memory.

The cross-talk between dopaminergic and nitric oxide systems in the medial septal nucleus, and their distinct effects on anxiety-like behaviors in male rats

Anxiety disorders, which have a noticeable global prevalence and may be caused by many factors, include a spectrum of disorders that share features of excessive fear- and anxiety-related behavioral disturbances. Different brain areas and neurotransmitter systems have been under investigation for anxiety-related disorders. In this study, we investigated the possible interaction between the dopaminergic and nitric oxide (NO) neurotransmitter systems in the medial septal nucleus and their roles in anxiety-like behaviors using elevated plus-maze (EPM) test in male rats. Our results showed that: (i) both D1-and D2-like receptor agonists, SKF-38393 and quinpirole, augmented anxiety-like behaviors at their two highest applied doses in the EPM test; (ii) both D1-and D2-like receptor antagonists, SCH- 23390 and sulpiride, reduced anxiety-like behaviors at their two highest applied doses in the EPM test; (iii) L-Arginine, a NO precursor, increased anxiety-like behaviors, but L-NAME, a non-specific nitric oxide synthase (NOS) inhibitor, reduced them in the EPM test; (iv) L-NAME could not reverse the anxiety-like parameters produced by SKF-38393, but it significantly reduced the anxiety-like behaviors induced by quinpirole; (v) Neither SCH- 23390 nor sulpiride changed anxiety-related behaviors induced by L-Arginine. It can be concluded that both dopaminergic and nitric oxide systems in the medial septal nucleus are involved in modulating anxiety-like behaviors. While NO has an involvement in the exerted effects by the D2-like agonist, such effects were not observed at the applied range of the doses for D1-and D2-like antagonists.

Interactions between the nitrergic and the endocannabinoid system in rats exposed to the elevated T-maze

OBJECTIVE

The aim of this study was to test the hypothesis that synthesis of nitric oxide (NO) and activation of CB1 receptors have opposite effects in a behavioural animal model of panic and anxiety.

METHODS

To test the hypothesis, male Wistar rats were exposed to the elevated T-maze (ETM) model under the following treatments: L-Arginine (L-Arg) was administered before treatment with WIN55,212-2, a CB1 receptor agonist; AM251, a CB1 antagonist, was administered before treatment with L-Arg. All treatments were by intraperitoneal route.

RESULTS

The CB1 receptor agonist, WIN55,212-2 (1 mg/kg), induced an anxiolytic-like effect, which was prevented by pretreatment with an ineffective dose of L-Arg (1 mg/kg). Administration of AM251 (1 mg/kg), a CB1 antagonist before treatment with L-Arg (1 mg/kg) did not produce anxiogenic-like responses.

CONCLUSION

Altogether, this study suggests that the anxiolytic-like effect of cannabinoids may occur through modulation of NO signalling.

Nitric oxide role in anxiety-like behavior, memory and cognitive impairments in animal model of chronic migraine

The occurrence of cognitive dysfunctions and anxiety and mood disorders has been shown to be higher in migraine patients. Nitric Oxide (NO) is a significant neurotransmitter in the pathophysiology of migraine, anxiety and neurodegenerative disorders. Therefore, the present study was conducted to evaluate the role of NO system in migraine-induced memory impairment and anxiety like behaviors. Nitroglycerin (NTG) was administered to the animals as an animal model of migraine and pretreatment with L-Arginine, L-NAME and saline were implemented to evaluate the role of NO system in possible cognitive impairments in animal model of migraine. Avoidance learning and memory performance, object recognition memory, anxiety-like behavior and motor activity were assessed using a shuttle box apparatus, novel object recognition, elevated plus-maze, and open field tests respectively. The data showed that the injection of nitroglycerin disturbs learning and memory and elicit anxiety like behavior in the animals. L-NAME administration suppressed the observed effect of nitroglycerin on memory and anxiety. Overall, the results indicated that nitric oxide system is implicated in memory impairments and anxiety like behavior in an animal model of migraine.

Morphine improved stress-induced amnesia and anxiety through interacting with the ventral hippocampal endocannabinoid system in rats

The present study aimed to investigate the possible role of the ventral hippocampal (VH) cannabinoid CB1 receptors in the improving effect of morphine on stress-induced memory formation impairment and anxiety. A step-through type passive avoidance task and a hole-board test were used to measure memory formation and anxiety-like exploratory behavior, respectively. The results showed that the exposure to 10-min stress immediately after the successful training phase impaired memory formation and also produced anxiogenic-like exploratory behaviour in adult male Wistar rats. Moreover, morphine administration before stress exposure improved the adverse effects of stress on memory formation and exploratory behaviour. After training, intra-VH microinjection of cannabinoid CB1/CB2 receptor agonist, WIN 55,212-2 (0.01-0.05 μg/rat) enhanced the response of an ineffective dose of morphine (0.5 mg/kg for memory; 5 mg/kg for anxiety, i.p.) on memory impairment and anxiogenic-like exploratory behaviour induced by acute stress. Intra-VH microinjection of the higher dose of WIN 55,212-2 alone impaired memory formation. Post-training microinjection of a cannabinoid CB1 receptor antagonist/inverse agonist, AM-251 (100-150 ng/rat) into the VH attenuated the response of an effective dose of morphine (5 mg/kg for memory; 6 mg/kg for anxiety, i.p.) in stress-exposed rats. Taken together, the present results showed that morphine administration could improve stress-induced memory impairment and anxiety in the rats exposed to the inescapable acute stress. Interestingly, the improving effect of morphine on the adverse effect of stress on memory formation and anxiety-like exploratory behaviour may be mediated through the VH endocannabinoid CB1/CB2 receptors mechanism.

Alzheimer's Disease: A Contextual Link with Nitric Oxide Synthase

Nitric oxide (NO) is a gasotransmitter with pleiotropic effects which has made a great impact on biology and medicine. A multidimensional neuromodulatory role of NO has been shown in the brain with specific reference to neurodegenerative disorders like Alzheimer's disease (AD) and cognitive dysfunction. It has been found that NO/cGMP signalling pathway has an important role in learning and memory. Initially, it was considered that indirectly NO exerted neurotoxicity in AD via glutamatergic excitotoxicity. However, considering the early development of cognitive functions involved in the learning memory process including long term potentiation and synaptic plasticity, NO has a crucial role. Increasing evidence uncovered the above facts that isoforms of NOS viz endothelial NO synthase (eNOS), neuronal NO synthase (nNOS) and inducible NO synthase (iNOS) having a variable expression in AD are mainly responsible for learning and memory activities. In this review, we focus on the role of NOS isoforms in AD parallel to NO. Further, this review provides convergent evidence that NO could provide a therapeutic avenue in AD via modulation of the relevant NOS expression.

Characterising lipoteichoic acid as an in vitro model of acute neuroinflammation

Toll-like receptor 2 (TLR2) is a primary sensor for pathogens, including those derived from gram-positive bacteria. It can also mediate the effects of endogenous inflammatory signals such as β-amyloid peptide (Aβ), thus promoting the microglial activation and subsequent neuronal dysfunction, characteristic of chronic neuroinflammatory conditions. More recently, a role for TLR2 has been proposed in the pathogenesis of disorders associated with acute inflammation, including anxiety and depression. The current study aims to characterise the acute effects of the TLR2 agonist lipoteichoic acid (LTA) on microglial activation and neuronal integrity, and to evaluate the influence of LTA exposure on sensitivity to the inflammation and neuronal dysfunction associated with Aβ. Using BV2 and N2a cells as an in vitro model, we highlight that acute exposure to LTA robustly promotes inflammatory cytokine and nitric oxide (NO) production in microglia but also in neurons, similar to that reported under longer-term and chronic inflammatory conditions. Moreover, we find that exposure to LTA can enhance sensitivity to subthreshold Aβ, promoting an 'M1'-like phenotype in microglia and provoking dysregulation of neuronal activity in acute hippocampal slices. Anti-inflammatory agents, including mimetics of brain-derived neurotrophic factor (BDNF), have proven effective at alleviating chronic neuroinflammatory complications. We further examined the effects of 7,8,3-trihydroxyflavone (7,8,3-THF), a small-molecule TrkB agonist, on LTA-induced microglial activation. We report that 7,8,3-THF can significantly ameliorate interleukin (IL)-6 and NO production in LTA-stimulated BV2 cells. Taken together, our findings offer support for exploration of TLR2 as a potential target for therapeutic intervention into acute neuroinflammatory conditions. Moreover we propose that exposure to gram-positive bacterial pathogens may promote sensitivity to the inflammatory changes characteristic of the aged brain.

Restraint stress induced gut dysmotility is diminished by a milk oligosaccharide (2'-fucosyllactose) in vitro

Background

Stress causes severe dysmotility in the mammalian gut. Almost all research done to date has concentrated on prevention of stress-induced altered gut motility but not on treatment. We had previously shown that intraluminal 2′FL could acutely moderate propulsive motility in isolated mouse colonic segments. Because 2′FL appeared to modulate enteric nervous system dependent motility, we wondered if the oligosaccharide could reverse the effects of prior restraint stress, ex vivo. We tested whether 2′FL could benefit the dysmotility of isolated jejunal and colonic segments from animals subjected to prior acute restraint stress.

Methods

Jejunal and colonic segments were obtained from male Swiss Webster mice that were untreated or subjected to 1 hour of acute restraint stress. Segments were perfused with Krebs buffer and propagating contractile clusters (PCC) digitally video recorded. 2′FL or β-lactose were added to the perfusate at a concentration of 1 mg/ml. Spatiotemporal maps were constructed from paired before and after treatment recordings, each consisting of 20 min duration and PCC analyzed for frequency, velocity and amplitude.

Key Results

Stress decreased propulsive motility in murine small intestine while increasing it in the colon. 2′FL in jejunum of previously stressed mice produced a 50% increase in PCC velocity (p = 0.0001), a 43% increase in frequency (p = 0.0002) and an insignificant decrease in peak amplitude. For stressed colon, 2′FL reduced the frequency by 23% (p = 0.017) and peak amplitude by 26% (p = 0.011), and was without effect on velocity. β-lactose had negligible or small treatment effects.

Conclusions & Inferences

We show that the prebiotic 2′FL may have potential as a treatment for acute stress-induced gut dysmotility, ex vivo, and that, as is the case for certain beneficial microbes, the mechanism occurs in the gut, likely via action on the enteric nervous system.

Concordance and incongruence in preclinical anxiety models: Systematic review and meta-analyses

Rodent defense behavior assays have been widely used as preclinical models of anxiety to study possibly therapeutic anxiety-reducing interventions. However, some proposed anxiety-modulating factors - genes, drugs and stressors - have had discordant effects across different studies. To reconcile the effect sizes of purported anxiety factors, we conducted systematic review and meta-analyses of the literature on ten anxiety-linked interventions, as examined in the elevated plus maze, open field and light-dark box assays. Diazepam, 5-HT1A receptor gene knockout and overexpression, SERT gene knockout and overexpression, pain, restraint, social isolation, corticotropin-releasing hormone and Crhr1 were selected for review. Eight interventions had statistically significant effects on rodent anxiety, while Htr1a overexpression and Crh knockout did not. Evidence for publication bias was found in the diazepam, Htt knockout, and social isolation literatures. The Htr1a and Crhr1 results indicate a disconnect between preclinical science and clinical research. Furthermore, the meta-analytic data confirmed that genetic SERT anxiety effects were paradoxical in the context of the clinical use of SERT inhibitors to reduce anxiety.

Substance use modulates stress reactivity: Behavioral and physiological outcomes

Drug addiction is a major public health concern in the United States costing taxpayers billions in health care costs, lost productivity and law enforcement. However, the availability of effective treatment options remains limited. The development of novel therapeutics will not be possible without a better understanding of the addicted brain. Studies in both clinical and preclinical models indicate that chronic drug use leads to alterations in the body and brain's response to stress. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may shed light on the ability of stress to increase vulnerability to relapse. Further, within both the HPA axis and limbic brain regions, corticotropin-releasing factor (CRF) is critically involved in the brain's response to stress. Alterations in both central and peripheral CRF activity seen following chronic drug use provide a mechanism by which substance use can alter stress reactivity, thus mediating addictive phenotypes. While many reviews have focused on how stress alters drug-mediated changes in physiology and behavior, the goal of this review is to focus on how substance use alters responses to stress.

Modulation of opioid-induced feeding behavior by endogenous nitric oxide in neonatal layer-type chicks

The current study was designed to evaluate the effects of central administration of L-arginine (The precursor of nitric oxide), N(G)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, selective opioid receptor agonists and involvement of central nitrergic/opioidergic systems on feeding behavior in neonatal layer-type chicks. The results of this study showed that the intracerebroventricular (ICV) injection of L-arginine (400 and 800 nmol) significantly decreased food intake (P < 0.001) but the injection of 200 nmol L-arginine had no effect on cumulative food intake in FD3 chickens (P > 0.05). The ICV injection of L-NAME (200 and 400 nmol) increased food intake (P < 0.001) but 100 nmol of L-NAME had no significant effect (P > 0.05). On the other hand, the co-injection of 100 nmol L-NAME significantly attenuated the anorexigenic effect of 800 nmol L-arginine (P < 0.001). Moreover, the food intake of chicks was significantly decreased by ICV injection of DAMGO (μ-opioid receptor agonist, 125 pmol) (P < 0.001) while both DPDPE (δ-opioid receptor agonist, 40 pmol) and U-50488H (κ-opioid receptor agonist, 30 nmol) significantly stimulated food intake (P < 0.001). In addition, the hypophagic effect of DAMGO was significantly amplified by administration of L-arginine (P < 0.001) while the administration of L-NAME attenuated the hypophagic effect of DAMGO (P < 0.001). In contrast, co-injection of L-arginine or L-NAME with DPDPE had no effect on the hyperphagia induced by DPDPE as well as the hyperphagic effect of U-50488H on food intake was not affected by concurrent injection of L-arginine or L-NAME (P > 0.05). These results suggest that nitrergic and opioidergic systems have an important role on feeding behavior in the CNS of neonatal layer-type chicks and it seems that interaction between them is mediated by μ-opioid receptor.

Stress and opioids: role of opioids in modulating stress-related behavior and effect of stress on morphine conditioned place preference

Research studies have defined the important role of endogenous opioids in modulating stress-associated behavior. The release of β-endorphins in the amygdala in response to stress helps to cope with a stressor by inhibiting the over-activation of HPA axis. Administration of mu opioid agonists reduces the risk of developing post-traumatic stress disorder (PTSD) following a traumatic event by inhibiting fear-related memory consolidation. Similarly, the release of endogenous enkephalin and nociceptin in the basolateral amygdala and the nucleus accumbens tends to produce the anti-stress effects. An increase in dynorphin levels during prolonged exposure to stress may produce learned helplessness, dysphoria and depression. Stress also influences morphine-induced conditioned place preference (CPP) depending upon the intensity and duration of the stressor. Acute stress inhibits morphine CPP, while chronic stress potentiates CPP. The development of dysphoria due to increased dynorphin levels may contribute to chronic stress-induced potentiation of morphine CPP. The activation of ERK/cyclic AMP responsive element-binding (CREB) signaling in the mesocorticolimbic area, glucocorticoid receptors in the basolateral amygdala, and norepinephrine and galanin system in the nucleus accumbens may decrease the acute stress-induced inhibition of morphine CPP. The increase in dopamine levels in the nucleus accumbens and augmentation of GABAergic transmission in the median prefrontal cortex may contribute in potentiating morphine CPP. Stress exposure reinstates the extinct morphine CPP by activating the orexin receptors in the nucleus accumbens, decreasing the oxytocin levels in the lateral septum and amygdala, and altering the GABAergic transmission (activation of GABAA and inactivation of GABAB receptors). The present review describes these varied interactions between opioids and stress along with the possible mechanism.

Endogenous opiates and behavior: 2013

This paper is the thirty-sixth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2013 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Differential modulatory effects of morphine on acute and chronic stress induced neurobehavioral and cellular markers in rats

The present study evaluated the effects of morphine treatments on elevated plus maze test parameters, oxidative stress markers and Hsp70 expression in normal and stressed rats. Acute and chronic stress caused neurobehavioral suppression, altered prooxidant-antioxidant balance and increased Hsp70 expression in brain homogenates in a differential manner. Morphine (1 and 5mg/kg) attenuated RS induced anxiogenesis, changes in MDA and GSH but further enhanced Hsp70 expression. Similar anxiolytic and Hsp70 enhancing effects were seen after morphine in normal rats (no RS). Exposure to chronic RS did not elicit any appreciable neurobehavioral response in EPM but enhanced MDA, lowered GSH and exaggerated the Hsp70 expression. Pretreatment with morphine did not affect the neurobehavioral response to chronic RS, but reverted the GSH and Hsp70 expression. The results suggest that morphine differentially influences acute and chronic stress induced changes in anxiety behavior and complex interactions between oxidative stress markers and Hsp70 expression which may contribute to these effects.

Prenatal hypoxia, habituation memory and oxidative stress

Hypoxia-ischemia (HI) is characterized by a reduced supply of oxygen during pregnancy, which leads to both central nervous system and peripheral injuries in the foetus, resulting in impairment in its development. The purpose of this study was to investigate behavioural changes and systemic oxidative stress in adult animals that have been affected by HI during pregnancy. HI was induced by the occlusion of the maternal uterine artery with aneurysm clamps for a period of 45 min on the 18th gestational day. Animals from the sham group were submitted to same surgical procedure as the HI animals, without occlusion of the maternal uterine artery. The control group consisted of non-manipulated healthy animals. At postnatal day 90, the pups were submitted to behavioural tests followed by blood collection. HI adult animals presented an increase in anxiety behaviour and a lack of habituation compared to both sham and control groups. Oxidative damage, assessed by protein and lipid oxidation in serum, did not differ between HI and sham-operated animals. However, HI animals presented reduced activity of the glutathione peroxidase enzyme and increased formation of nitrite, indicating alterations in the systemic antioxidant repair system. Our results suggest an association among HI, systemic oxidative stress and behavioural alterations.