Swim Stress Research Articles

Involvement of orexin-2 receptor in the ventral tegmental area in stress- and drug priming-induced reinstatement of conditioned place preference in rats

Orexin neurons originate from the lateral hypothalamus and send their projections broadly throughout the central nervous system including to the ventral tegmental area (VTA). In the current study, the reinstatement model has been used to examine the effects of intra-VTA administration of TCS-OX2-29, an orexin-2 receptor (OX2R) antagonist, on drug priming- and forced swim stress (FSS)-induced reinstatement of morphine-induced conditioned place preference (CPP). A total of 73 adult male Wistar rats weighing 200–280 g were bilaterally implanted with cannulas into the VTA. For induction of CPP, subcutaneous (sc) injection of morphine (5 mg/kg) was done daily during a 3-day conditioning phase. After a 24-h “off” period following achievement of extinction criterion, the rats were tested for drug priming-induced reinstatement with a priming dose of morphine (1 mg/kg;sc) or after application of FSS on the reinstatement day. The animals then received different doses of the OX2R antagonist, TCS-OX2-29 (0.3,3,1 and 10 nM) bilaterally in the VTA (0.3 μl/side) and were tested for FSS- and morphine priming-induced reinstatement of CPP. Our findings indicate that intra-VTA administration of OX2R antagonist suppresses FSS and morphine priming-induced reinstatement in a dose-dependent manner. The role of the orexinergic system in morphine-induced reinstatement through activation of OX2R in the VTA provides evidence that the OX2R antagonist could be a useful therapeutic target for prevention of reinstatement of morphine-induced CPP.

Neuroinflammation Contributes to High Salt Intake-Augmented Neuronal Activation and Active Coping Responses to Acute Stress.

High dietary salt intake increases risk of stress-related neuropsychiatric disorders. Here, we explored the contribution of high dietary salt intake-induced neuroinflammation in key stress-responsive brain regions, the hypothalamic paraventricular nucleus and basolateral amygdala, in promoting exaggerated neuronal activation and coping behaviors in response to acute psychogenic stress. Mice that underwent high dietary salt intake exhibited increased active stress coping behaviors during and after an acute swim stress, and these were reduced by concurrent administration of minocycline, an inhibitor of microglial activation, without affecting body fluid hyperosmolality caused by high dietary salt intake. Moreover, minocycline attenuated high dietary salt intake-induced increases of paraventricular nucleus tumor necrosis factor-α, activated microglia (ionized calcium-binding adaptor molecule 1), and acute swim stress-induced neuronal activation (c-Fos). In the basolateral amygdala, similar effects were observed on ionized calcium-binding adaptor molecule 1+ and c-Fos+ counts, but not tumor necrosis factor-α levels. These data indicate that high dietary salt intake promotes neuroinflammation, increasing recruitment of neurons in key stress-associated brain regions and augmenting behavioral hyper-responsivity to acute psychological stress.

Effect of Vitamin C and Atorvastatin on Male Fertility in Rats Subjected to Forced Swimming Stress

Effect of Vitamin C and Atorvastatin on Male Fertility in Rats Subjected to Forced Swimming Stress

Involvement of Endogenous Opioid System in Swim Stress-Induced Pain Modulation During the Interphase of the Formalin Test.

Introduction:Some evidence demonstrates endogenous inhibitory pathways of pain involved in the interphase (phase between early and later phase) of the formalin test. We previously showed that swimming stress modulates the pain-related behaviors during the interphase of the formalin test. In this study, we evaluated the role of the endogenous opioid system in modulating nociceptive responses of the formalin test.Methods:Swim stress was performed in different heights of water (5, 25, 50 cm) in a swimming tank. The mean nociceptive scores were measured during phase 1 (1–7 min), interphase (8–14 min), and phase 2 (15–90 min) of the formalin test. Opioid receptor antagonist, naloxone (3 mg/kg; IP) was injected immediately before swim stress.Results:Swim stress attenuated nociceptive behaviors in the first phase and increased the duration of interphase in the formalin test in a water-height-dependent manner, compared to the control group. Naloxone significantly increased nociceptive behaviors in the first phase, interphase, and the second phase of the formalin test, compared to the control group.Conclusion:Stress could affect the nociceptive response. Swim stress in different heights of water could have different effects on the nociception in different phases of the formalin test. In addition, the involvement of the endogenous opioid system is further demonstrated in the swim stress-induced modulation of pain behaviors in phase 1, phase 2, as well as interphase of formalin test in rats.

Role of Orexin-1 Receptor Within the Ventral Tegmental Area in Mediating Stress- and Morphine Priming-induced Reinstatement of Conditioned Place Preference in Rats.

Introduction:Orexin-containing neurons exist in the lateral hypothalamic region, sending their projections toward mesolimbic regions such as the Ventral Tegmental Area (VTA).Methods:In the current study, a Reinstatement model is used to examine the effects of intra-VTA administration of SB334867 as an Orexin-1 Receptor (OX1R) antagonist on drug priming- and Forced Swim Stress (FSS)-induced reinstatement of morphine. Eighty-eight male adult albino Wistar rats, weighing 200–280 g, were bilaterally implanted by cannulas into the VTA. We induced the Conditioned Place Preference (CPP) by Subcutaneous (SC) injection of morphine (5 mg/kg) daily in three days. Then, the CPP score was calculated. After a 24-h “off” period following achievement of extinction criterion, the rats were tested for drug priming-induced reinstatement by a priming dose of morphine (1 mg/kg, SC) and for FSS-induced reinstatement 10 min after FSS. In the next experiments, the animals received different doses of intra-VTA administration of SB334867 (0.3, 3, and 1 nM/0.3 μL 12% DMSO per side) and bilaterally were subsequently tested for FSS- and morphine priming-induced reinstatement.Results:Our findings indicated that the FSS could induce the reinstatement of seeking behaviors. Furthermore, intra-VTA administration of OX1R antagonists suppressed FSS- and drug priming-induced reinstatement dose-dependently.Conclusion:It is concluded that FSS and drug priming-induced reinstatement might be mediated, at least in part, by stimulation of orexin receptors in the VTA.

Antidepressant-like action of diacamphe against the background stress-induced behavioral depression

Background. It was find out the cerebroprotective properties of diacamphe – (±)-cis-3-(2’-benzimidazolyl)-1,2,2-trimethylcyclopentan-carbonic acid hydrochloride in vivo experiments in the some models of brain injury.
 Aim. To investigate the neuroprotective and antidepressant-like activities of diacamphe.
 Materials and Methods. It was investigated an impact of diacamphe on inhibition of the pyramidal neurons field synaptic potentials evoked by N-methyl-D-aspartate, procedure anoxia/neuroaglicemia, and H2O2 in the electrophysiological experiments on hippocampal slices for evaluating of diacamphe neuroprotective activity. It was explored in behavioral experiments the impacts of diacamphe and antidepressant imipramine on basic manifestations of behavioral depression evoked by five-days swimming stress – helplessness and anhedonia.
 Results. It was ascertained in experiments on the hippocampal slices that diacamphe especially at conditions of systemic administration diminished of injury of the pyramidal neurons synapses induced by procedure anoxya/aglicemia, oxidative stress, but not N-methyl-D-aspartate action. The chronic administration of diacamphe in dose 10 mg/kg reduced the manifestations of induced by swimming stress behavioral depression, decrease duration of immobility in forced swimming test (helplessness) and increase preference of intake of sweet solution comparably with water (dilution of anhedonia). Antidepressant-like action of diacamphe differences from action of traditional antidepressant imipramine so far as diacamphe did not diminishes immobilization duration in swimming test after single administration and by more slow developing of action.
 Conclusions. Diacamphe possesses neuroprotective action and therefore manifests antidepressant-like action against the background behavioral depression evoked by swimming stress.

Antidepressant-like action of diacamphe against the background stress-induced behavioral depression

Background. It was find out the cerebroprotective properties of diacamphe – (±)-cis-3-(2’-benzimidazolyl)-1,2,2-trimethylcyclopentan-carbonic acid hydrochloride in vivo experiments in the some models of brain injury.
 Aim. To investigate the neuroprotective and antidepressant-like activities of diacamphe.
 Materials and Methods. It was investigated an impact of diacamphe on inhibition of the pyramidal neurons field synaptic potentials evoked by N-methyl-D-aspartate, procedure anoxia/neuroaglicemia, and H2O2 in the electrophysiological experiments on hippocampal slices for evaluating of diacamphe neuroprotective activity. It was explored in behavioral experiments the impacts of diacamphe and antidepressant imipramine on basic manifestations of behavioral depression evoked by five-days swimming stress – helplessness and anhedonia.
 Results. It was ascertained in experiments on the hippocampal slices that diacamphe especially at conditions of systemic administration diminished of injury of the pyramidal neurons synapses induced by procedure anoxya/aglicemia, oxidative stress, but not N-methyl-D-aspartate action. The chronic administration of diacamphe in dose 10 mg/kg reduced the manifestations of induced by swimming stress behavioral depression, decrease duration of immobility in forced swimming test (helplessness) and increase preference of intake of sweet solution comparably with water (dilution of anhedonia). Antidepressant-like action of diacamphe differences from action of traditional antidepressant imipramine so far as diacamphe did not diminishes immobilization duration in swimming test after single administration and by more slow developing of action.
 Conclusions. Diacamphe possesses neuroprotective action and therefore manifests antidepressant-like action against the background behavioral depression evoked by swimming stress.

Antidepressant-like action of diacamphe against the background stress-induced behavioral depression

Background . It was find out the cerebroprotective properties of diacamphe – (±)-cis-3-(2’-benzimidazolyl)-1,2,2-trimethylcyclopentan-carbonic acid hydrochloride in vivo experiments in the some models of brain injury. Aim . To investigate the neuroprotective and antidepressant-like activities of diacamphe. Materials and Methods. It was investigated an impact of diacamphe on inhibition of the pyramidal neurons field synaptic potentials evoked by N-methyl-D-aspartate, procedure anoxia/neuroaglicemia, and H 2 O 2 in the electrophysiological experiments on hippocampal slices for evaluating of diacamphe neuroprotective activity. It was explored in behavioral experiments the impacts of diacamphe and antidepressant imipramine on basic manifestations of behavioral depression evoked by five-days swimming stress – helplessness and anhedonia. Results. It was ascertained in experiments on the hippocampal slices that diacamphe especially at conditions of systemic administration diminished of injury of the pyramidal neurons synapses induced by procedure anoxya/aglicemia, oxidative stress, but not N-methyl-D-aspartate action. The chronic administration of diacamphe in dose 10 mg/kg reduced the manifestations of induced by swimming stress behavioral depression, decrease duration of immobility in forced swimming test (helplessness) and increase preference of intake of sweet solution comparably with water (dilution of anhedonia). Antidepressant-like action of diacamphe differences from action of traditional antidepressant imipramine so far as diacamphe did not diminishes immobilization duration in swimming test after single administration and by more slow developing of action. Conclusions. Diacamphe possesses neuroprotective action and therefore manifests antidepressant-like action against the background behavioral depression evoked by swimming stress.

Sex‐dependent changes in neuroactive steroid concentrations in the rat brain following acute swim stress

Sex differences in hypothalamic‐pituitary‐adrenal (HPA) axis activity are well established in rodents. In addition to glucocorticoids, stress also stimulates the secretion of progesterone and deoxycorticosterone (DOC) from the adrenal gland. Neuroactive steroid metabolites of these precursors can modulate HPA axis function; however, it is not known whether levels of these steroids differ between male and females following stress. In the present study, we aimed to establish whether neuroactive steroid concentrations in the brain display sex‐ and/or region‐specific differences under basal conditions and following exposure to acute stress. Brains were collected from male and female rats killed under nonstress conditions or following exposure to forced swimming. Liquid chromatography‐mass spectrometry was used to quantify eight steroids: corticosterone, DOC, dihydrodeoxycorticosterone (DHDOC), pregnenolone, progesterone, dihydroprogesterone (DHP), allopregnanolone and testosterone in plasma, and in five brain regions (frontal cortex, hypothalamus, hippocampus, amygdala and brainstem). Corticosterone, DOC and progesterone concentrations were significantly greater in the plasma and brain of both sexes following stress; however, the responses in plasma were greater in females compared to males. This sex difference was also observed in the majority of brain regions for DOC and progesterone but not for corticosterone. Despite observing no stress‐induced changes in circulating concentrations of pregnenolone, DHDOC or DHP, concentrations were significantly greater in the brain and this effect was more pronounced in females than males. Basal plasma and brain concentrations of allopregnanolone were significantly higher in females; moreover, stress had a greater impact on central allopregnanolone concentrations in females. Stress had no effect on circulating or brain concentrations of testosterone in males. These data indicate the existence of sex and regional differences in the generation of neuroactive steroids in the brain following acute stress, especially for the 5α‐reduced steroids, and further suggest a sex‐specific expression of steroidogenic enzymes in the brain. Thus, differential neurosteroidogenesis may contribute to sex differences in HPA axis responses to stress.

Studies of the effect of cerebroprotective substances on the course of stress-induced behavioral depression

Introduction. Atrophic disturbances of neurons of the limbic structures of the brain, which lead to insufficient regulation of emotions and mood, cause depression. Substances with cerebroprotective activity have the ability to inhibit further development and even reverse atrophic damage to neurons.
 Materials and methods. Using electrophysiological techniques, the cerebroprotective activity of piracetam, diacamf – (±)-cis-3-(2-benzimidazolyl)-1,2,2-trimethylcyclopentanone-carboxylic acid hydrochloride and the compound R-86, or 3,2’-spiro-pyrrolo-2-oxindole, was investigated in rat hippocampal slices. In behavioral experiments, there was studied the influence of the above substances, which had been administered for 20 days, on the most important manifestations of behavioral depression in rats caused by a five-day swim stress, such as the time of immobilization in the forced swim test and the indicator of preference for consuming sucrose solution. In addition, the influence of piracetam and diacamf was studied on the effects of the classic antidepressant imipramine.
 Results and discussion. It was found that piracetam, diacamf and the compound R-86 in in vitro studies reduced the damage to the pyramidal hippocampal neurons caused by anoxia and aglycemia, the excitotoxic activity of N-methyl-D-aspartate and oxidative stress when hydrogen peroxide was applied to the slices. Cerebroprotective activity of the test substances, when they are systemically administered for 20 days, is linked with their antidepressant-like effect, which was manifested in a decrease in the immobilization time in the swim test and an increase in the sucrose solution consumption indicator. Co-administration of piracetam in rats potentiated antidepressant activity of imipramine, and diacamf showed additive synergism with the antidepressant.
 Conclusion. Substances with cerebroprotective activity in their chronic administration may show an antidepressant-like effect. Those that potentiate the action of classical anidepressants can be used in conjunction with antidepressants during episodes of exacerbation of the disease. Less active cerebroprotective drugs can be recommended during remission for its prolongation.

Kappa opioid regulation of depressive-like behavior during acute withdrawal and protracted abstinence from ethanol.

The dynorphin/kappa opioid receptor (DYN/KOR) system appears to be a key mediator of the behavioral effects of chronic exposure to alcohol. Although KOR opioid receptor antagonists have been shown to decrease stress-related behaviors in animal models during acute ethanol withdrawal, the role of the DYN/KOR system in regulating long-term behavioral changes following protracted abstinence from ethanol is not well understood. The objective of the current study was to further explore the role of the DYN/KOR system in regulating stress-related behavioral changes associated with acute withdrawal and protracted abstinence from ethanol. More specifically, the present experiments sought to examine the ability of the KOR antagonist norbinaltorphimine (nor-BNI) to reverse depressive-like behavior in the forced swim test in rats exposed to chronic ethanol. In the first experiment, rats were fed an ethanol or control liquid diet for 28–30 days, and then 24 hours after removal of the diet, were exposed to inescapable swim stress. Immediately following this procedure, rats were injected with nor-BNI (20 mg/kg) or saline and then tested 24 hours later in the forced swim test. A second experiment used a similar procedure to examine the effects of nor-BNI on behavioral changes during protracted abstinence in rats tested in the forced swim test 3 weeks after exposure to the ethanol liquid diet procedure. Ethanol-dependent rats showed increased immobility, which is thought to indicate a depressive-like state, when examined during acute withdrawal and protracted abstinence compared to controls, an effect attenuated by nor-BNI. These results suggest that the DYN/KOR system plays role in mediating both short- and long-term behavioral changes associated with depression following chronic alcohol exposure.

Comparison of the Role of D1- and D2-Like Receptors in the CA1 Region of the Hippocampus in the Reinstatement Induced by a Subthreshold Dose of Morphine and Forced Swim Stress in Extinguished Morphine-CPP in Rats

Reward-seeking and relapse to drug use are two characteristics of addiction and reports have indicated the role of hippocampal structures in reward learning. To find the best ways of treatment, the understanding of the neurobiological mechanisms of reward and its involved factors is a must. For this reason, in the present study, we aimed to investigate the role of D1- and D2-like dopamine receptors and compared their activities in the CA1 region, focusing on the reinstatement induced by forced swim stress (FSS) or the combination of FSS and a subthreshold dose of morphine in extinguished morphine-CPP in rats. The rats were bilaterally implanted by two separate cannulas into the CA1 region. The animals received different doses of SCH23390 or sulpiride (0.5, 2, and 4µg/0.5µl vehicle/side) into the CA1 region on the reinstatement day and were tested for FSS-induced reinstatement or the combination of FSS and a subthreshold dose of morphine in separate groups. Our findings indicated that the D1- and D2-like receptor antagonists attenuated the reinstatement induced by the combination of FSS and the subthreshold dose of morphine. The behavioral results were more prominent in the groups of animals that received SCH23390 as compared to sulpiride. The data may suggest a role for the dopamine receptors in the CA1 region in relapse to drugs of abuse, which may be induced by exposure to a stressor.

Involvement of orexinergic receptors in the nucleus accumbens, in the effect of forced swim stress on the reinstatement of morphine seeking behaviors

Orexinergic system is involved in primary rewards; the neural circuit of the ventral tegmental area (VTA), nucleus accumbens (NAc), prefrontal cortex and amygdala represents overlapping elements mediating the rewarding effects of drugs and stressful experiences. The NAc integrates reward-related information from the VTA. Also, it has been indicated that orexinergic system activates the mesolimbic dopamine projecting neurons to the NAc and promotes the development of reward in rodents. Therefore, in the present study, the conditioned place preference (CPP) paradigm was used to determine the role of the two types of orexin receptors (OXR) in the NAc in forced swim stress (FSS), as physical stress, and/or priming-induced reinstatement of morphine. The CPP was induced by injecting morphine (5 mg/kg, SC for 3 days) and lasted for eight free-morphine days; the reinstatement was induced by administration of effective priming dose of morphine (1 mg/kg; sc). The extinguished rats received intra-NAc injection of SB334867 as OX1R antagonist or TCSOX229 as OX2R antagonist before effective priming dose injection of morphine (1 mg/kg; sc). In others, the extinguished rats were given intra-NAc injection of SB334867 or TCSOX229 and then, they underwent FSS before injection of ineffective priming dose of morphine (0.5 mg/kg; sc). Our results showed that intra-accumbal administration of SB334867 or TCSOX229 could inhibit morphine priming- and FSS-induced reinstatement of extinguished morphine-seeking in the rats. It seems that OXR in the NAc may be involved in reward and could play an important role in the effect of stress on reinstatement of morphine-seeking behaviors in this area.

High-Salt Exposure During Perinatal Development Enhances Stress Sensitivity.

Excess consumption of dietary sodium during pregnancy has been shown to impair offspring cardiovascular function and enhance salt preference in adulthood, but little is known regarding the long-term impact of this nutritional surplus on offspring brain morphology and behavior. Using a combination of cellular and behavioral approaches, we examined the impact of maternal salt intake during the perinatal period on structural plasticity in the prefrontal cortex (PFC) and nucleus accumbens (NAc) in weanling and adult offspring as well as reward- and stress-driven behaviors in adult offspring. We found that weanling rats born to 4% NaCl-fed dams exhibited an increase and decrease in thin spine density in the infralimbic PFC (IL-PFC) and prelimbic PFC (PL-PFC), respectively, as well as an increase in mushroom spine density in the NAc shell, compared to 1% NaCl-fed controls. Structural changes in the IL-PFC and NAc shell persisted into adulthood, the latter of which is a phenotype that has been observed in rats exposed to early life stress. There was no effect of maternal salt intake on reward-driven behaviors, including sucrose preference, conditioned place preference (CPP) for cocaine, and forced swim stress (FSS)-induced reinstatement of cocaine-induced CPP. However, rats born to high-salt fed dams spent less time swimming in the FSS and displayed heightened plasma CORT levels in response to the FSS compared to controls, suggesting that early salt exposure increases stress sensitivity. Overall, our results suggest that perinatal salt exposure evokes lasting impacts on offspring physiology and behavior.

Increased Synthesis of Chondroitin Sulfate Proteoglycan Promotes Adult Hippocampal Neurogenesis in Response to Enriched Environment.

Chondroitin sulfate proteoglycan (CSPG) is a candidate regulator of embryonic neurogenesis. The aim of this study was to specify the functional significance of CSPG in adult hippocampal neurogenesis using male mice. Here, we showed that neural stem cells and neuronal progenitors in the dentate gyrus were covered in part by CSPG. Pharmacological depletion of CSPG in the dentate gyrus reduced the densities of neuronal progenitors and newborn granule cells. 3D reconstruction of newborn granule cells showed that their maturation was inhibited by CSPG digestion. The novel object recognition test revealed that CSPG digestion caused cognitive memory impairment. Western blot analysis showed that expression of β-catenin in the dentate gyrus was decreased by CSPG digestion. The amount of CSPG in the dentate gyrus was increased by enriched environment (EE) and was decreased by forced swim stress. In addition, EE accelerated the recovery of CSPG expression in the dentate gyrus from the pharmacological depletion and promoted the restoration of granule cell production. Conversely, the densities of newborn granule cells were also decreased in mice that lacked chondroitin sulfate N-acetylgalactosaminyltransferase 1 (CSGalNAcT1), a key enzyme for CSPG synthesis (T1KO mice). The capacity of EE to promote granule cell production and improve cognitive memory was impaired in T1KO mice. These findings indicate that CSPG is involved in the regulation of adult hippocampal neurogenesis and suggest that increased synthesis of CSPG by CSGalNacT1 may mediate promotion of granule cell production and improvement of cognitive memory in response to EE.SIGNIFICANCE STATEMENT Chondroitin sulfate proteoglycan (CSPG) is a candidate regulator of embryonic neurogenesis. Here, we specified the role of CSPG in adult neurogenesis in the mouse hippocampus. Digestion of CSPG in the dentate gyrus impaired granule cell production and cognitive memory. Enriched environment (EE) promoted the recovery of CSPG expression and granule cell production from the CSPG digestion. Additionally, adult neurogenesis was impaired in mice that lacked a key enzyme for CSPG synthesis (T1KO mice). The capacity of EE to promote granule cell production and cognitive memory was impaired in T1KO mice. Altogether, these findings indicate that CSPG underlies adult hippocampal neurogenesis and suggest that increased synthesis of CSPG may mediate promotion of granule cell production in response to EE.

Orexin prevents depressive-like behavior by promoting stress resilience

Hypothalamic neuropeptide orexin has been implicated in the pathophysiology of psychiatric disorders and accumulating clinical evidence indicates a potential link between orexin and depression. However, the exact role of orexin in depression, particularly the underlying neural substrates and mechanisms, remains unknown. In this study, we reveal a direct projection from the hypothalamic orexinergic neurons to the ventral pallidum (VP), a structure that receives an increasing attention for its critical position in rewarding processing, stress responses, and depression. We find that orexin directly excites GABAergic VP neurons and prevents depressive-like behaviors in rats. Two orexin receptors, OX1R and OX2R, and their downstream Na+–Ca2+ exchanger and L-type Ca2+ channel co-mediate the effect of orexin. Furthermore, pharmacological blockade or genetic knockdown of orexin receptors in VP increases depressive-like behaviors in forced swim test and sucrose preference test. Intriguingly, blockage of orexinergic inputs in VP has no impact on social proximity in social interaction test between novel partners, but remarkably strengthens social avoidance under an acute psychosocial stress triggered by social rank. Notably, a significantly increased orexin level in VP is accompanied by an increase in serum corticosterone in animals exposed to acute stresses, including forced swimming, food/water deprivation and social rank stress, rather than non-stress situations. These results suggest that endogenous orexinergic modulation on VP is especially critical for protecting against depressive reactions to stressful events. The findings define an indispensable role for the central orexinergic system in preventing depression by promoting stress resilience.

Angiotensin II type 1 receptor blocker losartan attenuates locomotor, anxiety-like behavior, and passive avoidance learning deficits in a sub-chronic stress model.

Objective(s):Stress alters sensory and cognitive function in humans and animals. Angiotensin (AT) receptors have demonstrated well-established interactions in sets of physiological phenomena. AT1 receptors can play a part in stress-induced activation of hypothalamic-pituitary-adrenal (HPA) axis; besides angiotensinergic neurotransmission plays a pivotal role in stress-evoked physiological responses. AT1 receptors are also involved in nociception and memory. The objective of the current study was to evaluate the effects of losartan as an AT1R antagonist in locomotor activity, nociception and memory impairments induced by sub-chronic swim stress.Materials and Methods:A two-session forced swimming stress protocol was administered to the rats. Pretreatment with losartan (10 mg/kg, IP) or saline was made before each swimming session. Locomotor activity, anxiety-like behavior, nociception, and passive avoidance learning were evaluated 24 hr after last swim stress session. Results:Swim stress induced increased anxiety-like behavior in the open field test, which pretreatment with losartan did counterbalance. Increased thermal threshold was observed in the nociceptive measurement after swim stress. Pretreatment with losartan attenuated the increased threshold and also inhibited a decreased step-through latency that was observed in the memory paradigm after swim stress. Conclusion:The results of this study indicate that sub-chronic swim stress impairs passive avoidance learning, anxiety-like behaviors, and nociception; and AT1 receptor seems to have a modulatory role in these alterations. However, further studies are suggested to examine the protective effect of AT1R inhibitors on stress-induced impairments in sensory and cognitive function.

Absence of Stress Response in Dorsal Raphe Nucleus in Modulator of Apoptosis 1-Deficient Mice

Modulator of apoptosis 1 (MOAP-1) is a Bcl-2-associated X Protein (BAX)-associating protein that plays an important role in regulating apoptosis. It is highly enriched in the brain but its function in this organ remains unknown. Studies on BAX−/− mice suggested that disruption of programmed cell death may lead to abnormal emotional states. We thus hypothesize that MOAP-1−/− mice may also display stress-related behavioral differences and perhaps involved in stress responses in the brain and investigated if a depression-like trait exists in MOAP-1−/− mice, and if so, whether it is age related, and how it relates to central serotonergic stress response in the dorsal raphe nucleus. Young MOAP-1−/− mice exhibit depression-like behavior, in the form of increased immobility time when compared to age-matched wild-type mice in the forced swimming test, which is abolished by acute treatment of fluoxetine. This is supported by data from the tail suspension and sucrose preference tests. Repeated forced swimming stress causes an up-regulation of tryptophan hydroxylase 2 (TPH2) and a down-regulation of brain-derived neurotrophic factor (BDNF) in the dorsal raphe nucleus (DRN) in young wild-type (WT) control mice. In contrast, TPH2 up-regulation was not observed in aged WT mice. Interestingly, such a stress response appears absent in both young and aged MOAP-1−/− mice. Aged MOAP-1−/− and WT mice also have similar immobility times on the forced swimming test. These data suggest that MOAP-1 is required in the regulation of stress response in the DRN. Crosstalk between BDNF and 5-HT appears to play an important role in this stress response.

Sensitivity to diazepam after a single session of forced swim stress in weaning Wistar rats.

The present study investigated the sensitivity to stress and diazepam in weaning (21-day old) Wistar rats. A single 15-min session of forced swimming was used to induce anxiety-like behavior. The group that was forced to swim exhibited an increase in anxiety-like behavior in the elevated plus maze (EPM) and open field test (OFT) compared to the non-stressed group. Diazepam (1 h before the tests) reduced anxiety-like behavior in rats forced to swim compared to the vehicle stressed group. The dose-response curve for diazepam indicated that the 0.5 mg kg-1 dose (1 h before the EPM and OFT) was the minimum effective dose in reducing anxiety-like behavior without altering locomotor activity in weaning rats. These results indicate that weaning rats can develop anxiety-like behavior after a brief, single session of stress, and that rats at this age are seemingly more sensitive to diazepam than adult rats, which may be taken into account for clinical applications.

Role of orexin-1 and orexin-2 receptors in the CA1 region of hippocampus in the forced swim stress- and food deprivation-induced reinstatement of morphine seeking behaviors in rats

Hippocampus (HIP) is an essential brain site to study reward-related learning tasks, such as conditioning place preference (CPP) that can measure the preference for environmental stimuli related to reward. Furthermore, orexin neurons, situated exclusively in the lateral hypothalamus (LH) and link the rewarding effects of drugs of abuse in the LH and the CA1 region of the HIP. Therefore, in this study adult male rats were conditioned with morphine using a CPP paradigm. After the eighth day of the extinction period, on the reinstatement day, orexin-1 and orexin-2 receptor antagonists were administered bilaterally into the CA1 region prior to acute stress. Using two different types of acute stress, forced swim stress (FSS) and food deprivation (FD), the role of orexin-1 and orexin-2 receptors in the CA1 brain region in FSS and FD induced reinstatement was investigated. Our results showed that application of the orexin-1 and orexin-2 antagonists, SB334867 and TCSOX2 29, respectively, reduced the CPP scores in the reinstatement phase. Moreover, it can be concluded that orexin neurons are activated in acute stress states, such as FSS and FD, as blocking the orexin receptors, decreased the effects of acute stress in triggering the reinstatement of morphine-CPP.