Chronic stress alters amphetamine effects on behavior and synaptophysin levels in female rats

Nrf2 activation rescues stress-induced depression-like behaviour and inflammatory responses in male but not female rats

BACKGROUND

Major depressive disorder (MDD) is a recurring affective disorder that is two times more prevalent in females than males. Evidence supports immune system dysfunction as a major contributing factor to MDD, notably in a sexually dimorphic manner. Nuclear factor erythroid 2-related factor 2 (Nrf2), a regulator of antioxidant signalling during inflammation, is dysregulated in many chronic inflammatory disorders; however, its role in depression and the associated sex differences have yet to be explored. Here, we investigated the sex-specific antidepressant and immunomodulatory effects of the potent Nrf2 activator dimethyl fumarate (DMF), as well as the associated gene expression profiles.

METHODS

Male and female rats were treated with vehicle or DMF (25 mg/kg) whilst subjected to 8 weeks of chronic unpredictable stress. The effect of DMF treatment on stress-induced depression- and anxiety-like behaviours, as well as deficits in recognition and spatial learning and memory were then assessed. Sex differences in hippocampal (HIP) microglial activation and gene expression response were also evaluated.

RESULTS

DMF treatment during stress exposure had antidepressant effects in male but not female rats, with no anxiolytic effects in either sex. Recognition learning and memory and spatial learning and memory were impaired in chronically stressed males and females, respectively, and DMF treatment rescued these deficits. DMF treatment also prevented stress-induced HIP microglial activation in males. Conversely, females displayed no HIP microglial activation associated with stress exposure. Last, chronic stress elicited sex-specific alterations in HIP gene expression, many of which were normalized in animals treated with DMF. Of note, most of the differentially expressed genes in males normalized by DMF were related to antioxidant, inflammatory or immune responses.

CONCLUSIONS

Collectively, these findings support a greater role of immune processes in males than females in a rodent model of depression. This suggests that pharmacotherapies that target Nrf2 have the potential to be an effective sex-specific treatment for depression.

Effectiveness of coenzyme Q10 on learning and memory and synaptic plasticity impairment in an aged Aβ-induced rat model of Alzheimer's disease: a behavioral, biochemical, and electrophysiological study

RATIONALE

Aging is the major risk factor for Alzheimer's disease (AD), and cognitive and memory impairments are common among the elderly. Interestingly, coenzyme Q10 (Q10) levels decline in the brain of aging animals. Q10 is a substantial antioxidant substance, which has an important role in the mitochondria.

OBJECTIVE

We assessed the possible effects of Q10 on learning and memory and synaptic plasticity in aged β-amyloid (Aβ)-induced AD rats.

METHODS

In this study, 40 Wistar rats (24-36 months old; 360-450 g) were randomly assigned to four groups (n = 10 rats/group)-group I: control, group II: Aβ, group III: Q10; 50 mg/kg, and group IV: Q10+Aβ. Q10 was administered orally by gavage daily for 4 weeks before the Aβ injection. The cognitive function and learning and memory of the rats were measured by the novel object recognition (NOR), Morris water maze (MWM), and passive avoidance learning (PAL) tests. Finally, malondialdehyde (MDA), total antioxidant capacity (TAC), total thiol group (TTG), and total oxidant status (TOS) were measured.

RESULTS

Q10 improved the Aβ-related decrease in the discrimination index in the NOR test, spatial learning and memory in the MWM test, passive avoidance learning and memory in the PAL test, and long-term potentiation (LTP) impairment in the hippocampal PP-DG pathway in aged rats. In addition, Aβ injection significantly increased serum MDA and TOS levels. Q10, however, significantly reversed these parameters and also increased TAC and TTG levels in the Aβ+Q10 group.

CONCLUSIONS

Our experimental findings suggest that Q10 supplementation can suppress the progression of neurodegeneration that otherwise impairs learning and memory and reduces synaptic plasticity in our experimental animals. Therefore, similar supplemental Q10 treatment given to humans with AD could possibly provide them a better quality of life.

Sex differences in cognition following variations in endocrine status

Spatial memory, mediated primarily by the hippocampus, is responsible for orientation in space and retrieval of information regarding location of objects and places in an animal's environment. Since the hippocampus is dense with steroid hormone receptors and is capable of robust neuroplasticity, it is not surprising that changes in spatial memory performance occur following a variety of endocrine alterations. Here, we review cognitive changes in both spatial and nonspatial memory tasks following manipulations of the hypothalamic-pituitary-adrenal and gonadal axes and after exposure to endocrine disruptors in rodents. Chronic stress impairs male performance on numerous behavioral cognitive tasks and enhances or does not impact female cognitive function. Sex-dependent changes in cognition following stress are influenced by both organizational and activational effects of estrogen and vary depending on the developmental age of the stress exposure, but responses to gonadal hormones in adulthood are more similar than different in the sexes. Also discussed are possible underlying neural mechanisms for these steroid hormone-dependent, cognitive effects. Bisphenol A (BPA), an endocrine disruptor, given at low levels during adolescent development, impairs spatial memory in adolescent male and female rats and object recognition memory in adulthood. BPA's negative effects on memory may be mediated through alterations in dendritic spine density in areas that mediate these cognitive tasks. In summary, this review discusses the evidence that endocrine status of an animal (presence or absence of stress hormones, gonadal hormones, or endocrine disruptors) impacts cognitive function and, at times, in a sex-specific manner.

Effect of Cold Stress on Neurobehavioral and Physiological Parameters in Rats

Objective: Cold stress is an important current issue and implementing control strategies to limit its sometimes harmful effects is crucial. Cold is a common stressor that can occur in our work and our occupational or leisure time activities every day. There are substantial studies on the effects of chronic stress on memory and behavior, although, the cognitive changes and anxiety disorders that can occur after exposure to chronic intermittent cold stress are not completely characterized. Therefore, the present study was undertaken with an aim to investigate the effects of chronic intermittent cold stress on body weight, food intake and working memory, and to elucidate cold stress related anxiety disorders using cognitive and behavioral test batteries. Methods: We generated a cold stress model by exposing rats to chronic intermittent cold stress for 5 consecutive days and in order to test for the potential presence of sex differences, a comparable number of male and female rats were tested in the current study. Then, we measured the body weights, food intake and the adrenal glands weight. Working memory and recognition memory were assessed using the Y maze and the Novel Object Recognition (NOR) tasks. While, sex differences in the effects of chronic stress on behavior were evaluated by the elevated plus maze (EPM), open field maze (OF), and Marble burying (MB) tests. Results: We found that 2 h exposure to cold (4°C) resulted in an increase in the relative weight of the adrenal glands in male rats. Given the same chronic stress 5 days of cold exposure (2 h per day), increased weight gain in male rats, while females showed decreased food intake and no change in body weight. Both sexes successfully performed the Y maze and object recognition (OR) tasks, indicating intact spatial working memory performance and object recognition abilities in both male and female rats. In addition, we have shown that stress caused an increase in the level of anxiety in male rats. In contrast, the behavior of the female rats was not affected by cold exposure. Conclusion: Overall, the current results provide preliminary evidence that chronic intermittent cold stress model may not be an efficient stressor to female rats. Females exhibit resilience to cold exposure that causes an increase in the level of anxiety in male rats, which demonstrates that they are affected differently by stress and the gender is an important consideration in experimental design.

Understanding stress: Insights from rodent models

Through incorporating both physical and psychological forms of stressors, a variety of rodent models have provided important insights into the understanding of stress physiology. Rodent models also have provided significant information with regards to the mechanistic basis of the pathophysiology of stress-related disorders such as anxiety disorders, depressive illnesses, cognitive impairment and post-traumatic stress disorder. Additionally, rodent models of stress have served as valuable tools in the area of drug screening and drug development for treatment of stress-induced conditions. Although rodent models do not accurately reproduce the biochemical or physiological parameters of stress response and cannot fully mimic the natural progression of human disorders, yet, animal research has provided answers to many important scientific questions. In this review article, important studies utilizing a variety of stress models are described in terms of their design and apparatus, with specific focus on their capabilities to generate reliable behavioral and biochemical read-out. The review focusses on the utility of rodent models by discussing examples in the literature that offer important mechanistic insights into physiologically relevant questions. The review highlights the utility of rodent models of stress as important tools for advancing the mission of scientific research and inquiry.

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Stressful life events may lead to the onset of severe psychopathologies in humans.

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Rodents may model many features of stress exposure in human populations.

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Induction of stress via pharmacological and psychological manipulations alter rodent behavior.

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Mechanistic rodent studies reveal key molecular targets critical for new therapeutic targets.

Chronic unpredictable intermittent restraint stress disrupts spatial memory in male, but not female rats

Chronic stress leads to sex-dependent outcomes on spatial memory by producing deficits in males, but not in females. Recently it was reported that compared to daily restraint, intermittent restraint (IR) produced more robust stress and anxiety responses in male rats. Whether IR would be sufficiently robust to impair hippocampal-dependent spatial memory in both male and female rats was investigated. IR involved mixing restraint with non-restraint days over weeks before assessing spatial memory and anxiety profile on the radial arm water maze, object placement, novel object recognition, Y-maze, open field and novelty suppressed feeding. Experiments 1 and 2 used Sprague-Dawley male rats only and determined that IR for 6 h/d (IR6), but not 2 h/d, impaired spatial memory and that task order was important. In experiment 3, IR6 was extended for 6wks before spatial memory testing commenced using both sexes. Unexpectedly, an extended IR6 paradigm failed to impair spatial memory in either sex, suggesting that by 6wks IR6 may have become predictable. In experiment 4, an unpredictable IR (UIR) paradigm was implemented, in which restraint duration (30 or 60-min) combined with orbital shaking, time of day, and the days off from UIR were varied. UIR impaired spatial memory in males, but not in females. Together with other reports, these findings support the interpretation that chronic stress negatively impairs hippocampal-dependent function in males, but not in females. We interpret these findings to show that females are more resilient to chronic stress than are males as it pertains to spatial ability.

Interaction of stress and stimulants in female rats: Role of chronic stress on later reactivity to methamphetamine

Previous research in humans and animals suggests that prior exposure to stress alters responsivity to drugs of abuse, including psychostimulants. Male rats show an augmented striatal dopamine response to methamphetamine following exposure to chronic unpredictable stress (CUS). Compared to males, female rats have been shown to be highly sensitive to the effects of stimulants and stress independently, however few studies have examined the interaction between stress and stimulants in female rats. Therefore, the current study investigated whether prior exposure to chronic stress potentiated the behavioral and neurochemical responses to an acute injection of methamphetamine in female rats. Adult female Sprague-Dawley rats were either exposed to CUS or left undisturbed (control) and then two weeks later received an injection of 1.0 or 7.5 mg/kg methamphetamine. Based on open field findings, a subsequent group of rats were exposed to CUS or left undisturbed and then two weeks later received 7.5 mg/kg methamphetamine and either dopamine efflux in the dorsal striatum or nucleus accumbens was measured or methamphetamine and amphetamine levels were measured in the brain and plasma. Female rats exposed to CUS traveled greater distances in the open field immediately following an injection of 7.5 mg/kg, but not 1.0 mg/kg, of methamphetamine and then showed high levels or stereotypy similar to control rats. Animals exposed to CUS had significantly greater increases in dorsal striatum dopamine following an acute injection of 7.5 mg/kg methamphetamine compared to control rats, but not in the nucleus accumbens. These differences were not due to group differences in levels of methamphetamine or amphetamine in the brain or plasma. The current findings demonstrate stress-augmented neurochemical responses to a dose of methamphetamine, similar to that self-administered, which increases understanding of the cross-sensitization between stress and methamphetamine in females.

The effects of cinnamaldehyde on acute or chronic stress-induced anxiety-related behavior and locomotion in male mice

Anxiety and stress are considered as universal psychiatric exhibitions of the present societies and lifestyles. Several experiments have been conducted to examine natural anxiolytic agents to find out an alternative to synthetic anxiolytic drugs. The present study investigated the anxiolytic effects of cinnamaldehyde (Cin) on mice behavior in the elevated plus maze (EPM) and open field (OF) tests. Sixty male Swiss mice, weighing 20-30 g, were divided into six groups including: acute stress + mazola oil; chronic stress + oil; acute stress + Cin (20 mg/kg); chronic stress + Cin; non-stress + oil; and non-stress + Cin groups. The groups were administered for seven days (once a day). The acute stress + Cin group showed a meaningful rise in the percentage of entries into the open arms compared to the acute stress + oil group (p <.05). The percentage of time spent in the open arms in the chronic stress + Cin group was significantly higher compared to the chronic stress + oil group (p < .01). The percentage of entries into the open arms increased significantly (p < .01) in the chronic stress + Cin group in comparison with the chronic stress + oil group. The Cin treated groups showed significant increases in the time spent in the center area and in the number of entries into the center area compared with the oil treated groups in OF test. The number of entries into the arms (total activity), as well as locomotor activity was not significant among groups. The results of the present study indicated that Cin, as a natural product, might have anxiolytic effects in mice behavior in the EPM and OF tests. Lay summary  The results demonstrated that the administration of cinnamaldehyde (Cin) produced anxiolytic effects in mice. Natural antioxidant products have been reported effective for anxiety. Synthetic medications have notable adverse effects. Therefore, these natural substances with broad therapeutic applicability are able to reduce anxiety-related behavior with rare side effects. According to the results, Cin could decrease anxiety-related behavior in mice.

Progesterone receptor expression in cajal-retzius cells of the developing rat dentate gyrus: Potential role in hippocampus-dependent memory

The development of medial temporal lobe circuits is critical for subsequent learning and memory functions later in life. The present study reports the expression of progesterone receptor (PR), a powerful transcription factor of the nuclear steroid receptor superfamily, in Cajal-Retzius cells of the molecular layer of the dentate gyrus of rats. PR was transiently expressed from the day of birth through postnatal day 21, but was absent thereafter. Although PR immunoreactive (PR-ir) cells did not clearly express typical markers of mature neurons, they possessed an ultrastructural morphology consistent with neurons. PRir cells did not express markers for GABAergic neurons, neuronal precursor cells, nor radial glia. However, virtually all PR cells co-expressed the calcium binding protein, calretinin, and the glycoprotein, reelin, both reliable markers for Cajal-Retzius neurons, a transient population of developmentally critical pioneer neurons that guide synaptogenesis of perforant path afferents and histogenesis of the dentate gyrus. Indeed, inhibition of PR activity during the first two weeks of life impaired adult performance on both the novel object recognition and object placement memory tasks, two behavioral tasks hypothesized to describe facets of episodic-like memory in rodents. These findings suggest that PR plays an unexplored and important role in the development of hippocampal circuitry and adult memory function.

Neuroprotective effects of melatonin on amphetamine-induced dopaminergic fiber degeneration in the hippocampus of postnatal rats

Chronic amphetamine (AMPH) abuse leads to damage of the hippocampus, the brain area associated with learning and memory process. Previous results have shown that AMPH-induced dopamine neurotransmitter release, reactive oxygen species formation, and degenerative protein aggregation lead to neuronal death. Melatonin, a powerful antioxidant, plays a role as a neuroprotective agent. The objective of this study was to investigate whether the protective effect of melatonin on AMPH-induced hippocampal damage in the postnatal rat acts through the dopaminergic pathway. Four-day-old postnatal rats were subcutaneously injected with 5-10 mg/kg AMPH and pretreated with 10 mg/kg melatonin prior to AMPH exposure for seven days. The results showed that melatonin decreased the AMPH-induced hippocampal neuronal degeneration in the dentate gyrus, CA1, and CA3. Melatonin attenuated the reduction in the expression of hippocampal synaptophysin, PSD-95, α-synuclein, and N-methyl-D-aspartate (NMDA) receptor protein and mRNA caused by AMPH. Melatonin attenuated the AMPH-induced reduction in dopamine transporter (DAT) protein expression in the hippocampus and the reduction in mRNA expression in the ventral tegmental area (VTA). Immunofluorescence demonstrated that melatonin not only prevented the AMPH-induced loss of DAT and NMDA receptor but also prevented AMPH-induced α-synuclein overexpression in the dentate gyrus, CA1, and CA3. Melatonin decreased the AMPH-induced reduction in the protein and mRNA of the NMDA receptor downstream signaling molecule, calcium/calmodulin-dependent protein kinase II (CaMKII), and the melatonin receptors (MT1 and MT2). This study showed that melatonin prevented AMPH-induced toxicity in the hippocampus of postnatal rats possibly via its antioxidative effect and mitochondrial protection.

The effects of methamphetamine and buprenorphine, and their interaction on anxiety-like behavior and locomotion in male rats

Methamphetamine (Meth) abuse and dependence are major global problems. Most of previous studies showed that Meth is anxiogenic. While buprenorphine (Bup) is used to treat anxiety-related behaviors, the effects of Meth in combination with Bup on anxiety-like behavior are unclear. In this study, we examined the effects of these drugs on anxiety-like behavior with the elevated plus maze (EPM) and open field (OF) tests, which are widely used to assess anxiety-like behavior in small rodents. Forty male Wistar rats were divided into four groups: sham, Meth, Bup, and Bup+Meth. The groups were administered their assigned treatments for 7days. The time spent in the open arms, and number of total entries into the arms (total activity) in the EPM were recorded. In addition, locomotor activity and number of entrances into the center area in the OF were recorded. The 7-day administration of Meth or Bup increased open arm exploration in the EPM. In contrast, the combined administration of Bup and Meth had the opposite effects. In addition, Meth and Bup had no effects on total and locomotor activity. Furthermore, the rats in the Meth and Bup groups spent more time in the center of the OF, while the group given both Bup and Meth spent less time in the center of the OF. The administration of Meth and Bup alone was anxiolytic in rats, whereas the coadministration of Bup and Meth was anxiogenic.

Sex differences in chronic stress effects on cognition in rodents

Chronic stress causes deleterious changes in physiological function in systems ranging from neural cells in culture to laboratory rodents, sub-human primates and humans. It is notable, however, that the vast majority of research in this area has been conducted in males. In this review, we provide information about chronic stress effects on cognition in female rodents and contrast it with responses in male rodents. In general, females show cognitive resilience to chronic stressors which impair male cognitive function using spatial tasks including the radial arm maze, radial arm water maze, Morris water maze, Y-maze and object placement. Moreover, stress often enhances female performance in some of these cognitive tasks. Memory in females is not affected by stress in non-spatial memory tasks like recognition memory and temporal order recognition memory while males show impaired memory following stress. We discuss possible bases for these sex-dependent differences including the use of different strategies by the sexes to solve cognitive tasks. Whether the sex differences result from changes in non-mnemonic factors is also considered. Sex-dependent differences in alcohol and drug influences on stress responses are also described. Finally, the role of neurally derived estradiol in driving sex differences and providing resilience to stress in females is shown. The importance of determining the nature and extent of sex differences in stress responses is that such differences may provide vital information for understanding why some stress related diseases have different incidence rates between the sexes and for developing novel therapeutic treatments.

Estradiol: Mediator of memories, spine density and cognitive resilience to stress in female rodents

Estradiol rapidly activates, within minutes, various physiological functions and behaviors including cognition in rodents. This review describes rapid effects of estradiol on hippocampal dependent learning and memory tasks in rodents. Mechanisms underlying the memory enhancements including the activation of signaling molecules and the enhancement of dendritic spinogenesis are briefly reviewed. In addition, the role of estradiol in the cognitive resilience to chronic stress exhibited only in females is discussed including contributions of ovarian as well as intra-hippocampally derived estrogens to this sex difference. Finally, speculations on possible physiologic functions for rapid mnemonic changes mediated by estrogens are made. Overall, the emergence of a novel and powerful mechanism for regulation of cognition by estradiol is described.

Female rats exposed to stress and alcohol show impaired memory and increased depressive-like behaviors

Exposure to daily life stressors is associated with increases in anxiety, depression, and overall negative affect. Alcohol or other psychoactive drugs are often used to alleviate stress effects. While females are more than twice as likely to develop mood disorders and are more susceptible to dependency than males, they are infrequently examined. In this study, female rats received no stress/no alcohol control (CON), alcohol alone (ALC), stress alone (STR), or stress plus alcohol (STR+ALC). Stress consisted of restraint for 6h/day/7days, and alcohol was administered immediately following restraint via gastric gavage at a dose of 2.0g/kg. Dependent measures included tests utilizing object recognition (OR), Y-maze, elevated plus maze (EPM), forced swim (FST), blood alcohol content, corticosterone levels, and body weights. ALC, STR+ALC, but not stress alone, impaired memory on OR. All treatments impaired spatial memory on the Y-maze. Anxiety was not affected on the EPM, but rats treated with alcohol or in combination with stress showed increased immobility on the FST, suggestive of alcohol-induced depression. Previously, we found alcohol reversed deleterious effects of stress on memory and mood in males, but current results show that females reacted negatively when the two treatments were combined. Thus, responses to alcohol, stress and their combination suggest that sex specific treatments are needed for stress-induced behavioral changes and that self-medicating with alcohol to cope with stress maybe deleterious in females.

Prenatal loud music and noise: differential impact on physiological arousal, hippocampal synaptogenesis and spatial behavior in one day-old chicks

Prenatal auditory stimulation in chicks with species-specific sound and music at 65 dB facilitates spatial orientation and learning and is associated with significant morphological and biochemical changes in the hippocampus and brainstem auditory nuclei. Increased noradrenaline level due to physiological arousal is suggested as a possible mediator for the observed beneficial effects following patterned and rhythmic sound exposure. However, studies regarding the effects of prenatal high decibel sound (110 dB; music and noise) exposure on the plasma noradrenaline level, synaptic protein expression in the hippocampus and spatial behavior of neonatal chicks remained unexplored. Here, we report that high decibel music stimulation moderately increases plasma noradrenaline level and positively modulates spatial orientation, learning and memory of one day-old chicks. In contrast, noise at the same sound pressure level results in excessive increase of plasma noradrenaline level and impairs the spatial behavior. Further, to assess the changes at the molecular level, we have quantified the expression of functional synapse markers: synaptophysin and PSD-95 in the hippocampus. Compared to the controls, both proteins show significantly increased expressions in the music stimulated group but decrease in expressions in the noise group. We propose that the differential increase of plasma noradrenaline level and altered expression of synaptic proteins in the hippocampus are responsible for the observed behavioral consequences following prenatal 110 dB music and noise stimulation.

The interaction of chronic restraint stress and voluntary alcohol intake: effects on spatial memory in male rats

Alcohol consumption and exposure to stressful life events activate similar neural pathways and thus result in several comparable physiological and behavioral effects. Alcoholics in treatment claim that life stressors are the leading cause of continued drinking or relapse. However, few studies have investigated the interactive effects of stress and alcohol on cognitive behavior. The effects of restraint stress, alcohol, and stress in combination with alcohol were examined on a spatial memory test, the object placement (OP) task. In addition, intake levels were measured to determine if stress altered general consumption of alcohol. Male Sprague-Dawley rats were assigned to one of four conditions: no alcohol/no stress control (CON), stress alone (STR), alcohol alone (ALC), and STR+alcohol (STR+ALC). Following each restraint stress bout, the STR+ALC and the ALC groups were given access to 8% alcohol for 1h using the two-bottle choice limited access paradigm. As predicted, the STR+ALC group significantly increased alcohol consumption, while the ALC group had consistent drinking over the 10-day treatment. On the OP task, STR and ALC groups performed at chance levels, whereas the CON and STR+ALC groups significantly discriminated between objects in the new and old locations. These data show that stress increases alcohol intake and the intake of alcohol is associated with reduction of the stress-induced impairment of spatial memory. The data have important implications for the development of alcohol abuse and its treatment.

Effects of Glycyrrhizae Radix on Repeated Restraint Stress-induced Neurochemical and Behavioral Responses

Glycyrrhizae radix (GR) is an herbal medicine that is commonly used in the East Asia for treating a variety of diseases, including stomach disorders. The objective of the present study was to examine the anti-stress effects of GR on repeated stress-induced alterations of anxiety, learning and memory in rats. Restraint stress was administered for 14 days (2 h/day) to the rats in the Control and GR groups (400 mg/kg/day, PO). Starting on the eighth day, the rats were tested for spatial memory on the Morris water maze test (MW) and for anxiety on the elevated plus maze (EPM). We studied the changes of the expressions of cholineacetyl transferase (ChAT) and tyrosine hydroxylase (TH) in the locus coerleus (LC) using immunohistochemistry. The results showed that the rats treated with GR had significantly reduced stress-induced deficits on their learning and memory on the spatial memory tasks. In addition, the ChAT immunoreactivities were increased. Gor the EPM, treatment with GR increased the time spent in the open arms (p<0.001) as compared to that of the control group. Moreover, GR treatment also normalized the increases of the TH expression in the LC (p<0.001). In conclusion, administration of GR improved spatial learning and memory and reduced stress-induced anxiety. Thus, the present results suggest that GR has the potential to attenuate the behavioral and neurochemical impairments caused by stress.

The Effects of Astragalus Membranaceus on Repeated Restraint Stress-induced Biochemical and Behavioral Responses

Astragalus Membranaceus (AM) is a useful Korean herb that has been clinically prescribed for stress-related illness. The objective of the present study was to examine the anti-stress effects of AM on repeated stress-induced alterations of anxiety, learning and memory in rats. Restraint stress was administered for 14 days (2h/day) and AM (400mg/kg) given by oral administration, in the AM group, for the same period. Starting on the eighth day, the rats were tested for spatial memory on the Morris water maze test (MW) and for anxiety on the elevated plus maze (EPM). Changes of expression on immunohistochemistry were studied for cholineacetyl transferase (ChAT) and tyrosine hydroxylase (TH) in the brain. The results showed that the rats treated with AM had significantly reduced stress-induced deficits on learning and memory on the spatial memory tasks. In addition, the ChAT immunoreactivities were increased. In the EPM, treatment with AM increased the time spent in the open arms (p<0.001) compared to the control group. In addition, AM treatment also normalized increases of TH expression in the LC (p<0.001). In conclusion, administration of AM improved spatial learning and memory and reduced stress-induced anxiety. Thus, the present results suggest that AM is able to recover behavioral and neurochemical impairments induced by stress.

Combined effects of acute stress and amphetamine on serial memory retrieval pattern in mice

INTRODUCTION

This study investigated the dose-effect of amphetamine on contextual serial (contextual serial discrimination (CSD)) and serial (serial discrimination (SD)) memory in acutely stressed versus nonstressed C57 Bl/6 Jico mice.

MATERIALS AND METHODS

Memory was first evaluated in nonstress condition. Mice learned two consecutive discriminations (D1 and D2) in a four-hole board involving either distinct (CSD) or identical (SD) internal contextual cues. All mice received i.p. injections of vehicle before acquisition and vehicle or amphetamine 20 min before the memory retrieval phase occurring 24 h after acquisition.

RESULTS

Results showed that: (1) vehicle group expressed in both tasks a similar memory retrieval pattern, D2 being better retrieved than D1; (2) 2 mg/kg amphetamine significantly enhanced D1 but not D2 performance in both tasks, whereas 4 mg/kg amphetamine enhanced D2 but not D1 retrieval. Thus, amphetamine more specifically modulates serial order memory retrieval in a context-independent manner. In a further step, we studied the effect of an acute stress (electric foot shocks 5 min before retrieval) specifically on D1 performance of the CSD task in 2 mg/kg amphetamine-treated mice. Immediately after testing, blood was sampled to measure plasma corticosterone levels. Results showed that acute stress significantly improved D1 performance in vehicles but blocked the memory-enhancing effect of 2 mg/kg amphetamine, as compared to the nonstress condition. However, statistical analysis failed to evidence a significant interaction between treatments and conditions (stress vs nonstress) on corticosterone levels, contrary to another vigilance-enhancing drug, modafinil (Béracochéa, Psychopharmacology 196:1-13, 2008).

Chronic stress and neural function: accounting for sex and age

Cognitive responses to stress follow the temporally dependent pattern originally established by Selye (1) wherein short-term stressors elicit adaptive responses whereas continued stress (chronic) results in maladaptive changes--deleterious effects on physiological systems and impaired cognition. However, this pattern for cognitive effects appears to apply to only half the population (males) and, more specifically, to young, adult males. Females show different cognitive responses to stress. In contrast to impaired cognition in males after chronic stress, female rodents show enhanced performance on the same memory tasks after the same stress. Not only cognition, but anxiety, shows sex-dependent changes following chronic stress--stress is anxiolytic in males and anxiogenic in females. Moreover, behavioral responses to chronic stress are different in developing as well as aging subjects (both sexes) as compared to adults. In aged rats, chronic stress enhances recognition memory in both sexes, does not alter spatial memory, and anxiety effects are opposite to young adults. When pregnant dams are exposed to chronic stress, at adulthood the offspring display yet different consequences of stress on anxiety and cognition, and, in contrast to adulthood when the behavioral effects of stress are reversible, prenatal stress effects appear enduring. Changing levels of estradiol in the sexes over the lifespan appear to contribute to the differences in response to stress. Thus, theories of stress dependent modulations in CNS function--developed solely in male models, focused on peripheral physiological processes and tested in adults--may require revision when applied to a more diverse population (age- and sex-wise) at least in relation to the neural functions of cognition and anxiety. Moreover, these results suggest that other stressors and neural functions should be investigated to determine whether age, sex and gonadal hormones also have an impact.

Prenatal restraint stress and motherless rearing disrupts expression of plasticity markers and stress-induced corticosterone release in adult female Sprague–Dawley rats

This study investigated the effects of prenatal stress and complete maternal deprivation, using the artificial rearing (AR) paradigm, on the expression of neural plasticity markers and hypothalamic-pituitary-adrenal (HPA) axis responsivity to stress. Rats were exposed to stress during gestation (day 10-21) and postnatally were either artificially reared (AR) or mother reared (MR). AR involves complete separation of the pup from both the dam and the litter throughout the pre-weaning period. In adulthood, we measured levels of corticosterone (CORT) in response to restraint stress. Also, we examined the expression of synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex (MPFC) and the nucleus accumbens (Nacc), areas of the brain that mediate behavioral activation and attention, among other behaviors. Earlier work on the same rats indicated that these behavioral endpoints, such as locomotor activity and sensorimotor gating, are affected by our prenatal and postnatal manipulations. Prenatal stress decreased CORT at 20 and 90 min post-stressor in MR, but not in AR, animals. Also, in comparison to MR groups, AR decreased SYN and BDNF expression in the MPFC and Nacc. Additional somatosensory 'licking-like' stroking stimulation partially reversed the effects of AR. Prenatal stress did not have a robust main effect but affected the impact of the postnatal rearing condition on SYN expression and stress-induced CORT. These results suggest that both prenatal and postnatal adversities have an influence on HPA axis responsivity and alter the expression of plasticity related neuronal proteins.