Mineralocorticoid receptors in the medial prefrontal cortex and hippocampus mediate rats' unconditioned fear behaviour

Corticosterone is released from the adrenal cortex in response to stress, and binds to glucocorticosteroid receptors (GRs) and mineralocorticosteroid receptors (MRs) in the brain. Areas such as the dorsal hippocampus (DH), ventral hippocampus (VH) and medial prefrontal cortex (mPFC) all contain MRs and have been previously implicated in fear and/or memory.The purpose of the following experiments was to examine the role of these distinct populations of MRs in rats’ unconditioned fear and fear memory.The MR antagonist (RU28318) was microinfused into the DH, VH, or mPFC of rats. Ten minutes later, their unconditioned fear was tested in the elevated plus-maze and the shock-probe tests, two behavioral models of rat “anxiety.” Twenty-four hours later, conditioned fear of a non-electrified probe was assessed in rats re-exposed the shock-probe apparatus.Microinfusions of RU28318 into each of the three brain areas reduced unconditioned fear in the shock-probe burying test, but only microinfusions into the VH reduced unconditioned fear in the plus-maze test. RU28318 did not affect conditioned fear of the shock-probe 24 hr later.MRs in all three areas of the brain mediated unconditioned fear to a punctate, painful stimulus (probe shock). However, only MRs in the ventral hippocampus seemed to mediate unconditioned fear of the more diffuse threat of open spaces (open arms of the plus maze). In spite of the known roles of the hippocampus in spatial memory and conditioned fear memory, MRs within these sites did not appear to mediate memory of the shock-probe.     

The Effects of Inhaled <Emphasis Type="Italic">Pimpinella peregrina</Emphasis> Essential Oil on Scopolamine-Induced Memory Impairment,Anxiety, and Depression in Laboratory Rats

In the present study, we identified the effects of inhaled Pimpinella peregrina essential oil (1 and 3 %, for 21 continuous days) on scopolamine-induced memory impairment, anxiety, and depression in laboratory rats. Y-maze and radial arm-maze tests were used for assessing memory processes. Also, the anxiety and depressive responses were studied by means of the elevated plus-maze and forced swimming tests. The scopolamine alone-treated rats exhibited the following: decrease of the spontaneous alternation percentage in Y-maze test, increase of the number of working and reference memory errors in radial arm-maze test, along with decrease of the exploratory activity, the percentage of the time spent and the number of entries in the open arm within elevated plus-maze test and decrease of swimming time and increase of immobility time within forced swimming test. Inhalation of the P. peregrina essential oil significantly improved memory formation and exhibited anxiolytic- and antidepressant-like effects in scopolamine-treated rats. Our results suggest that the P. peregrina essential oil inhalation ameliorates scopolamine-induced memory impairment, anxiety, and depression. Moreover, studies on the P. peregrina essential oil may open a new therapeutic window for the prevention of neurological abnormalities closely related to Alzheimer’s disease.     

Chronic stress effects on memory: sex differences in performance and monoaminergic activity

Increasing evidence suggests that the time course of advantageous versus deleterious effects of stress on physiologic function is also apparent in some brain functions, including learning and memory. This article reviews the effects of chronic stress on behavioral performance and, more importantly, shows that sex of the subject, as well as duration and intensity of stress, is an important determinant of the functional/behavioral, neurochemical, and anatomical consequences of the stress. Following chronic stress (7-28 days of restraint, 6 h/day), male and female rats were tested on a visual memory task (object recognition) and two spatial memory tasks (object placement and radial arm maze). At 21 days, stress impaired males on all tasks while females were either enhanced (spatial memory tasks) or not impaired (nonspatial memory tasks). Additionally, the influence of the hypothalamic-pituitary-adrenocortical axis in mediating the sex-specific responses to stress is considered. Behavioral and neurochemical assessments following chronic stress in ovariectomized females, with and without estradiol, suggest that estrogen exerts both organizational and activational influences on the observed sex differences in response to stress. Furthermore, stress differentially affected central transmitter levels in the frontal cortex, hippocampus, and amygdala depending on sex. The possible role of these sex-specific changes in neurotransmitter levels in mediating behavioral differences in response to stress is discussed. While these results are thus far limited to a few studies and require both further investigation and verification, chronic stress appears to be associated with distinct, sex-differentiated behavioral/cognitive and neurochemical responses. We conclude that sex differences must be taken into account when investigating or describing stress and associated sequalae.     

Effects of hypoxic preconditioning on memory evaluated using the T-maze behavior test

Perioperative brain ischemia and stroke are leading causes of morbidity and mortality. Brief hypoxic preconditioning is known to have protective effects against hypoxic-ischemic insult in the brain. Current studies on the neuroprotective effects of ischemic preconditioning are based on histologic findings and biomarker changes. However, studies regarding effects on memory are rare. To precondition zebrafish to hypoxia, they were exposed to a dissolved oxygen (DO) concentration of 1.0?±?0.5?mg/L in water for 30?s. The hypoxic zebrafish were then exposed to 1.0?±?0.5?mg/L DO until the third stage of hypoxia, for 10 min?±?30?s. Zebrafish were assessed for memory retention after the hypoxic event. Learning and memory were tested using the T-maze, which evaluates memory based on whether or not zebrafish moves to the correct target compartment. In the hypoxic preconditioning group, infarct size was reduced compared with the hypoxic-only treated zebrafish group; memory was maintained to a degree similar to that in the hypoxia-untreated group. The hypoxic-only group showed significant memory impairments. In this study, we used a hypoxic zebrafish model and assessed the effects of ischemic preconditioning not only on histological damages but also on brain function, especially memory. This study demonstrated that a brief hypoxic event has protective effects in hypoxic brain damage and helped maintain memory in zebrafish. In addition, our findings suggest that the zebrafish model is useful in rapidly assessing the effects of ischemic preconditioning on memory.     

Effect of beta-lactotensin on acute stress and fear memory

β-Lactotensin (β-LT) is a bioactive peptide derived from bovine milk β-lactoglobulin and is a natural ligand for neurotensin receptors. We examined the effect of β-LT on restraint stress and fear memory in mice. Mice subjected to acute restraint stress exhibited a decreased number of head-dips and increased head-dip latency compared to non-stressed controls in the hole-board test, reflecting increased stress-induced behaviors. However, prior administration of β-LT improved the behaviors caused by stress. The anti-stress effect of β-LT was blocked by levocabastine, a neurotensin receptor subtype 2 (NTR2) antagonist. In the fear-conditioning test, the duration of freezing responses by cued fear conditioning was significantly reduced in mice administered β-LT compared with control mice. These results suggest that β-LT has an anti-stress effect and promotes the extinction of fear memory, which may be mediated by NTR2.     

Long-term individual housing in C57BL/6J and DBA/2 mice: assessment of behavioral consequences

The aim of the present study was to investigate the effects of individual housing on mouse behavior. The male mice of the C57BL/6J and DBA/2 strains were separated at the age of 4 weeks and kept in individual housing for 7 weeks until behavioral testing began. Their behavior was compared to the group-housed mice in a battery of tests during the following 7 weeks. The single-housed mice were hyperactive and displayed reduced habituation in the tests assessing activity and exploration. Reduced anxiety was established in the elevated plus-maze, but an opposite effect was observed in the dark-light (DL) and hyponeophagia tests. Immobility in the forced swimming test was reduced by social isolation. The DBA mice displayed higher anxiety-like behavior than the B6 mice in the plus-maze and DL exploration test, but hyponeophagia was reduced in the DBA mice. Moreover, all effects of individual housing on the exploratory and emotional behavior were more evident in the DBA than in the B6 mice. Novel object recognition and fear conditioning (FC) were significantly impaired in the single-housed mice, whereas water-maze (WM) learning was not affected. Marked strain differences were established in all three learning tests. The B6 mice performed better in the object recognition and FC tasks. Initial spatial learning in the WM was faster and memory retention slightly enhanced in the B6 mice. The DBA mice displayed lower preference to the new and enhanced preference to the old platform location than the B6 mice after reversal learning in the WM. We conclude that individual housing has strong strain- and test-specific effects on emotional behavior and impairs memory in certain tasks.     

The effects of 5-HT1B characterizing agents in the mouse elevated plus-maze

Although the serotonergic system has been implicated in the modulation of anxiety states, the specific receptor subtypes that mediate these states require clarification. The effects of drugs that act preferentially at 5-HT1B receptors were evaluated on the behavior elicited in the elevated plus-maze, an animal model of anxiety. Variations in the intensity of light affected mouse behavior in the plus-maze; lower light intensity increased the entries to and time spent on the open arm in a manner similar to that seen with stress-attenuating circumstances. Opposite effects were observed in high light-intensity, similar to effects seen under elevated stress conditions. Chlordiazepoxide produced increased entries and time spent on the open arm, whereas pentylenetetrazol (PTZ) produced opposite effects. The preferential 5-HT1B agents TFMPP and mCPP exhibited a profile similar to PTZ. The effects of TFMPP in the plus-maze were reversed by chlordiazepoxide, but not by the benzodiazepine receptor antagonist flumazenil, which suggests that this effect is not directly mediated by benzodiazepine receptors. The decreased entries and time spent on the open arm of the maze following TFMPP or mCPP administration was possibly mediated by an antagonistic action at 5-HT1B receptors, since this effect was reversed by the selective 5-HT1B agonist CGS 12066B. The present study further demonstrates the utility of mouse behavior in the elevated plus-maze as a model for identifying anxio-modulatory substances.     

Anxiolytic-like effect of the selective neuropeptide Y Y2 receptor antagonist BIIE0246 in the elevated plus-maze

The involvement of Neuropeptide Y (NPY) in the pathophysiology of mood disorders has been suggested by clinical and preclinical evidence. NPY Y1 and Y2 receptors have been proposed to mediate the NPY modulation of stress responses and anxiety related behaviors. To further investigate the role of Y2 receptors in anxiety we studied the effect of BIIE0246, a selective Y2 receptor antagonist, in the elevated plus-maze test. Rats treated with 1.0 nmol BIIE0246 showed an increase in the time spent on the open arm of the maze. In addition, to study the effects of the Y2 antagonism on NPY protein level, NPY-like immunoreactivity was measured in different brain regions following treatment with BIIE0246, but no statistically significant effects were observed. These results suggest that BIIE0246 has an anxiolytic-like profile in the elevated plus-maze.     

Alterations of behavior and spatial learning after unilateral entorhinal ablation of rats

The entorhinal cortex (EC) is the key input and output structure of the hippocampus. It plays a crucial role in sensory processing, memory and learning, as well as in mechanisms of epileptic seizures. Our previous studies on the 4-aminopyridin induced epilepsy model of rats showed that ablation of unilateral EC prompted weakening of limbic seizure manifestation, thus the possibility of therapeutical benefit of this kind of surgery can be risen. Open field, elevated plus-maze and Morris water-maze test were performed to analyze changes of the basal activity level, exploratory behavior, and spatial memory capacity, respectively, of adult Wistar rats having undergone left EC excision. Compared with the sham-operated control group, rats with lesions of the EC showed enhanced locomotor activity in the open-field test. The elevated plus-maze test revealed higher frequency of entries and more time spent in the open arms. Morris water-maze test suggested impairment of the spatial learning capacity following left lateral EC lesion. Therefore, our data showed that EC lesions induced hyperactivity, increased exploratory behavior, and impaired spatial learning. Entorhinal cortex ablation, as a potential method for controlling epileptic seizures has multiple effects on animals' behavior and spatial learning. To determine the cost-benefit ratio of a potential surgical intervention needs further experimental and human investigations.     

Spatial memory: are lizards really deficient?

In many animals, behaviours such as territoriality, mate guarding, navigation and food acquisition rely heavily on spatial memory abilities; this has been demonstrated in diverse taxa, from invertebrates to mammals. However, spatial memory ability in squamate reptiles has been seen as possible, at best, or non-existent, at worst. Of the few previous studies testing for spatial memory in squamates, some have found no evidence of spatial memory while two studies have found evidence of spatial memory in snakes, but have been criticized based on methodological issues. We used the Barnes maze, a common paradigm to test spatial memory abilities in mammals, to test for spatial memory abilities in the side-blotched lizard (Uta stansburiana). We found the existence of spatial memory in this species using this spatial task. Thus, our study supports the existence of spatial memory in this squamate reptile species and seeks to parsimoniously align this species with the diverse taxa that demonstrate spatial memory ability.     

Bisphenol A Does Not Affect Memory Performance in Adult Male Rats

Bisphenol A (BPA) is an estrogenic endocrine disruptor used for producing polycarbonate plastics and epoxy resins. This study investigated the effects of oral BPA administration on memory performance, general activity, and emotionality in adult male Sprague Dawley rats using a battery of behavioral tests, including an appetite-motivated maze test (MAZE test) used to assess spatial memory performance. In addition, in order to confirm the effects of BPA on spatial memory performance, we examined whether intrahippocampal injection of BPA affects spatial memory consolidation. In the MAZE test, although oral BPA administration at 10 mg/kg significantly altered the number of entries into the incorrect area compared to those of vehicle-treated rats, male rats given BPA through either oral administration or intrahippocampal injection failed to show significant differences in latencies to reach the reward. Also, oral BPA administration did not affect fear-motivated memory performance in the step-through passive avoidance test. Oral BPA administration at 0.05 mg/kg, the lowest dose used in this study, was correlated with a decrease in locomotor activity in the open-field test, whereas oral administration at 10 mg/kg, the highest dose used in this study, was correlated with a light anxiolytic effect in the elevated plus-maze test. The present study suggests that BPA in adulthood has little effect on spatial memory performance in male rats.     

Adding preferred color to a conventional reward method improves the memory of zebrafish in the T-maze behavior model

Zebrafish have become a useful model for studying behavior and cognitive functions. Recent studies have shown that zebrafish have natural color preference and the ability to form associative memories with visual perception. It is well known that visual perception enhances memory recall in humans, and we suggest that a similar phenomenon occurs in zebrafish. This study proposes that adding a visual perception component to a conventional reward method would enhance memory recall in zebrafish. We found that zebrafish showed greater preference for red cellophane over yellow in the training session but could not remember the preferred place in the memory test. However, the test memory recall was greater when the zebrafish were exposed to the red cellophane with a food reward during the training session, when compared with the use of food reward only. Furthermore, the red cellophane with food reward group showed more predictable memory recall than the food reward only group. These results propose that visual perception can increase memory recall by enhancing the consolidation processes. We suggest that color-cued learning with food reward is a more discriminative method than food reward alone for examining the cognitive changes in the zebrafish.

Abbreviations: WM: working memory; LTM: long-term memory     

Roles of testosterone and amygdaloid LTP induction in determining sex differences in fear memory magnitude

Women are thought to form fear memory more robust than men do and testosterone is suspected to play a role in determining such a sex difference. Mouse cued fear freezing was used to study the sex-related susceptibility and the role of testosterone in fear memory in humans. A 75-dB tone was found to provoke weak freezing, while 0.15-mA and 0.20-mA footshock caused strong freezing responses. No sex differences were noticed in the tone- or footshock-induced (naïve fear) freezing. Following the conditionings, female mice exhibited greater tone (cued fear)-induced freezing than did male mice. Nonetheless, female mice demonstrated indistinctive cued fear freezing across the estrous phases and ovariectomy did not affect such freezing in female mice. Orchidectomy enhanced the cued fear freezing in male mice. Systemic testosterone administrations and an intra-lateral nucleus of amygdala (LA) testosterone infusion diminished the cued fear freezing in orchidectomized male mice, while pretreatment with flutamide (Flu) eradicated these effects. Long-term potentiation (LTP) magnitude in LA has been known to correlate with the strength of the cued fear conditioning. We found that LA LTP magnitude was indeed greater in female than male mice. Orchidectomy enhanced LTP magnitude in males' LA, while ovariectomy decreased LTP magnitude in females' LA. Testosterone decreased LTP magnitude in orchidectomized males' LA and estradiol enhanced LTP magnitude in ovariectomized females' LA. Finally, male mice had lower LA GluR1 expression than female mice and orchidectomy enhanced the GluR1 expression in male mice. These findings, taken together, suggest that testosterone plays a critical role in rendering the sex differences in the cued fear freezing and LA LTP. Testosterone is negatively associated with LA LTP and the cued fear memory in male mice. However, ovarian hormones and LA LTP are loosely associated with the cued fear memory in female mice.     

fMRI Hippocampal Activity During a VirtualRadial Arm Maze

Numerous studies have shown that the hippocampus is critical for spatial memory. Within nonhuman research, a task often used to assess spatial memory is the radial arm maze. Because of the spatial nature of this task, this maze is often used to assess the function of the hippocampus. Our goal was to extrapolate this task to humans and examine whether healthy undergraduates utilize their hippocampus while performing a virtual reality version of the radial arm maze task. Thirteen undergraduates performed a virtual radial arm maze during functional magnetic resonance imaging. The brain maps of activity reveal bilateral hippocampal BOLD signal changes during the performance of this task. However, paradoxically, this BOLD signal change decreases during the spatial memory component of the task. Additionally, we note frontal cortex activity reflective of working memory circuits. These data reveal that, as predicted by the rodent literature, the hippocampus is involved in performing the virtual radial arm maze in humans. Hence, this virtual reality version may be used to assess the integrity of hippocampus so as to predict risk or severity in a variety of psychiatric disorders.     

香水莲花提取物对东莨菪碱诱导记忆障碍小鼠学习记忆能力的影响

探究香水莲花提取物(Nymphaea hybrid extract,NHE)对东莨菪碱诱导记忆障碍小鼠的学习记忆能力的影响。采用腹腔注射东莨菪碱建立记忆障碍模型,Morris水迷宫实验测定小鼠空间学习和记忆能力。水迷宫实验结束后,断头处死小鼠,进行生化指标的测定。结果表明,与模型组小鼠相比,NHE干预后,小鼠的逃避潜伏期明显缩短(P <0. 01),目标象限停留时间百分比和穿越平台次数增加(P <0. 05或P <0. 01),小鼠海马和皮质区的SOD和GSH-PX活力显著升高(P <0. 01或P <0. 05),MDA含量极显著降低(P <0. 01),ACh E活性显著降低(P <0. 01),ACh含量增加(P <0. 01或P <0. 05)。同时,免疫印迹结果表明,NHE能够改善东莨菪碱引起小鼠海马和皮质中ERK、CREB磷酸化水平和BDNF蛋白表达的减少。综上,香水莲花提取物可以提高东莨菪碱诱导的记忆障碍小鼠的学习记忆能力,具体机制涉及缓解大脑的氧化应激损伤,平衡胆碱能系统,激活ERK-CREB-BDNF信号通路。     

Effects of lead exposure on the expression of amyloid β and phosphorylated tau proteins in the C57BL/6 mouse hippocampus at different life stages

The objective of this study was to investigate the effects of lead exposure on spatial learning and memory capacity and the expression of amyloid β and phosphorylated tau proteins in the mouse hippocampus. A total of 24 adult C57BL/6 mice (12 of each sex) were mated at a 1:1 ratio. After delivery, the litters were normalised to 6 pups per litter. During the lactation period, the pups were randomly separated into four groups: control, early exposure, late exposure, or long-term exposure. These groups were not exposed to lead, exposed to lead from birth to week 24, exposed to lead from week 24 to week 48, or exposed to lead from birth to 48 weeks of age, respectively. Lead exposure was induced by providing Pb-contaminated drinking water at a concentration of 0.1%. All of the pups were fed until 72 weeks of age, at which time their spatial learning and memory capacity was evaluated via the Morris water maze test. Then, the lead levels in their blood and hippocampus were measured via graphite furnace atomic absorption spectrometry. The protein expression of amyloid β and phosphorylated tau in the hippocampus was detected via Western blot. The results revealed that the hippocampal and blood lead levels were significantly higher in all of the groups exposed to lead than the control group (P < 0.05). The spatial learning and memory performances of the lead-exposed groups were much poorer than those of the control group (P < 0.05). The expression levels of amyloid β and phosphorylated tau proteins were increased in the lead-exposed groups compared to the control group (P < 0.05). The enhanced expressions of amyloid β and phosphorylated tau proteins might contribute to the impairment in spatial learning and memory in the lead-exposed mice.     

慢性束缚应激对SD和Wistar大鼠学习记忆能力的影响

目的探讨慢性束缚应激对Wistar、SD两种品系大鼠学习记忆能力的影响,为应激模型中实验动物的选择提供依据。方法对两种品系大鼠(Wistar、SD)采用每天束缚10 h,束缚28 d建立慢性应激模型。采用物体认知新物体识别实验和Morris水迷宫空间学习、工作记忆行为学检测方法,观察束缚应激对两种品系实验动物学习记忆能力的影响。结果束缚28 d后,物体识别实验中,Wistar、SD模型组的辨别指数(discrimination index,DI)均低于对照组,但只有SD两组间差异存在显著性(P0.05);水迷宫空间学习阶段,SD模型组潜伏期高于对照组,第5天差异有显著性(P0.05),而Wistar模型组与对照组间的潜伏期没有差异;水迷宫工作记忆阶段,SD大鼠模型组与正常组比较,潜伏期显著增加(P0.05),Wistar模型大鼠的潜伏期与对照组比较没有显著差异。结论新物体识别实验和水迷宫实验,这两种反应动物不同学习记忆能力的行为学实验结果都表明,慢性束缚应激(10 h,28 d)对SD大鼠学习记忆能力的损伤较Wistar大鼠明显。SD大鼠可能更适合作为慢性应激所致学习记忆损伤动物模型。     

Radial arm maze performance of rats following repeated low level microwave radiation exposure

We examined the possibility of changes in "working" memory of rats following whole body exposure to microwave (MW) radiation. During each of 10 days, we exposed rats within circularly polarized waveguides for 45 min to 2450 MHz fields at whole body SARs of 0.6 W/kg (2 micros pulses, 500 pps), followed by testing in a 12 arm, radial arm maze (RAM). Rats received a preexposure injection of one of three psychoactive compounds or saline, to determine whether a compound would interact with MW exposure to affect performance in the maze. Error rate, i.e., reentry into arms already visited, and time to criterion data for 10 consecutive days of testing were analyzed by a three way analysis of variance (ANOVA) using main effects of "exposure" and "drug" and a repeated factor of "test day." Our alpha limit for significance was P <.05. Analyzes of error rates revealed no significant exposure effect, no significant drug effect and no significant interaction between the two main factors. There was a significant difference in test days, as expected, with repeated test-trial days, which indicates that learning was accomplished. There was no significant interaction of test day and the other two factors. The results of our analyzes of time to criterion data included no significant exposure effect, a significant drug effect, a significant test day effect, and a significant interaction between drug and test day factors. Post hoc analyzes of the drug factor revealed that rats treated with either physostigmine or nalrexone hydrochloride, took significantly longer to complete the maze task than rats pretreated with saline or with naloxone methodide. We conclude that there is no evidence from the current study that exposure to of MW radiation under parameters examined caused decrements in the ability of rats to learn the spatial memory task.     

复合不育剂EP-1对小鼠空间记忆与焦虑行为的影响

EP-1是由炔雌醚和左炔诺孕酮按照1∶2的比例配制而成的一种用于鼠类不育控制的激素类复合不育剂,对鼠类的繁殖及繁殖行为等有一定影响,但对鼠类空间学习与记忆、焦虑行为等非繁殖行为的影响还没有报道。为此,用0(对照)、1.0、2.0、3.0 mg/kg剂量的EP-1对昆明小鼠(Mus musculus)进行灌胃处理,然后用Morris水迷宫和高架十字迷宫分别测定其空间记忆、焦虑行为。结果发现灌胃后15 d,剂量为2.0 mg/kg的EP-1使小鼠空间记忆能力显著下降,但30 d后其空间记忆能力有所恢复,表明2.0 mg/kg剂量的EP-1可以在一定时间范围内降低小鼠的空间记忆能力。但不同剂量的EP-1对小鼠焦虑行为无显著影响。该结果可以为从对非繁殖行为的影响的角度研究EP-1对鼠类的作用提供一定启示。