Variations in illumination, closed wall transparency and/or extramaze space influence both baseline anxiety and response to diazepam in the rat elevated plus-maze

Comparison of predictive validity of two autism spectrum disorder rat models: Behavioural investigations

The valproic acid model has been shown to reproduce ASD-like behaviours observed in patients and is now widely validated for construct, face, and predictivity as ASD model in rat. The literature agrees on using a single exposition to 500 mg/kg of VPA at gestational day 12 to induce ASD phenotype with the intraperitoneal route being the most commonly used. However, some studies validated this model with repeated exposure by using oral route. The way of administration may be of great importance in the induction of the ASD phenotype and a comparison is greatly required. We compared two ASD models, one induced by a unique IP injection of 500 mg/kg of body weight at GD12 and the other one by repeated PO administration of 500 mg/kg of body weight/day between GD11 and GD13. The behavioural phenotypes of the offspring were assessed for the core signs of ASD (impaired social behaviour, stereotypical/repetitive behaviours, sensory/communication deficits) as well as anxiety as comorbidity, at developmental and juvenile stages in both sexes. The VPA IP model induced a more literature-compliant ASD phenotype than the PO one. These results confirmed that the mode of administration as well as the window of VPA exposure are key factors in the ASD-induction phenotype. Interestingly, the effects of VPA administration were similar at the developmental stage between both sexes and then tended to differ later in life.

Three methods of behavioural testing to measure anxiety - A review

Behavioural test is very useful to assess the anxiety activity, screen new anxiolytic drugs, explore the pathogenesis of anxiety disorders. Methods of behavioural testing that reflects different aspects of anxiety emotionality simultaneously have always been a critical issue for academics. In this paper, we reviewed previous methods to use behavioural test to evaluate the anxiety activity. A single test was used to measure only one aspect of anxiety emotionality. A battery of behavioural tests could get a comprehensive information of anxiety profile. In one single trial, open field test, elevated plus maze and light/dark box are integrated to assess different types of emotional behaviours. This new paradigm is useful for evaluating multiple dimensions of behaviours simultaneously, minimizing general concerns about previous test experience and inter-test intervals between tests. It is proposed as a promising alternative to using test battery.

Improving Translational Relevance in Preclinical Psychopharmacology (iTRIPP)

Animal models are important in preclinical psychopharmacology to study mechanisms and potential treatments for psychiatric disorders. A working group of 14 volunteers, comprising an international team of researchers from academia and industry, convened in 2021 to discuss how to improve the translational relevance and interpretation of findings from animal models that are used in preclinical psychopharmacology. The following paper distils the outcomes of the working group's discussions into 10 key considerations for the planning and reporting of behavioural studies in animal models relevant to psychiatric disorders. These form the iTRIPP guidelines (Improving Translational Relevance In Preclinical Psychopharmacology). These guidelines reflect the key considerations that the group thinks will likely have substantial impact in terms of improving the translational relevance of behavioural studies in animal models that are used to study psychiatric disorders and their treatment. They are relevant to the research community when drafting and reviewing manuscripts, presentations and grant applications. The iTRIPP guidelines are intended to complement general recommendations for planning and reporting animal studies that have been published elsewhere, by enabling researchers to fully consider the most appropriate animal model for the research purpose and to interpret their findings appropriately. This in turn will increase the clinical benefit of such research and is therefore important not only for the scientific community but also for patients and the lay public.

Effect of apparatus characteristics on anxiety-like behavior in young adult and old mice of both sexes assessed by the elevated plus maze assay

Incidence of anxiety-like disorders in humans has been shown to decrease with aging; however, it is still under debate whether there are similarities in mice, which would support the use of mouse models in understanding the neuronal network changes that regulate anxiety-like behavior in aging. One of the most common tests used to assess anxiety-like behavior in laboratory animals is the elevated plus maze (EPM). Although several variables, such as room brightness and width of the maze arms, have been shown to influence the spontaneous animal behavior during the EPM test, none of these variables have ever been evaluated in aging to understand their possible differential effect on younger and older mice. We therefore decided to investigate the effect of apparatus construction on young adult and old mice of both sexes on EPM test performance. Our results show that distance traveled during the test is the variable that is most affected by apparatus characteristics independent of age and sex. We also found that apparatus construction was key in demonstrating that old mice spent more time and had relatively more entries in the open arms as compared to young mice, suggesting a decrease in anxiety-like behavior with age. Taken together, our data demonstrate that EPM apparatus characteristics dramatically affect test outcome with a wider arm apparatus being more effective in revealing age-dependent changes in anxiety-like behavior, thus, suggesting the use of a wider arm EPM when conducting aging studies in mice.

miRNA-132/212 Deficiency Disrupts Selective Corticosterone Modulation of Dorsal vs. Ventral Hippocampal Metaplasticity

Cortisol is a potent human steroid hormone that plays key roles in the central nervous system, influencing processes such as brain neuronal synaptic plasticity and regulating the expression of emotional and behavioral responses. The relevance of cortisol stands out in the disease, as its dysregulation is associated with debilitating conditions such as Alzheimer's Disease, chronic stress, anxiety and depression. Among other brain regions, cortisol importantly influences the function of the hippocampus, a structure central for memory and emotional information processing. The mechanisms fine-tuning the different synaptic responses of the hippocampus to steroid hormone signaling remain, however, poorly understood. Using ex vivo electrophysiology and wild type (WT) and miR-132/miR-212 microRNAs knockout (miRNA-132/212-/-) mice, we examined the effects of corticosterone (the rodent's equivalent to cortisol in humans) on the synaptic properties of the dorsal and ventral hippocampus. In WT mice, corticosterone predominantly inhibited metaplasticity in the dorsal WT hippocampi, whereas it significantly dysregulated both synaptic transmission and metaplasticity at dorsal and ventral regions of miR-132/212-/- hippocampi. Western blotting further revealed significantly augmented levels of endogenous CREB and a significant CREB reduction in response to corticosterone only in miR-132/212-/- hippocampi. Sirt1 levels were also endogenously enhanced in the miR-132/212-/- hippocampi but unaltered by corticosterone, whereas the levels of phospo-MSK1 were only reduced by corticosterone in WT, not in miR-132/212-/- hippocampi. In behavioral studies using the elevated plus maze, miRNA-132/212-/- mice further showed reduced anxiety-like behavior. These observations propose miRNA-132/212 as potential region-selective regulators of the effects of steroid hormones on hippocampal functions, thus likely fine-tuning hippocampus-dependent memory and emotional processing.

Acute and long-term sex-dependent effects of social instability stress on anxiety-like and social behaviours in Wistar rats

Adolescence is a critical time of social learning in which both the quantity and quality of social interactions shape adult behavior and social function. During adolescence, social instability such as disrupting or limiting social interactions can lead to negative life-long effects on mental health and well-being in humans. Animal models on social instability are critically important in understanding those underlying neurobiological mechanisms. However, studies in rats using these models have produced partly inconsistent results and can be difficult to generalize. Here we assessed in a sex and age consistent manner the long-term behavioural consequences of social instability stress (SIS - 1-hr daily isolation and change in cage mate between postnatal day (PD30-45)) in Wistar rats. Female and male rats underwent a battery of tests for anxiety-like, exploratory, and social behaviour over five days beginning either in adolescence (PD46) or in adulthood (PD70). Social instability led to reduced anxiety-like behaviour in the elevated plus maze in both sexes in adolescence and in adulthood. Social interactions were also reduced in rats that underwent SIS - an effect that was independent of sex and age when tested. SIS improved social recognition memory in both sexes whereas a sex-dependent effect was seen in the social novelty preference test where male rats that underwent SIS spent more time in social approach toward a novel peer than toward their cage mate. In comparison, control male and female groups did not differ in this test, in time spent with novel versus the cage mate. Thus, overall, social instability stress in Wistar rats altered the behavioural repertoire, with enduring alterations in social behaviour, enhanced exploratory behaviour, and reduced anxiety-like behaviour. In conclusion, the social instability stress paradigm may better be interpreted as a form of enrichment in Wistar rats than as a stressor.

Behavioral outcomes of complete Freund adjuvant-induced inflammatory pain in the rodent hind paw: a systematic review and meta-analysis

ABSTRACT

Many analgesics inadequately address the psychiatric comorbidities of chronic and persistent pain, but there is no standard preclinical model of pain-altered behavior to support the development of new therapies. To explore this conflicting and inconclusive literature, we conducted a focused systematic review and meta-analysis on the effect of complete Freund adjuvant-induced (CFA) rodent hind paw inflammation on multiple classical indicators of exploratory behavior, stress coping, and naturalistic behavior. Our primary objective was to define CFA's effect on assays including, but not limited to, the elevated plus maze and forced swim test. Our secondary objective was to discover how variables such as species and strain may influence outcomes in such assays. We searched Ovid MEDLINE, Embase, Scopus, and Web of Science in April and October 2020 for studies with adult rodents injected with CFA into the hind paw and subsequently tested for aspects of "anxiety-like" or "depressive-like" behaviors. Forty-four studies evaluated performance in the elevated plus or zero maze, open field test, light-dark box, place escape and avoidance paradigm, forced swim test, tail suspension test, sucrose preference test, wheel running, and burrowing assay. Complete Freund adjuvant modestly but significantly decreased exploratory behavior, significantly increased passive stress coping in the tail suspension test but not the forced swim test, and significantly decreased preference for sucrose and naturally rewarding activity. Subgroup analyses revealed significant differences between species and animal sourcing. Based on the evidence provided here, we conclude future studies should focus on CFA's effect on natural rewards and naturalistic behaviors.

Glucocorticoid Abnormalities in Female Rats Exposed to a Predator-Based Psychosocial Stress Model of PTSD

People with post-traumatic stress disorder (PTSD) exhibit heightened anxiety and enhanced negative feedback of the hypothalamus-pituitary-adrenal (HPA) axis. We previously reported that male rats exposed to a predator-based psychosocial stress model of PTSD exhibited comparable changes in anxiety-like behavior and HPA axis activity, including lower baseline levels of corticosterone and a greater suppression of corticosterone after dexamethasone administration. Here, we assessed whether we would observe similar effects in female rats exposed to this model. Adult female Sprague-Dawley rats were exposed to a cat on two occasions (separated by 10 days), in combination with chronic social instability. Three weeks after the second cat exposure, we assessed anxiety-like behavior on an elevated plus maze (EPM) and collected blood samples from rats in the absence or presence of dexamethasone to quantify serum corticosterone levels. Although stressed females did not display heightened anxiety on the EPM, they exhibited significantly lower overall corticosterone levels and a greater suppression of corticosterone after dexamethasone administration. The observation of significantly lower overall corticosterone levels in stressed females was replicated in a separate, independent experiment. These findings suggest that the predator-based psychosocial stress model of PTSD may be useful for studying mechanisms that underlie changes in HPA axis function in females exposed to trauma.

Assessment of 9-OH- and 7,8-diol-benzo[a]pyrene in Blood as Potent Markers of Cognitive Impairment Related to benzo[a]pyrene Exposure: An Animal Model Study

The potent neurotoxicity of benzo[a]pyrene (B[a]P) has been suggested to be a susceptibility factor accelerating the onset of brain tumours and the emergence of neurobehavioural disturbances. B[a]P has been shown to be neurotoxic, acting directly on both the central and peripheral nervous systems, as well as indirectly via peripheral organs like liver and gut. By using a realistic B[a]P exposure scenario (0.02-200 mg/kg/day, 10 days) in mice, we elucidated brain-specific B[a]P metabolism and at identified hydroxylated B[a]P metabolites in serum which could be used as markers of cognitive impairment. Repeated oral administration of B[a]P led to, at the doses of 20 and 200 mg/kg/day, significant overexpression of Cyp1a1/Cyp1b1 in 2 out of the 3 brain regions considered, thereby suggesting the ability of the brain to metabolize B[a]P itself. At the same doses, mice exhibited a reduction in anxiety in both the elevated plus maze and the hole board apparatus. Concomitantly, B[a]P triggered dose-dependent changes in Nmda subunit expression (Nr1 and Nr2a/Nr2b) in areas involved in cognition. We detected 9-OH-B[a]P and 7,8-diol-B[a]P in serum at the level for which cognitive impairment was observed. We suggest that these metabolites may, in the future be exploited as potent biomarkers of B[a]P-induced cognitive impairments.

Effects of test experience, closed-arm wall color, and illumination level on behavior and plasma corticosterone response in an elevated plus maze in male C57BL/6J mice: a challenge against conventional interpretation of the test

The elevated plus maze test is a widely used test for assessing anxiety-like behavior and screening novel therapeutic agents in rodents. Previous studies have shown that a variety of internal factors and procedural variables can influence elevated plus maze behavior. Although some studies have suggested a link between behavior and plasma corticosterone levels, the relationships between them remain unclear. In this study, we investigated the effects of experience with a battery of behavioral tests, the wall color of the closed arms, and illumination level on the behavior and plasma corticosterone responses in the elevated plus maze in male C57BL/6J mice. Mice were either subjected to a series of behavioral tests, including assessments of general health and neurological function, a light/dark transition test, and an open field test, or left undisturbed until the start of the elevated plus maze test. The mice with and without test battery experience were allowed to freely explore the elevated plus maze. The other two independent groups of naïve mice were tested in mazes with closed arms with different wall colors (clear, transparent blue, white, and black) or different illumination levels (5, 100, and 800 lx). Immediately after the test, blood was collected to measure plasma corticosterone concentrations. Mice with test battery experience showed a lower percentage of open arm time and entries and, somewhat paradoxically, had lower plasma corticosterone levels than the mice with no test battery experience. Mice tested in the maze with closed arms with clear walls exhibited higher open arm exploration than mice tested in the maze with closed arms with black walls, while there were no significant differences in plasma corticosterone levels between the different wall color conditions. Illumination levels had no significant effects on any measure. Our results indicate that experience with other behavioral tests and different physical features of the maze affect elevated plus maze behaviors. Increased open arm time and entries are conventionally interpreted as decreased anxiety-like behavior, while other possible interpretations are considered: open arm exploration may reflect heightened anxiety and panic-like reaction to a novel situation under certain conditions. With the possibility of different interpretations, the present findings highlight the need to carefully consider the test conditions in designing experiments and drawing conclusions from the behavioral outcomes in the elevated plus maze test in C57BL/6J mice.

A Japanese herbal medicine attenuates anxiety-like behavior through GABAA receptor and brain-derived neurotrophic factor expression in a rat model of premenstrual syndrome

Inochinohaha White (IHW) is a Japanese herbal medicine for treating women with anxiety associated with premenstrual syndrome (PMS). In this study, we examined the effects of IHW on anxiety-like behavior in rats undergoing progesterone withdrawal (PWD), a model for PMS. Female rats were injected daily with progesterone for 21 days. Water and ethanol extracts of IHW (WE-IHW and EE-IHW, respectively) were administered orally 15 days after the initiation of progesterone injections. Anxiety-like behavior in an elevated plus maze was evaluated 48 h after the final injection of progesterone. PWD induced anxiety-like behavior, and EE-IHW (300 mg/kg), but not WE-IHW, significantly attenuated this behavior. Administration of the GABA agonists, diazepam or muscimol, significantly attenuated PWD-induced anxiety-like behavior. To investigate the underlying mechanisms of IHW action, we analyzed GABAA receptor expression in the amygdala of these rats. EE-IHW ameliorated the PWD-induced decrease in GABAA receptor β2-subunit mRNA, although β2-subunit protein was unchanged. Brain-derived neurotrophic factor (BDNF) has been reported to have anxiolytic effects and enhance GABAergic synaptic transmission. We found that EE-IHW increased BDNF levels in a dose-dependent manner. Our results suggest that EE-IHW attenuates PWD-induced anxiety-like behavior by increasing GABAA receptor-mediated signaling via increases in β2-subunit and BDNF in the amygdala.

Podoplanin Gene Disruption in Mice Promotes in vivo Neural Progenitor Cells Proliferation, Selectively Impairs Dentate Gyrus Synaptic Depression and Induces Anxiety-Like Behaviors

Podoplanin (Pdpn), a brain-tumor-related glycoprotein identified in humans and animals, is endogenously expressed in several organs critical for life support such as kidney, lung, heart and brain. In the brain, Pdpn has been identified in proliferative nestin-positive adult neural progenitor cells and in neurons of the neurogenic hippocampal dentate gyrus (DG), a structure associated to anxiety, critical for learning and memory functions and severely damaged in people with Alzheimer's Disease (AD). The in vivo role of Pdpn in adult neurogenesis and anxiety-like behavior remained however unexplored. Using mice with disrupted Pdpn gene as a model organism and applying combined behavioral, molecular biological and electrophysiological assays, we here show that the absence of Pdpn selectively impairs long-term synaptic depression in the neurogenic DG without affecting the CA3-Schaffer's collateral-CA1 synapses. Pdpn deletion also enhanced the proliferative capacity of DG neural progenitor cells and diminished survival of differentiated neuronal cells in vitro. In addition, mice with podoplanin gene disruption showed increased anxiety-like behaviors in experimentally validated behavioral tests as compared to wild type littermate controls. Together, these findings broaden our knowledge on the molecular mechanisms influencing hippocampal synaptic plasticity and neurogenesis in vivo and reveal Pdpn as a novel molecular target for future studies addressing general anxiety disorder and synaptic depression-related memory dysfunctions.

Exposure of Developing Male Rats to One or Multiple Noise Sessions and Different Housing Conditions: Hippocampal Thioredoxin Changes and Behavioral Alterations

Exposure of developing rats to noise has shown to induce hippocampal-related behavioral alterations that were prevented after a week of housing in an enriched environment. However, neither the effect of repeated exposures nor its impact on key endogenous antioxidants had been studied yet. Thus, the aim of the present work was to reveal novel data about hippocampal oxidative state through the measurement of possible age-related differences in the levels of hippocampal thioredoxins in rats exposed to noise at different developmental ages and subjected to different schemes and housing conditions. In addition, the possibility that oxidative changes could underlie hippocampal-related behavioral changes was also analyzed. Developing male Wistar rats were exposed to noise for 2 h, either once or for 5 days. Upon weaning, some animals were transferred to an enriched cage for 1 week, whereas others were kept in standard cages. One week later, auditory and behavioral assessments, as well as measurement of hippocampal thioredoxin, were performed. Whereas no changes in the auditory function were observed, significant behavioral differences were found, that varied according to the age, scheme of exposure and housing condition. In addition, a significant increase in Trx-1 levels was found in all noise-exposed groups housed in standard cages. Housing animals in an enriched environment for 1 week was effective in preventing most of these changes. These findings suggest that animals become less susceptible to undergo behavioral alterations after repeated exposure to an environmental challenge, probably due to the ability of adaptation to an unfavorable condition. Moreover, it could be hypothesized that damage to younger individuals could be more easily prevented by a housing manipulation.

Effects of the LPA1 Receptor Deficiency and Stress on the Hippocampal LPA Species in Mice

Lysophosphatidic acid (LPA) is an important bioactive lipid species that functions in intracellular signaling through six characterized G protein-coupled receptors (LPA_1-6). Among these receptors, LPA₁ is a strong candidate to mediate the central effects of LPA on emotion and may be involved in promoting normal emotional behaviors. Alterations in this receptor may induce vulnerability to stress and predispose an individual to a psychopathological disease. In fact, mice lacking the LPA₁ receptor exhibit emotional dysregulation and cognitive alterations in hippocampus-dependent tasks. Moreover, the loss of this receptor results in a phenotype of low resilience with dysfunctional coping in response to stress and induces anxiety and several behavioral and neurobiological changes that are strongly correlated with mood disorders. In fact, our group proposes that maLPA1-null mice represent an animal model of anxious depression. However, despite the key role of the LPA-LPA₁-pathway in emotion and stress coping behaviors, the available information describing the mechanisms by which the LPA-LPA₁-pathway regulates emotion is currently insufficient. Because activation of LPA₁ requires LPA, here, we used a Matrix-Assisted Laser Desorption/ Ionization mass spectrometry-based approach to evaluate the effects of an LPA₁ receptor deficiency on the hippocampal levels of LPA species. Additionally, the impact of stress on the LPA profile was also examined in both wild-type (WT) and the Malaga variant of LPA1-null mice (maLPA₁-null mice). Mice lacking LPA₁ did not exhibit gross perturbations in the hippocampal LPA species, but the LPA profile was modified, showing an altered relative abundance of 18:0 LPA. Regardless of the genotype, restraint stress produced profound changes in all LPA species examined, revealing that hippocampal LPA species are a key target of stress. Finally, the relationship between the hippocampal levels of LPA species and performance in the elevated plus maze was established. To our knowledge, this study is the first to detect, identify and profile LPA species in the hippocampus of both LPA₁-receptor null mice and WT mice at baseline and after acute stress, as well as to link these LPA species with anxiety-like behaviors. In conclusion, the hippocampal LPA species are a key target of stress and may be involved in psychopathological conditions.

Testing Animal Anxiety in Rats: Effects of Open Arm Ledges and Closed Arm Wall Transparency in Elevated Plus Maze Test

The elevated plus maze test is a behavioral test for assessing animal anxiety in rodents. Although this test is widely applied in the field of behavioral science, conflicting outcomes are often provided from different laboratories. To identify reasons for the different outcomes, we previously focused on arm features, which differ between laboratories, most notably the presence/absence of ledges at the sides of open arms and the transparency/opaqueness of closed arm walls. In a previous report, we used a custom designed container to compare rat behavior on different combinations of open and closed arm designs under otherwise identical experimental conditions, and showed that differences in arm features interfere with experimental outcomes. In brief, open arm ledges significantly increased anxiety-like behavior in rats, while transparent arms may also have decreased this behavior. Furthermore, we verified a higher detection sensitivity of the effect of an anxiolytic drug in a combination of no-ledged open arm + opaque walled closed arm compared with a combination of ledged open arm + transparent walled closed arm. In this report, we introduce our protocol for the elevated plus maze test, together with discussion of the key results from the previous report and our experimental experience. We believe this report will provide useful information for researchers who have employed or who plan to use the elevated plus maze in their studies.

Sex matters: females in proestrus show greater diazepam anxiolysis and brain-derived neurotrophin factor- and parvalbumin-positive neurons than males

In humans and animal models, sex differences are reported for anxiety-like behavior and response to anxiogenic stimuli. In the current work, we studied anxiety-like behavior and response to the prototypical anti-anxiety drug, diazepam. We used 6th generation outbred lines of adult Long Evans rats with high and low anxiety-like behavior phenotypes to investigate the impact of proestrus on the baseline and diazepam-induced behavior. At three doses of diazepam (0, 0.1, and 1.0 mg/kg, i.p.), we measured anxiogenic responses on the elevated plus maze of adult male and female rats. We assessed parvalbumin and brain-derived neurotrophin protein levels in forebrain and limbic structures implicated in anxiety/stress using immunohistochemistry. At baseline, we saw significant differences between anxiety lines, with high anxiety lines displaying less time on the open arms of the elevated plus maze, and less open arm entries, regardless of sex. During proestrus, high anxiety females showed less anxiety-like behavior at 0.1 mg/kg, while low anxiety females displayed less anxiety-like behavior at 0.1 and 1.0 doses, relative to males. Brain-derived neurotrophin protein was elevated in females in the medial prefrontal cortex and central amygdala, while parvalbumin-immunoreactive cells were greater in males in the medial prefrontal cortex. Parvalbumin-positive cells in high anxiety females were higher in CA2 and dentate gyrus relative to males from the same line. In sum, when tested in proestrus, females showed greater anxiolytic effects of diazepam relative to males, and this correlated with increases in neurotrophin and parvalbumin neuron density in corticolimbic structures.

Palmitoylethanolamide Ameliorates Hippocampal Damage and Behavioral Dysfunction After Perinatal Asphyxia in the Immature Rat Brain

Perinatal asphyxia (PA) is an obstetric complication associated with an impaired gas exchange. This health problem continues to be a determinant of neonatal mortality and neurodevelopmental disorders. Palmitoylethanolamide (PEA) has exerted neuroprotection in several models of brain injury and neurodegeneration. We aimed at evaluating the potential neuroprotective role of PEA in an experimental model, which induces PA in the immature rat brain. PA was induced by placing Sprague Dawley newborn rats in a water bath at 37°C for 19 min. Once their physiological conditions improved, they were given to surrogate mothers that had delivered normally within the last 24 h. The control group was represented by non-fostered vaginally delivered pups, mimicking the clinical situation. Treatment with PEA (10 mg/kg) was administered within the first hour of life. Modifications in the hippocampus were analyzed with conventional electron microscopy, immunohistochemistry (for NeuN, pNF-H/M, MAP-2, and GFAP) and western blot (for pNF H/M, MAP-2, and GFAP). Behavior was also studied throughout Open Field (OF) Test, Passive Avoidance (PA) Task and Elevated Plus Maze (EPM) Test. After 1 month of the PA insult, we observed neuronal nucleus degeneration in CA1 using electron microscopy. Immunohistochemistry revealed a significant increase in pNF-H/M and decrease in MAP-2 in CA1 reactive area. These changes were also observed when analyzing the level of expression of these markers by western blot. Vertical exploration impairments and anxiety-related behaviors were encountered in the OF and EPM tests. PEA treatment attenuated PA-induced hippocampal damage and its corresponding behavioral alterations. These results contribute to the elucidation of PEA neuroprotective role after PA and the future establishment of therapeutic strategies for the developing brain.

Estrogen receptor β activation within dorsal raphe nucleus reverses anxiety-like behavior induced by food restriction in female rats

Severe food restriction (FR), as observed in disorders like anorexia nervosa, has been associated to the reduction of estrogen levels, which in turn could lead to anxiety development. Estrogen receptors, mainly ERβ type, are commonly found in the dorsal raphe nucleus (DRN) neurons, an important nucleus related to anxiety modulation and the primary source of serotonin (5-HT) in the brain. Taking together, these findings suggest an involvement of estrogen in anxiety modulation during food restriction, possibly mediated by ERβ activation in serotonergic DRN neurons. Thus, the present study investigated the relationship between food restriction and anxiety-like behavior, and the involvement of DRN and ERβ on the modulation of anxiety-like behaviors in animals subjected to FR. For that, female Fischer rats were grouped in control group, with free access to food, or a FR group, which received 40% of control intake during 14 days. Animals were randomly treated with 17β-estradiol (E2), DPN (ERβ selective agonist), or their respective vehicles, PBS and DMSO. Behavioral tests were performed on Elevated T-Maze (ETM) and Open Field (OF). Our results suggest that FR probably reduced the estrogen levels, since the remained in the non-ovulatory cycle phases, and their uterine weight was lower when compared to control group. The FR rats showed increased inhibitory avoidance latency in theETM indicating that FR is associated with the development of an anxiety-like state. The injections of both E2 and DPN into DRN of FR animals had an anxiolytic effect. Those data suggest thatanxiety-like behavior induced by FR could be mediated by a reduction of ERβ activation in the DRN neurons, probably due to decreased estrogen levels.

Voluntary alcohol intake after noise exposure in adolescent rats: Hippocampal-related behavioral alterations

Different physical or chemical agents, such as noise or alcohol, can induce diverse behavioral and biochemical alterations. Considering the high probability of young people to undergo consecutive or simultaneous exposures, the aim of the present work was to investigate in an animal model if noise exposure at early adolescence could induce hippocampal-related behavioral changes that might be modified after alcohol intake. Male Wistar rats (28-days-old) were exposed to noise (95-97 dB, 2 h). Afterwards, animals were allowed to voluntarily drink alcohol (10% ethanol in tap water) for three consecutive days, using the two-bottle free choice paradigm. After that, hippocampal-related memory and anxiety-like behavior tests were performed. Results show that whereas noise-exposed rats presented deficits in habituation memory, those who drank alcohol exhibited impairments in associative memory and anxiety-like behaviors. In contrast, exposure to noise followed by alcohol intake showed increases in exploratory and locomotor activities as well as in anxiety-like behaviors, unlike what was observed using each agent separately. Finally, lower levels of alcohol intake were measured in these animals when compared with those that drank alcohol and were not exposed to noise. Present findings demonstrate that exposure to physical and chemical challenges during early adolescence might induce behavioral alterations that could differ depending on the schedule used, suggesting a high vulnerability of rat developing brain to these socially relevant agents.

Effects of Jasminum multiflorum leaf extract on rodent models of epilepsy, motor coordination and anxiety

Jasmine flowers and leaves are used extensively in folk medicine in different parts of the world to treat a variety of diseases. However, there are very few published reports on the neuropsychiatric effects of Jasmine extracts. Hence, the objectives of the present study were to examine the effects of an alcohol extract of Jasminum multiflorum leaves on topically-applied bicuculline (a model of acute simple partial epilepsy) and maximal electroshock (MES, a model of generalized tonic-clonic seizure) in male Sprague-Dawley rats. The objectives also included an examination of the anxiolytic properties of the extract using an elevated plus maze and the effect of the extract on motor coordination using a rotarod treadmill. Phytochemical analysis of the extract showed the presence of three flavonoids and four additional compounds belonging to the steroid, terpenoid, phenol or sugar classes of compounds. The Jasmine alcohol extract, diluted with water and given orally or intraperitoneally, reduced the number of bicuculline-induced epileptiform discharges in a dose-dependent manner. The extract did not cause a significant increase in the current needed to induce hind limb extension in MES experiments. The extract significantly affected motor coordination when injected at 500mg/kg but not at 200mg/kg. At the latter dose, the extract increased open-arm entries and duration in the elevated plus maze to a level comparable to that of diazepam at 2mg/kg. We conclude that Jasmine leaf extract has a beneficial effect against an animal model of acute partial complex epilepsy, and significant anxiolytic effect at a dose that does not affect motor co-ordination.

Evaluation of the antidepressant- and anxiolytic-like effects of a hydrophilic extract from the green seaweed Ulva sp. in rats

OBJECTIVES

The green seaweed Ulva sp. contains a large amount of ulvans, a family of sulphated polysaccharides. The present study was designed to investigate in rats the antidepressant- and anxiolytic-like effects of a hydrophilic extract of Ulva sp. (MSP) containing about 45% of ulvans.

METHODS

After a 14-day administration of MSP at doses of 10, 20 and 40 mg/kg/day, 48 and 60 male adult Wistar rats were respectively tested in the elevated plus-maze (EPM) and the forced swimming test (FST). In the FST, MSP effects were compared to the reference antidepressant drug imipramine (IMI) (10 mg/kg/day). Acute and sub-chronic toxicities of the extract were also assessed in male and female rats following OECD guidelines.

RESULTS

MSP treatment did not modify anxiety-related behaviour in the EPM. In contrast, MSP induced a dose-dependent reduction of immobility behaviour in the FST. At the highest tested dose of 40 mg/kg, MSP displayed a significant antidepressant-like effect similar to IMI. MSP did not modify the exploratory behaviour of rats in the open field test and did not produce any toxic effect.

DISCUSSION

MSP may potentially represent a good adjunct or alternative to existing antidepressant therapeutics. Further studies are necessary to confirm the mechanism of action of MSP and its modulation of brain functioning.

Preclinical animal anxiety research - flaws and prejudices

The current tests of anxiety in mice and rats used in preclinical research include the elevated plus-maze (EPM) or zero-maze (EZM), the light/dark box (LDB), and the open-field (OF). They are currently very popular, and despite their poor achievements, they continue to exert considerable constraints on the development of novel approaches. Hence, a novel anxiety test needs to be compared with these traditional tests, and assessed against various factors that were identified as a source of their inconsistent and contradictory results. These constraints are very costly, and they are in most cases useless as they originate from flawed methodologies. In the present report, we argue that the EPM or EZM, LDB, and OF do not provide unequivocal measures of anxiety; that there is no evidence of motivation conflict involved in these tests. They can be considered at best, tests of natural preference for unlit and/or enclosed spaces. We also argued that pharmacological validation of a behavioral test is an inappropriate approach; it stems from the confusion of animal models of human behavior with animal models of pathophysiology. A behavioral test is developed to detect not to produce symptoms, and a drug is used to validate an identified physiological target. In order to overcome the major methodological flaws in animal anxiety studies, we proposed an open space anxiety test, a 3D maze, which is described here with highlights of its various advantages over to the traditional tests.

Noise exposure of immature rats can induce different age-dependent extra-auditory alterations that can be partially restored by rearing animals in an enriched environment

It has been previously shown that different extra-auditory alterations can be induced in animals exposed to noise at 15 days. However, data regarding exposure of younger animals, that do not have a functional auditory system, have not been obtained yet. Besides, the possibility to find a helpful strategy to restore these changes has not been explored so far. Therefore, the aims of the present work were to test age-related differences in diverse hippocampal-dependent behavioral measurements that might be affected in noise-exposed rats, as well as to evaluate the effectiveness of a potential neuroprotective strategy, the enriched environment (EE), on noise-induced behavioral alterations. Male Wistar rats of 7 and 15 days were exposed to moderate levels of noise for two hours. At weaning, animals were separated and reared either in standard or in EE cages for one week. At 28 days of age, different hippocampal-dependent behavioral assessments were performed. Results show that rats exposed to noise at 7 and 15 days were differentially affected. Moreover, EE was effective in restoring all altered variables when animals were exposed at 7 days, while a few were restored in rats exposed at 15 days. The present findings suggest that noise exposure was capable to trigger significant hippocampal-related behavioral alterations that were differentially affected, depending on the age of exposure. In addition, it could be proposed that hearing structures did not seem to be necessarily involved in the generation of noise-induced hippocampal-related behaviors, as they were observed even in animals with an immature auditory pathway. Finally, it could be hypothesized that the differential restoration achieved by EE rearing might also depend on the degree of maturation at the time of exposure and the variable evaluated, being younger animals more susceptible to environmental manipulations.

Higher detection sensitivity of anxiolytic effects of diazepam by ledge-free open arm with opaque walled closed arm elevated plus maze in male rats

The elevated plus maze (EPM) is an established method for testing animal anxiety. However, EPM apparatuses and their features can differ among laboratories, most notably in the presence/absence of ledges on the open arm and/or the transparency/opaqueness of walls on the closed arm. The combined effects of these variable arm features on EPM behavior are not yet fully understood. In the present study, we prepared four types of EPM apparatus - open arms with (0.5 cm) or without (0 cm) ledges×closed arms with transparent or opaque walls - and compared the maze-exploration behavior of male Sprague-Dawley rats. We found that the presence of open arm ledges significantly increased the incidence of open arm exploration. Furthermore, time spent in the distal segment of the open arm was shortest in the apparatus that had open arms with no ledges and opaque closed arms (No-Ledges/Opaque), and was longest in the apparatus that had open arms with ledges and transparent closed arms (Ledges/Transparent). Additionally, the No-Ledges/Opaque apparatus could detect the effect of 0.5mg/kg diazepam, an anxiolytic drug, whereas the Ledges/Transparent apparatus could not. These results indicate that arm structure (features of both open and closed arms) significantly influences maze-exploratory behavior in rats, and that No-Ledges/Opaque apparatuses have higher detection sensitivity for anxiolytic effects of diazepam than that of Ledges/Transparent apparatuses.

Multivariate temporal pattern analysis applied to the study of rat behavior in the elevated plus maze: methodological and conceptual highlights

Aim of this article is to illustrate the application of a multivariate approach known as t-pattern analysis in the study of rat behavior in elevated plus maze. By means of this multivariate approach, significant relationships among behavioral events in the course of time can be described. Both quantitative and t-pattern analyses were utilized to analyze data obtained from fifteen male Wistar rats following a trial 1-trial 2 protocol. In trial 2, in comparison with the initial exposure, mean occurrences of behavioral elements performed in protected zones of the maze showed a significant increase counterbalanced by a significant decrease of mean occurrences of behavioral elements in unprotected zones. Multivariate t-pattern analysis, in trial 1, revealed the presence of 134 t-patterns of different composition. In trial 2, the temporal structure of behavior become more simple, being present only 32 different t-patterns. Behavioral strings and stripes (i.e. graphical representation of each t-pattern onset) of all t-patterns were presented both for trial 1 and trial 2 as well. Finally, percent distributions in the three zones of the maze show a clear-cut increase of t-patterns in closed arm and a significant reduction in the remaining zones. Results show that previous experience deeply modifies the temporal structure of rat behavior in the elevated plus maze. In addition, this article, by highlighting several conceptual, methodological and illustrative aspects on the utilization of t-pattern analysis, could represent a useful background to employ such a refined approach in the study of rat behavior in elevated plus maze.

Administration of an anabolic steroid during the adolescent phase changes the behavior, cardiac autonomic balance and fluid intake in male adult rats

Few data are available on adolescent users because most behavioral studies on anabolic-androgenic steroids (AAS) abuse have been performed in adults. Studies evaluating the impact of long-term effects of AAS abuse on the prepubertal phase are even more uncommon. Accordingly, this study was developed to test the hypothesis that changes induced by the use of AAS during the adolescent phase may be noted in the adult phase even when the AAS treatment cycle is discontinued. Therefore, not only behavioral changes but also possible autonomic and electrolyte disorders were evaluated. For this purpose, we used male prepubertal, 26-day-old (P26) Wistar rats that were treated with vehicle (control, n=10) or testosterone propionate (TP; 5 mg/kg intramuscular (IM) injection, AAS, n=10) five times per week for 5 weeks, totaling 25 applications during the treatment. Aggression tests were performed at the end of the cycle (P54-56), whereas open-field tests (OFTs), elevated plus maze (EPM) behavioral tests and measurements of heart rate variability (HRV), fluid intake and pathology were conducted in the adult phase (P87-92). The AAS group showed greater aggressiveness in the pubertal phase and higher levels of horizontal and vertical exploration and anxiety-related behavior in the adult phase than the control group (P<0.05). HRV tests showed an increase in sympathetic autonomic modulation, and hydroelectrolytic assessment showed lower basal intake levels of hypertonic saline than the control group (P<0.05), without statistically significant changes in the basal intake of water. These data together suggest that the use of AAS during the prepubertal phase induces behavioral, autonomic and hydroelectrolytic changes that manifest in the adult phase even when treatment is discontinued in late adolescence in rats.

Hydroalcoholic extract of Urtica circularis: a neuropharmacological profile

CONTEXT

The genus Urtica has been known since ancient times. It has known to be useful for the treatment of different human ailments.

OBJECTIVE

The present work evaluated the neuropharmacological effects of a hydroalcoholic extract of Urtica circularis (Hicken) Sorarú (Urticaceae). materials and method: The effect on central nervous system of U. circularis hydroalcoholic extract (from leaves and stems) administered by the intraperitoneal route in mice was evaluated by several tests: Pentobarbital- and midazolam-induced hypnosis, open field, hole board, elevated plus-maze and forced swimming. Phytochemical analysis was performed by high-performance liquid chromatography.

RESULTS

A total of 300 mg/kg i.p. of the extract produced a significant prolongation of pentobarbital- (40 mg/kg i.p.; 60.1 min versus 25.4 min) and midazolam- (50 mg/kg i.v.; 53.4 min versus 25.1 min) induced sleeping time. The extract's administration caused a marked reduction of the head-dipping response (DE50: 373 mg/kg i.p.) in the hole-board test. Urtica circularis extract (DE50: 46 mg/kg i.p.) reduced the spontaneous locomotor activity in the open field test. Flumazenil and atropine significantly antagonized the extract's effect on the locomotor activity. No motor coordination disturbance was observed in the rota rod test at any doses. In the forced swimming test, the extract did not produce any change in the immobility time and it had no significant effects in elevated plus maze test. The phytochemical analysis revealed the presence of chlorogenic acid, vanillic acid, caffeic acid, vicenin-2, p-cumaric acid, ferulic acid, vitexin and isovitexin.

CONCLUSION

This study revealed that U. circularis hydroalcoholic extract possesses sedative activity, facilitating GABAergic and cholinergic transmission.

Neurobehavioral toxicity of a repeated exposure (14 days) to the airborne polycyclic aromatic hydrocarbon fluorene in adult Wistar male rats

Fluorene is one of the most abundant polycyclic aromatic hydrocarbons in air and may contribute to the neurobehavioral alterations induced by the environmental exposure of humans to PAHs. Since no data are available on fluorene neurotoxicity, this study was conducted in adult rats to assess the behavioral toxicity of repeated fluorene inhalation exposure. Male rats (n = 18/group) were exposed nose-only to 1.5 or 150 ppb of fluorene 6 hours/day for 14 consecutive days, whereas the control animals were exposed to non-contaminated air. At the end of the exposure, animals were tested for activity and anxiety in an open-field and in an elevated-plus maze, for short-term memory in a Y-maze, and for spatial learning in an eight-arm maze. The results showed that the locomotor activity and the learning performances of the animals were unaffected by fluorene. In parallel, the fluorene-exposed rats showed a lower level of anxiety than controls in the open-field, but not in the elevated-plus maze, which is probably due to a possible difference in the aversive feature of the two mazes. In the same animals, increasing blood and brain levels of fluorene monohydroxylated metabolites (especially the 2-OH fluorene) were detected at both concentrations (1.5 and 150 ppb), demonstrating the exposure of the animals to the pollutant and showing the ability of this compound to be metabolized and to reach the cerebral compartment. The present study highlights the possibility for a 14-day fluorene exposure to induce some specific anxiety-related behavioral disturbances, and argues in favor of the susceptibility of the adult brain when exposed to volatile fluorene.

Anxiolytic effects of the GABA(A) receptor partial agonist, L-838,417: impact of age, test context familiarity, and stress

The partial α2,3,5 GABA(A) receptor agonist, L-838,417 has been reported to have anxiolytic effects in adult rodents. Although maturational differences exist for the GABA(A) receptor subunits, the anxiolytic effects of L-838,417 have not been tested in younger animals. The goal of the present experiments was to determine whether L-838,417 reverses anxiety-like behavior induced by either an unfamiliar environment (Experiment 1) or repeated restraint stress (Experiment 2) differentially in adolescent and adult, male and female Sprague-Dawley rats using a modified social interaction test. In Experiment 1, rats were injected with 0, 0.5, 1.0, 2.0, or 4.0 mg/kg L-838,417, i.p. and tested 30 min later in an unfamiliar test context for 10 min. In Experiment 2, rats were exposed to restraint stress (90 min daily for 5 days). Immediately after the last restraint session, animals were injected with L-838,417 and placed alone for 30 min in the test apparatus to familiarize them to this context prior to the 10 min social interaction test. In Experiment 1, L-838,417 produced anxiolytic effects in adults at 1.0 mg/kg, as indexed by a transformation of social avoidance into preference and an increase in social investigation. In adolescents, a dose of 2.0 mg/kg eliminated social avoidance, but had no anxiolytic effects on social investigation. Testing under familiar circumstances (Experiment 2) after repeated restraint stress eliminated age differences in sensitivity to L-838,417, with 0.5 mg/kg reversing the anxiogenic effects of prior stress regardless of age, but with doses ≥ 1 mg/kg decreasing social investigation, an effect possibly due in part to locomotor-impairing effects of this compound. Although locomotor activity was suppressed in both experiments, higher doses of L-838,417 were necessary to suppress locomotor activity in Experiment 1. Thus, anxiolytic effects of L-838,417 were found to be context-, age-, and stress-dependent.

Mathematical methods to model rodent behavior in the elevated plus-maze

The elevated plus maze is a widely used experimental test to study anxiety-like rodent behavior. It is made of four arms, two open and two closed, connected at a central area forming a plus shaped maze. The whole apparatus is elevated 50 cm from the floor. The anxiety of the animal is usually assessed by the number of entries and duration of stay in each arm type during a 5-min period. Different mathematical methods have been proposed to model the mechanisms that control the animal behavior in the maze, such as factor analysis, statistical inference on Markov chains and computational modeling. In this review we discuss these methods and propose possible extensions of them as a direction for future research.

Interaction between neonatal allopregnanolone administration and early maternal separation: effects on adolescent and adult behaviors in male rat

Endogenous neurosteroid level fluctuations are related to several emotional and behavioral alterations. Neurosteroids also have important roles during neurodevelopment, with there being a relationship between modification of their levels in neurodevelopmental periods and behavioral alterations in adolescence and adulthood. Early maternal separation (EMS) is a stressful event that also alters neurodevelopment and adolescent and adult behaviors. The aim of the present study is to analyze the interaction between the effects of the neonatal alteration of allopregnanolone (AlloP), neurosteroid that increase its levels after acute stress presentation, and EMS on adolescent exploration and adult anxiety and sensorimotor gating in male rats. AlloP (10 mg/kg s.c.) was administrated between postnatal day 5 (PN5) and PN9, and a single 24-hour period of EMS was carried out on PN9. Exploration was analyzed at PN40 and PN60. At adult age (PN85), anxiety was tested by means of the elevated plus-maze test (EPM), and sensorimotor gating by means of prepulse inhibition test (PPI). PPI deterioration has been considered as a reliable indicator of diseases such as schizophrenia. Results showed that the previous neonatal AlloP administration neutralized the effects of EMS in the adolescent exploration (increase of traveled distance and decrease of head-dips). In adult age, an anxiolytic-like profile was observed as a consequence of EMS. Finally, EMS and neonatal AlloP disrupted PPI. Taken together, these data show the important role that physiological neonatal AlloP levels and stressful events play in neural development, adult behavior and vulnerability to neurodevelopmental disorders such as schizophrenia.

Standardized environmental enrichment supports enhanced brain plasticity in healthy rats and prevents cognitive impairment in epileptic rats

Environmental enrichment of laboratory animals influences brain plasticity, stimulates neurogenesis, increases neurotrophic factor expression, and protects against the effects of brain insult. However, these positive effects are not constantly observed, probably because standardized procedures of environmental enrichment are lacking. Therefore, we engineered an enriched cage (the Marlau™ cage), which offers: (1) minimally stressful social interactions; (2) increased voluntary exercise; (3) multiple entertaining activities; (4) cognitive stimulation (maze exploration), and (5) novelty (maze configuration changed three times a week). The maze, which separates food pellet and water bottle compartments, guarantees cognitive stimulation for all animals. Compared to rats raised in groups in conventional cages, rats housed in Marlau™ cages exhibited increased cortical thickness, hippocampal neurogenesis and hippocampal levels of transcripts encoding various genes involved in tissue plasticity and remodeling. In addition, rats housed in Marlau™ cages exhibited better performances in learning and memory, decreased anxiety-associated behaviors, and better recovery of basal plasma corticosterone level after acute restraint stress. Marlau™ cages also insure inter-experiment reproducibility in spatial learning and brain gene expression assays. Finally, housing rats in Marlau™ cages after severe status epilepticus at weaning prevents the cognitive impairment observed in rats subjected to the same insult and then housed in conventional cages. By providing a standardized enriched environment for rodents during housing, the Marlau™ cage should facilitate the uniformity of environmental enrichment across laboratories.

Effects of ethylenediamine in rodent models of seizure, motor coordination and anxiety

Ethylenediamine (EDA) activates GABA(A) receptors via both direct and indirect mechanisms. EDA has been shown to reduce seizures caused by systemic injection of proconvulsants in an animal model of generalized tonic-clonic seizures. However, there does not appear to have been any report on the effects of EDA in other seizure models. Hence, we used male Sprague-Dawley rats to test the effects of EDA on topically applied bicuculline (a model of simple partial seizures) and on maximal electroshock (MES, a model of generalized tonic-clonic seizures). We also examined the effects of EDA on motor coordination using a rotarod treadmill, and its potential anxiolytic properties using an elevated plus maze (EPM). EDA at concentrations of 50 μM and above reduced the frequency of epileptiform spikes on an electrocorticogram in a concentration-dependent manner. EDA at 100 and 1000 mg/kg i.p. increased the threshold for inducing limb extension on the MES. EDA did not affect the time spent by rats on the rotarod at 10 or 100mg/kg, but significantly reduced the time spent at doses of 1000 mg/kg. In the EPM, EDA at 10 or 100mg/kg significantly increased the frequency of entries and time spent in the open arms. We conclude that EDA has antiepileptic and anxiolytic activity at doses that do not affect motor coordination.

Effect of early life housing manipulation on baseline and drug-induced behavioural responses on neurochemistry in the male rat

Employing environmental enrichment (EE) provides continual sources of dynamic interaction for animals. Though an established discipline in behavioural science, the consequences of EE on behavioural pharmacological tests have not been extensively examined. The purpose of this study was to examine the consequences of EE (or isolation housing) on a range of behavioural pharmacological tests and brain monoamine and brain-derived neurotrophic factor (BDNF) expression in the rat. Male rats were randomly assigned to IC (isolation), SC (standard group-housed) or EE conditions. IC and SC animals were housed singly or in groups of four in standard cages, whilst the EE group were housed in groups of four in larger cages enriched with a variety of wooden, cardboard and plastic objects. After 5weeks of housing, its impact on the effects of diazepam (DZP) in the elevated plus maze (EPM); desipramine (DMI) in the forced swim test (FST) and amphetamine (AMP) effects on homecage activity were assessed. Post-mortem monoamine and BDNF levels were analysed using HPLC and ELISA. EE rats displayed reduced activity in the OFT, however no other differences were found in baseline behaviours. DMI reduced immobility time in the FST, but only for rats housed in IC, while AMP effects were somewhat greater for socially-housed animals than those in IC. There were no housing effects on monoamine or BDNF levels in discreet brain regions. The results suggest that post-weaning enrichment had no significant effect on baseline behaviours or monoamine and BDNF levels, thus it is suitable to implement as a commonplace husbandry practice, however, caution must be taken when investigating responsiveness to psychotropic drugs.

Sex differences in baseline and drug-induced behavioural responses in classical behavioural tests

Behavioural pharmacology relies on animal models which are primarily validated using the male laboratory rat. Many researchers solely employ male animals in studies; this is primarily due to concerns about the impact of variations in the female estrous cycle on behavioural responses. The objective of the present study therefore was to examine whether sex has any effect in some commonly employed behavioural pharmacology tests. Male and female Sprague Dawley rats were examined in the following behavioural pharmacology tests: diazepam (DZP) effects on anxiolytic behaviour in the elevated plus maze (EPM); desipramine (DMI) effects on immobility time in the forced swim test (FST); amphetamine (AMP) and apomorphine (APO) effects on locomotor activity in the homecage monitoring apparatus (HCMA). Baseline investigations revealed that females were more active than males in all three tests. DZP increased open arm time and entries for males but not for females. Similarly, significant reduction in immobility time with DMI was found for males in the FST, with no effect observed in females. There was a significant effect of AMP dose on distance moved for both sexes; the peak locomotor stimulating effects were seen following 1-2 mg kg⁻¹ AMP doses for males, while 0.5 mg kg⁻¹ produced the greatest effect in females. APO impaired locomotor activity in both sexes. These results demonstrate that male and female rats respond differently to psychotropic drugs. The absence of female responses to the effects of DZP and DMI in the EPM and FST respectively was due to the high baseline activity levels seen with females; thus behavioural tests must be designed to account for sex differences in baseline behaviours to allow for unambiguous extrapolation of the results.

Impairment of the organization of locomotor and exploratory behaviors in bile duct-ligated rats

Hepatic encephalopathy (HE) arises from acute or chronic liver diseases and leads to several problems, including motor impairment. Animal models of chronic liver disease have extensively investigated the mechanisms of this disease. Impairment of locomotor activity has been described in different rat models. However, these studies are controversial and the majority has primarily analyzed activity parameters. Therefore, the aim of the present study was to evaluate locomotor and exploratory behavior in bile duct-ligated (BDL) rats to explore the spatial and temporal structure of behavior. Adult female Wistar rats underwent common bile duct ligation (BDL rats) or the manipulation of common bile duct without ligation (control rats). Six weeks after surgery, control and BDL rats underwent open-field, plus-maze and foot-fault behavioral tasks. The BDL rats developed chronic liver failure and exhibited a decrease in total distance traveled, increased total immobility time, smaller number of rearings, longer periods in the home base area and decreased percentage of time in the center zone of the arena, when compared to the control rats. Moreover, the performance of the BDL rats was not different from the control rats for the elevated plus-maze and foot-fault tasks. Therefore, the BDL rats demonstrated disturbed spontaneous locomotor and exploratory activities as a consequence of altered spatio-temporal organization of behavior.

Use of the light-dark box to compare the anxiety-related behavior of virgin and postpartum female rats

Postpartum female rodents are less anxious than diestrous virgins and this difference contributes to dams' ability to adequately care for pups and defend the nest. Low postpartum anxiety has been observed in many behavioral paradigms but the results of previous studies using the light-dark box have been inconsistent. We here reexamined the usefulness of the light-dark box to assess differences between postpartum and diestrous virgin female rats in their anxiety-related behavior. We found a significant effect of reproductive state, such that dams spent more time in the light chamber than did diestrous virgins. This difference required recent physical contact with pups because a four-hour separation from pups reduced dams' time spent in the light chamber by half, similar to what we previously found for litter-separated dams tested in an elevated plus maze. We then examined if dams' low-anxiety behavior in the light-dark box depends on high GABA(A) receptor activity by inhibiting the receptor at different binding sites using (+)-Bicuculline to target the GABA site, FG-7142 to target the benzodiazepine site, and pentylenetetrazol to target the picrotoxin site. Only pentylenetetrazol was consistently anxiogenic in dams, while having little effect in diestrous virgins. Thus, the light-dark box can be a useful paradigm to study differences between postpartum and diestrous virgin female rats in their anxiety-related behaviors, and this difference is influenced by dams' recent contact with pups and GABA(A) receptor neurotransmission particularly affected by activity at the picrotoxin site.

Continuous enriched environment improves learning and memory in adult NMRI mice through theta burst-related-LTP independent mechanisms but is not efficient in advanced aged animals

INTRODUCTION

Effects of 3-month continuous environmental enrichment (EE) on cognitive abilities and on theta burst-related synaptic plasticity of CA1 hippocampal neuronal networks have been assessed in 6- and 20-month old NMRI female mice.

RESULTS

EE decreased anxiety-like behavior and improved learning and memory performances in adult but not in aged mice. Electrophysiological results in CA1 hippocampal slices showed that basal synaptic transmission was not affected by EE in adult mice whereas it was partially improved in aged animals, even though not sufficient to rescue the decrease related to aging. Besides, no effect of EE on N-methyl-d-aspartate receptor activation and theta-burst-induced long-term potentiation was found in adult or aged animals.

DISCUSSION

These results indicate that continuous EE is able to improve cognitive abilities in adult NMRI female mice, that does not correlate with changes in theta burst-related synaptic plasticity within neuronal networks. In addition, the lack of effects in aged animals suggests the existence of a critical delay for the beneficial effects of EE on cognitive aging.

Decision-making performance is related to levels of anxiety and differential recruitment of frontostriatal areas in male rats

In humans, high levels of anxiety are associated with poor performance in the Iowa Gambling Task (IGT). The IGT measures decision-making under conditions of uncertainty. In this study, we investigated the association between anxiety and decision-making in rats. Rats were screened for anxiety on the elevated plus maze (EPM) and subsequently tested in a rat analogue of the IGT (r-IGT). We explored the role of frontostriatal areas related to r-IGT performance using c-fos immunohistochemistry following the last training-session. High levels of anxiety were associated with poor r-IGT performance: high anxious rats made fewer choices for the advantageous option and collected fewer sucrose pellets in the r-IGT than low anxious rats. Analysis of win-stay/lose-shift behaviour of choices for the advantageous option revealed that good performing-low anxious subjects showed an increase in win-stays and a decrease in lose-shifts across trial blocks while poor performing-high anxious subjects did not. Furthermore, decision-making performance and, indirectly, anxiety levels were related to neural activity in parts of the medial prefrontal cortex, that is prelimbic and infralimbic cortex, and in parts of the striatum, that is nucleus accumbens shell and core. These data suggest a similar frontostriatal circuitry underlying affective decision-making in humans and rats.

Brief light as a practical aversive stimulus for the albino rat

Bright light was an effective aversive stimulus for Wistar rats in punishment, escape, and avoidance paradigms. Contingent punishment of lever pressing maintained by concurrent schedules of food delivery shifted presses to an alternate lever, and depressed overall response rates. Periodic non-contingent presentation of the light prompted escape responding (head entry into a hole). Unsignaled avoidance contingencies were not effective, but pre-pulse signaling of light supported avoidance behavior. These results demonstrate a possible alternative to foot-shock, one with greater ecological validity, and one that might avoid some of the physiological effects that accompany electric shock.