Stressors affect the response of male and female rats to clomipramine in a model of behavioral despair (forced swim test)

Environmental stress during adolescence promotes depression-like behavior and endocrine abnormalities in rats

OBJECTIVE

To assess the ability of environmental stress (ES) during adolescence on depression-like behaviors and endocrinology in rats.

METHODS

Male and female Sprague-Dawley rats before or during puberty were divided into three groups: control group (CON), low-frequency ES group (LF), and high-frequency ES group (HF). ES included water/food deprivation and reversal of day and night. After 4 weeks of ES, the behavioral tests were performed. Plasma concentrations of hormones and peptides were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS

ES induced a significant decrease in sucrose preference value in female adolescent rats but not males. In prepubertal rats, the reductions in sucrose preference upon ES were observed without a sex-specific effect. Compared with the CON group, female adolescent rats showed a significant increase, while male adolescent rats showed a significant decrease in plasma corticosterone (CORT) after ES. Also, ES significantly increased plasma leptin in female and male adolescent rats. Moreover, ES significantly increased plasma cholecystokinin (CCK), neuropeptide Y (NPY), and testosterone (TS) levels in adolescent female rats but not in males. No significant differences were found in plasma progesterone and E2 among adolescent rats. The prepubertal male rats showed significant plasma E2 and TS increase after ES, while there were no significant differences between groups in plasma CORT, leptin, CCK, NPY, and progesterone.

CONCLUSIONS

ES may cause depression-like behaviors in adolescent female rats. Our findings supplement the scientific basis for formulating strategies to treat and prevent adolescent depression.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

Sex differences in affective states and association with voluntary ethanol intake in Sprague-Dawley rats

Alcohol use disorders (AUDs) are a major problem across the USA. While AUD remains a complex human condition, it is difficult to isolate the directionality of anxiety and ethanol (EtOH) drinking from outside influences. The present study sought to investigate the relationship between affective states and EtOH intake using male and female Sprague-Dawley rats. Using complementary tests of anxiety- and depressive-like behavior, we found sex- and test-specific differences in basal affective behavior such that females displayed enhanced anxiety-like behavior in the splash test and males displayed enhanced anxiety-like behavior in the novelty-suppressed feeding test. Although, there were no sex differences in EtOH intake and no correlation between baseline anxiety-like behavior and subsequent EtOH intake, we did find that depressive-like behavior predicted future EtOH intake in female rats only. In addition, we observed an increase in depressive-like behavior is male rats in both the water and EtOH drinking groups (compared to baseline levels). Furthermore, post-drinking anxiety-like behavior, but not depressive-like behavior predicted subsequent EtOH intake in female rats. Lastly, we found a history of EtOH intake decreased pain thresholds in male and female rats, but increased anxiety-like and depressive-like behavior was associated with decreased thermal sensitivity only in EtOH-drinking males. Together, these experiments provide important information on the complex interaction between negative affect and EtOH intake and how these two contexts reciprocally do, or do not, influence each other in a sex-specific manner.

Effects of mirabegron on depression, anxiety, learning and memory in mice

Mirabegron is the first b3-adrenoceptor agonist to enter clinical practice and has been approved for the treatment of symptoms of OAB. The aim of this study is to investigate whether the mirabegron has an effect on depression, anxiety, learning, and memory. We investigated the effects of mirabegron on depression, anxiety, learning and memory by using forced swimming test, elevated plus maze test, passive avoidance and Morris water maze in mice. Imipramine and mirabegron (3, 6 and 9 mg/kg) significantly reduced immobility time in forced swimming test. Diazepam and mirabegron (3, 6 and 9 mg/kg) significantly increased the time spent in open arms and the number of entries to the open arms in elevated plus maze test. Furthermore, cognitive performance impaired with scopolamine has been significantly improved with 9 mg/kg mirabegron. Mirabegron (6 and 9 mg/kg) significantly increased the time spent in the target quadrant in naive mice. While scopolamine significantly increased the swimming speed, mirabegron (9 mg/kg) significantly decreased the swimming speed in scopolamine-treated mice. Mirabegron might be clinically useful for the treatment of OAB in elderly patients that should use drugs against depression and anxiety, without disrupt learning and memory.

Strain-, Sex-, and Time-Dependent Antidepressant-like Effects of Cannabidiol

Cannabidiol (CBD) is a non-intoxicating compound extracted from Cannabis sativa, showing antidepressant-like effects in different rodent models. However, inconsistent results have been described depending on the species and the strain used to assess depressive-like behavior. Moreover, only a few studies investigated the effect of CBD in female rodents. Therefore, we aimed to (i) investigate the effects of CBD in two different strains of mice (Swiss and C57BL/6) and a rat model of depression based on selective breeding (Flinders Sensitive and Resistant Lines, FSL and FRL) subjected to tests predictive of antidepressant-like effects and (ii) investigate the influence of sex in the effects of CBD in both mice and rats. CBD induced an antidepressant-like effect in male Swiss but not in female Swiss or C57BL/6 mice in the tail suspension test (TST). In male FSL rats, CBD produced an antidepressant-like effect 1 h post injection. However, in female FSL, CBD induced a bimodal effect, increasing the immobility time at 1 h and decreasing it at 2 h. In conclusion, strain, sex, and administration time affect CBD's behavioral response to rodents exposed to tests predictive of antidepressant effects.

Facilitation of dopamine-dependent long-term potentiation in the medial prefrontal cortex of male rats follows the behavioral effects of stress

The effect of stress on animal behavior and brain activity has been attracting growing attention in the last decades. Stress dramatically affects several aspects of animal behavior, including motivation and cognitive functioning, and has been used to model human pathologies such as post-traumatic stress disorder. A key question is whether stress alters the plastic potential of synaptic circuits. In this work, we evaluated if stress affects dopamine (DA)-dependent synaptic plasticity in the medial prefrontal cortex (mPFC). On male adolescent rats, we characterized anxiety- and depressive-like behaviors using behavioral testing before and after exposure to a mild stress (elevated platform, EP). After the behavioral protocols, we investigated DA-dependent long-term potentiation (DA-LTP) and depression (DA-LTD) on acute slices of mPFC and evaluated the activation of DA-producing brain regions by western and dot blot analysis. We show that exposure to the EP stress enhances DA-LTP and that desipramine (DMI) treatment abolishes this effect. We also found that DA-LTD is not affected by EP stress unless when this is followed by DMI treatment. In addition, EP stress reduces anxiety, an effect abolished by both DMI and ketamine, while motivation is promoted by previous exposure to EP stress independently of pharmacological treatments. Finally, this form of stress reduces the expression of the early gene cFOS in the ventral tegmental area. These findings support the idea that mild stressors can promote synaptic plasticity in PFC through a dopaminergic mechanism, an effect that might increase the sensitivity of mPFC to subsequent stressful experiences.

The Effect of Gentle Handling on Depressive-Like Behavior in Adult Male Mice: Considerations for Human and Rodent Interactions in the Laboratory

Environmental factors play a significant role in well-being of laboratory animals. Regulations and guidelines recommend, if not require, that stressors such as bright lighting, smells, and noises are eliminated or reduced to maximize animal well-being. A factor that is often overlooked is handling and how researchers interact with their animals. Researchers, lab assistants, and husbandry staff in animal facilities may use inconsistent handling methods when interacting with rodents, but humans should be considered a part of the animal's social environment. This study examined the effects of different handling techniques on depressive-like behavior, measured by the Porsolt forced swim test, in adult C57BL/6J male mice. The same two researchers handled the mice in a gentle, aggressive, or minimal (control) fashion over approximately two weeks prior to testing. The results demonstrated a beneficial effect of gentle handling: gentle handling reduced swimming immobility in the forced swim test compared to mice that were aggressively or minimally handled. We argue that gentle handling, rather than methodical handling, can foster a better relationship between the handlers and rodents. Although handling is not standardized across labs, consistent gentle handling allows for less challenging behavioral testing, better data collection, and overall improved animal welfare.

Sex-specific diurnal immobility induced by forced swim test in wild type and clock gene deficient mice

Objective: The link between alterations in circadian rhythms and depression are well established, but the underlying mechanisms are far less elucidated. We investigated the circadian characteristics of immobility behavior in wild type (WT) mice and mice with mutations in core Clock genes. Methods: All mice were tested with forced swim test (FST) at 4 h intervals. Results: These experiments revealed significant diurnal rhythms associated with immobility behavior in both male and female WT mice with sex-different circadian properties. In addition, male mice showed significantly less immobility during the night phase in comparison to female mice. Female Per1^Brdm1 mice also showed significant rhythmicity. However, the timing of rhythmicity was very different from that observed in female wild type mice. Male Per1^Brdm1 mice showed a pattern of rhythmicity similar to that of wild type mice. Furthermore, female Per1^Brdm1 mice showed higher duration of immobility in comparison to male Per1^Brdm1 mice in both daytime and early night phases. Neither Per2^Brdm1 nor Clock^Δ19 mice showed significant rhythmicity, but both female Per2^Brdm1 and Clock^Δ19 mice had lower levels of immobility, compared to males. Conclusions: This study highlights the differences in the circadian characteristics of immobility induced by FST in WT, Clock^Δ19, Per1, and Per2 deficient mice.

Adolescent exposure to THC in female rats disrupts developmental changes in the prefrontal cortex

Current concepts suggest that exposure to THC during adolescence may act as a risk factor for the development of psychiatric disorders later in life. However, the molecular underpinnings of this vulnerability are still poorly understood. To analyze this, we investigated whether and how THC exposure in female rats interferes with different maturational events occurring in the prefrontal cortex during adolescence through biochemical, pharmacological and electrophysiological means. We found that the endocannabinoid system undergoes maturational processes during adolescence and that THC exposure disrupts them, leading to impairment of both endocannabinoid signaling and endocannabinoid-mediated LTD in the adult prefrontal cortex. THC also altered the maturational fluctuations of NMDA subunits, leading to larger amounts of gluN2B at adulthood. Adult animals exposed to THC during adolescence also showed increased AMPA gluA1 with no changes in gluA2 subunits. Finally, adolescent THC exposure altered cognition at adulthood. All these effects seem to be triggered by the disruption of the physiological role played by the endocannabinoid system during adolescence. Indeed, blockade of CB1 receptors from early to late adolescence seems to prevent the occurrence of pruning at glutamatergic synapses. These results suggest that vulnerability of adolescent female rats to long-lasting THC adverse effects might partly reside in disruption of the pivotal role played by the endocannabinoid system in the prefrontal cortex maturation.

Sex differences in animal models of psychiatric disorders

Psychiatric disorders are characterized by sex differences in their prevalence, symptomatology and treatment response. Animal models have been widely employed for the investigation of the neurobiology of such disorders and the discovery of new treatments. However, mostly male animals have been used in preclinical pharmacological studies. In this review, we highlight the need for the inclusion of both male and female animals in experimental studies aiming at gender-oriented prevention, diagnosis and treatment of psychiatric disorders. We present behavioural findings on sex differences from animal models of depression, anxiety, post-traumatic stress disorder, substance-related disorders, obsessive-compulsive disorder, schizophrenia, bipolar disorder and autism. Moreover, when available, we include studies conducted across different stages of the oestrous cycle. By inspection of the relevant literature, it is obvious that robust sex differences exist in models of all psychiatric disorders. However, many times results are conflicting, and no clear conclusion regarding the direction of sex differences and the effect of the oestrous cycle is drawn. Moreover, there is a lack of considerable amount of studies using psychiatric drugs in both male and female animals, in order to evaluate the differential response between the two sexes. Notably, while in most cases animal models successfully mimic drug response in both sexes, test parameters and treatment-sensitive behavioural indices are not always the same for male and female rodents. Thus, there is an increasing need to validate animal models for both sexes and use standard procedures across different laboratories.

Evidence that the anxiolytic-like effects of the beta3 receptor agonist amibegron involve serotoninergic receptor activity

Anxiety disorders are the most common behavioral disorders, and they exhibit high comorbidity rates. The aim of the present study was to confirm the effects of Amibegron, the first selective beta 3 adrenergic agent, on anxiety and to demonstrate that different serotoninergic receptor subtypes are involved in this effect. We administered the serotonin 5-HT1A receptor antagonist WAY-100635, the serotonin 5-HT2A receptor antagonist Ketanserin and the serotonin 5-HT3 receptor antagonist Ondansetron in mice and evaluated their performance in the elevated plus-maze test. Mice administered with Amibegron (5 and 10 mg/kg) showed a dose-dependent prolonged time spent in the open arms and an increase in the number of entries into the open arms during the elevated plus-maze (EPM) test. However, in the control mice, administration of WAY, Ketanserin and Ondansetron demonstrated no effect on the time spent in the open arms and the number of entries into the open arms. In addition, these treatments all significantly reversed the effect of the Amibegron-induced (10 mg/kg) increase in the time spent in the open arms. However, only WAY and Ketanserin treatments reversed the Amibegron-induced increase in the number of entries into the open arms. In conclusion, Amibegron exerted a significant anxiolytic effect, which was as effective as Diazepam, in mice during the EPM test. This effect of Amibegron may be mediated by interactions with the serotonin 5-HT1A, 5-HT2A and 5-HT3 receptors.

Factors influencing behavior in the forced swim test

The forced swim test (FST) is a behavioral test in rodents which was developed in 1978 by Porsolt and colleagues as a model for predicting the clinical efficacy of antidepressant drugs. A modified version of the FST added the classification of active behaviors into swimming and climbing, in order to facilitate the differentiation between serotonergic and noradrenergic classes of antidepressant drugs. The FST is now widely used in basic research and the pharmaceutical screening of potential antidepressant treatments. It is also one of the most commonly used tests to assess depressive-like behavior in animal models. Despite the simplicity and sensitivity of the FST procedure, important differences even in baseline immobility rates have been reported between different groups, which complicate the comparison of results across studies. In spite of several methodological papers and reviews published on the FST, the need still exists for clarification of factors which can influence the procedure. While most recent reviews have focused on antidepressant effects observed with the FST, this one considers the methodological aspects of the procedure, aiming to summarize issues beyond antidepressant action in the FST. The previously published literature is analyzed for factors which are known to influence animal behavior in the FST. These include biological factors, such as strain, age, body weight, gender and individual differences between animals; influence of preconditioning before the FST: handling, social isolation or enriched environment, food manipulations, various kinds of stress, endocrine manipulations and surgery; schedule and routes of treatment, dosage and type of the drugs as well as experimental design and laboratory environmental effects. Consideration of these factors in planning experiments may result in more consistent FST results.

Behavioural and neurochemical changes induced by stress-related conditions are counteracted by the neurokinin-2 receptor antagonist saredutant

These experiments were undertaken to assess the mechanisms underlying the antidepressant-like effects of the neurokinin-2 (NK(2)) receptor antagonist saredutant (SR48968) in rats tested in the forced swim test (FST), by analysing hippocampal brain-derived neurotrophic factor (BDNF) and plasma corticosterone [as index of hypothalamic-pituitary-adrenal (HPA) axis activity]. Male Wistar rats received three intraperitoneal injections over 24 h of vehicle, saredutant (5 mg/kg), citalopram (15 mg/kg), clomipramine (50 mg/kg). Rats were subjected to restraint stress (4 h) 24 h prior to the FST procedure. This stress procedure increased immobility and decreased swimming behaviour in the FST; furthermore, it lowered hippocampal BDNF protein expression and increased plasma corticosterone levels. Saredutant and clomipramine or citalopram, used here as positive controls, reduced the immobility time in the FST both under basal conditions and after stress exposure. This effect was not attributable to changes in locomotion, because locomotor activity was unchanged when assessed in the open field test. Pretreatment with para-cholorophenylalanine (150 mg/kg, 72 h and 48 h prior to FST) abolished the effect of citalopram and saredutant on immobility time. At neurochemical level, saredutant attenuated activation of HPA axis in stressed animals more than clomipramine or citalopram. The behavioural effects of saredutant support the hypothesis that NK(2) receptor activity is involved in stress-related disorders. These effects of saredutant may be related to normalization of the HPA axis. Moreover, saredutant increases BDNF expression in the hippocampus, confirming the role of NK(2) receptor blockade in BDNF activation following stressor application.

Effects of stimulation and blockade of d(2) receptor on depression-like behavior in ovariectomized female rats

The aim of the present study was to explore the hedonic effects of D₂ receptor agonist, quinpirole and D₂ receptor antagonist, and sulpiride alone or in combination with a low dose of 17β-E₂-estradiol (17β-E₂) in the adult ovariectomized female rats (OVX). OVX rats of Wistar strain were used in all experiments. Two weeks after surgery rats were chronically treated with vehicle, a low dose of 17β-E₂ (5.0 μg/rat), quinpirole (0.1 mg/kg), sulpiride (10.0 mg/kg), quinpirole plus 17β-E₂, or sulpiride plus 17β-E₂ for 14 days before the forced swimming test. We found that sulpiride significantly decreased immobility time in the OVX females. A combination of sulpiride with a low dose of 17β-E₂ induced more profound decrease of immobility time in the OVX rats compared to the rats treated with sulpiride alone. On the contrary, quinpirole failed to modify depression-like behavior in the OVX rats. In addition, quinpirole significantly blocked the antidepressant-like effect of 17β-E₂ in OVX rats. Thus, the D₂ receptor antagonist sulpiride alone or in combination with a low dose of 17β-E₂ exerted antidepressant-like effect in OVX female rats, while the D₂ receptor agonist quinpirole produced depressant-like profile on OVX rats.

Passive Response to Stress in Adolescent Female and Adult Male Mice after Intermittent Nicotine Exposure in Adolescence

Smoking is frequently co-morbid with depression. Although it is recognized that depression increases the risk for smoking, it is unclear if early smoking exposure may increase the risk for depression. To test this possibility we assessed the effects of adolescent nicotine exposure on the Forced Swim Test (FST), which is used as a measure of passive coping, and depressive-like behavior in rodents, and on the open field test (OFT), which is used as a measure of locomotion and exploratory behavior. Male and female mice received daily saline or nicotine (0.3 or 0.6 mg/kg) injections from postnatal day (PD) 30 to PD 44. FST and OFT were performed either 1 or 30 days after the last injection (PD 45 and PD 74, respectively). In females, treatment with 0.3 mg/kg nicotine lead to increased FST immobility (64%) and decreased OFT locomotor activity (12%) one day following the last nicotine injection (PD 45); while no effects were observed in adulthood (PD 74). In contrast, on PD45, nicotine treatment did not change the male FST immobility but lead to lower OFT locomotor activity (0.6 mg/kg, 10%). In adulthood (PD 74), both nicotine doses lead to higher FST immobility (87%) in males while 0.6 mg/kg nicotine to lower OFT locomotor activity (13%). The results (i) identify females as more vulnerable to the immediate withdrawal that follows nicotine discontinuation in adolescence and (ii) suggest that adolescent nicotine exposure may enhance the risk for passive response towards unavoidable stress in adult males.

Effect of repeated restraint stress and clomipramine on Na+/K+-ATPase activity and behavior in rats

Activation of the limbic-hypothalamic-pituitary-adrenal axis (LHPA) and the release of glucocorticoids are fundamental for the adaptive response and immediate survival of an organism in reaction to acute stimuli. However, high levels of glucocorticoids in the brain may produce neuronal injury and a decrease of Na(+)/K(+)-ATPase activity, with effects on neurotransmitter signaling, neural activity, as well as the whole animal behavior. Clomipramine is a tricyclic antidepressant that inhibits the reuptake of serotonin and norepinephrine by indirect actions on the dopaminergic system and LHPA axis. Its chronic use increases the body's ability to cope with stress; however, high doses can potentiate its side effects on memory, learning, and sensory motor function. The purpose of the present study was to compare the effect of repeated restraint stress and clomipramine treatment on Na(+)/K(+)-ATPase activity and on the behavior of male rats. Changes in the behavioral response were evaluated by measuring the memory, learning, anxiety, and exploratory responses. Our results showed that exposure to repeated restraint stress reduced levels of Na(+)/K(+)-ATPase in brain structures and changed short and long-term memory, learning, and exploratory response when compared to the control group. Exposure to clomipramine treatment increased anxiety levels and reduced Na(+)/K(+)-ATPase activity in the cerebral cortex as well as short term memory, learning, and exploratory response. In conclusion, the present results provide additional evidence concerning how repeated restraint stress and clomipramine chronically administered at higher dose levels affect the neural activity and behavior of male rats.

Antidepressant-like effects of mineralocorticoid but not glucocorticoid antagonists in the lateral septum: interactions with the serotonergic system

The lateral septum (LS) is a limbic brain region that receives serotonergic projections from raphe neurons and participates in the modulation of stress responses and affective states. The present study determined whether mineralocorticoid receptors (MRs) and/or glucocorticoid receptors (GRs) located in the LS interact with the serotonergic system in the regulation of depressive-like behavior of rats subjected to the forced swimming test (FST). We also studied the effect of corticosterone release induced by the FST on MR- and GR-mRNA expression in the LS. Specifically, we studied the antidepressant-like effects of spironolactone (a MR antagonist), mifepristone (a GR antagonist), and the antidepressant clomipramine (CMI) administered directly into the LS. In addition, spironolactone and CMI actions were studied in animals with serotonergic depletion induced by dl-p-chlorophenylalanine (pCPA). Finally, adrenalectomized and Sham-operated rats were subjected to the FST to determine MR- and GR-mRNA expression in the LS at different post-FST intervals. The results showed that intraseptal injection of spironolactone, but not mifepristone induced antidepressant-like actions in the FST; this effect was blocked by pCPA treatment. CMI and spironolactone increased 5-HT concentrations in the LS of rats subjected to the FST. Increases in corticosterone release, induced by the FST, correlated with a decrease in MR-mRNA expression in the LS; no correlation was found with GR-mRNA expression. In conclusion, MRs in the lateral septum, but not GRs, participate in the regulation of depressive-like behavior of animals subjected to the FST. Both serotonin and corticosterone play an important role in MR actions in the LS.

The beta3 adrenoceptor agonist, amibegron (SR58611A) counteracts stress-induced behavioral and neurochemical changes

These experiments were made to study the mechanisms underlying the antidepressant-like effects of the beta(3) adrenoceptor agonist amibegron (SR58611A). To this purpose, the expression levels of the hippocampal cyclic adenosine monophosphate (cAMP)-response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), B-cell lymphoma-2 (Bcl-2) and Bax proteins were assessed, by using western blot analysis, in rats tested in the forced swim test (FST). Under basal conditions (no previous exposure to stressors), different groups of male Wistar rats received acutely or repeatedly (once/day for 7days) intraperitoneal (i.p.) injections of amibegron (1, 5 and 10mg/kg), the tricyclic antidepressant (TCA) clomipramine (50mg/kg), the selective serotonin reuptake inhibitor (SSRI) citalopram (15mg/kg) or their vehicles. The influence of stress-related conditions was studied in rats subjected to acute (4h) or repeated (4h/day for 7days) restraint stress, applied prior to the FST procedure. Compared to the control groups, both stressor procedures increased the immobility time in the FST and reduced hippocampal BDNF and Bcl-2/Bax ratio proteins expression, which were counteracted by amibegron (5 and 10mg/kg) treatment. Opposite effects were found in the CREB expression, since it was lower after acute and higher after repeated stress procedure, respectively. Again, these effects were reversed by amibegron treatment. Different results were obtained in animals treated with clomipramine or citalopram. Hence, it is likely that the observed behavioral effects of amibegron could be due, at least in part, to its action on hippocampal expression of neurotrophic and/or anti-apoptotic factors, supporting the hypothesis that beta(3) adrenoceptors may be a therapeutic target for the treatment of stress-related disorders.

Forced swim test behavior in postpartum rats

This study was undertaken to determine whether depression-like behavior can be observed in gonadally intact females that have experienced normal pregnancy. When tested on the forced swim test (FST) on postpartum days 1-7, previously pregnant rats spent slightly more time immobile, significantly less time swimming and diving, and defecated more than virgin controls. Subchronic treatment with nomifensine (DA reuptake inhibitor, 2.5mg/kg) but not sertraline (serotonin reuptake inhibitor, 10mg/kg) or desipramine (norepinephrine reuptake inhibitor, 10mg/kg) significantly decreased immobility on postpartum day 2. In rats pre-exposed to the FST in mid-pregnancy, neither subchronic nor chronic treatment with desipramine or sertraline decreased immobility on postpartum day 2; in contrast, chronic desipramine significantly decreased immobility in virgin controls. These results indicate that postpartum female rats, compared to virgin controls, show a reduction in some "active coping behaviors" but no significant increase in immobility when tested during the early postpartum period, unlike ovariectomized females that have undergone hormone-simulated pregnancy (HSP). Additionally, immobility that is increased by FST pre-exposure is not readily prevented by treatment with standard antidepressant medications in postpartum females. Depression-like behaviors previously observed in females that have undergone HSP may result from the more dramatic changes in estradiol, prolactin or corticosterone that occur during the early "postpartum" period, compared to the more subtle changes in these hormones that occur in actual postpartum females.

Shaping brain development: mouse communal nesting blunts adult neuroendocrine and behavioral response to social stress and modifies chronic antidepressant treatment outcome

Early experiences shape brain function and behavior and, consequently, vulnerability to psychopathology at adulthood. Here we exploited the mouse communal nest (CN) paradigm in order to investigate the effect of the early social environment on the emergence of endophenotypes of depression and on antidepressant efficacy at adulthood. CN, which consists in a single nest where three mothers keep their pups together and share care-giving behavior until weaning, is characterized by high levels of maternal behavior and peer interactions, thus representing an highly stimulating environment. Our results show that, when compared to mice reared in standard laboratory conditions (SN), adult CN mice exhibited greater sucrose preference on the first days of the test, displayed reduced anhedonia during social stress and had lower corticosterone levels after acute and prolonged social stress. Furthermore, in line with previous work, CN displayed longer immobility than SN mice in the forced swim test. Here we show that such behavioral response is differently affected by antidepressants according to early experiences. A 3-week fluoxetine treatment affected only SN mice, leading to an increase of immobility duration up to the levels showed by CN mice, while acute fluoxetine administration decreased immobility duration in both groups. These results show that being reared in a CN profoundly changes developmental trajectories, reducing the adult display of endophenotypes of depression and modifying response to antidepressants. The present findings suggest that early experiences represent one of those factors to be taken into account to identify the appropriate individual pharmacological strategy to treat depression in patients.

Dopamine is involved in the antidepressant-like effect of allopregnanolone in the forced swimming test in female rats

Evidence from both animal and human studies suggests a role for dopamine in the therapeutic effect of antidepressant drugs. Consistently, dopamine receptor antagonists antagonize the effect of antidepressant drugs in different experimental models of depression. Neurosteroids, and in particular allopregnanolone, seem to be involved both in the pathophysiology of depression and in the mechanism of action of antidepressant drugs, and their role seems to be particularly important in the understanding of mood disturbances related to the different phases of the reproductive life in women. The aim of this study was to investigate the possible role of dopamine on the antidepressant-like effect of allopregnanolone in a model of depression. Thus, we examined (i) the behaviour of female Sprague-Dawley rats in the forced swimming test during estrus and diestrus and their response to allopregnanolone treatment (0.5, 1 and 2 mg/kg), and (ii) the effect of the dopamine D1-like and D2-like receptor antagonists SCH 23390 (0.01 and 0.025 mg/kg) and raclopride (0.05 and 0.2 mg/kg) on the antidepressant-like effect of allopregnanolone (2 mg/kg) in the same experimental model. We failed to observe differences in depressive-like behaviour between estrous phases, and allopregnanolone administration in both estrus and diestrus resulted in an antidepressant-like effect consisting in an increase of swimming behaviour. The allopregnanolone effect was unaffected by a dose of the dopamine D1-like receptor antagonist SCH 23390 displaying a marked inhibitory effect on basal activity, while it was turned into a potentiation of the depressive-like behaviour of the forced swimming condition by treatment with the higher dose of raclopride. The present results indicate an involvement of dopamine transmission in the allopregnanolone antidepressant-like effect in the forced swimming model of depression, and suggest that this effect depends mainly on stimulation of dopamine D2-like receptors.

Sex-related differential response to clomipramine treatment in a rat model of depression

Research in affective disorders is often performed without considering sex differences, although women are predominantly affected. Consequently, the potential sex-dependent action of antidepressants remains elusive. We investigated whether Flinders sensitive line (FSL) of rats, a model of depression, would present sex-differentiated responses to antidepressant treatment. FSL and Sprague-Dawley rats were treated with clomipramine 10 mg/kg/day for 14 days. Subsequently, they were subjected to either a single session of the forced swim test or an estimation of serotonergic function in the prefrontal cortex, hippocampus, amygdala and hypothalamus. Male FSL displayed increased immobility duration, decreased active behaviours, increased serotonin tissue levels and a reduced serotonin turnover rate in most brain areas studied. Female FSL showed a distinct profile, consisting of decreased immobility latency, increased climbing duration, limited serotonergic deviations and no difference in the serotonin turnover rate in comparison with controls. Interestingly, despite baseline differences, clomipramine treatment reversed all relevant behavioural responses and increased the serotonin turnover rate in both sexes. However, the latter effect was remarkably more pronounced in females. It is concluded that, in this animal model of depression, chronic clomipramine treatment attenuated baseline sex differences in the phenotype while maintaining or intensifying the sex differentiation in the serotonergic endophenotype.

Acute restraint stress produces behavioral despair in weanling rats in the forced swim test

Stressful experiences in the rat during early life increase the vulnerability to later signs of behavioral despair in adulthood, reflected in increased immobility in the forced swim test (FST). However, the possible immediate effects of stress in weanling rats have only been partially described. The present study tested whether a single session of mild restraint stress modifies immobility in the FST in 21-day-old Wistar rats. After evaluating any possible changes in locomotion using the open field test (OFT), the latency and total duration of immobility were assessed in a single FST session. Regardless of gender, mild restraint stress significantly reduced crossings in the OFT, shortened the latency to the first period of immobility, and increased immobility in the FST compared with a control group devoid of stress. We conclude that a single mild physical stress session, as early as postnatal day 21, produces signs of behavioral despair.

Adult female wildtype, but not oestrogen receptor beta knockout, mice have decreased depression-like behaviour during pro-oestrus and following administration of oestradiol or diarylpropionitrile

Studies in people and animal models suggest that depression is influenced by natural fluctuations in the levels of 17beta-oestradiol (E(2)), as well as administration of E(2)-based therapies, such as selective oestrogen receptor modulators (SERMs). Elucidating the effects and mechanisms of E(2) is important to improve future E(2)-based therapeutics. An important question is whether effects of E(2) or SERMs for mood regulation act at the alpha or beta isoform of the oestrogen receptor (ER) because some of the unwanted trophic effects of E(2)-based therapies may involve actions at ERalpha, rather than ERbeta. In the present study, whether there are sex differences in depression-like behaviour of adult mice (experiment 1), and the effects of natural fluctuations in E(2) (experiment 2), or administration of E(2) or a SERM that has higher affinity for ERbeta than for ERalpha (diarylpropionitrile; DPN) to ovariectomised (experiment 3) wildtype and ERbeta knockout (betaERKO) mice were investigated. Results of this study supported our hypotheses that: there would be sex differences favouring males for depression-like behaviour and endogenous increases in, or exogenous administration of, E(2) or administration of an ERbeta SERM would decrease depression-like behaviour in wildtype, but not betaERKO, mice. In experiment 1, adult male mice spent less time immobile in the forced swim test (i.e., showed less depression-like behaviour) compared with female mice. In experiment 2, pro-oestrous (higher circulating E(2) levels), compared with dioestrous (lower circulating E(2) levels), mice had reduced immobility in the forced swim test; this effect was not observed in betaERKO mice. In experiment 3, administration of E(2) or DPN to ovariectomised wildtype, but not betaERKO, mice decreased immobility compared with vehicle administration, these data suggest that ERbeta may be required for some of the anti-depressant-like effects of E(2).

Progesterone modulation of alpha5 nAChR subunits influences anxiety-related behavior during estrus cycle

Smokers often report an anxiolytic effect of cigarettes. In addition, stress-related disorders such as anxiety, post-traumatic stress syndrome and depression are often associated with chronic nicotine use. To study the role of the alpha5 nicotinic acetylcholine receptor subunit in anxiety-related responses, control and alpha5 subunit null mice (alpha5(-/-)) were subjected to the open field activity (OFA), light-dark box (LDB) and elevated plus maze (EPM) tests. In the OFA and LDB, alpha5(-/-) behaved like wild-type controls. In the EPM, female alpha5(-/-) mice displayed an anxiolytic-like phenotype, while male alpha5(-/-) mice were undistinguishable from littermate controls. We studied the hypothalamus-pituitary-adrenal axis by measuring plasma corticosterone and hypothalamic corticotropin-releasing factor. Consistent with an anxiolytic-like phenotype, female alpha5(-/-) mice displayed lower basal corticosterone levels. To test whether gonadal steroids regulate the expression of alpha5, we treated cultured NTera 2 cells with progesterone and found that alpha5 protein levels were upregulated. In addition, brain levels of alpha5 mRNA increased upon progesterone injection into ovariectomized wild-type females. Finally, we tested anxiety levels in the EPM during the estrous cycle. The estrus phase (when progesterone levels are low) is anxiolytic-like in wild-type mice, but no cycle-dependent fluctuations in anxiety levels were found in alpha5(-/-) females. Thus, alpha5-containing neuronal nicotinic acetylcholine receptors may be mediators of anxiogenic responses, and progesterone-dependent modulation of alpha5 expression may contribute to fluctuations in anxiety levels during the ovarian cycle.

Nicotine (NC)-induced "depressive" behavioral symptoms and effects of antidepressants including cannabinoids (CBs)

Depression is one of the frequently-observed psychiatric symptoms associated with nicotine (NC) use. In the present study, considering the unique effects of NC (e.g. antidepressant effects have also been reported), the time course of the NC-induced depressive behavioral alterations in a mouse model was compared with a typical depression-inducing stressor. Furthermore, based on the involvement of cannabinoid (CB) receptors in the behavioral effects of NC, the effects of antidepressants including CB ligands (CBs) against the NC-induced behavioral alterations were also investigated. Repeated subcutaneous NC treatments (0.3 mg/kg, 4 days), like repeated immobilization stress (IM) treatments (10 min, 4 days), caused prolonged depressive effects (increased immobility time) at both 2 hr and 1 day time points after the last treatment in the tail suspension test. However, in the NC group, depressive effects (suppressed swimming behaviors) were observed only at the 2 hr time point in the forced swimming test. The antidepressants amitriptyline, clomipramine and fluvoxamine, the endogenous mixed CB agonist/antagonist virodhamine and the anandamide-like cannabimimetic O-2093 provided antagonistic effects against the depressive behaviors in the tail suspension test. However, in the forced swimming test, NC-induced depressive behaviors were antagonized only by the CBs virodhamine and O-2093. The present results demonstrated depressive effects of NC in two typical behavioral tests, which support the risk of repeated NC use. The shortened behavioral alterations in the forced swimming test, as compared to the IM group, seemed to reflect the neuronal modifications peculiar to NC, which are antagonized by some CBs.

A postpartum model in rat: behavioral and gene expression changes induced by ovarian steroid deprivation

BACKGROUND

Postpartum depression (PPD) affects approximately 10% to 20% of women during the first 4 weeks of the postpartum period and is characterized by labile mood with prominent anxiety and irritability, insomnia, and depressive mood. During the postpartum period, elevated ovarian hormones abruptly decrease to the early follicular phase levels that are postulated to play a major role in triggering PPD. However, the underlying neurobiological mechanisms that contribute to PPD have not been determined.

METHODS

In the present study, we examined the effect of ovarian steroids, administered at levels that occur during human pregnancy followed by rapid withdrawal to simulate postpartum conditions, on behavior and gene expression in the rat.

RESULTS

The results of behavioral testing reveal that the hormone-simulated postpartum treatment results in the development of a phenotype relevant to PPD, including vulnerability for helplessness, increased anxiety, and aggression. Real-time quantitative polymerase chain reaction (PCR) demonstrated transient regulation of several genes, including Ca(2+)/calmodulin-dependent protein kinase II (CAMKII), serotonin transporter (SERT), myocyte enhancer factor 2A (MEF2A), brain-derived neurotrophic factor (BDNF), gamma-aminobutyric acid type A receptor alpha 4 (GABAARA4), mothers against decapentaplegic homolog 4 (SMAD4), and aquaporin 4 (AQP4) that could underlie these behavioral effects.

CONCLUSIONS

These studies provide an improved understanding of the effects of withdrawal from high doses of ovarian hormones on behavior and gene expression changes in the brain that could contribute to the pathophysiology of PPD.

Behavioral effects of dietary cholesterol in rats tested in experimental models of mild stress and cognition tasks

Abnormalities in serum cholesterol levels of patients with mood disorders have been identified in epidemiological studies. However, evidence for an influence of dietary cholesterol on behavioral models is poor. Here, we investigated the behavioral changes of Wistar male rats fed a 2% cholesterol-enriched diet for 2 months in experimental models of depression and anxiety, such as the forced swim test (FST) paradigm and the novelty-induced grooming sampling test (NGT). The correlation between behavioral depression and impaired cognitive capacity was also examined testing rats in the Morris water maze (MWM) task one day after the FST. Different groups of rats fed various dietary regimens, were subjected to acute or repeated treatment (14 days) with clomipramine hydrochloride (50 or 25 mg/kg), diazepam (1 mg/kg) or with the peripheral benzodiazepine receptors (PBRs) antagonist, isoquinoline PK11195 (1 mg/kg) injected intraperitoneally (i.p.). Rats fed the cholesterol-enriched diet showed a significant decrease of grooming score in the NGT and of immobility time in the FST in comparison to animals fed a standard diet. Furthermore, the anxiolytic and antidepressant effects of diazepam and clomipramine were not affected by the different diets. Only after repeated treatment, PK11195 impaired the performance of animals fed a standard diet in the FST, and exhibited an anxiolytic-like profile in animals fed either the cholesterol-enriched or the standard diet. The improved performance in the FST was followed by a better learning performance in the acquisition phase of the MWM. These results suggest that effects of cholesterol-enriched diet on the behavioral reaction of rats in experimental models of mild stress may involve PBRs. They deserve attention in order to clarify the clinical correlation between plasma cholesterol levels and mood disorders in humans.

Behavioral effects of saredutant, a tachykinin NK2 receptor antagonist, in experimental models of mood disorders under basal and stress-related conditions

The present study was made to investigate the role of tachykinin NK2 receptors in the expression of stress-related behaviors in animals. Under basal conditions, intraperitoneal (i.p.) administration of the selective tachykinin NK2 receptor antagonist, saredutant (1 and 3 mg/kg) or diazepam (1 mg/kg) exerted anxiolytic-like effects in rodents, as they reduced grooming score of Wistar male rats tested in the novelty-induced grooming sampling test (NGT) and increased percentage of time and entries in open arms of Swiss male mice tested in the elevated plus maze (EPM) test. After previous exposure to stress-related conditions, as induced by a 2-min forced swim made 5 min prior to the EPM test, saredutant but not diazepam, exhibited anxiolytic-like effects in mice. To study the antidepressant-like activity of tachykinin NK2 receptor antagonist under basal conditions, different groups of rats were injected i.p. with saredutant (2.5, 5 and 10 mg/kg) or the tricyclic antidepressant, clomipramine (50 mg/kg) and tested in the forced swim test (FST), a widely used antidepressant-responsive test. The influence of stress-related conditions was studied in rats subjected to electric foot-shocks (1 mA, 1 s) 24, 5 and 1 h prior to FST, after drugs injection. In the FST, clomipramine decreased the immobility time only under basal conditions, but not after application of acute foot-shocks. To the contrary, saredutant-treated rats also exhibited more active behavior in FST after previous exposure to stressors. These results give further support to the hypothesis that tachykinin NK2 receptors may be a therapeutic target for pharmacological treatment of stress-related diseases, such as anxiety and depression.

Intranasal immune challenge induces sex-dependent depressive-like behavior and cytokine expression in the brain

The association between activation of the immune system and mood disorders has been reported by several studies. However, the mechanisms by which the immune system affects mood are only partially understood. In the present study, we detected depressive-like behavior in a rat animal model which involves the induction of inflammation in the nasal cavities by intranasal (i.n.) instillation of bacterial lipopolysaccharides (LPS). Female rats showed depressive-like behavior as evidenced by the forced swim test after repeated i.n. administration of LPS. These responses were not paralleled by alterations in motor activity as measured by the open field test. In the same animals, corticosterone responses after the swimming sessions were the highest of all the groups evaluated. Real-time RT PCR was used to analyze the transcriptional regulation of the cytokines interleukin-1beta, tumor necrosis factor-alpha, and interleukin-6 in several brain regions. Increased tumor necrosis factor-alpha was detected in the hippocampus and brainstem of female rats challenged with i.n. LPS. These results suggest that peripheral inflammation in the upper respiratory tract is an immune challenge capable of inducing depressive-like behavior, promoting exaggerated glucocorticoid responses to stress, and increasing cytokine transcription in the brain. These results further our understanding of the role that the immune system may play in the pathophysiology of depression.

Behavioral effects of the β3 adrenoceptor agonist SR58611A: Is it the putative prototype of a new class of antidepressant/anxiolytic drugs?

A large body of evidence corroborates the notion that deficiencies of serotonergic system are likely involved in the pathogenesis of both depression and anxiety. Activation of beta(3) adrenoceptors has been shown to increase brain tryptophan content suggesting an elevation of brain serotonin (5HT) synthesis. SR58611A is a selective beta(3) adrenergic agent possessing a profile of antidepressant activity in routine rodents' experimental models of depression. The present study was undertaken to evaluate in rodents the antidepressant properties of SR58611A and to assess its putative anxiolytic value in experimental models of depression and anxiety. Compared to the control group, SR58611A (0.1, 1, 5 or 10 mg/kg) caused a dose-dependent reduction in immobility of Wistar male rats in the forced swim test. The maximum dose appeared to be equivalent to an effective dose of clomipramine (50 mg/kg). In addition, acute injection of SR58611A induced in rats a dose-dependent decrease in grooming response to a novel environment (novelty-induced grooming test). For any dose, the effect was lower than that of diazepam (1 mg/kg). Chronic treatment with SR58611A resulted also in an increased social interaction time in the social interaction test without affecting motor activity of rats. Furthermore, similarly to diazepam a chronic treatment with the highest doses of SR58611A was followed by increased exploratory behavior in Swiss male mice exposed to the elevated plus maze test. These effects are mediated by beta(3) adrenoceptors since i.p. pretreatment with the selective beta(3) adrenoceptor antagonist SR59230A (5 mg/kg) blocked the effects of SR58611A. Finally, also the 5HT antagonist methysergide (2 mg/kg) prevented the antidepressant and anxiolytic-like activity of SR58611A indicating that 5HT transmission is strictly involved in its action.

Gender differences of acute and chronic administration of dehydroepiandrosterone in rats submitted to the forced swimming test

Previous pre-clinical and clinical studies investigating the antidepressant potential of DHEA revealed conflicting results. In this study, the effects of exogenous DHEA on performance in the forced swimming test (FST) were examined in male and female Wistar rats in different phases of the estrous cycle. Furthermore, the effects of treatment and of the FST, on corticosterone and DHEA serum levels were investigated. Acute administration of DHEA (2 mg/kg) significantly increased freezing only in proestrus female rats. Similarly, the chronic administration of DHEA (2 mg/kg) increased freezing duration and decreased climbing behavior but only in females in diestrus II compared to those given vehicle. These results demonstrate that chronically administered DHEA induces a depressant-like effect, and this effect is sex dependent. There was no direct correlation between corticosterone levels or the corticosterone/DHEA ratio and the behaviors studied. After the FST, serum DHEA and corticosterone levels were increased, with females showing higher DHEA levels than males. Nevertheless, corticosterone levels were unaltered with chronic procedure; an effect that was independent of sex and treatment. These findings are relevant for research examining alternative treatment for depression and may elucidate the gender differences involved in stress-related diseases.

Effects of physiological covariables on pharmacokinetic parameters of clomipramine in a large population of cats after a single oral administration

This study was conducted to confirm an interindividual variability in pharmacokinetic parameters of clomipramine in a large population of cats and to identify potential covariables that would explain the presence of such pharmacokinetic variability after a single dose of Clomicalm. Clomipramine hydrochloride was administered orally according to a weight-dose chart from 0.32 to 0.61 mg/kg, to 76 cats and five blood samples were then taken by direct venipuncture at 1, 3, 6, 12, and 24 h. Plasma concentrations of clomipramine and desmethylclomipramine (DCMP) were measured by LC-MS/MS. The Standard Two-Stage technique was used to assess differences and detect correlations between pharmacokinetic parameter estimates and individual covariables. A large interindividual variability in all pharmacokinetic parameters (CV% 64-124) was detected. Statistically significant gender-related differences were detected in MR and Cl/F, where female cats had a higher mean MR (0.53) and faster Cl/F (0.36 L/h.kg) than males (0.36 and 0.21 L/h.kg, respectively). No correlation could be found between clomipramine AUC0-24 h or DCMP AUC0-24 h and sedation scores. Further feline studies are required to assess these findings after multiple dosing of clomipramine and DCMP to allow clinical extrapolation.

Differential progesterone effects on defensive burying and forced swimming tests depending upon a gradual decrease or an abrupt suppression schedules

A single dose of progesterone reduces the cumulative time in the defensive burying test and the immobility in the forced swim test, whereas the abrupt suppression of repeated doses increases the anxiety indicators. Whether anxiety and despair indicators reduce by a gradually decreased schedule of progesterone is unknown. Therefore, we subjected adult ovariectomized Wistar rats to open field, defensive burying and forced swim tests. One group received a constant schedule of progesterone (0.50 mg, daily), abruptly suppressed (AS) after five days. Another group received a gradual reduction schedule of progesterone (GR: 0.84, 0.67, 0.50, 0.33, 0.17 mg, each day). Control group received vehicle (VEH). The GR group displayed similar crossing in the open field test as the VEH group (F(2,19) = 8.78, p < 0.002), but also the shortest cumulative time in defensive burying (F(2,28) = 13.3, p < 0.0001) and the shortest time in freezing (F(2,24) = 6.39, p < 0.006). In the forced swim test, the GR group displayed the shortest immobility time (F(2,19) = 12.1, p < 0.0005), the lowest number of immobility periods (F(2,19) = 4.26, p < 0.03) and the longest latency to the first period of immobility (F(2,1) = 4.06, p < 0.03). It is concluded that a gradually reduced schedule of progesterone reduces anxiety and despair in the Wistar rat.