Early maternal separation promotes alterations in the thermoregulatory profile of adult Wistar rats

"The wrong tools for the right job": a critical meta-analysis of traditional tests to assess behavioural impacts of maternal separation

RATIONALE

Unconditioned tasks in rodents have been the mainstay of behavioural assessment for decades, but their validity and sensitivity to detect the behavioural consequences of early life stress (ELS) remains contentious and highly variable.

OBJECTIVES

In the present study, we carried out a meta-analysis to investigate whether persistent behavioural effects, as assessed using unconditioned procedures in rats, are a reliable consequence of early repeated maternal separation, a commonly used procedure in rodents to study ELS.

METHODS

A literature search identified 100 studies involving maternally separated rats and the following unconditioned procedures: the elevated plus maze (EPM); open field test (OFT); sucrose preference test (SPT) and forced swim task (FST). Studies were included for analysis if the separation of offspring from the dam was at least 60 min every day during the pre-weaning period prior to the start of adolescence.

RESULTS

Our findings show that unconditioned tasks are generally poor at consistently demonstrating differences between control and separated groups with pooled effect sizes that were either small or non-existent (EPM: Hedge's g =  - 0.35, p = 0.01, OFT: Hedge's g =  - 0.32, p = 0.05, SPT: Hedge's g =  - 0.33, p = 0.21, FST: Hedge's g = 0.99, p = 0.0001). Despite considerable procedural variability between studies, heterogeneity statistics were low; indicating the lack of standardization in the maternal separation protocol was the not the cause of these inconsistent effects.

CONCLUSIONS

Our findings indicate that in general, unconditioned tests of depression and anxiety are not sufficient to reveal the full behavioural repertoire of maternal separation stress should not be relied upon in isolation. We argue that more objective tasks that sensitively detect specific cognitive processes are better suited for translational research on stress-related disorders such as depression.

The effect of maternal separation stress-induced depression on ovarian reserve in Sprague Dawley Rats: The possible role of imipramine and agmatine through a mTOR signal pathway

PURPOSE

To examine the possible role of impramine and agmatine through a mTOR signal pathway on rat ovary after maternal separation stress-induced depression.

METHODS

Sprague Dawley neonatal female rats were divided into control, maternal separation (MS), MS+imipramine, and MS+agmatine groups. Rats were subjected to MS for 4 hours daily from postnatal day (PND) 2 to PND 21 and pups were exposed to social isolation (SI) on PND23 for 37 days for model establishment treated with imipramine (30 mg/kg; ip) or agmatine (40 mg/kg; ip) for 15 days. In order to examine behavioral changes rats were all subjected to locomotor activity and forced swimming tests (FST). Ovaries were isolated for morphological evaluation, follicle counting and mTOR signal pathway protein expression levels were detected.

RESULTS

Increased number of primordial follicles and diminished ovarian reserve in the MS groups were detected. Imipramine treatment caused diminished ovarian reserve and atretic follicle; however, agmatine treatment provided the maintenance of ovarian follicular reserve after MS. mTOR signal pathway may have an important role during rat ovarian follicular development in model of MS.

CONCLUSIONS

Our findings suggest that agmatine may help to protect ovarian reserve during follicular development by controlling cell growth.

Maternal separation affects Anxiety like behavior begin in adolescence continue through adulthood and related to Dnmt3a expression

Early life stress, including maternal separation, is among one of the main causes of anxiety in adolescents. DNA methyltransferase 3A (Dnmt3a) is a key molecule that regulates DNA methylation and is found to be associated with anxiety-like behavior. It is not clear whether maternal separation affects anxiety levels in mice at different developmental stages, or whether Dnmt3a plays a role in this process. Here, by using open field test to exploring the effect of maternal separation on anxiety-like behavior in mice of different age, it was found that maternal separation could successfully induce anxiety-like behavior in adolescent mice, and which continued through adulthood. By using western blot, we found the levels of Dnmt3a in the hippocampus and cortex have shown different trends in maternal separation mice on P17. Further, by using immunostaining, we have found that the expression levels of Dnmt3a in the cortex and hippocampus were significantly different, and decreased to varying degrees with the age of mice, which being the reason for different trends. Our results provide an experimental basis for further development of anxiety/depression treatment programs more suitable for adolescence.

Long-term activation of hippocampal glial cells and altered emotional behavior in male and female adult rats after different neonatal stressors

Early life stress increases the risk of developing psychiatric diseases in adulthood. Severe neonatal infections can also contribute to the development of affective illnesses. Stress and infections both trigger the immediate activation of the neuroimmune system. We compared the long-term effects of neonatal single or combined stress-immune challenges on emotional behavior and glial cell responses in the hippocampus. Male and female Sprague Dawley rats were randomly allocated across four conditions: (1) control + vehicle; (2) maternal separation (MS, 3 h/day on postnatal days [PN] 1-14) + vehicle; (3) control + lipopolysaccharide (LPS, 0.5. mg/kg, PN14); (4) MS + LPS. The rats' behaviors were analyzed from PN120 in males and from PN150 in diestrous females. LPS, but not MS, increased anxiety-like behavior in male rats; however, in females, it increased with both challenges. Depressive-like behavior increased after MS-but not LPS-in males and females. Combined stressors increased depressive-like behavior in both sexes. All stressors promoted microglial activation in CA3 and hilus in males and females. MS and LPS increased the astrocytic density within the male hilus, but LPS only increased it in CA3. MS prevented the rise in astrocytic density with LPS. In females, MS reduced the astrocytic population of the hilus and CA3 areas. Taken together, the behavioral and glial cell responses to early life challenges are sex-dependent and cell-type specific. This suggests a sexual dimorphism in the nature of the adverse event faced. These results have implications for understanding the emergence of psychiatric illnesses.

Early-life stress exacerbates the effects of WIN55,212-2 and modulates the cannabinoid receptor type 1 expression

Early-life stress induces an abnormal brain development and increases the risk of psychiatric diseases, including depression, anxiety and substance use disorders. We have developed a reliable model for maternal neglect, named maternal separation with early weaning (MSEW) in CD1 mice. In the present study, we evaluated the long-term effects on anxiety-like behaviours, nociception as well as the Iba1-positive microglial cells in this model in comparison to standard nest (SN) mice. Moreover, we investigated whether MSEW alters the cannabinoid agonist WIN55,212-2 effects regarding reward, spatial and emotional memories, tolerance to different cannabinoid responses, and physical dependence. Adult male offspring of MSEW group showed impaired responses on spatial and emotional memories after a repeated WIN55,212-2 treatment. These behavioural impairments were associated with an increase in basolateral amygdala and hippocampal CB1-expressing fibres and higher number of CB1-containing cells in cerebellum. Additionally, MSEW promotes a higher number of Iba1-positive microglial cells in basolateral amygdala and cerebellum. As for the cannabinoid-induced effects, rearing conditions did not influence the rewarding effects of WIN55,212-2 in the conditioned place preference paradigm. However, MSEW mice showed a delay in the development of tolerance to the cannabinoid effects. Moreover, CB1-positive fibres were reduced in limbic areas in MSEW mice after cannabinoid withdrawal precipitated with the CB1 antagonist SR141617A. These findings support that early-life stress promotes behavioural and molecular changes in the sensitivity to cannabinoids, which are mediated by alterations in CB1 signalling in limbic areas and it induces an increased Iba1-microglial marker which could interfere in emotional memories formation.

Altered Experienced Thermoregulation in Depression-No Evidence for an Effect of Early Life Stress

Objectives: Accumulating evidence suggests that individuals with depression are characterised by difficulties in thermoregulatory cooling. The aim of this study was to investigate, for the first time, whether depressed individuals are aware of these alterations, what their physical consequences are and whether they may be rooted in early life stress. Methods: A total of N = 672 medically healthy individuals from the general population were recruited to participate in an online survey. Participants were divided into depressed vs. non-depressed using the Patient Health Questionnaire. Experienced autonomic and behavioural thermoregulation as well as vigilance problems in response to temperature increases were assessed by the Experienced Temperature Sensitivity and Regulation Survey. The Childhood Trauma Questionnaire was administered to assess early life stress. Results: Controlling for age, sex, body mass index, and physical activity, depressed vs. non-depressed individuals did not differ in their experienced autonomic and behavioural responses to temperature increases. However, the depressed individuals reported comparably greater difficulties in concentrating and drowsiness/fatigue in warm environments (p = 0.029), during physical exertion (p = 0.029), and during stress (p < 0.001). There were no differences in the experienced thermoregulation between depressed individuals with vs. without early life stress. Conclusions: Depressed individuals experienced more severe physical impairments (i.e., greater vigilance problems) in response to intense warmth when compared to non-depressed individuals. These differences were not attributable to comorbid illnesses, the intake of medication, or physical deconditioning. Further enquiries in clinical populations are warranted to investigate to what extent the observed alterations map onto specific symptoms of depression (e.g., sleep disturbances).

Comparison of neurotransmitter levels, physiological conditions, and emotional behavior between isolation-housed rats with group-housed rats

Brain monoaminergic neurotransmitters, such as dopamine (DA), serotonin (5-HT), and noradrenaline (NA), play crucial roles in neuronal and physiological functions, including social behaviors. Isolation housing may induce behavioral and neurochemical abnormalities in rats, although its influence on neurotransmitter levels remains obscure. This study investigated the influence of isolation- or group-housing on core body temperature (T_core ), locomotor activity (ACT), emotional behavior, and neurotransmitter levels in male Wistar rats. Behavioral changes were monitored using the open field test (OFT) and social interaction test (SIT). After 4 weeks, brain tissues were collected to quantify 5-HT, DA, and NA concentrations. Body weight and basal T_core during both the light and dark phase were higher in isolation-housed than in group-housed rats, although no significant difference was seen in ACT. No significant differences were observed during the OFT. Isolation-housed rats showed increased line crossing and decreased social behavior during the SIT. Isolation-housed rats exhibited decreased levels of 5-HT in the caudate putamen and amygdala, and elevated and decreased NA levels in the paraventricular hypothalamic nucleus and hippocampus, respectively. However, DA levels were unaffected. Thus, housing environments may affect brain areas that regulate various neuronal and physiological functions, such as memory, stress responses, and emotional behavior.

Early maternal separation accelerates the progression of endometriosis in adult mice

BACKGROUND

A large body of research highlights the importance of early-life environmental impact on the health outcome in adulthood. However, whether early-life adversity (ELA) has any impact on the development of endometriosis is completely unclear. In this study, we tested the hypothesis that ELA, as manifested by neonatal separation, can accelerate the progression of endometriosis in mouse through activation of the adrenergic receptor β2 (ADRB2) signaling pathway, leading to increased angiogenesis and progression of endometriotic lesions.

METHODS

Eight female Balb/C mice, in late pregnancy, were used used for this study, which later gave birth to 22 female newborn pubs. Eleven additional female Balb/C mice were also used as donors of uterine tissues. The 22 newborn pubs were randomly divided into 2 equal-sized groups, maternal separation (MS) and no separation (NS). Pubs in the MS group were separated from their dams for 3 h/day from postnatal day (PND) 1 to 21, while those in the NS control remained in the home cage with their dams. In adulthood (8-week old), 3 mice in each group were randomly selected to undergo a battery of behavior tests. The remaining 8 mice in each group were induced with endometriosis by intraperitoneal injection of uterine fragments from donor mice. Four weeks after the induction, all mice were sacrificed and their endometriotic lesions were excised for quantification and then prepared for immunohistochemistry analysis.

RESULTS

We confirmed that MS during infancy resulted in anxiety and depression-like behaviors as previously reported. We also found that in MS mice the lesion weight was increased by over 2 folds and generalized hyperalgesia was also significantly increased as compared with NS mice. Immunostaining analysis demonstrated that MS accelerated the development of endometriosis likely through decreased dopamine receptor D2 (DRD2) expression and activation of the ADRB2/cAMP-response element binding protein (CREB) signaling pathway, leading to increased angiogenesis and progression of endometriotic lesions.

CONCLUSIONS

Exposure of female mouse pups to ELA such as MS during their infancy period accelerates the progression of endometriosis, possibly through altered neuronal wiring and hyperactivity of the hypothalamic-pituitary-adrenal axis.

Systematic review and meta-analysis: effects of maternal separation on anxiety-like behavior in rodents

The mechanisms by which childhood maltreatment increases anxiety is unclear, but a propensity for increased defensive behavior in rodent models of early life stress (ELS) suggests that work in rodents may clarify important mechanistic details about this association. A key challenge in studying the effects of ELS on defensive behavior in rodents is the plethora of inconsistent results. This is particularly prominent with the maternal separation (MS) literature, one of the most commonly used ELS models in rodents. To address this issue we conducted a systematic review and meta-analysis, examining the effects of MS on exploratory-defensive behavior in mice and rats using the open field test (OFT) and the elevated plus maze (EPM). This search yielded a total of 49 studies, 24 assessing the effect of MS on behavior in the EPM, 11 tested behavior in the OFT, and 14 studies provided data on both tasks. MS was associated with increased defensive behavior in rats (EPM: Hedge's g = -0.48, p = 0.02; OFT: Hedge's g = -0.33, p = 0.05), effect sizes that are consistent with the anxiogenic effect of early adversity reported in humans. In contrast, MS did not alter exploratory behavior in mice (EPM: Hedge's g = -0.04, p = 0.75; OFT: Hedge's g = -0.03, p = 0.8). There was a considerable amount of heterogeneity between studies likely related to the lack of standardization of the MS protocol. Together, these findings suggest important differences in the ability of MS to alter circuits that regulate defensive behaviors in mice and rats.

Effect of environmental exposure to a maternally-learned odorant on anxiety-like behaviors at weaning in mice

Early sensory experience, such as exposure to maternal or other environmental factors, is considered to influence neurocognitive development and behaviors. In many species, exposure to odorants during pregnancy or lactation impacts the morpho-functional development of the olfactory circuitry with changes in olfactory sensitivity, feeding behavior and food preferences at birth or later. However, few studies have investigated the impact of a perinatal exposure to odorants on the anxiety-like behavior of animals to stressfull stimuli. Here, we exposed mice to heptaldehyde (HEP) during pregnancy and lactation and measured the anxiety-like behavior of their offspring to stress-inducing novel stimuli at weaning in presence or absence of odorants. We applied a combined social and maternal separation as a stressor and measured the anxiety-like behavior in an open field (OF) in presence of two odorants, HEP or α-pinene (AP) as a control odorant. Although the presence of the odorant during the social separation did not influence anxiety-like behavior, we found that, if mice born to non-odorized mothers exhibited a decreased exploratory behavior in the presence of both odorants, the effect was restricted to AP for the mice perinatally exposed to HEP. These results show that anxiety-like behaviors during a stress-inducing event could be reduced by the presence of a familiar odorant. We propose that the recall of an early olfactory experience could contribute to the improvement of animal welfare in various situations associated with husbandry practices.