Prenatal Stress Rats Research Articles

Anxiety induced by prenatal stress is associated with suppression of hippocampal genes involved in synaptic function

Exposure of pregnant women or animals to stress during a critical period of foetal brain development increases the likelihood of anxiety, depression and learning deficits that are associated with structural alterations in the offspring hippocampus. In this study, we report the effect of gestational stress in rats on anxiogenic behaviour and hippocampal gene expression of their 23-day-old female offspring. As the rat brain continues to develop after birth, we also used the procedure of handling (H) during the first 10 days of life to reverse the anxiogenic behaviour of prenatally stressed (PS) rats. By means of micro-array analysis on hippocampal extracts, we found that the expression of about 6.1% of 9505 valid genes was significantly altered by prenatal stress (p<0.05). Of these, 48% were over-expressed and 52% under-expressed. The latter included approximately 300 genes that participate in axonal growth, regulation of ion channels and transporters, trafficking of synaptic vesicles and neurotransmitter release. About 30% of the genes that were down-regulated in PS rats were restored to control levels by H. These include genes that play a role in pre-synaptic organization and function. Our results provide a possible relationship between hippocampal gene expression and changes in behaviour resulting from prenatal stress.

Maternal adrenal hormone secretion mediates behavioural alterations induced by prenatal stress in male and female rats

Prenatal stress in rats has been shown to impair the regulation of the hypothalamic pituitary adrenal (HPA) axis and predispose to anxiogenic and depressive-like behaviour. In a previous study, abolition of excess corticosterone (COR) release during stress by maternal adrenalectomy prevented the dysregulation of the HPA axis. In the present study, we determined whether excess maternal COR is also responsible for the alterations in offspring behaviour. Pregnant Wistar rats were adrenalectomized or sham-operated on day 11 of gestation and subjected once daily to mild restraint for 30 min on days 14–21 of gestation. An undisturbed group of pregnant females served as controls. All experiments were performed in male and female offspring. Pup weight and anogenital distance of males were measured after birth; anxiogenic behaviour was assessed in the elevated plus maze (EPM) at the age of 5 weeks and spatial memory in the Morris water maze in littermates at 3–4 months. Prenatally stressed (PS) males did not show a reduction in anogenital distance, and their increase in anxiogenic behaviour in the EPM was less than that in PS females. On the other hand, impairment of spatial learning was only seen in PS males. Both the anxiogenic behaviour of PS males and females and the learning deficit in males were completely abolished by adrenalectomy. These data show that excess stress-induced COR can alter the programming of the foetal brain and predispose it to alterations in behaviour that are gender specific.

Prenatal stress alters Fos protein expression in hippocampus and locus coeruleus stress-related brain structures

Prenatal stress (PS) durably influences responses of rats from birth throughout life by inducing deficits of the hypothalamo-pituitary-adrenal (HPA) axis feedback. The neuronal mechanisms sustaining such alterations are still unknown. The purpose of the present study was to determine whether in PS and control rats, the exposure to a mild stressor differentially induces Fos protein in hippocampus and locus coeruleus, brain areas involved in the feedback control of the HPA axis. Moreover, Fos protein expression was also evaluated in the hypothalamic paraventricular nucleus (PVN) that reflect the magnitude of the hormonal response to stress. Basal plasma corticosterone levels were not different between the groups, while, PS rats exhibited higher number of Fos-immunoreactive neurons than controls, in the hippocampus and locus coeruleus in basal condition. A higher basal expression of a marker of GABAergic synapses, the vGAT, was also observed in the hypothalamus of PS rats. Fifteen minutes after the end of the exposure to the open arm of the elevated plus-maze (mild stress) a similar increased plasma corticosterone levels was observed in both groups in parallel with an increased number of Fos-immunoreactive neurons in the PVN. Return to basal plasma corticosterone values was delayed only in the PS rats. On the contrary, after stress, no changes in Fos-immunoreactivity were observed in the hippocampus and locus coeruleus of PS rats compared to basal condition. After stress, only PS rats presented an elevation of the number of activated catecholaminergic neurons in the locus coeruleus. In conclusion, these results suggest for the first time that PS alters the neuronal activation of hippocampus and locus coeruleus implicated in the feedback mechanism of the HPA axis. These data give anatomical substrates to sustain the HPA axis hyperactivity classically described in PS rats after stress exposure.

Postnatal Stimulation of the Pups Counteracts Prenatal Stress-Induced Deficits in Hippocampal Neurogenesis

Prenatal stress constitutes a developmental risk factor for later psychopathology. The behavioral disorders are sustained by neurobiological alterations including long-term reduction of hippocampal neurogenesis; its deregulation has been involved in cognitive impairments, mood disorders and addiction. A major goal is to define periods in development and strategies for intervening to prevent the effects of early stressful events. We investigated the ability of a postnatal infantile stimulation to prevent prenatal stress-induced alteration in hippocampal neurogenesis. The influence of postnatal handling on prenatal stress-induced changes in hippocampal neurogenesis was examined in 4 and 26 month-old male rats. Three distinct phases of the neurogenesis were studied: proliferation, survival and neuronal differentiation. Prenatal stress reduced hippocampal cell proliferation all throughout life. Furthermore, the survival rate of newborn cells, the number of immature neurons and the number of differentiated new neurons were reduced in young and old prenatally-stressed rats. All those deleterious effects were counteracted by neonatal handling. These data show that finer aspects of brain shaping can be rewired by environmental influences occurring at sensitive phase of development. They also suggest that infantile stimulation may reverse the appearance of behavioral disorders induced by early life stress.

Prenatal stress in rats attenuates hippocampal long-term potentiation and induces deficits in synaptic plasticity

Prenatal stress in rats attenuates hippocampal long-term potentiation and induces deficits in synaptic plasticity

S.07.02 Prenatal stress in rats attenuates hippocampal long-term potentiation and induces deficits in synaptic plasticity

S.07.02 Prenatal stress in rats attenuates hippocampal long-term potentiation and induces deficits in synaptic plasticity

Prenatal stress affects the developmental trajectory of the rat amygdala

The amygdala plays a critical role in generating the emotion of fear, and alterations in amygdala fear processing are thought to underlie the acquisition and maintenance of anxiety disorders. The prenatally stressed (PS) rat displays hormonal, behavioral and brain anatomical similarities to anxious humans and is useful to study the neurobiological underpinnings of pathological anxiety. We studied PS and control male rats at postnatal days 7 (P7), P25, P45 and P60. Using unbiased stereological analyses we examined the volumes, anterior–posterior lengths and total numbers of neurons and glia of the basolateral (BL), central (Ce) and lateral (La) amygdalar nuclei. We found prenatal stress-associated differences in the developmental trajectories of each nucleus. These were apparent in some measures as early as P7, most extensive at P25 and resolved by P45, at least as seen by Nissl staining. These changes were not a result of differential brain growth. This early divergence in developmental trajectories seen here may be the harbinger of PS rat amygdalas that ultimately function very differently in adulthood.

Prenatal stress and neonatal rat brain development

Chronic or repeated stress during human fetal brain development has been associated with various learning, behavioral, and/or mood disorders, including depression in later life. The mechanisms accounting for these effects of prenatal stress are not fully understood. The aim of this study was to investigate the effects of prenatal stress on early postnatal brain development, a disturbance of which may contribute to this increased vulnerability to psychopathology. We studied the effects of prenatal stress on fetal growth, stress-induced corticosterone secretion, brain cell proliferation, caspase-3-like activity and brain-derived neurotrophic factor protein content in newborn Fischer 344 rats. In addition to a slight reduction in birth weight, prenatal stress was associated with elevated corticosterone levels (33.8%) after 1 h of maternal deprivation on postnatal day 1, whereas by postnatal day 8 this pattern was reversed (−46.5%). Further, prenatal stress resulted in an approximately 50% decrease in brain cell proliferation just after birth in both genders with a concomitant increase in caspase-3-like activity within the hippocampus at postnatal day 1 (36.1%) and at postnatal day 5 (females only; 20.1%). Finally, brain-derived neurotrophic factor protein content was reduced in both the olfactory bulbs (−24.6%) and hippocampus (−28.2%) of prenatally stressed male offspring at postnatal days 1 and 5, respectively. These detrimental central changes observed may partly explain the increased susceptibility of prenatally stressed subjects to mood disorders including depression in later life.

Early emergence of increased fearful behavior in prenatally stressed rats

We have been studying the mildly prenatally stressed (PS) rat as a potentially useful animal model of anxiety disorders. Previously we have demonstrated that there are anatomical and biochemical alterations in the amygdalas of adult PS offspring and that these offspring show increased fearful behaviors. However, human data indicate that anxiety disorders often present first in early childhood and then persist throughout adolescence and adulthood. To determine if PS rats also model this characteristic of human anxiety disorders, here we asked whether behavioral indices of increased fear would be detectable at an early age. We tested the hypotheses that young PS rats would show increased behavioral fearfulness in response to an acute stressor and that this would increase with age. A mild prenatal stressor, consisting of removal of the dam from the home cage and administration of a subcutaneous injection of 0.1 ml of 0.9% saline daily, was administered during the last week of pregnancy. Offspring were tested in the defensive–withdrawal apparatus before and after exposure to restraint stress at 25, 45 and 60 days of age. PS animals showed increased defensive–withdrawal behavior following the stressor and were more fearful following restraint when compared to controls (CON). This was significant at P45 and increased to P60. Hence, fearful behaviors in PS rats emerge prior to sexual maturation and increase in magnitude thereafter, further validating our model as a means to investigate the underpinnings of anxiety disorders.

Prenatal stress influences 8-OH-DPAT modulated startle responding and [ 3H]-8-OH-DPAT binding in rats

The present study was to investigate some aspects of the 5-HT1A receptor system in adult-aged rats (50–60 days) that were either exposed to prenatal stress (PS) or not exposed to prenatal stress (CON). In the first series of experiments, rats were pretreated with vehicle, the 5-HT1A agonist 8-OH-DPAT or the 5-HT1A antagonist, WAY-100635 and exposed to 120 acoustic startle stimuli (95 dB) using a 30 s inter-trial interval. 8-OH-DPAT produced a dose-dependent increase in acoustic startle responding in CON and PS rats, with the PS rats exhibiting greater responding than CON rats. WAY-100635 depressed startle amplitudes only in the CON group. Finally, radioligand binding studies using [ 3H]-8-OH-DPAT indicated a significant decrease in receptor density in hippocampal homogenates from PS rats but no difference in [ 3H]-8-OH-DPAT binding from homogenates of the amygdala. Our results are consistent with earlier reports indicating that prenatal stress alters the serotonergic system. Specifically, our results indicate that gestational exposure to chronic mild stress enhances startle amplitudes following 8-OH-DPAT administration, prevents the depression in startle amplitudes following WAY-100635 administration and reduces [ 3H]-8-OH-DPAT binding in hippocampal preparations.

Effect of chronic treatment with ladostigil (TV-3326) on anxiogenic and depressive-like behaviour and on activity of the hypothalamic–pituitary–adrenal axis in male and female prenatally stressed rats

The aim of the study is to investigate the effect of ladostigil, a cholinesterase and brain-selective monoamine oxidase (MAO) inhibitor, on anxiogenic and depressive-like behaviour and the response of the hypothalamic-pituitary-adrenal axis to stress in prenatally stressed (PS) male and female rats. Ladostigil (17 mg/kg/day) was administered daily for 6 weeks to control and PS rats aged 6 weeks. Behaviour was assessed in the elevated plus maze (EPM) and forced swim tests (FST). Plasma corticosterone (COR) was measured before, 30 and 90 min after exposure to stress. Ladostigil inhibited brain MAO-A and B by more than 60%, significantly reduced hyperanxiety of male and female PS rats in the EPM and depressive-like behaviour in the FST without affecting that of controls and restored the delayed return to baseline of plasma COR in PS rats after exposure to stress to that of control rats. A novel brain-selective MAO inhibitor, ladostigil can selectively reverse the behavioural and neurochemical effects induced by prenatal stress without affecting the behaviour of controls.

Chronic treatment with imipramine reverses immobility behaviour, hippocampal corticosteroid receptors and cortical 5-HT 1A receptor mRNA in prenatally stressed rats

Prenatal stress in the rat induces enhanced reactivity of the hypothalamus–pituitary–adrenal (HPA) axis, disturbances in a variety of circadian rhythms and increased anxiety-like behaviour. Such abnormalities parallel those found in human depressed patients. Prenatally stressed (PS) rats could represent, therefore, an interesting animal model for the evaluation of the efficacy of pharmacotherapeutic intervention in psychiatric disorders that has often been addressed using control animals. In the present study, PS and non-stressed rats were chronically treated with the tricyclic antidepressant imipramine (10 mg/kg i.p. for 21 days) and assessed in the forced swim test. Glucocorticoid receptor binding sites in the hippocampus were measured and 5-HT 1A receptor mRNA levels in the frontal cortex were also assessed. PS rats were characterised by increased immobility in the forced swim test, reduced hippocampal corticosteroid receptor binding and increased levels of cortical 5-HT 1A mRNA. All these parameters were significantly reversed by chronic imipramine treatment. Conversely, no significant effects were observed for non-stressed rats. All these effects are consistent with the expected pharmacotherapy of depression-like abnormalities in PS rats. These results further indicate that PS rats are a relevant animal model of depression.

Attenuation by a sigma1 (σ1) receptor agonist of the learning and memory deficits induced by a prenatal restraint stress in juvenile rats

1. Stress during pregnancy results in complex neurochemical and behavioral alterations throughout the offspring lifetime. We here examined the impact of prenatal stress (PS) on memory functions in male and female offspring and report the efficacy of a selective sigma(1) (sigma(1)) receptor agonist, igmesine, in alleviating the observed deficits. 2. Dams received an unpredictable 90-min duration restraint stress from gestational day E17 to E20. Learning was examined in offspring between day P24 and P36 using spontaneous alternation in the Y-maze, delayed alternation in the T-maze, water-maze learning and passive avoidance. 3. Both male and female PS rats showed impairments of spontaneous and delayed alternation performances. Acquisition of a fixed platform position in the water-maze was unchanged in PS rats, but the probe test revealed a diminution of time spent in the training quadrant. Acquisition of a daily changing platform position demonstrated impaired working memory for male and female PS rats. Finally, passive avoidance deficits were observed. 4. Pretreatment with the selective sigma(1) agonist igmesine (1-10 mg x kg(-1) i.p.) reversed the PS-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 failed to affect performances alone but blocked the igmesine effect, confirming the involvement of the sigma(1) receptor. 5. PS thus induces delayed memory deficits, affecting spatial and nonspatial, short- and long-term memories in juvenile male and female offspring rats. Activation of the sigma(1) neuromodulatory receptor allows a significant recovery of the memory functions in PS rats.

Prenatal stress alters cardiovascular responses in adult rats.

Environmental factors in early life are clearly established risk factors for cardiovascular disease in later life. Most studies have focused on nutritional programming and analysed basal cardiovascular parameters rather than responses. In the present study we have investigated whether prenatal stress has long-term effects on cardiovascular responses in adult offspring. Female pregnant Sprague-Dawley rats were subjected to stress three times daily from day 15 to day 21 of gestation. Litters from stressed and control females were cross-fostered at birth to control for mothering effects. When the offspring were 6 months old, blood pressure was measured in the conscious rats through implanted catheters at rest, during restraint stress and during recovery. Basal haemodynamic parameters were similar in the different groups but the pattern of cardiovascular responses during stress and recovery differed markedly between prenatally stressed (PS) and control animals. PS rats had higher and longer-lasting systolic arterial pressure elevations to restraint stress than control animals. They also showed elevated systolic and diastolic blood pressure values during the recovery phase. PS rats demonstrated a greater increase in blood pressure variability compared with control animals during exposure to restraint stress, and showed more prolonged heart rate responses to acute stress and delayed recovery than controls. There was no effect of prenatal stress on baroreflex regulation of heart rate. PS females showed a greater increase in systolic arterial pressure and blood pressure variability and delayed heart rate recovery following return to the home cage then did PS males. These findings demonstrate for the first time that prenatal stress can induce long-term, sex-related changes in the sensitivity of the cardiovascular system to subsequent stress.

Environmental enrichment during adolescence reverses the effects of prenatal stress on play behaviour and HPA axis reactivity in rats.

Prenatal stress (PS) can produce profound and long-lasting perturbations of individual adaptive capacities, which in turn can result in an increased proneness to behavioural disorders. Indeed, in PS rats there is evidence of impaired social play behaviour, disturbances in a variety of circadian rhythms, enhanced anxiety and increased hypothalamic-pituitary-adrenal (HPA) axis reactivity. This study was designed to experimentally investigate the degree of reversibility of PS-induced disturbances of social play and HPA reactivity by assessing the effect of the enrichment of the physical environment on PS rats during periadolescence. PS subjects showed a reduced expression of social play behaviour and a prolonged corticosterone secretion in response to restraint stress, but both these effects were markedly reversed following environmental enrichment. Interestingly, the enrichment procedure increased social behaviour but had no effect on corticosterone secretion in nonstressed animals, indicating a differential impact of the postnatal environment as a function of prenatal background. As a whole, results clearly indicate that rats prenatally exposed to stress can benefit during periadolescence from the modulatory effects of an enriched environment. Moreover, they confirm that PS may well represent a suitable animal model for the design and testing of new therapeutic strategies for behavioural disorders produced by early insults.

Effect of prenatal stress and gonadal hormone condition on depressive behaviors of female and male rats

Whether prenatal stress (PNS) and gonadal hormones may influence depressive behavior of rats in the forced swim test was investigated. In Experiment I, adult diestrous female rats had increased immobility, which is indicative of depression, but did not show any significant difference in the duration of struggling compared to intact adult males. In Experiment 2, the behavior of adult intact, castrated, or castrated dihydrotestosterone (DHT)- or estrogen (E 2)-replaced offspring of dams that were restrained under lights for 45 min on gestational day 18 (PNS) or were not subjected to gestational stress (non-PNS, control condition) were compared. There were no effects of PNS, but DHT and E 2 produced anti-depressant effects on behavior of male rats. Castration decreased struggling and increased immobility compared to intact rats. DHT or E 2 replacement was able to partially reinstate struggling and immobility behavior but not to levels of intact males. In Experiment 3, behavior of PNS or control rats that were in proestrus or were ovariectomized and DHT, E 2, or vehicle-replaced were compared. Ovariectomy decreased struggling and increased immobility compared to that of proestrous rats. E 2 or DHT to control females increased anti-depressant struggling behavior compared to ovariectomized control or PNS rats administered vehicle, which demonstrated greater duration of struggling than did E 2-primed, PNS rats. E 2 or DHT administration decreased immobility of PNS and control females. These findings suggest that E 2 and DHT have some anti-depressant effects but that modest PNS may alter E 2's ability to alleviate some depressive behavior in female, but not male rats.

Sex differences in learning deficits induced by prenatal stress in juvenile rats

Stress during pregnancy results in neurochemical and behavioral alterations observed throughout adulthood and aging. We here examined the impact of prenatal stress (PS) on cognitive functions in juvenile—4-week-old—rats, focusing on putative sex differences. Dams received an unpredictable 90-min duration contention stress between gestational day E17 and E20. Locomotion and learning ability were examined in offsprings between day P24 and P29 using actimetry, spontaneous alternation in the Y-maze, delayed alternation in the T-maze, and passive avoidance. Both male and female PS rats showed increased activity. In the Y-maze, diminished spontaneous alternation (males: −20%; females: −29%) were seen for PS rats compared to non-PS rats. The number of arm entries was unchanged among groups. In the T-maze, PS rats failed to perform delayed alternation, as shown by equal time spent and number of entries in both the novel and previously explored arms. In the passive avoidance test, PS resulted in significant impairments for female offspring only of both step-through latency and percentage of animals to criterion. PS thus induced severe learning impairments affecting both short-term and long-term memories that could be observed early in lifetime, in 4-week-old, juvenile rats. In addition, marked sex differences were evidenced, particularly in the passive avoidance response that may reflect differential developmental neuroadaptations in precise brain structures.

Prenatal stress in rats predicts immobility behavior in the forced swim test: Effects of a chronic treatment with tianeptine

Prenatally-stressed (PS) rats are characterized by a general impairment of the hypothalamo-pituitary-adrenal (HPA) axis and sleep disturbances indicating that this model has face validity with some clinical features observed in a subpopulation of depressed patients. The prolonged corticosterone secretion shown by PS rats in response to stress was positively correlated with an increased immobility behavior in the forced swim test. To investigate the predictive validity of this model, a separate group of animals was chronically treated with the antidepressant tianeptine (10 mg/kg i.p. for 21 days). Such chronic treatment reduced in PS rats immobility time in the forced swim test. These findings suggest that the PS rat is an interesting animal model for the evaluation of antidepressant treatment.

Mild prenatal stress in rats is associated with enhanced conditioned fear

We tested the hypothesis that prenatal stress would enhance conditioned fear in adult rats. Pregnant Sprague–Dawley rats were stressed by exposure to a novel environment and subcutaneous injection of saline (0.1 ml 0.9% NaCl) at random times daily from Days 14 to 21 of pregnancy. When compared to adult control (CON) male rats from unmanipulated pregnancies, adult prenatally stressed (PS) male rats showed increased freezing behavior in response to acute footshock as well as increased freezing behavior the next day in the same context, without shock delivery. In another experiment, the gestational stressor was examined for elevations in corticosterone and ACTH. At gestational days (G)15, G17, G19 and G21, maternal and fetal plasma was collected. Analysis showed elevations in corticosterone and ACTH in the PS dams when compared to the CON dams. Additionally, increased corticosterone was found in the PS fetuses when compared to the CON fetuses. Finally, some CON and PS litters were examined for alterations in length of gestation, number of pups born, bodyweight on postnatal day (P)1 and anogenital distance on P1 and differences were not found. In conclusion, our data demonstrate that a mild stressor during gestation, sufficient to raise plasma corticosterone and ACTH, is associated with enhanced conditioned fear during adulthood.

Prenatal stress produces deficits in socio-sexual behavior of cycling, but not hormone-primed, Long–Evans rats

Prenatal stress (PNS) alters behavior of adult offspring in novel environments or in social interactions; variable effects of PNS on female reproductive behavior have been reported. Effects of exposure to restraint and lights for 45 min/day on Gestational Days 14–20 were examined on the motor and socio-sexual behavior of adult female offspring. In a novel arena, proestrous PNS rats displayed greater behavioral inhibition as indicated by significantly fewer beam breaks made in the horizontal crossing task compared to that of proestrous non-PNS rats. In a standard mating test, in which females are exposed to males in a relatively small space for a restricted time or number of sexual contacts, PNS females in proestrus were found to have significant decreases in the intensity of lordosis and in the number of solicitation behaviors that they directed towards the male compared to non-PNS rats. In a seminatural mating test, in which females can control the timing of the sexual contacts from the male, PNS females in proestrus engaged in significantly less pacing of their sexual contacts compared to that of the non-PNS females. When additional PNS and non-PNS rats were ovariectomized (ovx) and tested following hormone priming, behavioral differences were abrogated. PNS decreased motor behavior in a novel arena, lordosis intensity, and solicitation behavior in a standard mating paradigm, as well as adaptive, approach–avoidance behavior in a seminatural mating situation of endogenously cycling proestrous rats but not ovx, hormone-primed rats. Thus, hormone priming may override or mask effects of PNS on some aspects of socio-sexual behavior.