Materno-fetal coordination of stress-induced Fos expression in the hypothalamic paraventricular nucleus during pregnancy

How is prenatal stress transmitted from the mother to the fetus?

Prenatal stress programmes long-lasting neuroendocrine and behavioural changes in the offspring. Often this programming is maladaptive and sex specific. For example, using a rat model of maternal social stress in late pregnancy, we have demonstrated that adult prenatally stressed male, but not prenatally stressed female offspring display heightened anxiety-like behaviour, whereas both sexes show hyperactive hypothalamo-pituitary-adrenal (HPA) axis responses to stress. Here, we review the current knowledge of the mechanisms underpinning dysregulated HPA axis responses, including evidence supporting a role for reduced neurosteroid-mediated GABAergic inhibitory signalling in the brains of prenatally stressed offspring. How maternal psychosocial stress is signalled from the mother to the fetuses is unclear. Direct transfer of maternal glucocorticoids to the fetuses is often considered to mediate the programming effects of maternal stress on the offspring. However, protective mechanisms including attenuated maternal stress responses and placental 11β-hydroxysteroid dehydrogenase-2 (which inactivates glucocorticoids) should limit materno-fetal glucocorticoid transfer during pregnancy. Moreover, a lack of correlation between maternal stress, circulating maternal glucocorticoid levels and circulating fetal glucocorticoid levels is reported in several studies and across different species. Therefore, here we interrogate the evidence for a role for maternal glucocorticoids in mediating the effects of maternal stress on the offspring and consider the evidence for alternative mechanisms, including an indirect role for glucocorticoids and the contribution of changes in the placenta in signalling the stress status of the mother to the fetus.

Effect of rapid eye movement sleep deprivation during pregnancy on glucocorticoid receptor regulation of HPA axis function in female offspring

Poor maternal sleep quality during the different phases of pregnancy acts as a prenatal stress and is critical for fetal development. Despite the potential adverse effects of maternal stress on the behavior and physiology of the offspring, the mechanisms remain poorly understood. The present study investigates the effects of maternal sleep deprivation (SD) at different stages of pregnancy on the hypothalamic-pituitary-adrenal (HPA) axis in female offspring. The pregnant rats were subjected to sleep deprivation of 12 h per day at different stages; early (ESD), mid (MSD), and late (LSD) stages, on pregnancy days 1-7, 8-14, and 14-20, respectively. At postnatal day 60, levels of corticosterone (CORT), hypothalamic corticotropin-releasing factor receptor 1 (CRF-R1), and hippocampal glucocorticoid receptors (GR) were evaluated in the offspring. Although the hypothalamic CRF-R1 level was increased in the offspring of SD dams, immunohistochemical staining showed reduced immunoreactivity of GR in ESD and LSD offspring hippocampal area. Altogether, the data suggests that a critical period for adverse effects of SD on the HPA axis in female offspring of Wistar rats may be during early and late pregnancy.

Transcriptional and epigenetic changes of brain derived neurotrophic factor following prenatal stress: A systematic review of animal studies

Gestational period plays critical role in neuropsychological development. One of the genes that undergoes changes by prenatal stress (PNS) exposure, is the gene coding brain derived neurotrophic factor (BDNF). Studies have reported different patterns of change following PNS in BDNF, which emphasizes the complexity of the issue. In this review, systematic search of PubMed, Scopus, Web of Science and Cochrane CENTRAL databases was performed. Primary searches resulted in 2132 studies and finally 43 studies were found to meet the inclusion criteria. Transcriptional and epigenetic changes of BDNF gene in the brain were recorded. Decreased or unchanged BDNF total mRNA and BDNF mature protein, with hypermethylation of the coding exons were the most reported changes. However, stress paradigm, gender of the fetus and the day of sacrifice were found to significantly affect the results. Hippocampus and prefrontal cortex are the most vulnerable regions. They can show long lasting and persistent transcriptional and epigenetics changes of BDNF gene following PNS. Further studies evaluating the importance of these findings in humans are essential.

Giving a good start to a new life via maternal brain allostatic adaptations in pregnancy

Successful pregnancy requires adjustments to multiple maternal homeostatic mechanisms, governed by the maternal brain to support and enable survival of the growing fetus and placenta. Such adjustments fit the concept of allostasis (stability through change) and have a cost: allostatic load. Allostasis is driven by ovarian, anterior pituitary, placental and feto-placental hormones acting on the maternal brain to promote adaptations that support the pregnancy and protect the fetus. Many women carry an existing allostatic load into pregnancy, from socio-economic circumstances, poor mental health and in 'developed' countries, also from obesity. These pregnancies have poorer outcomes indicating negative interactions (failing allostasis) between pre-pregnancy and pregnancy allostatic loads. Use of animal models, such as adult prenatally stressed female offspring with abnormal neuroendocrine, metabolic and behavioural phenotypes, to probe gene expression changes, and epigenetic mechanisms in the maternal brain in adverse pregnancies are discussed, with the prospect of ameliorating poor pregnancy outcomes.

Patterns of cell death in the perinatal mouse forebrain

The importance of cell death in brain development has long been appreciated, but many basic questions remain, such as what initiates or terminates the cell death period. One obstacle has been the lack of quantitative data defining exactly when cell death occurs. We recently created a "cell death atlas," using the detection of activated caspase-3 (AC3) to quantify apoptosis in the postnatal mouse ventral forebrain and hypothalamus, and found that the highest rates of cell death were seen at the earliest postnatal ages in most regions. Here we have extended these analyses to prenatal ages and additional brain regions. We quantified cell death in 16 forebrain regions across nine perinatal ages from embryonic day (E) 17 to postnatal day (P) 11 and found that cell death peaks just after birth in most regions. We found greater cell death in several regions in offspring delivered vaginally on the day of parturition compared with those of the same postconception age but still in utero at the time of collection. We also found massive cell death in the oriens layer of the hippocampus on P1 and in regions surrounding the anterior crossing of the corpus callosum on E18 as well as the persistence of large numbers of cells in those regions in adult mice lacking the pro-death Bax gene. Together these findings suggest that birth may be an important trigger of neuronal cell death and identify transient cell groups that may undergo wholesale elimination perinatally. J. Comp. Neurol. 525:47-64, 2017. © 2016 Wiley Periodicals, Inc.

The consequences of early-life adversity: neurobiological, behavioural and epigenetic adaptations

During the perinatal period, the brain is particularly sensitive to remodelling by environmental factors. Adverse early-life experiences, such as stress exposure or suboptimal maternal care, can have long-lasting detrimental consequences for an individual. This phenomenon is often referred to as 'early-life programming' and is associated with an increased risk of disease. Typically, rodents exposed to prenatal stress or postnatal maternal deprivation display enhanced neuroendocrine responses to stress, increased levels of anxiety and depressive-like behaviours, and cognitive impairments. Some of the phenotypes observed in these models of early-life adversity are likely to share common neurobiological mechanisms. For example, there is evidence for impaired glucocorticoid negative-feedback control of the hypothalamic-pituitary-adrenal axis, altered glutamate neurotransmission and reduced hippocampal neurogenesis in both prenatally stressed rats and rats that experienced deficient maternal care. The possible mechanisms through which maternal stress during pregnancy may be transmitted to the offspring are reviewed, with special consideration given to altered maternal behaviour postpartum. We also discuss what is known about the neurobiological and epigenetic mechanisms that underpin early-life programming of the neonatal brain in the first generation and subsequent generations, with a view to abrogating programming effects and potentially identifying new therapeutic targets for the treatment of stress-related disorders and cognitive impairment.

Effects of maternal exposure to social stress during pregnancy: consequences for mother and offspring

A suboptimalin uteroenvironment, for example, as a result of maternal stress, can have detrimental effects on the pregnancy and long-term adverse ‘programming’ effects on the offspring. This article focuses on the effects of prenatal social stress on the mother, her pregnancy and the offspring, since these issues have ethological relevance in both animals and humans. The consequences of social stress exposure depend on when during pregnancy the stress occurs, and many of the effects on the offspring are sex specific. Social stress during early pregnancy tends to result in pregnancy loss, whereas stress exposure later in pregnancy, when the mother has already invested considerable resources in the foetuses, results in programmed offspring of low birth weight: a risk factor for various adulthood diseases. Neuroendocrine and behavioural responses to stress in the offspring are particularly sensitive to foetal programming by prenatal stress, indicated by enhanced hypothalamo-pituitary–adrenal (HPA) axis responses and increased anxiety behaviour, which result from permanent changes in the offspring's brain. The dysregulation of HPA axis function may also interfere with other systems, for example, the hypothalamic–pituitary–gonadal axis, as there is evidence for alterations in steroidogenesis, reproductive potential and impaired reproductive/social behaviours in prenatally stressed offspring. Prenatal social stress also programmes future maternal behaviour, highlighting the potential for negative phenotypes to be transmitted to future generations. The possible mechanisms through which maternal stress during pregnancy is transmitted to the foetuses and the foetal brain is programmed by prenatal stress and the potential to overwrite programming of the offspring are discussed.

Corticosterone mediates some but not other behavioural changes induced by prenatal stress in rats

The effect of daily varied stress from days 13-21 of gestation in Wistar rats was investigated by tests of learning and memory and anxiogenic behaviour in the 60-day-old offspring of both sexes. Prenatal stress decreased the anogenital distance in males at 1 day of age. Anxiogenic behaviour in the elevated plus maze was seen in prenatally-stressed rats of both genders. There was no significant gender difference in the rate of spatial learning in the Morris water maze but prenatal stress only slowed that of males. In the object recognition test with an inter-trial interval of 40 min, females but not males, discriminated between a familiar and novel object. Prenatal stress did not affect object discrimination in females but feminised that in males. Maternal adrenalectomy with replacement of basal corticosterone levels in the drinking fluid prevented all of the above effects of prenatal stress in the offspring. To mimic the peak corticosterone levels and time course of elevation in response to stress, corticosterone (3 mg/kg) was injected twice (0 and 30 min) on days 13-16 and once on days 17-20 of gestation to adrenalectomised mothers. This treatment re-instated anxiogenic behaviour similar to that induced by prenatal stress, indicating that it is mediated by exposure of the foetal brain to raised levels of corticosterone. However, steroid administration to adrenalectomised dams did not decrease anogenital distance, feminise object recognition memory or slow spatial learning in their male offspring. The findings indicate that other adrenal hormones are necessary to induce these effects of prenatal stress.

Resetting the dynamic range of hypothalamic-pituitary-adrenal axis stress responses through pregnancy

The hypothalamic-pituitary-adrenal (HPA) axis plays a key role in the neuroendocrine response to stress. Dynamic changes in HPA axis regulation and hence HPA responsivity occur over the lifetime of an animal. This article focuses on two extremes of the spectrum. The first occurs naturally during pregnancy when stress responses are dampened. The second, at the opposite end of the scale, occurs in offspring of mothers who were exposed to stress during pregnancy and display exaggerated HPA axis stress responses. Reduced glucocorticoid output in response to stress in pregnancy may have important consequences for conserving energy supply to the foetus(es), in modulating immune system adaptations and in protecting against adverse foetal programming by glucocorticoids. Understanding the mechanisms underpinning this adaptation in pregnancy may provide insights for manipulating HPA axis responsiveness in later life, particularly in the context of resetting HPA axis hyperactivity associated with prenatal stress exposure, which may underlie several major pathologies, including cardiovascular disease, diabetes mellitus type 2, obesity, cognitive decline and mood disorders.

Roles for gamma-aminobutyric acid in the development of the paraventricular nucleus of the hypothalamus

The development of the hypothalamic paraventricular nucleus (PVN) involves several factors that work together to establish a cell group that regulates neuroendocrine functions and behaviors. Several molecular markers were noted within the developing PVN, including estrogen receptors (ER), neuronal nitric oxide synthase (nNOS), and brain-derived neurotrophic factor (BDNF). By contrast, immunoreactive gamma-aminobutyric acid (GABA) was found in cells and fibers surrounding the PVN. Two animal models were used to test the hypothesis that GABA works through GABA(A) and GABA(B) receptors to influence the development of the PVN. Treatment with bicuculline to decrease GABA(A) receptor signaling from embryonic day (E) 10 to E17 resulted in fewer cells containing immunoreactive (ir) ERalpha in the region of the PVN vs. control. GABA(B)R1 receptor subunit knockout mice were used to examine the PVN at P0 without GABA(B) signaling. In female but not male GABA(B)R1 subunit knockout mice, the positions of cells containing ir ERalpha shifted from medial to lateral compared with wild-type controls, whereas the total number of ir ERalpha-containing cells was unchanged. In E17 knockout mice, ir nNOS cells and fibers were spread over a greater area. There was also a significant decrease in ir BDNF in the knockout mice in a region-dependent manner. Changes in cell position and protein expression subsequent to disruption of GABA signaling may be due, in part, to changes in nNOS and BDNF signaling. Based on the current study, the PVN can be added as another site where GABA exerts morphogenetic actions in development.

Prenatal social stress in the rat programmes neuroendocrine and behavioural responses to stress in the adult offspring: sex-specific effects

Stress exposure during pregnancy can 'programme' adult behaviour and hypothalamic-pituitary-adrenal (HPA) axis stress responsiveness. In the present study, we utilised an ethologically relevant social stressor to model the type of stress that pregnant women may experience. We investigated the effects of social defeat by a resident lactating rat over 5 days during the last week of pregnancy on the pregnant intruder rat HPA axis, and on HPA responsivity to stress and anxiety-related behaviour in the adult offspring of the socially-defeated intruder rats. HPA axis responses after social defeat were attenuated in the pregnant rats compared to virgin females. In the adult offspring, systemic interleukin (IL)-1beta or restraint increased adrenocorticotrophic hormone and corticosterone secretion in male and female control rats; however, in prenatally stressed (PNS) offspring, HPA responses were greatly enhanced and peak hormone responses to IL-1beta were greater in females versus males. Male PNS rats displayed increased anxiety behaviour on the elevated plus maze; however, despite marked changes in anxiety behaviour across the oestrous cycle, there were no differences between female control and PNS rats. Investigation of possible mechanisms showed mineralocorticoid mRNA levels were reduced in the hippocampus of male and female PNS offspring, whereas glucocorticoid receptor mRNA expression was modestly reduced in the CA2 hippocampal subfield in female PNS rats only. Corticotropin-releasing hormone mRNA and glucocorticoid receptor mRNA expression in the central amygdala was greater in PNS males and females compared to controls. The data obtained in the present study indicate that prenatal social stress differentially programmes anxiety behaviour and HPA axis responses to stress in male and female offspring. Attenuated glucocorticoid feedback mechanisms in the limbic system may underlie HPA axis hyper-reactivity to stress in PNS offspring.

The long-term behavioural consequences of prenatal stress

Maternal distress during pregnancy increases plasma levels of cortisol and corticotrophin releasing hormone in the mother and foetus. These may contribute to insulin resistance and behaviour disorders in their offspring that include attention and learning deficits, generalized anxiety and depression. The changes in behaviour, with or independent of alterations in the function of the hypothalamic pituitary adrenal (HPA) axis, can be induced by prenatal stress in laboratory rodents and non-human primates. The appearance of such changes depends on the timing of the maternal stress, its intensity and duration, gender of the offspring and is associated with structural changes in the hippocampus, frontal cortex, amygdala and nucleus accumbens. The dysregulation of the HPA axis and behaviour changes can be prevented by maternal adrenalectomy. However, only the increased anxiety and alterations in HPA axis are re-instated by maternal injection of corticosterone.

CONCLUSION

Excess circulating maternal stress hormones alter the programming of foetal neurons, and together with genetic factors, the postnatal environment and quality of maternal attention, determine the behaviour of the offspring.

Effects of the Chinese Traditional Prescription Xiaoyaosan Decoction on Chronic Immobilization Stress-induced Changes in Behavior and Brain BDNF, TrkB, and NT-3 in Rats

The Xiaoyaosan (XYS) decoction, a Chinese traditional prescription containing eight commonly used herbs, has been used for treatment of mental disorders such as depression for centuries in China. However, the mechanism underlying its antidepressant activity is poorly understood. In rats with chronic immobilization stress (CIS), we examined the effects of the XYS decoction on tail suspension behavior and the levels of brain-derived neurotrophic factor (BDNF), tyroxine hydroxylase (TrkB), and neurotrophin 3 (NT-3) in the frontal cortex and hippocampus. Rats subjected to CIS exhibited decreases in weight-gain, food intake, and ambulation in the open field test; they also showed an increase in immobility in the tail suspension test. These were all attenuated by the XYS decoction. Biochemically, the XYS decoction also reversed CIS-induced decreases in BDNF and increases in TrkB and NT-3 in the frontal cortex and the hippocampal CA(1) subregion. The behavioral effects of the XYS were correlated to the biochemical actions. These results suggest that the XYS decoction produces an antidepressant-like effect, which appears to be involved by BDNF in the brain.

Effect of Gabapentin on c-Fos Expression in the CNS after Paw Surgery in Rats

Gabapentin (neurontin), a GABA analogue anticonvulsant has proven to be effective in anti-nociceptive activity as well as for the treatment of anxiety. Gabapentin (GBP) is well tolerated and shows very favorable side effects profile: The exact molecular mechanism of action of GBP to block postoperative pain and stress is not known. Therefore, to identify the functional neuroanatomical target sites of GBP in post-surgery as well as its effect on postsurgical process, we examined the effects of GBP on c-Fos expression in the supraspinal part of the central nervous system in rats. Using a well-validated rat model of surgical pain, we studied the neuroanatomical functional target sites of gabapentin after paw surgery. The effect of GBP was examined by means of c-Fos immunohistochemistry. A single intraperitoneal injection (i.p.) of GBP (150 mg/kg) or saline (control) was administered 20 min before surgical incision in the paw under anesthesia. Ninety minutes after surgical incision, the deeply anesthetized rats were perfused transcardially with 4% paraformaldehyde. Serial 40-microm-thick sections of whole brain (except spinal cord) were cut and processed by immunohistochemistry to locate and quantify the sites and number of neurons with c-Fos immunoreactivity. Detection of c-Fos protein was performed using the peroxidase-antiperoxidase detection protocol. Our present study demonstrated that compared to control, administration of GBP (150 mg/kg, i.p.) before paw surgery significantly (p < 0.01) attenuated the incision-induced c-Fos expression only in the paraventricular nucleus of the hypothalamus. In addition, GBP-induced increase in c-Fos expression was observed in the dorsal raphe (DRN) and in the nucleus raphe magnus. Present results indicate that GBP may differentially modulate c-Fos expression in surgical paw incision. Moreover, this study provides some clue to examine whether GBP exerts its action simultaneously through two separate pathways in post-surgery.

Chronic intracerebral prolactin attenuates neuronal stress circuitries in virgin rats

Prolactin (PRL) has been shown to promote maternal behaviour, and to regulate neuroendocrine and emotional stress responses. These effects appear more important in the peripartum period, when the brain PRL system is highly activated. Here, we studied the mechanisms that underlie the anti-stress effects of PRL. Ovariectomized, estradiol-substituted Wistar rats were implanted with an intracerebroventricular cannula and treated with ovine PRL (0.01, 0.1 or 1 microg/h; 5 days via osmotic minipumps) or vehicle, and their responses to acute restraint stress was assessed. Chronic PRL treatment exerted an anxiolytic effect on the elevated plus-maze, and attenuated the acute restraint-induced rise in plasma adrenocorticotropin, corticosterone and noradrenaline. At the neuronal level, in situ hybridization revealed PRL effects on the expression patterns of the immediate-early gene c-fos and corticotropin-releasing factor (CRF). Under basal conditions, PRL significantly reduced c-fos mRNA expression within the central amygdala. In response to restraint, the expression of both c-fos mRNA and protein and of CRF mRNA was decreased in the parvocellular part of the paraventricular nucleus (PVN) of PRL-treated compared with vehicle-treated animals. In conclusion, our data demonstrate that chronic elevation of PRL levels within the brain results in reduced neuronal activation within the hypothalamus, specifically within the PVN, in response to an acute stressor. Thus, PRL acting at various relevant brain regions exerts profound anxiolytic and anti-stress effects, and is likely to contribute to the attenuated stress responsiveness found in the peripartum period, when brain PRL levels are physiologically upregulated.

Gender differences in the effects of prenatal stress on brain development and behaviour

An increased incidence of anxiety, depression and attention deficits in children has been linked to psychological stress during pregnancy. Subjection of a pregnant rat to stress at a time when the foetal limbic and hypothalamic pituitary adrenal (HPA) axes develop results in anxiogenic and depressive behaviour and learning and attention deficits in the offspring, which depend on its gender, intensity and timing of the maternal stress and behaviour being tested. Maternal stress increases corticosterone levels in the foetal brain, decreases foetal testosterone and brain aromatase activity in males, and alters brain catecholamine activity to that in females. Learning deficits, reductions in hippocampal neurogenesis, LTP and dendritic spine density in the prefrontal cortex are more readily seen in prenatally-stressed males, while anxiety, depression and increased response of the HPA axis to stress are more prevalent in females. Genders may differ in the sensitivity of developing brain areas to stress hormones.

Expression of the immediate early gene, c-fos, in fetal brain after whole of gestation exposure of pregnant mice to global system for mobile communication microwaves

AIMS

To study immediate early gene, c-fos, expression as a marker of neural stress after whole of gestation exposure of the fetal mouse brain to mobile telephone-type radiofrequency fields.

METHODS

Using a purpose-designed exposure system at 900 MHz, pregnant mice were given a single, far-field, whole body exposure at a specific absorption rate of 4 W/kg for 60 min/day from day 1 to day 19 of gestation. Pregnant control mice were sham-exposed or freely mobile in a cage without further restraint. Immediately prior to parturition on gestational day 19, fetal heads were collected, fixed in 4% paraformaldehyde and paraffin embedded. Any stress response in the brain was detected by c-fos immunohistochemistry in the cerebral cortex, basal ganglia, thalamus, hippocampus, midbrain, cerebellum and medulla.

RESULTS

c-fos expression was of limited, but consistent, neuroanatomical distribution and there was no difference in immunoreactivity between exposed and control brains.

CONCLUSION

In this animal model, no stress response was detected in the fetal brain using c-fos immunohistochemistry after whole of gestation exposure to mobile telephony.

Differential effects of prenatal stress on the morphological maturation of hippocampal neurons

The present study was designed to clarify an intensity-dependent effect of prenatal stress on the morphological development of hippocampal neurons in rats. In addition, the involvement of receptors for glucocorticoids, i.e. mineralocorticoid receptors and glucocorticoid receptors, in stress-induced changes in the morphology of hippocampal neurons was examined by an in vitro pharmacological approach. The effects of mild prenatal stress on neurogenesis and long-term potentiation in the hippocampus were also investigated in adult offspring. Prenatal stress affected the morphological development of the hippocampus in an intensity-dependent manner. Short-lasting, mild prenatal stress enhanced neonatal neurogenesis and differentiation of processes of hippocampal neurons, whereas long-lasting, severe stress impaired their morphology. Mineralocorticoid receptor was found to mediate enhancement of neurogenesis and differentiation of processes of cultured hippocampal neurons. In contrast, glucocorticoid receptor was involved in the suppression of their morphology. Short-lasting, mild prenatal stress, which has previously been shown to enhance learning performance in adult offspring, facilitated neurogenesis and long-term potentiation in the adult hippocampus. These findings suggest that prenatal stress has enhancing and suppressing effects on the development of hippocampal neurons depending on intensity, and that mineralocorticoid receptors and glucocorticoid receptors contribute to stress-induced morphological changes.

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.

Effect of Local Anaesthesia on Neuronal c-fos Expression in the Spinal Dorsal Horn and Hypothalamic Paraventricular Nucleus after Surgery in Rats

The surgical stress response is the neurophysiologic reflex response to surgery, which involves activation of the hypothalamic-pituitary-adrenal axis and is regulated by the hypothalamic paraventricular nucleus. The effect of pre-operative use of local anaesthetics on activation of neurones in the paraventricular nucleus during surgery was studied by quantification of the neuronal expression of the c-fos-gene after a standardized plantar incision in rats. Furthermore, c-fos expression in the spinal dorsal horn was used as a measure of spinal nociception. Six halothane-anaesthetized animals underwent surgery following infiltration with lidocaine and bupivacaine, six animals were operated without local anaesthetics, and six control animals were subjected to the anaesthetic procedures. After two hours, the animals were perfused with 4% formaldehyde and the spinal cords and brains were collected and processed by immunohistochemistry for stereological quantification of the number of neurones with Fos-like immunoreactivity. Furthermore, brain and spinal cord were sampled from nine control animals right after induction of halothane anaesthesia. Surgery without local anaesthetics caused a significant increased number of neurones with Fos-like immunoreactivity in the spinal cord (4258+/-1710; mean+/-S.D.; P<0.01) compared to the anaesthesia control group (1204+/-436). Local anaesthetics reduced this number to 2029+/-919 (P<0.05), which was not significantly different from the anaesthesia control group. After surgery, the number of neurones with Fos-like immunoreactivity in paraventricular nucleus increased from 2948+/-1365 in the anaesthetized control group to 5550+/-3875 and 5191+/-1558 in the surgery and local anaesthetics plus surgery group, respectively, although significance was only reached for the group receiving local anaesthetics (P<0.05). In conclusion, preoperative local anaesthetic infiltration did not reduce the surgery-induced c-fos expression in paraventricular nucleus after paw surgery in rats, although spinal nociception was reduced.

Variations of maternal care differentially influence 'fear' reactivity and regional patterns of cFos immunoreactivity in response to the shock-probe burying test

Natural variations in maternal care in the rat influence the development of neuronal systems that regulate endocrine and behavioral responses to stress. Thus, as adults, rats that received higher levels of maternal licking/grooming (LG) in infancy are less 'fearful' in response to novelty, compared with adult offspring of Low LG mothers. The present study examined the influence of maternal care on behavioral and neuronal responses to a more specific, localizable form of threat using an electrified probe in the shock-probe burying test. Even under these conditions, adult offspring of High LG mothers displayed lower levels of fear reactivity (i.e. less shock-induced freezing and probe burying) throughout the test than did offspring of Low LG mothers. These differences in fearfulness were associated with differential patterns of cFos immunoreactivity (cFos-IR), 120 min following test exposure. Relative to control rats exposed to a non-electrified probe, cFos-IR was increased in the offspring of High LG mothers exposed to an electrified probe in the dentate gyrus, ventral subiculum, lateral and medial septum, nucleus accumbens and the dorsal periaqueductal gray. Shock-exposed offspring of Low LG dams displayed a very different pattern of neuronal activation characterized by both increases (area CA1 of the ventral hippocampus and the inferior colliculus) and decreases (paraventricular nucleus of the hypothalamus and the ventrolateral periaqueductal gray) in cFos-IR compared with the no-shock controls. Together these results suggest that maternal care serves to 'program' neuronal circuits that modulate fear-related responding in the rat resulting in qualitatively different neuronal responses to stress.

Effects of repeated maternal stress on FOS expression in the hypothalamic paraventricular nucleus of fetal rats

The effects of repeated prenatal stress with different severity (restraint and immobilization) on Fos expression in the maternal and fetal hypothalamic paraventricular nucleus (PVN) were examined in rats. Acute stress treatment was performed for 30 min on gestational day 21, and repeated stress treatment for 30 min daily for 5 days from gestational days 17-21. In the parvocellular region of the maternal PVN, the stress-induced increases in the number of Fos-immunoreactive neurons were smaller in the repeated stress groups than the acute stress groups, indicating an adaptation of Fos expression to repeated stress. The attenuated Fos expression observed in the maternal PVN following repeated mild stress did not occur in the fetal PVN. In contrast, repeated immobilization stress caused a much smaller increase in Fos expression in the fetal PVN than did acute immobilization stress. The reduced Fos expression in the fetal PVN following repeated severe stress was thought to be due to cell death, since the fetal PVN in the chronic immobilization group revealed a reduction in the total number of cells and an increase in the number of apoptotic cells. In the female but not male fetuses, repeated restraint stress induced a significant increase in the number of apoptotic cells in the PVN. These findings suggest that the fetal PVN shows no adaptation of Fos expression to repeated maternal stress, but great vulnerability to cell death, including apoptosis. In addition, stress-induced apoptosis may more easily occur in the fetal PVN in females than males.