Periodic maternal deprivation and lesion of anterodorsal thalami nuclei induce alteration on hypophyso adrenal system activity in adult rats

Traumatic Injury to the Developing Brain: Emerging Relationship to Early Life Stress

Despite the high incidence of brain injuries in children, we have yet to fully understand the unique vulnerability of a young brain to an injury and key determinants of long-term recovery. Here we consider how early life stress may influence recovery after an early age brain injury. Studies of early life stress alone reveal persistent structural and functional impairments at adulthood. We consider the interacting pathologies imposed by early life stress and subsequent brain injuries during early brain development as well as at adulthood. This review outlines how early life stress primes the immune cells of the brain and periphery to elicit a heightened response to injury. While the focus of this review is on early age traumatic brain injuries, there is also a consideration of preclinical models of neonatal hypoxia and stroke, as each further speaks to the vulnerability of the brain and reinforces those characteristics that are common across each of these injuries. Lastly, we identify a common mechanistic trend; namely, early life stress worsens outcomes independent of its temporal proximity to a brain injury.

Maternal separation induces long-term changes in mineralocorticoid receptor in rats subjected to chronic stress and treated with tianeptine

PURPOSE

The aim of this study was to analyze whether early maternal separation would result in long-term, persistent alterations in stress response in adulthood, altering mineralocorticoid receptor immunoreactivity (MR-ir) in the dorsal hippocampal areas [CA1, CA2, CA3 and dentate gyrus (DG)], paraventricular nucleus of the hypothalamus and medial and central nucleus of the amygdala, key structures involved in stress response regulation. We also analyzed whether chronic treatment with the antidepressant tianeptine reverses these possible changes.

MATERIAL AND METHODS

Male Wistar rats were subjected to daily maternal separation for 4.5 h during 3 weeks or left undisturbed. As adults, they were exposed to chronic stress during 24 days or left undisturbed, and they were also daily treated with tianeptine (10 mg/kg i.p.) or isotonic solution.

RESULTS

In the CA2 and DG areas of the dorsal hippocampus, there was an increase in MR-ir in non-maternally separated and chronic stressed groups. Tianeptine raised MR-ir in the CA3. In the DG, control and maternally separated + chronic stress groups treated with tianeptine showed more MR-ir than their respective vehicle groups. In the paraventricular nucleus, tianeptine decreased MR-ir in non-separated groups, but not in maternally separated rats.

CONCLUSIONS

Our results support findings that early-life events induce long-term changes in stress response regulation, persistent into adulthood, which are manifested during challenges in later life, and that treatment with tianeptine, which tends to attenuate the hypothalamus-pituitary-adrenal axis dysregulation, depends on the individual experience of each rat.

Maternal separation in early life modifies anxious behavior and Fos and glucocorticoid receptor expression in limbic neurons after chronic stress in rats: effects of tianeptine

Early-life adversity can lead to long-term consequence persisting into adulthood. Here, we assess the implications of an adverse early environment on vulnerability to stress during adulthood. We hypothesized that the interplay between early and late stress would result in a differential phenotype regarding the number of neurons immunoreactive for glucocorticoid receptor (GR-ir) and neuronal activity as assessed by Fos immunoreactivity (Fos-ir) in brain areas related to stress responses and anxiety-like behavior. We also expected that the antidepressant tianeptine could correct some of the alterations induced in our model. Male Wistar rats were subjected to daily maternal separation (MS) for 4.5 h during the first 3 weeks of life. As adults, the rats were exposed to chronic stress for 24 d and they were treated daily with tianeptine (10 mg/kg intraperitoneal) or vehicle (isotonic saline). Fos-ir was increased by MS in all structures analyzed. Chronic stress reduced Fos-ir in the hippocampus, but increased it in the paraventricular nucleus. Furthermore, chronic stress increased GR-ir in hippocampus (CA1) and amygdala in control non-MS rats. By contrast, when MS and chronic stress were combined, GR-ir was decreased in these structures. Additionally, whereas tianeptine did not affect Fos-ir, it regulated GR-ir in a region-dependent manner, in hippocampus and amygdala opposing in some cases the stress or MS effects. Furthermore, tianeptine reversed the MS- or stress-induced anxious behavior. The interplay between MS and chronic stress observed indicates that MS rats have a modified phenotype, which is expressed when they are challenged by stress in later life.

Effect of Suckling Systems on Serum Oxytocin and Cortisol Concentrations and Behavior to a Novel Object in Beef Calves

We investigated differences between effects of natural- and bucket-suckling methods on basal serum oxytocin (OT) and cortisol concentrations, and the effect of OT concentration on affiliative and investigative behavior of calves to a novel object. Ten Japanese Black calves, balanced with birth order, were allocated evenly to natural-suckling (NS) and bucket suckling (BS) groups. Blood samples were collected at the ages of 1 and 2 months (1 week after weaning) calves, and serum OT and cortisol concentrations were measured using enzyme-linked immunosorbent assay and enzymeimmunoassay tests, respectively. Each calf at the age of 2 months (2 weeks after weaning) was released into an open-field with a calf decoy, and its investigative and affiliative behaviors were recorded for 20 minutes. In 1-month-old calves, the basal serum OT concentration (25.5±4.9 [mean±standard deviation, pg/mL]) of NS was significantly higher than that of BS (16.9±6.7) (p<0.05), whereas the basal cortisol concentration (5.8±2.5 [mean±standard deviation, ng/mL]) of NS was significantly lower than that in BS (10.0±2.8) (p<0.05). Additionally, a negative correlation was noted between serum OT and cortisol concentrations in 1-month-old calves (p = 0.06). Further, the higher serum OT concentration the calves had at 1 month old, the more investigative the calves were at 2 months old but not affiliative in the open-field with a calf decoy. Thus, we concluded that the natural suckling method from a dam elevates the basal serum OT concentration in calves, and high serum OT concentrations induce investigative behavior and attenuate cortisol concentrations.

Effects of maternal deprivation on the somatotrophic axis and neuropeptide Y in the hypothalamus and pituitary in female lambs. The histomorphometric study

The effects of maternal deprivation on the somatotrophic axis and neuropeptide Y (NPY) neuronal system in the hypothalamus of female lambs were evaluated. Twelve-week-old lambs were divided into two groups: the control (lambs stayed with mothers) and maternally deprived (MD; lambs separated for 3 days from mothers). The expression of immunoreactive (ir) somatostatin in the neurons of the periventricular nucleus (PEV) and in nerve terminals of the median eminence (ME), growth hormone (GH) in the adenohypophyseal cells and NPY in the neurons of the PEV and arcuate (ARC) nuclei of the hypothalamus using immunohistochemistry followed by the image analysis were estimated. Concentrations of GH in the blood plasma were determined by radioimmunoassay. The expression of ir somatostatin in the PEV and ME, ir NPY in the ARC and PEV, ir GH in adenohypophyseal cells, and blood plasma GH concentrations were greater (p<0.05) in MD than in the control lambs. In conclusion, MD affects the somatotrophic axis by enhancement of GH secretion via restraining of somatostatin output. The simultaneous increase of expression of hypothalamic ir NPY suggests NPY involvement in the regulation of psychoemotional stress through the somatotrophic axis in the female lambs.

Early maternal separation and chronic variable stress in adulthood changes the neural activity and the expression of glucocorticoid receptor in limbic structures

There is increasing evidence that early adverse experience contributes to the development of stress susceptibility, and increases the onset of stress-related psychiatric disorders in stressful environments in adulthood. This study addressed whether or not prolonged maternal separation, a well-established model of early stress, affects adult limbic areas related to the regulation of the hypothalamic-pituitary-adrenal axis in exposure to chronic variable stress in adulthood. Rats were subjected to daily maternal separation for 4.5h during postnatal days 1-21. As adults, the animals were exposed to a variable chronic stress paradigm of 24 days. Persistent changes were assessed in glucocorticoid receptor density and Fos activity in the anterodorsal thalamic nuclei, mammillary nuclei and retrosplenial cortex. Immunohistochemical analysis revealed that adult maternally separated animals had increased levels of c-Fos immunoreactivity in the anterodorsal thalamic nuclei as well as in the mammillary nuclei compared to normal non-maternally separated animals. Chronic variable stress in maternally separated and non-maternally separated animals diminished glucocorticoid receptor density in the anterodorsal thalamic nuclei but not in the rest of the nuclei analyzed. These results indicate that c-Fos immunoreactivity as well as glucocorticoid receptor expression in the anterodorsal thalamic nuclei and mammillary nuclei exhibit long-term alterations in adult rats following repeated maternal separation and subsequent stress exposure. Recognition of these adaptations helps to define the brain regions and neural circuitry associated with persistent alterations induced by early life environment and the development of stress-associated disorders.

Amitriptyline treatment under chronic stress conditions: effect on circulating catecholamines and anxiety in early maternally separated rats

The aim of this work was to determine the effect of amitriptyline (AMI) on peripheral outcomes such as plasma epinephrine (E) and norepinephrine (NE) concentration and anxiety-like behavior displayed in the plus maze test in adult male Wistar rats under variable chronic stress and daily oral administration of AMI (5 mg/kg). Animals were previously isolated from the mother for 4.5 hr every day for the first 3 weeks of life. Administration of the antidepressant AMI reduced anxiety-like behavior in animals submitted only to chronic stress but not in early maternally separated (MS) subjects or in animals subjected to the two types of stresses.

Early maternal separation and chronic variable stress as adults differentially affect Fos expression in the anterodorsal thalami nuclei

The present study examined the participation of the anterodorsal thalamic nuclei (ADTN) in mediating the long-term effects of early maternal separation on the stress/hypothalamic-pituitary-adrenal axis response of adult animals. The study measured Fos and glucocorticoid receptor immunoreactivity (GR-ir) in the ADTN of maternally separated female rats subsequently exposed to variable chronic stress. Maternal separation increased the number of neurons immunoreactive to Fos in the ADTN of chronically stressed adult rats. GR-ir was absent in the ADTN. Linking these results with previous endocrine evidence led the authors to propose a dual role of these nuclei. Maternal separation and chronic stress enhance the neuronal activity of the ADTN, nevertheless it is not regulated, at least directly, via GR.

Behavioral and hypothalamic‐pituitary‐adrenal responses to anterodorsal thalami nuclei lesions and variable chronic stress in maternally separated rats

In maternally separated rats, variable chronic stress decreased the emotional reactivity and provoked a state of hypoactivity of the hypothalamic-pituitary-adrenal system at 3 months old but increased its activity after the open field test. The anterodorsal thalami nuclei control of the endocrine response under stress conditions was not manifested however its seems activate grooming behavior. The development of behavioral and endocrine response to stress is influenced by early postnatal environment. On the other hand, the anterodorsal thalami nuclei exert an inhibitory influence on the hypothalamic-pituitary-adrenal system under basal and stressful conditions. The aim of this work is to determine the magnitude of behavioral and hypothalamic-pituitary-adrenal responses to variable chronic stress in adult female rats with anterodorsal thalami nuclei lesions, previously isolated for 4.5 h daily during the first 3 weeks of life. The groups were: non-maternally separated sham and lesioned, maternally separated sham and lesioned with variable chronic stress with and without open field test. At 3 months old, under variable chronic stress, maternal separation provoked an increase in ambulation in sham and lesioned animals (P<0.01) but this parameter was not modified by lesion in either non-maternally separated or maternally separated groups. Neither the lesion nor the maternal separation changed the defecation and rearing parameter. Grooming behavior was lower in maternally separated lesioned rats (P<0.05). Under variable chronic stress maternal separation decreased adrenocorticotrophin hormone in comparison with non-maternally separated (P<0.001) and the lesion did not alter this response. Regarding corticosterone concentrations, maternal separation did not affect this hormone under variable chronic stress conditions and after the open field test there was an increase of this in both non-maternally separated and maternally separated sham and lesioned (P<0.001).

Maternal deprivation in neonatal rats alters the expression of circadian system under light-dark cycles and restricted daily feeding in adulthood

Effects of maternal deprivation (MD) with different conditions were examined on the circadian rhythms in plasma corticosterone and locomotor activity in adult rats under ad libitum and restricted daily feeding (RF), in which rats had free access to food for 2 h for 3 weeks. Three different types of MD were performed from postnatal day 1 (P1) to day 6 (P6); MD for 12 h/day (MD12), for 3 h/day in the morning (MD3am) and in the afternoon (MD3pm). Under ad libitum feeding, corticosterone levels at 08:00 h and 24:00 h were significantly increased in MD12 rats. A similar increase was detected in MD3am rats, but not in MD3pm rats. Under the RF, corticosterone levels at 08:00 h, 24:00 h, and 04:00 h were significantly increased in MD12 rats. Similar elevations were detected in MD3am rats, but not in MD3pm rats. Furthermore, prefeeding locomotor activities under the RF increased significantly in MD12 rats. A similar increase was observed in MD3am rats, but not in MD3pm rats. Keeping ambient temperature and humidity at 37 degrees C and 70-80% during MD attenuated the effects of MD on the corticosterone rhythmicities under RF as well as ad lib feeding. It is concluded that MD in the early postnatal period influences the expressions of circadian rhythms in plasma corticosterone and locomotor activity in adult rats. Not only the length but also the time of day of MD seems to be critical for these effects. Ambient temperature and/or humidity are suggested to be one of the factors by which MD exerts its effect.

Maternal deprivation in neonatal rats of different conditions affects growth rate, circadian clock, and stress responsiveness differentially

Effects of periodic maternal deprivation (MD) were examined in rat pups on growth rate, circadian phase and period at weaning, and stress responsiveness in adulthood. MD was performed from postnatal day 1 to day 6 or day 7, with or without keeping ambient temperature at 37 degrees C and humidity at 70-80% during deprivation. Times of day and length of MD were also changed. Body weights were significantly reduced at weaning in MD12 (MD for 12 h) and MD6am (MD for 6 h in the morning) pups, whereas they were not changed in MD6pm (MD in the afternoon) and all MD3 groups. At 8 weeks old, body weight was still significantly lower in MD12 than the control, but not different from the control in other groups. Circadian phases of free-running locomotor rhythm at weaning were almost reversed in MD12, MD6am and MD6pm as compared with those in the control. Intermediate phase-shifts were observed in MD3Eam (3 h MD in the first quarter of the light phase; early am) and MD3Lam (late am; the second quarter), whereas no phase-shift was detected in MD3Epm (early pm; the third quarter) and MD3Lpm (late pm; the fourth quarter). Elevation of plasma corticosterone level after novelty exposure at 8 weeks old was more robustly in MD12 and MD3Lam than in the control, but the hormone response in MD3Lpm was not different from the control. Keeping ambient temperature at 37 degrees C during MD did not rescue the MD-induced body weight loss, but attenuated the phase-shifts of the circadian clock, and completely cancelled the stress-induced hormone response in MD12 rats. These findings indicate that MD in rat pups differentially affects growth rate, circadian clock, and stress responsiveness in adulthood, depending on time of day, length of MD and ambient temperature during MD.

Sex differences in rats: Effects of chronic stress on sympathetic system and anxiety

In this study we tested whether periodic maternal deprivation (MD) (4.5 h daily during the first 3 weeks of life) caused chronic changes in anxiety and medullo-adrenal responses to chronic stress in either male or female adult (2.5 months of age) rats, or both. Repeated maternal deprivation had a sex-specific effect on epinephrine (E) and norepinephrine (NE) levels: an increase in both measures was observed only in females. Unpredictable stress did not produce changes on plasma catecholamine levels either in males or females. However, when the females were maternally deprived as well as stressed they showed an increase in plasma NE p < 0.05. On the other hand, non-maternally deprived (NMD), maternally-deprived and stressed males showed high levels of catecholamines compared to females p < 0.001. In the elevated plus maze test, MD-treated males displayed a slight increase in anxiety-related behavior compared with NMD rats. This was indicated by a reduction in the time spent on the open arms, whereas females showed less anxiety, indicated by an increase in the number of entries, and in the time spent on the open arms. After exposure to chronic stress only the females displayed decreased anxiety-related behavior. These results suggest that there are sex-induced effects in emotional reactivity, perception of the stressor and in the evaluation of novel situations. Thus, maternal deprivation and chronic variable stress caused both long-term alterations in sympathetic response and gender-dependent changes in the anxiety index of adult rats.

The role of the anterodorsal thalami nuclei in the regulation of adrenal medullary function, beta-adrenergic cardiac receptors and anxiety responses in maternally deprived rats under stressful conditions

Maternal separation can interfere with growth and development of the brain and represents a significant risk factor for adult psychopathology. In rodents, prolonged separation from the mother affects the behavioral and endocrine responses to stress for the lifetime of the animal. Limbic structures such as the anterodorsal thalamic nuclei (ADTN) play an important role in the control of neuroendocrine and sympathetic-adrenal function. In view of these findings we hypothesized that the function of the ADTN may be affected in an animal model of maternal deprivation. To test this hypothesis female rats were isolated 4.5 h daily, during the first 3 weeks of life and tested as adults. We evaluated plasma epinephrine (E) and norepinephrine (NE), cardiac adrenoreceptors and anxiety responses after maternal deprivation and variable chronic stress (VCS) in ADTN-lesioned rats. Thirty days after ADTN lesion, in non-maternally deprived rats basal plasma NE concentration was greater and cardiac beta-adrenoreceptor density was lower than that in the sham-lesioned group. Maternal deprivation induced a significant increase in basal plasma NE concentration, which was greater in lesioned rats, and cardiac beta-adrenoreceptor density was decreased in lesioned rats. After VCS plasma catecholamine concentration was much greater in non-maternally deprived rats than in maternally-deprived rats; cardiac beta-adrenoreceptor density was decreased by VCS in both maternally-deprived and non-deprived rats, but more so in non-deprived rats, and further decreased by the ADTN lesion. In the plus maze test, the number of open arm entries was greater in the maternally deprived and in the stressed rats. Thus, sympathetic-adrenal medullary activation produced by VCS was much greater in non-deprived rats, and was linked to a down regulation of myocardial beta-adrenoceptors. The ADTN are not responsible for the reduced catecholamine responses to stress in maternally-deprived rats. Maternal deprivation or chronic stress also induced a long term anxiolytic effect, which was also not affected by ADTN lesion.

Influence of sex and experimental protocol on the effect of maternal deprivation on rectal sensitivity to distension in the adult rat

Neonatal maternal separation induces visceral hyperalgesia before and after stress in male rats. This study compares the effects on sensitivity to rectal distension in adult male and female rats, using two protocols of deprivation. Between postnatal days 1 and 14, maternal deprivation was performed for 2 h per day according to a protocol of type M (removal of all pups from home cage) or type P (separation of half of littermates). Visceral sensitivity was assessed at 12 weeks of age by the number of abdominal contractions induced by rectal distension before and after restraint stress. Calcitonin gene-related peptide (CGRP) was identified in the rectal wall by immunohistochemistry. In basal conditions, both separation protocols induced hyperalgesia, that was greater after type M than type P, and in females than in males for type P separation. Acute restraint stress induced hyperalgesia in control females only, and this effect was similarly enhanced by both type P and M separation. No difference was found between controls and deprived rats in rectal CGRP immunoreactivity which was greater in females and increased after rectal distension. These results indicate that long-term visceral hyperalgesia depends upon the type of maternal deprivation and that females are more sensitive than males.