Amita Kapoor

Short periods of prenatal stress affect growth, behaviour and hypothalamo-pituitary-adrenal axis activity in male guinea pig offspring.

Prenatal stress can have profound long‐term influences on physiological function throughout the course of life. We hypothesized that focused periods of moderate prenatal stress at discrete time points in late gestation have differential effects on hypothalamo–pituitary–adrenal (HPA) axis function in adult guinea pig offspring, and that changes in HPA axis function will be associated with modification of anxiety‐related behaviour. Pregnant guinea pigs were exposed to a strobe light for 2 h on gestational days (GD) 50, 51, 52 (PS50) or 60, 61, 62 (PS60) (gestation length ∼70 days). A control group was left undisturbed throughout pregnancy. Behaviour was assessed in male offspring on postnatal day (PND)25 and PND70 by measurement of ambulatory activity and thigmotaxis (wall‐seeking behaviour) in a novel open field environment. Subsequent to behavioural testing, male offspring were cannulated (PND75) to evaluate basal and activated HPA axis function. Body weight was significantly decreased in adult PS50 and PS60 offspring and this effect was apparent soon after weaning. The brain‐to‐body‐weight ratio was significantly increased in adult PS50 males. Basal plasma cortisol levels were elevated in PS50 male offspring throughout the 24 h sampling period compared with controls. In response to an ACTH challenge and to exposure to an acute stressor, PS60 male offspring exhibited elevated plasma cortisol responses. Plasma testosterone concentrations were strikingly decreased in PS50 offspring. Thigmotaxis in the novel environment was increased in PS50 male offspring at PND25 and PND70, suggesting increased anxiety in these animals. In conclusion, prenatal stress during critical windows of neuroendocrine development programs growth, HPA axis function, and stress‐related behaviour in adult male guinea pig offspring. Further, the nature of the effect is dependant on the timing of the maternal stress during pregnancy.

Prenatal glucocorticoid exposure alters hypothalamic-pituitary-adrenal function and blood pressure in mature male guinea pigs.

Pregnant guinea pigs were treated with dexamethasone (1 mg kg−1) or vehicle on days 40–41, 50–51 and 60–61 of gestation, after which animals delivered normally. Adult male offspring were catheterized at 145 days of age and subjected to tests of hypothalamic–pituitary–adrenal (HPA) axis function in basal and activated states. Animals exposed to dexamethasone in utero (mat‐dex) exhibited increased hippocampus‐to‐brain weight ratio, increased adrenal‐to‐body weight ratio and increased mean arterial pressure. There were no effects on gestation length, birth weight and postnatal growth. There were no overall differences in diurnal plasma adrenocorticotropic hormone (ACTH) and cortisol profiles, though there were subtle differences during the subjective afternoon between control and mat‐dex offspring. A significant decrease in initial ACTH suppression was observed following dexamethasone injection in mat‐dex offspring compared to control offspring. Molecular analysis revealed significantly increased MR mRNA expression in the limbic system and particularly in the dentate gyrus in mat‐dex offspring. In the anterior pituitary, both pro‐opiomelanocortin (POMC) and glucocorticoid receptor (GR) mRNA levels were significantly elevated in mat‐dex offspring. In conclusion, (1) repeated prenatal treatment with synthetic glucocorticoid (sGC) permanently programmes organ growth, blood pressure and HPA regulation in mature male offspring and these changes involve modification of corticosteroid receptor expression in the brain and pituitary; (2) the effects of prenatal sGC exposure on HPA function appear to change as a function of age, indicating the importance of investigating HPA and cardiovascular outcome at multiple time points throughout life.

Proximal Cerebral Arteries Develop Myogenic Responsiveness in Heart Failure via Tumor Necrosis Factor-α–Dependent Activation of Sphingosine-1-Phosphate Signaling

Background— Heart failure is associated with neurological deficits, including cognitive dysfunction. However, the molecular mechanisms underlying reduced cerebral blood flow in the early stages of heart failure, particularly when blood pressure is minimally affected, are not known. Methods and Results— Using a myocardial infarction model in mice, we demonstrate a tumor necrosis factor-&agr; (TNF&agr;)–dependent enhancement of posterior cerebral artery tone that reduces cerebral blood flow before any overt changes in brain structure and function. TNF&agr; expression is increased in mouse posterior cerebral artery smooth muscle cells at 6 weeks after myocardial infarction. Coordinately, isolated posterior cerebral arteries display augmented myogenic tone, which can be fully reversed in vitro by the competitive TNF&agr; antagonist etanercept. TNF&agr; mediates its effect via a sphingosine-1-phosphate (S1P)–dependent mechanism, requiring sphingosine kinase 1 and the S1P2 receptor. In vivo, sphingosine kinase 1 deletion prevents and etanercept (2-week treatment initiated 6 weeks after myocardial infarction) reverses the reduction of cerebral blood flow, without improving cardiac function. Conclusions— Cerebral artery vasoconstriction and decreased cerebral blood flow occur early in an animal model of heart failure; these perturbations are reversed by interrupting TNF&agr;/S1P signaling. This signaling pathway may represent a potential therapeutic target to improve cognitive function in heart failure.

Testosterone is involved in mediating the effects of prenatal stress in male guinea pig offspring

Studies in humans have demonstrated a link between stress during pregnancy and altered behaviour and stress reactivity in children. In guinea pigs, we have previously shown that a short period of maternal stress during gestation leads to increased anxiety, elevated basal cortisol levels and decreased testosterone levels in adult males. We hypothesized that restoring testosterone to normal levels in the adult males born to prenatally stressed mothers would reverse the changes in behaviours and endocrine function. We found differences in attention and anxiety‐related behaviours and basal stress endocrine activity between the prenatally stressed and control males. Administration of testosterone reversed the behavioural differences in the prenatally stressed offspring. There was, however, little effect of postnatal testosterone administration on stress‐related endocrine activity. This study provides new information to begin to address the mechanism underlying the interplay between prenatal stress, gonadal steroids and postnatal behaviours.

Proximal Cerebral Arteries Develop Myogenic Responsiveness in Heart Failure via TNFα-Dependent Activation of S1P Signaling

Background— Heart failure is associated with neurological deficits, including cognitive dysfunction. However, the molecular mechanisms underlying reduced cerebral blood flow in the early stages of heart failure, particularly when blood pressure is minimally affected, are not known. Methods and Results— Using a myocardial infarction model in mice, we demonstrate a tumor necrosis factor-&agr; (TNF&agr;)–dependent enhancement of posterior cerebral artery tone that reduces cerebral blood flow before any overt changes in brain structure and function. TNF&agr; expression is increased in mouse posterior cerebral artery smooth muscle cells at 6 weeks after myocardial infarction. Coordinately, isolated posterior cerebral arteries display augmented myogenic tone, which can be fully reversed in vitro by the competitive TNF&agr; antagonist etanercept. TNF&agr; mediates its effect via a sphingosine-1-phosphate (S1P)–dependent mechanism, requiring sphingosine kinase 1 and the S1P2 receptor. In vivo, sphingosine kinase 1 deletion prevents and etanercept (2-week treatment initiated 6 weeks after myocardial infarction) reverses the reduction of cerebral blood flow, without improving cardiac function. Conclusions— Cerebral artery vasoconstriction and decreased cerebral blood flow occur early in an animal model of heart failure; these perturbations are reversed by interrupting TNF&agr;/S1P signaling. This signaling pathway may represent a potential therapeutic target to improve cognitive function in heart failure.

Sex differences in effects of dopamine D1 receptors on social withdrawal

Dopamine signaling in the nucleus accumbens (NAc) plays a critical role in the regulation of motivational states. Recent studies in male rodents show that social defeat stress increases the activity of ventral tegmental dopamine neurons projecting to the NAc, and that this increased activity is necessary for stress-induced social withdrawal. Domestic female mice are not similarly aggressive, which has hindered complementary studies in females. Using the monogamous California mouse (Peromyscus californicus), we found that social defeat increased total dopamine, DOPAC, and HVA content in the NAc in both males and females. These results are generally consistent with previous studies in Mus, and suggest defeat stress also increases NAc dopamine signaling in females. However, these results do not explain our previous observations that defeat stress induces social withdrawal in female but not male California mice. Pharmacological manipulations provided more insights. When 500 ng of the D1 agonist SKF38393 was infused in the NAc shell of females that were naïve to defeat, social interaction behavior was reduced. This same dose of SKF38393 had no effect in males, suggesting that D1 receptor activation is sufficient to induce social withdrawal in females but not males. Intra-accumbens infusion of the D1 antagonist SCH23390 increased social approach behavior in females exposed to defeat but not in females naïve to defeat. This result suggests that D1 receptors are necessary for defeat-induced social withdrawal. Overall, our results suggest that sex differences in molecular pathways that are regulated by D1 receptors contribute to sex differences in social withdrawal behavior.

Effects of Sertraline and Fluoxetine on P-Glycoprotein at Barrier Sites: In Vivo and In Vitro Approaches

Background and Purpose Retention of substances from systemic circulation in the brain and testes are limited due to high levels of P-glycoprotein (P-gp) in the luminal membranes of brain and testes capillary endothelial cells. From a clinical perspective, P-gp rapidly extrudes lipophilic therapeutic agents, which then fail to reach efficacious levels. Recent studies have demonstrated that acute administration of selective serotonin reuptake inhibitors (SSRI) can affect P-gp function, in vitro and in vivo. However, little is known concerning the time-course of these effects or the effects of different SSRI in vivo. Experimental Approach The P-gp substrate, tritiated digoxin ([3H] digoxin), was co-administered with fluoxetine or sertraline to determine if either compound increased drug accumulation within the brains and testes of mice due to inhibition of P-gp activity. We undertook parallel studies in endothelial cells derived from brain microvessels to determine the dose-response and time-course of effects. Key Results In vitro, sertraline resulted in rapid and potent inhibition of P-gp function in brain endothelial cells, as determined by cellular calcein accumulation. In vivo, a biphasic effect was demonstrated. Brain accumulation of [3H] digoxin was increased 5 minutes after treatment with sertraline, but by 60 minutes after sertraline treatment, brain accumulation of digoxin was reduced compared to control. By 240 minutes after sertraline treatment brain digoxin accumulation was elevated compared to control. A similar pattern of results was obtained in the testes. There was no significant effect of fluoxetine on P-gp function, in vitro or in vivo. Conclusions and Implications Acute sertraline administration can modulate P-gp activity in the blood-brain barrier and blood-testes barrier. This clearly has implications for the ability of therapeutic agents that are P-gp substrates, to enter the brain when co-administered with SSRI.

Hormones in infant rhesus monkeys' (Macaca mulatta) hair at birth provide a window into the fetal environment

Background:It is established that maternal parity can affect infant growth and risk for several disorders, but the prenatal endocrine milieu that contributes to these outcomes is still largely unknown. Recently, it has been shown that hormones deposited in hair can provide a retrospective reflection of hormone levels while the hair was growing. Taking advantage of this finding, our study utilized hair at birth to investigate if maternal parity affected fetal hormone exposure during late gestation.Methods:Hair was collected from primiparous and multiparous mother and infant monkeys at birth and used to determine steroid hormones embedded in hair while the infant was in utero. A high-pressure liquid chromatography–triple quadrupole mass spectrometry technique was refined, which enabled the simultaneous measurement of eight hormones.Results:Hormone concentrations were dramatically higher in neonatal compared to maternal hair, reflecting extended fetal exposure as the first hair was growing. Further, hair cortisone was higher in primiparous mothers and infants when compared to the multiparous dyads.Conclusion:This research demonstrates that infant hair can be used to track fetal hormone exposure and a panel of steroid hormones can be quantified from hair specimens. Given the utility in nonhuman primates, this approach can be translated to a clinical setting with human infants.

Neuroestradiol in the Stalk Median Eminence of Female Rhesus Macaques Decreases in Association With Puberty Onset

In primates, despite the fact that GnRH neurons are mature at birth, a gonadal steroid independent central inhibition restrains the initiation of puberty. The neural substrates responsible for this central inhibition, however, are unclear. In this study, we tested the hypothesis that neuroestradiol release in the hypothalamus decreases prior to the pubertal increase in GnRH release. We found that in female monkeys at the prepubertal stage, when GnRH release was low, estradiol (E2) levels in the stalk-median eminence of the hypothalamus were higher than those in older, early pubertal females in which nocturnal GnRH release begins to increase. Furthermore, estrone (E1) levels were higher in the stalk-median eminence of prepubertal and early pubertal monkeys compared with midpubertal monkeys, which have the highest GnRH release. The elevated E2 and E1 levels at the prepubertal stage are likely hypothalamic in origin because circulating E2 and E1 levels in prepubertal and early pubertal monkeys were much lower than those in midpubertal monkeys. Heightened synthesis and release of neuroestradiol during the prepubertal period and subsequent reduction at puberty onset indicate possible roles for neuroestradiol in central inhibition of GnRH release. The mechanism governing the reduction in neuroestradiol synthesis at puberty onset remains to be determined.

Hormone levels in neonatal hair reflect prior maternal stress exposure during pregnancy

Hormones present in hair provide summative information about endocrine activity while the hair was growing. Therefore, it can be collected from an infant after birth and still provide retrospective information about hormone exposure during prenatal development. We employed this approach to determine whether a delimited period of maternal stress during pregnancy affected the concentrations of glucocorticoids and gonadal hormones in the hair of neonatal rhesus monkeys. Hair from 22 infant monkeys exposed to 5 weeks of gestational disturbance was compared to specimens from 13 infants from undisturbed control pregnancies. Using an LC/MS/MS based technique, which permitted seven steroid hormones to be quantified simultaneously, we found 2 hormones were significantly different in infants from disturbed pregnancies. Cortisol and testosterone levels were lower in the hair of both male and female neonates. Maternal hair hormone levels collected on the same day after delivery no longer showed effects of the disturbance earlier during pregnancy. This study documents that a period of acute stress, lasting for 20% of gestation, has sustained effects on the hormones to which a developing fetus is exposed.