Elevated corticosterone and inhibition of ACTH responses to CRH and ether in the neonatal rat: effect of hypoxia from birth

Glucocorticoid Receptor Antagonist Alters Corticosterone and Receptor-sensitive mRNAs in the Hypoxic Neonatal Rat

Hypoxia, a common stressor with preterm birth, increases morbidity and mortality associated with prematurity. Glucocorticoids (GCs) are administered to the preterm infant to improve oxygenation; prolonged use of GCs remains controversial. We evaluated a selective glucocorticoid receptor (GR) antagonist (CORT113176) in our neonatal rat model of human prematurity to assess how fasting and hypoxia-induced increases in neonatal corticosterone affects endogenous hormones and endocrine pancreas function. Neonatal rat pups at postnatal day (PD) 2, PD8, and PD15 were pretreated with CORT113176 and, after 60 minutes of separation and fasting, exposed to hypoxia (8% O2) or control (normoxia) for 30 or 60 minutes while fasting was continued. Plasma corticosterone, ACTH, glucose, and insulin were measured and fasting Homeostatic Model Assessment of Insulin Resistance was calculated. Glucocorticoid and insulin receptor-sensitive gene mRNAs were analyzed in liver, muscle, and adipose to evaluate target tissue biomarkers. CORT113176 pretreatment augmented baseline and hypoxia-induced increases in corticosterone and attenuated hypoxia-induced increases in insulin resistance at PD2. Normoxic and hypoxic stress increased the hepatic GR-sensitive gene mRNAs, Gilz and Per1; this was eliminated by pretreatment with CORT113176. CORT113176 pretreatment decreased baseline insulin receptor-sensitive gene mRNAs Akt2, Irs1, Pik3r1, and Srebp1c at PD2. We show that CORT113176 variably augments the stress-induced increases in corticosterone concentrations (attenuation of negative feedback) and that GR is critical for hepatic responses to stress in the hypoxic neonate. We also propose that measurement of Gilz and Per1 mRNA expression may be useful to evaluate the effectiveness of GR antagonism.

Bidirectional Crosstalk Between Hypoxia Inducible Factors and Glucocorticoid Signalling in Health and Disease

Glucocorticoid-induced (GC) and hypoxia-induced transcriptional responses play an important role in tissue homeostasis and in the regulation of cellular responses to stress and inflammation. Evidence exists that there is an important crosstalk between both GC and hypoxia effects. Hypoxia is a pathophysiological condition to which cells respond quickly in order to prevent metabolic shutdown and death. The hypoxia inducible factors (HIFs) are the master regulators of oxygen homeostasis and are responsible for the ability of cells to cope with low oxygen levels. Maladaptive responses of HIFs contribute to a variety of pathological conditions including acute mountain sickness (AMS), inflammation and neonatal hypoxia-induced brain injury. Synthetic GCs which are analogous to the naturally occurring steroid hormones (cortisol in humans, corticosterone in rodents), have been used for decades as anti-inflammatory drugs for treating pathological conditions which are linked to hypoxia (i.e. asthma, ischemic injury). In this review, we investigate the crosstalk between the glucocorticoid receptor (GR), and HIFs. We discuss possible mechanisms by which GR and HIF influence one another, in vitro and in vivo, and the therapeutic effects of GCs on HIF-mediated diseases.

Systematic Review and Methodological Considerations for the Use of Single Prolonged Stress and Fear Extinction Retention in Rodents

Posttraumatic stress disorder (PTSD) is a mental health condition triggered by experiencing or witnessing a terrifying event that can lead to lifelong burden that increases mortality and adverse health outcomes. Yet, no new treatments have reached the market in two decades. Thus, screening potential interventions for PTSD is of high priority. Animal models often serve as a critical translational tool to bring new therapeutics from bench to bedside. However, the lack of concordance of some human clinical trial outcomes with preclinical animal efficacy findings has led to a questioning of the methods of how animal studies are conducted and translational validity established. Thus, we conducted a systematic review to determine methodological variability in studies that applied a prominent animal model of trauma-like stress, single prolonged stress (SPS). The SPS model has been utilized to evaluate a myriad of PTSD-relevant outcomes including extinction retention. Rodents exposed to SPS express an extinction retention deficit, a phenotype identified in humans with PTSD, in which fear memory is aberrantly retained after fear memory extinction. The current systematic review examines methodological variation across all phases of the SPS paradigm, as well as strategies for behavioral coding, data processing, statistical approach, and the depiction of data. Solutions for key challenges and sources of variation within these domains are discussed. In response to methodological variation in SPS studies, an expert panel was convened to generate methodological considerations to guide researchers in the application of SPS and the evaluation of extinction retention as a test for a PTSD-like phenotype. Many of these guidelines are applicable to all rodent paradigms developed to model trauma effects or learned fear processes relevant to PTSD, and not limited to SPS. Efforts toward optimizing preclinical model application are essential for enhancing the reproducibility and translational validity of preclinical findings, and should be conducted for all preclinical psychiatric research models.

Salivary alpha amylase and cortisol levels as stress biomarkers in children with cerebral palsy and their association with a physical therapy program

INTRODUCTION

Cerebral palsy (CP) is one of the main causes of physical disabilities in childhood. There is evidence that CP children display high levels of stress, which could interfere with learning processes and interpretation of relevant sensory information during motor skills acquisition and socialization.

OBJECTIVE

This study aims to compare basal levels of stress biomarkers (cortisol and alpha-amylase) of healthy children (HC) and children with CP, and to investigate whether a physical therapy session using the neurodevelopmental technique (NDT) interferes with these levels.

METHODS

A cross-sectional design was used. A total of 86 children (HC: n = 45 and CP: n = 41) with matching age, sex, socioeconomic status, and sampling time. Salivary cortisol and alpha-amylase levels were measured by means of electrochemiluminescence and spectrophotometry methods. A single saliva sample was collected in the HC group to determine basal levels. For CP group three samples were collected: a first sample was taken 20-30 min prior to the intervention, while two post-intervention samples were collected (5 and 20 min) to evaluate individual changes in salivary stress biomarkers.

RESULTS

Higher basal cortisol concentration was found in CP children when compared to HC group. Moreover, CP children showed a significant reduction in cortisol levels 20 min after NDT intervention. No significant differences were observed in alpha-amylase values.

CONCLUSION

Present results show that CP causes alteration in basal cortisol values at childhood and suggest that CP children respond to environmental regulatory factors such as NDT, in attempt to reduce stress.

A Long-Acting Neutralizing Monoclonal ACTH Antibody Blocks Corticosterone and Adrenal Gene Responses in Neonatal Rats

The control of steroidogenesis in the neonatal adrenal gland is of great clinical interest. We have previously demonstrated that the postnatal day (PD) 2 rat exhibits a large plasma corticosterone response to hypoxia in the absence of an increase in plasma ACTH measured by RIA, whereas the corticosterone response to exogenous ACTH is intact. By PD8, the corticosterone response to hypoxia is clearly ACTH-dependent. We hypothesized that this apparently ACTH-independent response to hypoxia in the newborn rat is due to an increase in a bioactive, nonimmunoassayable form of ACTH. To evaluate this phenomenon, we pretreated neonatal rats with a novel, specific, neutralizing anti-ACTH antibody (ALD1611) (20 mg/kg or 1 mg/kg IP) on the morning of PD1, PD7, and PD14. Twenty-four hours later, we measured hypoxia- or ACTH-stimulated plasma ACTH and corticosterone. For long-term effects, ALD1611 was given on PD1 and pups were studied on PD8 and PD15. Pretreatment with ALD1611 significantly decreased baseline corticosterone and completely blocked the corticosterone response to hypoxia and exogenous ACTH stimulation at all ages. The effect of 1 mg/kg ALD1611 on PD1 had dissipated by PD15. The decrease in corticosterone in ALD1611-treated pups was associated with decreases in baseline and hypoxia- and ACTH-stimulated adrenal Ldlr, Mrap, and Star mRNA expression at all ages. The adrenal response to hypoxia in the newborn rat is ACTH-dependent, suggesting the release of nonimmunoassayable, biologically active forms of ACTH. ALD1611 is useful as a tool to attenuate stress-induced, ACTH-dependent adrenal steroidogenesis in vivo.

Programming of the Adult HPA Axis After Neonatal Separation and Environmental Stress in Male and Female Rats

Maternal separation, hypoxia, and hypothermia are common stressors in the premature neonate. Using our rat model of human prematurity, we evaluated sexual dimorphisms in the long-term effects of these neonatal stressors on behavior of the hypothalamic-pituitary-adrenal (HPA) axis in adult rats. Neonatal rats were exposed daily on postnatal days 2 to 6 to maternal separation with normoxia, with hypoxia allowing spontaneous hypothermia, with hypothermia per se, and with hypoxia while maintaining isothermia with external heat. The major findings were that (a) prior maternal-neonatal separation during the first week of postnatal life attenuated the plasma ACTH and corticosterone response to restraint stress in adult male but not female rats, (b) prior neonatal hypothermia augmented the plasma ACTH and corticosterone response to restraint stress in adult male rats, but not female rats, and (c) changes in hypothalamic, pituitary, and adrenal mRNA expression did not account for most of these HPA axis effects. Most of the programming effects on adult HPA axis was attributed to prior maternal-neonatal separation alone (with normoxia) because the addition of hypoxia with spontaneous hypothermia, hypothermia per se, and hypoxia while preventing hypothermia during maternal-neonatal separation had minimal effects on the HPA axis. These results may inform strategies to prevent sexually dimorphic sequelae of neonatal stress including those due to medical interventions.

Sex-Specific Consequences of Neonatal Stress on Cardio-Respiratory Inhibition Following Laryngeal Stimulation in Rat Pups

The presence of liquid near the larynx of immature mammals triggers prolonged apneas with significant O2 desaturations and bradycardias. When excessive, this reflex (the laryngeal chemoreflex; LCR) can be fatal. Our understanding of the origins of abnormal LCR are limited; however, perinatal stress and male sex are risk factors for cardio-respiratory failure in infants. Because exposure to stress during early life has deleterious and sex-specific consequences on brain development it is plausible that respiratory reflexes are vulnerable to neuroendocrine dysfunction. To address this issue, we tested the hypothesis that neonatal maternal separation (NMS) is sufficient to exacerbate LCR-induced cardio-respiratory inhibition in anesthetized rat pups. Stressed pups were separated from their mother 3 h/d from postnatal days 3 to 12. At P14-P15, pups were instrumented to monitor breathing, O2 saturation (Spo2), and heart rate. The LCR was activated by water injections near the larynx (10 µl). LCR-induced apneas were longer in stressed pups than controls; O2 desaturations and bradycardias were more profound, especially in males. NMS increased the frequency and amplitude of spontaneous EPSCs (sEPSCs) in the dorsal motor nucleus of the vagus (DMNV) of males but not females. The positive relationship between corticosterone and testosterone observed in stressed pups (males only) suggests that disruption of neuroendocrine function by stress is key to sex-based differences in abnormal LCR. Because testosterone application onto medullary slices augments EPSC amplitude only in males, we propose that testosterone-mediated enhancement of synaptic connectivity within the DMNV contributes to the male bias in cardio-respiratory inhibition following LCR activation in stressed pups.

Stimulatory Effect of Intermittent Hypoxia on the Production of Corticosterone by Zona Fasciculata-Reticularis Cells in Rats

Hypoxia or intermittent hypoxia (IH) have known to alter both synthesis and secretion of hormones. However, the effect of IH on the production of adrenal cortical steroid hormones is still unclear. The aim of present study was to explore the mechanism involved in the effect of IH on the production of corticosterone by rat ZFR cells. Male rats were exposed at 12% O₂ and 88% N₂ (8 hours per day) for 1, 2, or 4 days. The ZFR cells were incubated at 37 °C for 1 hour with or without ACTH, 8-Br-cAMP, calcium ion channel blockers, or steroidogenic precursors. The concentration of plasma corticosterone was increased time-dependently by administration of IH hypoxia. The basal levels of corticosterone production in cells were higher in the IH groups than in normoxic group. IH resulted in a time-dependent increase of corticosterone production in response to ACTH, 8-Br-cAMP, progesterone and deoxycorticosterone. The production of pregnenolone in response to 25-OH-C and that of progesterone in response to pregnenolone in ZFR cells were enhanced by 4-day IH. These results suggest that IH in rats increases the secretion of corticosterone via a mechanism at least in part associated with the activation of cAMP pathway and steroidogenic enzymes.

Effect of Novel Melanocortin Type 2 Receptor Antagonists on the Corticosterone Response to ACTH in the Neonatal Rat Adrenal Gland In Vivo and In Vitro

Stress-induced increases in neonatal corticosterone demonstrate a unique shift from ACTH independence to ACTH dependence between postnatal day 2 (PD2) and day 8 (PD8) in newborn rats. This shift could be due to the binding of a bioactive, non--immunoreactive plasma ligand to the adrenocortical melanocortin 2 receptor (MC2R) (ACTH receptor). A potent MC2R antagonist would be useful to evaluate this phenomenon in the neonate. Therefore, we investigated the acute corticosterone response to ACTH(1-39) injection in rat pups pretreated with newly developed MC2R antagonists (GPS1573 and GPS1574), which have not been tested in vivo. The doses used in vivo were based on their in vitro potency, with GP1573 being more potent than GPS1574. GPS1573 (PD2 and PD8), GPS1574 (PD2 only), or vehicle were injected intraperitoneally (ip) 10 min before baseline sampling. Then, 0.001 mg/kg of ACTH(1-39) was injected ip, and subsequent blood samples obtained for the measurement of plasma corticosterone. Pretreatment of PD2 pups with GPS1573 demonstrated augmentation, rather than inhibition, of the corticosterone response to ACTH. In PD8 pups, pretreatment with 0.1 mg/kg GPS1573, but not 4 mg/kg, augmented the corticosterone response to ACTH. Pretreatment with GPS1574 attenuated the plasma corticosterone response to ACTH at 30 min in PD2 pups. The activity of these two compounds in vivo do not match their potency in vitro, with GPS1573 leading to a small augmentation of the corticosterone response to ACTH in vivo while GPS1574 resulted in inhibition.

Adrenocortical sensitivity to ACTH in neonatal rats: correlation of corticosterone responses and adrenal cAMP content

A coordinated hypothalamic-pituitary-adrenal axis response is important for the survival of newborns during stress. We have previously shown that prior to postnatal day (PD) 5, neonatal rats exposed to hypoxia (one of the most common stressors effecting premature neonates) exhibit a large corticosterone response with a minimal increase in immunoassayable plasma ACTH and without a detectable increase in adrenal cAMP content (the critical second messenger). To explore the phenomenon of ACTH-stimulated steroidogenesis in the neonate, we investigated the adrenal response to exogenous ACTH in the normoxic neonatal rat. Rat pups at PD2 and PD8 were injected intraperitoneally with porcine ACTH at low, moderate, or high doses (1, 4, or 20 μg/kg body wt). Trunk blood and whole adrenal glands were collected at baseline (before injection) and 15, 30, or 60 min after the injection. ACTH stimulated corticosterone release in PD2 and PD8 pups. In PD2 pups, plasma corticosterone at baseline and during the response to ACTH injection was greater than values measured in PD8 pups, despite lower adrenal cAMP content in PD2 pups. Specifically, the low and moderate physiological ACTH doses produced a large corticosterone response in PD2 pups without a change in adrenal cAMP content. At extremely high, pharmacological levels of plasma ACTH in PD2 pups (exceeding 3,000 pg/ml), an increase in adrenal cAMP was measured. We conclude that physiological increases in plasma ACTH may stimulate adrenal steroidogenesis in PD2 pups through a non-cAMP-mediated pathway.

Adrenocortical control in the neonatal rat: ACTH- and cAMP-independent corticosterone production during hypoxia

We have previously demonstrated that the neonatal corticosterone response to acute hypoxia shifts from ACTH independence to ACTH dependence between postnatal days two (PD2) and eight (PD8). Cyclic AMP (cAMP) is the obligatory intracellular second messenger of ACTH action, and we hypothesized that corticosterone production in neonatal rats shifts from a cAMP-independent mechanism to cAMP-dependent mechanism between PD2 and PD8. Plasma ACTH and corticosterone and adrenal cAMP and cGMP responses to acute severe hypoxia (8% O₂ for 5, 10, 20, 30, and 180 min) were measured in neonatal rats at PD2, PD8, and PD15. Plasma ACTH and corticosterone were measured by radioimmunoassay, and adrenal cAMP and cGMP were measured by ELISA. Plasma corticosterone-binding globulin (CBG) was measured in normoxic pups by ELISA. The largest corticosterone response was observed in PD2 pups, despite only a small increase in plasma ACTH that was not sustained. The PD2 ACTH-independent increase in corticosterone occurred with no change in adrenal cAMP or cGMP content. Plasma CBG concentration was lowest in PD2 pups. Large corticosterone responses were measured during the first 30 min of hypoxia. Differences in corticosterone responses between PD2 and PD8 pups cannot be attributed to changes in plasma protein binding capacity, and the PD2 corticosterone response is consistent with a nongenomic mechanism of action. We conclude that the sustained corticosterone response to hypoxia in PD2 pups occurs with small and transient ACTH responses and independently of increases in adrenal cAMP or cGMP.

Circadian rhythm of salivary cortisol in infants with congenital heart disease

Children with congenital heart disease (CHD) have associated extracardiac co-morbidities at the time of surgery and during ongoing growth and development. Perioperative events include disrupted glucose homeostasis, capillary leak, and fluid retention. The hypothalamic-pituitary-adrenal (HPA) axis has an important role in homeostasis in that the secretion of cortisol contributes to the response to stress, glucose regulation, blood volume control, and immune regulation. We investigated the diurnal rhythm of the HPA axis in infants with CHD by measuring salivary cortisol in the morning (0600-0900 h-circadian peak) and evening (2100-2400 h-circadian nadir). Twenty-nine infants aged 12 weeks to 1 year were included: 16 with acyanotic disease (SpO₂ ≥ 90 %) and 13 with cyanotic disease (SpO2 < 90 %). Morning salivary cortisol was similar between the two groups [acyanotic 7.0 nmol/L (1.8-23.1); cyanotic 9.7 nmol/L (0.9-15.6); p = 0.68]. Evening salivary cortisol was similar between the two groups [acyanotic 0.9 nmol/L (0.2-8.5); cyanotic 1.4 nmol/L (0.5-14.9); p = 0.32]. Both cyanotic and acyanotic groups demonstrated an intact diurnal rhythm. In conclusion, chronic hypoxia secondary to cyanotic CHD does not affect the circadian rhythm of the HPA axis. By 12 weeks of age, infants with hypoxia secondary to cyanotic CHD have a normal cortisol diurnal rhythm.

Adrenocorticotropic hormone and corticosterone responses to acute hypoxia in the neonatal rat: effects of body temperature maintenance

The corticosterone response to acute hypoxia in neonatal rats develops in the 1st wk of life, with a shift from ACTH independence to ACTH dependence. Acute hypoxia also leads to hypothermia, which may be protective. There is little information about the endocrine effects of body temperature maintenance during periods of neonatal hypoxia. We hypothesized that prevention of hypothermia during neonatal hypoxia would augment the adrenocortical stress response. Rat pups separated from their dams were studied at postnatal days 2 and 8 ( PD2 and PD8). In one group of pups, body temperature was allowed to spontaneously decrease during a 30-min prehypoxia period. Pups were then exposed to 8% O2 for 3 h and allowed to become spontaneously hypothermic or externally warmed (via servo-controlled heat) to maintain isothermia. In another group, external warming was used to maintain isothermia during the prehypoxia period, and then hypoxia with or without isothermia was applied. Plasma ACTH and corticosterone and mRNA expression of genes for upstream proteins involved in the steroidogenic pathway were measured. Maintenance of isothermia during the prehypoxia period increased baseline plasma ACTH at both ages. Hypothermic hypoxia caused an increase in plasma corticosterone; this response was augmented by isothermia at PD2, when the response was ACTH-independent, and at PD8, when the response was ACTH-dependent. In PD8 rats, isothermia also augmented the plasma ACTH response to hypoxia. We conclude that maintenance of isothermia augments the adrenocortical response to acute hypoxia in the neonate. Prevention of hypothermia may increase the stress response during neonatal hypoxia, becoming more pronounced with increased age.

Adenosine A1 receptor mediated suppression of adrenal activity in near-term fetal sheep

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is a critical response to perinatal hypoxia. Recent data show that adenosine appears to inhibit baseline levels of fetal cortisol and to restrict the increase in ACTH and cortisol during moderate hypoxia. Because adenosine increases substantially during profound asphyxia, it is possible, but untested, that counterintuitively it might restrict the HPA response to more severe insults. It is unclear which receptors mediate the effects of adenosine on the HPA axis; however, adenosine A1 receptor activation is important for adaptation to hypoxia. We therefore investigated whether adenosine A1 receptor blockade modulates ACTH and cortisol levels in fetal sheep at 118 to 126 days gestation, randomly allocated to receive an intravenous infusion of either vehicle (vehicle-occlusion, n = 7) or 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, an A1 receptor antagonist, DPCPX-occlusion, n = 7) infused 60 min before and during 10 min of umbilical cord occlusion, or infusion of DPCPX for 70 min without occlusion (DPCPX-sham, n = 6). Experiments were terminated after 72 h. Fetal ACTH levels increased significantly ( P < 0.01) during occlusion, but not sham occlusion, and returned to baseline values by 60 min after occlusion. In the vehicle-occlusion group, fetal cortisol and cortisone plasma levels increased significantly ( P < 0.05) 60 min after the occlusion and returned to baseline values by 24 h. In contrast, there was a marked increase in both fetal cortisol and cortisone during DPCPX infusion before occlusion to a level greater even than the maximum rise seen after occlusion alone. This increase was sustained after occlusion, with increased cortisol levels compared with occlusion alone up to 72 h. In conclusion, fetal cortisol concentrations are suppressed by adenosine A1 receptor activity, largely though a direct adrenal mechanism. This suppression can be partially overcome by supraphysiological stimuli such as asphyxia.

Development of the ACTH and corticosterone response to acute hypoxia in the neonatal rat

Acute episodes of severe hypoxia are among the most common stressors in neonates. An understanding of the development of the physiological response to acute hypoxia will help improve clinical interventions. The present study measured ACTH and corticosterone responses to acute, severe hypoxia (8% inspired O(2) for 4 h) in neonatal rats at postnatal days (PD) 2, 5, and 8. Expression of specific hypothalamic, anterior pituitary, and adrenocortical mRNAs was assessed by real-time PCR, and expression of specific proteins in isolated adrenal mitochondria from adrenal zona fascisulata/reticularis was assessed by immunoblot analyses. Oxygen saturation, heart rate, and body temperature were also measured. Exposure to 8% O(2) for as little as 1 h elicited an increase in plasma corticosterone in all age groups studied, with PD2 pups showing the greatest response ( approximately 3 times greater than PD8 pups). Interestingly, the ACTH response to hypoxia was absent in PD2 pups, while plasma ACTH nearly tripled in PD8 pups. Analysis of adrenal mRNA expression revealed a hypoxia-induced increase in Ldlr mRNA at PD2, while both Ldlr and Star mRNA were increased at PD8. Acute hypoxia decreased arterial O(2) saturation (SPo(2)) to approximately 80% and also decreased body temperature by 5-6 degrees C. The hypoxic thermal response may contribute to the ACTH and corticosterone response to decreases in oxygen. The present data describe a developmentally regulated, differential corticosterone response to acute hypoxia, shifting from ACTH independence in early life (PD2) to ACTH dependence less than 1 wk later (PD8).

Epidermal growth factor and parathyroid hormone-related peptide mRNA in the mammary gland and their concentrations in milk: effects of postpartum hypoxia in lactating rats

The physiological adaptations of the neonatal rat to hypoxia from birth include changes in gastrointestinal function and intermediary metabolism. We hypothesized that the hypoxic lactating dam would exhibit alterations in mammary gland function leading to changes in the concentration of milk peptides that are important in neonatal gastrointestinal development. The present study assessed the effects of chronic hypoxia on peptides produced by the mammary glands and present in milk. Chronic hypoxia decreased the concentration of epidermal growth factor (EGF) in expressed milk and pup stomach contents and decreased maternal mammary gland EGF mRNA. The concentration of parathyroid hormone-related protein (PTHrp) was unchanged in milk and decreased in pup stomach contents; however, mammary PTHLH mRNA was increased by hypoxia. There was a significant increase in adiponectin concentrations in milk from hypoxic dams. Chronic hypoxia decreased maternal body weight, and pair feeding normoxic dams an amount of food equivalent to hypoxic dam food intake decreased body weight to an equivalent degree. Decreased food intake did not affect the expression of EGF, PTHLH, or LEP mRNA in mammary tissue. The results indicated that chronic hypoxia modulated mammary function independently of hypoxia-induced decreases in maternal food intake. Decreased EGF and increased adiponectin concentrations in milk from hypoxic dams likely affect the development of neonatal intestinal function.

Seasonal changes in testosterone and corticosterone levels in four social classes of a desert dwelling sociable rodent

Animals have to adjust their physiology to seasonal changes, in response to variation in food availability, social tactics and reproduction. I compared basal corticosterone and testosterone levels in free ranging striped mouse from a desert habitat, comparing between the sexes, breeding and philopatric non-breeding individuals, and between the breeding and the non-breeding season. I expected differences between breeders and non-breeders and between seasons with high and low food availability. Basal serum corticosterone was measured from 132 different individuals and serum testosterone from 176 different individuals of free living striped mice. Corticosterone and testosterone levels were independent of age, body weight and not influenced by carrying a transmitter. The levels of corticosterone and testosterone declined by approximately 50% from the breeding to the non-breeding season in breeding females as well as non-breeding males and females. In contrast, breeding males showed much lower corticosterone levels during the breeding season than all other classes, and were the only class that showed an increase of corticosterone from the breeding to the non-breeding season. As a result, breeding males had similar corticosterone levels as other social classes during the non-breeding season. During the breeding season, breeding males had much higher testosterone levels than other classes, which decreased significantly from the breeding to the non-breeding season. My results support the prediction that corticosterone decreases during periods of low food abundance. Variation in the pattern of hormonal secretion in striped mice might assist them to cope with seasonal changes in energy demand in a desert habitat.

Augmented hypothalamic corticotrophin-releasing hormone mRNA and corticosterone responses to stress in adult rats exposed to perinatal hypoxia

Stressful events before or just after parturition alter the subsequent phenotypical response to stress in a general process termed programming. Hypoxia during the period before and during parturition, and in the postnatal period, is one of the most common causes of perinatal distress, morbidity, and mortality. We have found that perinatal hypoxia (prenatal day 19 to postnatal day 14) augmented the corticosterone response to stress and increased basal corticotrophin-releasing hormone (CRH) mRNA levels in the parvocellular portion of the paraventricular nucleus (PVN) in 6-month-old rats. There was no effect on the levels of hypothalamic parvocellular PVN vasopressin mRNA, anterior pituitary pro-opiomelanocortin or CRH receptor-1 mRNA, or hippocampus glucocorticoid receptor mRNA. We conclude that hypoxia spanning the period just before and for several weeks after parturition programmes the hypothalamic-pituitary-adrenal axis to hyper-respond to acute stress in adulthood, probably as a result of drive from the parvocellular CRH neurones.

Glucocorticoid feedback control of corticotropin in the hypoxic neonatal rat

The objective of this study was to determine the effects of manipulating glucocorticoid negative feedback on acute ACTH and corticosterone responses to corticotropin-releasing hormone (CRH) injection in 7-day-old rats exposed to normoxia or hypoxia from birth. Chemical adrenalectomy was achieved with aminoglutethimide, and glucocorticoids were replaced with a low dose of dexamethasone. Hypoxia per se increased basal plasma corticosterone and attenuated the plasma ACTH response to CRH. Aminoglutethimide per se decreased plasma corticosterone and strongly increased basal plasma ACTH and anterior pituitary POMC gene expression. Dexamethasone partially attenuated elevations in basal plasma ACTH due to aminoglutethimide in both normoxic and hypoxic pups, but inhibited anterior pituitary POMC expression and CRH-induced plasma ACTH only in hypoxic pups. Despite this inhibition, hypoxic pups treated with both dexamethasone and aminoglutethimide still exhibited a significant CRH-induced increment in plasma ACTH, which was lacking in hypoxic pups not treated with either dexamethasone or aminoglutethimide. We conclude that ACTH responses to acute stimuli in hypoxic neonatal rats are prevented by ACTH-independent increases in corticosterone, rather than by intrinsic hypothalamic-pituitary hypoactivity.

Animal models concerning the role of dopamine in attention-deficit hyperactivity disorder

Several models of attention-deficit hyperactivity disorder (ADHD) have been proposed, ranging from administration of neurotoxins to genetically manipulated models. These models are used to gain insight into ADHD as a disorder and assist in the discovery of new therapeutic strategies. However, the information gained from these models differs, depending to a large extent on the validity (or otherwise) of the model. Thus the insights gained from these models with respect to the pathophysiology and aetiology of ADHD remains inconclusive. No animal model resembles the clinical situation of ADHD perfectly but good animal models of ADHD should mimic its characteristics, confirm to an underlying theory of ADHD and ultimately make predictions of future therapies. While the involvement of dopamine (DA) in ADHD has been established, the evaluation of rodent models of ADHD particularly with respect to dopaminergic systems is attempted here. It is concluded that the neonatal 6-hydroxy-dopamine lesioned rat and DA transporter knockout/knockdown mice have the highest degree of validity for ADHD.

Neonatal novelty exposure ameliorates anoxia-induced hyperactivity in the open field

We investigated in an animal model of neonatal anoxia whether effects of oxygen deprivation on emotional reactivity can be reversed by neonatal novelty exposure, a behavioral method, involving daily 3min away from the home cage for the first 3 weeks of life. Male neonates were exposed to either 100% N2 gas (Anoxia) or room air (Control) for 25min on postnatal day 1. Within each of the two treatment conditions, one-half of the neonates were further individually exposed to relatively novel non-home cages for 3min daily during postnatal days 2-21 (Novel: NAnoxia=20; NControl=16), while the other half remained in the home cage (Home: NAnoxia=19; NControl=19). Emotional reactivity to an open field was evaluated on postnatal day 25 during four 20-s trials. Among home rats, temporal patterns of open-field activity across multiple trials and initial-trial activity significantly differed between the Anoxia and Control rats. In contrast, these differences were eliminated among the Novel rats. These results show that neonatal novelty exposure, an early-stimulation method that has recently been shown to enhance spatial and social memory, adaptive control of stress response, and hippocampal synaptic plasticity, can also eliminate neonatal anoxia-induced changes in emotional reactivity. These findings suggest that brief and repeated, but mild, changes in the postnatal environment may serve to counteract some of the aversive effects induced by neonatal trauma associated with oxygen deprivation.

Plasma leptin and ghrelin in the neonatal rat: interaction of dexamethasone and hypoxia

Ghrelin, leptin, and endogenous glucocorticoids play a role in appetite regulation, energy balance, and growth. The present study assessed the effects of dexamethasone (DEX) on these hormones, and on ACTH and pituitary proopiomelanocortin (POMC) and corticotropin-releasing hormone receptor-1 (CRHR1) mRNA expression, during a common metabolic stress - neonatal hypoxia. Newborn rats were raised in room air (21% O2) or under normobaric hypoxia (12% O2) from birth to postnatal day (PD) 7. DEX was administered on PD3 (0.5 mg/kg), PD4 (0.25 mg/kg), PD5 (0.125 mg/kg), and PD6 (0.05 mg/kg). Pups were studied on PD7 (24 h after the last dose of DEX). DEX significantly increased plasma leptin and ghrelin in normoxic pups, but only increased ghrelin in hypoxic pups. Hypoxia alone resulted in a small increase in plasma leptin. Plasma corticosterone and pituitary POMC mRNA expression were decreased 24 h following the last dose of DEX, whereas plasma ACTH and pituitary CRHR1 mRNA expression had already increased (normoxia and hypoxia). Hypoxia alone increased corticosterone, but had no effect on ACTH or pituitary POMC and CRHR1 mRNA expression. Neonatal DEX treatment, hypoxia, and the combination of both affect hormones involved in energy homeostasis. Pituitary function in the neonate was quickly restored following DEX-induced suppression of the hypothalamic-pituitary-adrenal axis. The changes in ghrelin, leptin, and corticosterone may be beneficial to the hypoxic neonate through the maintenance of appetite and shifts in intermediary metabolism.

Corticosterone secretion induced by chronic isolation in neonatal rats is sexually dimorphic and accompanied by elevated ACTH

Rat pups repeatedly subjected to brief periods of isolation during the stress hyporesponsive period (SHRP) exhibit varied neuroendocrine and behavioral changes as neonates and as adults. For example, neonatal rats exhibit increased circulating corticosterone after 1-h isolation on postnatal day 9 (P9) only if they were isolated daily from P2 to P8 [McCormick, C.M., Kehoe, P., Kovacs, S., 1998. Corticosterone release in response to repeated, short episodes of neonatal isolation: evidence of sensitization. Int. J. Dev. Neurosci. 16, 175-185]. It is not known if the increase in adrenocortical response on P9 following repeated isolation is mediated by increased pituitary ACTH secretion. The present study examined the responsivity of the hypothalamic-pituitary-adrenal (HPA) axis during the SHRP following brief, repeated isolation or acute pharmacological manipulation. Removal from the nest for 1 h daily on P4-8 increased circulating corticosterone after 1-h isolation on P9 by approximately twofold. Neither unhandled nor handled controls showed a corticosterone response to 1-h isolation on P9. The increased corticosterone was sexually dimorphic, with only females showing the sensitization response. Other findings suggest that the hormonal response is centrally mediated; chronically isolated pups of both sexes exhibit increased plasma ACTH following 1-h isolation on P9. While we could not detect an increase in Fos immunoreactivity (IR) on P9 in the hypothalamic paraventricular nucleus (PVN) of chronically isolated pups, acute pharmacological activation of serotonin 2A/2C receptors produced robust activation of ACTH and corticosterone secretion as well as expression of Fos in the PVN on P9. We conclude that chronic isolation stress limited to the SHRP stimulates the neonatal HPA axis, and that the adrenal response is sexually dimorphic. In addition, PVN neurons can express Fos IR on P9 in response to a very potent activation of the HPA axis.

Basal and adrenocorticotropin-stimulated corticosterone in the neonatal rat exposed to hypoxia from birth: modulation by chemical sympathectomy

We previously demonstrated that 7-d-old rat pups exposed to hypoxia from birth exhibit ACTH-independent increases in corticosterone associated with an increase in steroidogenic acute regulatory (StAR) and peripheral-type benzodiazepine receptor (PBR) proteins. The purpose of the present study was to determine whether this increase in corticosterone could be attenuated by chemical sympathectomy induced with guanethidine treatment. Rat pups were exposed to normoxia or hypoxia from birth and treated with vehicle or guanethidine and studied at 7 d of age. Hypoxia per se resulted in an increase in plasma corticosterone without a change in plasma ACTH. Guanethidine treatment attenuated the increase in basal corticosterone in hypoxic pups but did not attenuate ACTH-stimulated corticosterone production. This effect was specific as basal and ACTH-stimulated aldosterone was not affected. Guanethidine also attenuated the increase in StAR protein induced by hypoxia. Neither the effect of hypoxia nor that of guanethidine could be explained by changes in the levels of adrenal tyrosine hydroxylase, StAR, or P450scc mRNA, adrenal tyrosine hydroxylase immunohistochemistry, or adrenal catecholamine content. We conclude that chemical sympathectomy normalizes basal corticosterone levels but has no effect on ACTH-stimulated corticosterone levels in 7-d-old rats exposed to hypoxia from birth. The mechanism of the effect of guanethidine to normalize hypoxia-stimulated basal corticosterone remains to be identified, although StAR protein may be an important mediator. This ACTH-independent increase in corticosterone may be a mechanism by which the neonate can increase circulating glucocorticoids necessary for survival while bypassing the hyporesponsiveness of the neonatal hypothalamic-pituitary-adrenal axis.