Glucocorticoids regulate the development of intracellular signaling: enhanced forebrain adenylate cyclase catalytic subunit activity after fetal dexamethasone exposure

Prenatal synthetic glucocorticoid exposure alters hypothalamic-pituitary-adrenal regulation and pregnancy outcomes in mature female guinea pigs

Preterm delivery occurs in approximately 10% of all pregnancies. Prenatal exposure to synthetic glucocorticoids (sGCs) reduces the incidence of respiratory distress syndrome (RDS) in these babies. Therefore, administration of multiple courses of sGCs became common practice. Animal and human studies have demonstrated that multiple courses of sGCs can have long-term effects. While the majority of animal studies have been undertaken in male offspring, it is emerging that there are profound sex differences in the consequences of prenatal sGC exposure. To our knowledge, no studies have determined the effects of prenatal sGC exposure on hypothalamic-pituitary-adrenal (HPA) axis function in female offspring while accounting for reproductive cycle status, or determined if there are effects on pregnancy parameters. Pregnant guinea pigs were administered three courses of betamethasone (Beta), dexamethasone (Dex) or vehicle on gestational days 40/41, 50/51 and 60/61. In adulthood (age range: postnatal days 126-165), basal and activated HPA axis function were assessed at various stages of the reproductive cycle. The female offspring were then mated and underwent an undisturbed pregnancy. Females were killed in the luteal phase of the reproductive cycle following litter weaning, and molecular analysis undertaken. In the luteal phase, Beta-exposed females exhibited significantly lower basal salivary cortisol levels (P < 0.05). Dex-exposed females also exhibited significantly lower basal salivary cortisol levels during the luteal phase (P < 0.05), but increased basal salivary cortisol levels during the ostrous phase (P < 0.01). The Beta-exposed females exhibited increased glucocorticoid receptor (GR) mRNA expression in the CA1/2 region of the hippocampus (P < 0.05) and MC2R mRNA in the adrenal cortex (P < 0.05). The Dex-exposed animals exhibited higher hippocampal GR and mineralocorticoid receptor (MR) mRNA levels (P < 0.05). Beta-exposed females showed reduced fecundity (P < 0.05). In Dex-exposed females there was a lower male to female sex ratio. In conclusion, prenatal sGC exposure affects HPA axis activity, in a cycle-dependent manner, and long-term reproductive success. The clinical implications of the findings on endocrine function and pregnancy in females are profound and further follow-up is warranted in human cohorts. Furthermore, we have shown there are considerable difference in phenotypes between the Beta- and Dex-exposed females and the specific endocrine and maternal outcome is contingent on the specific sGCs administered during pregnancy.

Postnatal behavioral and physiological responses of piglets from gilts housed individually or in groups during gestation

Gestational housing of sows remains a controversial issue that may affect the well-being of both sows and piglets. Therefore, 2 types of gestational housing were used to evaluate the stress imposed on pregnant gilts by each system and the effects on the offspring by comparing production, physiology, and behavioral measures of the piglets. Forty-eight Landrace x Yorkshire gilts were randomly assigned to groups (G) of 4 per pen (n = 8 pens; 3.9 m x 2.4 m) or to individual stalls (S; n = 16 stalls; 2.21 m x 0.61 m). Gilts were moved into individual farrowing crates 5 d before the expected farrowing date. Piglets were weighed at birth, d 14, and d 35. Two barrows from each litter were weaned at d 14 (early weaning) and housed together in pens. Maintenance behaviors (head in feeder, drinking, lying, eating mash) were videotaped and observed for the first 3 d after weaning using a 10-min interval scan sampling. Belly nosing and play/fight interactions were recorded from video observations for 3 d postweaning. An isolation test (30-min duration) was performed on one piglet from each pen of barrows on d 35. Time spent lying, the number of jumps against test box walls, and grunts and squeals were recorded in real time. Salivary cortisol was collected at 30-min intervals from baseline, and 0, 30, 60, and 90 min posttest. Jugular blood was collected from 2 barrows from each litter on d 1, 7, 14, 17, 21, and 28. Plasma TNF-alpha was analyzed by ELISA, and haptoglobin, alpha1-acid glycoprotein, and immunoglobulin G were analyzed by radial immunodiffusion. More piglets from the S treatment needed to be fed a liquid feed at weaning and drank more frequently on d 2 postweaning (P < 0.05). Additionally, by d 35 piglets from S gilts had a lighter BW (10.3 kg) than G piglets (12.8 kg; P < 0.01). Piglets from S gilts also grunted more during the 30-min isolation test (number of grunts = 356) than G piglets (number of grunts = 138; P < 0.01). Salivary cortisol and immune measures were not different. These data show some behavioral and production differences between piglets from individually stalled gilts and group-housed gilts. Therefore, there may be production advantages to housing first parity gilts in groups.

Inhibition of 11beta-hydroxysteroid dehydrogenase, the foeto-placental barrier to maternal glucocorticoids, permanently programs amygdala GR mRNA expression and anxiety-like behaviour in the offspring

Glucocorticoids may underlie the association between prenatal stress, low birth weight and adult stress-associated disorders, e.g. hypertension and type 2 diabetes, increased hypothalamic-pituitary-adrenal (HPA) activity and affective dysfunction. Normally, 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) rapidly inactivates glucocorticoids in placenta and many foetal tissues, thus acting as a 'barrier' to maternal steroids. We investigated the effect of inhibiting foeto-placental 11beta-HSD in rats, using carbenoxolone (CBX), on subsequent HPA activity and regulation and stress-induced behaviour in adult offspring. Pregnant Wistar rats were injected with CBX (12.5 mg s.c.) or vehicle daily throughout pregnancy. CBX treatment reduced birth weight. Adult offspring of CBX-treated dams had persistently reduced body weight, increased basal corticosterone (CORT) levels, increased corticotropin-releasing hormone (CRH) and reduced glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus, though hippocampal GR and mineralocorticoid receptor (MR) mRNA expression were unaltered. In addition, these animals showed less grooming and rearing in an open field and reduced immobility in a forced swim test, and had increased GR mRNA expression in the basolateral (BLA), central (CEA) and medial (MEA) nuclei of the amygdala, with unaltered MR mRNA. These data suggest that disturbance of the foeto-placental enzymatic barrier to maternal glucocorticoids reduces birth and body weight, and produces permanent alterations of the HPA axis and anxiety-like behaviour in aversive situations. The behavioural and HPA effects may reflect GR gene programming in amygdala and hypothalamus, respectively. Foetal overexposure to endogenous glucocorticoids (prenatal stress or reduced activity of foeto-placental 11beta-HSD) may represent a common link between the prenatal environment, foetal growth and adult neuroendocrine and affective disorders.

Glucocorticoid administration alters nuclear transcription factors in fetal rat brain: implications for the use of antenatal steroids

A recent Consensus Conference endorsed antenatal steroid use in prematurity, but indicated the need for future work on molecular and cellular effects on the developing brain. In the current study, pregnant rats were given dexamethasone during late gestation, in doses spanning those recommended for use, and effects on nuclear transcription factors were evaluated. Within the first hour after a single dose of dexamethasone, and intensifying over 4 h, marked induction of brain c-fos was seen. With repeated administration, c-fos became suppressed in some brain regions, but remained elevated in others. Dexamethasone also elicited suppression of the AP-1 family of nuclear binding proteins, but with a slower time course than seen for c-fos induction. The magnitude of the effects of late gestational exposure to dexamethasone on these transcription factors was comparable to those seen when repeated doses were administered to midgestation embryos in the context of dysmorphogenesis. Similarly, the effects on brain c-fos expression were substantially greater than those in the liver, an archetypal glucocorticoid target tissue. These results indicate that even a single, low dose of glucocorticoids used in late gestation, can disrupt the transcription factors that regulate brain cell differentiation.

Convergent control of serotonin transporter expression by glucocorticoids and cocaine in fetal and neonatal rat brain

Serotonin plays a trophic role in brain cell differentiation. In this study, expression of the serotonin presynaptic transporter protein, which regulates the extracellular serotonin concentration, was measured with [3H]paroxetine in rats exposed to dexamethasone or cocaine prenatally. Within 24 h of a single dose of dexamethasone, significant increases were seen in fetal brain, and the effect persisted into the postnatal period. Chronic prenatal cocaine exposure elicited similar changes. These data indicate that exposures to apparently disparate drugs can elicit similar endpoints that may lead to behavioral teratogenesis.

Programming of brainstem serotonin transporter development by prenatal glucocorticoids

Prenatal stress or exposure to excess glucocorticoids are known to alter central nervous system function and to result in lasting changes in reactions to stress. The potential involvement of specific elements of brainstem serotonergic neurons was examined in the current study. Pregnant rats were given 0.05, 0.2 or 0.8 mg/kg of dexamethasone on gestational days 17, 18 and 19, and the effects on development of the serotonin presynaptic transporter were assessed from birth to young adulthood by measurement of [3H]paroxetine binding to membrane preparations. Dexamethasone produced a dose-dependent retardation of body and brainstem growth but evoked a significant elevation of [3H]paroxetine binding that persisted into adulthood. Effects on [3H]paroxetine binding were robust even at the lowest dose, which did not suppress growth, indicating that the programming of this transporter is more sensitive to glucocorticoids than is general development. At the highest dose, promotional effects on serotonin transporter expression were offset by impaired growth, so that the peak effect was seen at the intermediate dose of dexamethasone. There were no comparable effects on serotonin transmitter levels, indicating selectivity toward promotion of transporter expression as distinct from simply increasing the number of serotonergic nerve terminals or all nerve terminal components. As the effect of prenatal dexamethasone treatment on the serotonin transporter is more persistent than those on other monoamine transporters, and is not shared by postnatal treatment or by treatment in adulthood, it likely represents specific programming by glucocorticoids during the prenatal period. Aberrant serotonergic transporter expression may contribute to alterations of synaptic function that ultimately produce the physiological abnormalities seen after prenatal stress or glucocorticoid treatment.

Atypical regulation of hepatic adenylyl cyclase and adrenergic receptors during a critical developmental period: agonists evoke supersensitivity accompanied by failure of receptor down-regulation

Ordinarily, beta-adrenergic receptors and responses linked to the receptors increase with development but in the liver, beta-receptors are higher in the fetus and neonate than in adulthood. We examined how hepatic beta-receptor signaling mediated through adenylyl cyclase is regulated in rats of different ages. In each case, animals were pretreated with isoproterenol for 4 d, and on the 5th d, hepatic membrane preparations were examined for adenylyl cyclase activity and receptor binding capabilities. Uniquely in 6-d-old animals, the cyclase response to isoproterenol was enhanced by chronic pretreatment, caused by heterologous sensitization mediated through effects on total catalytic activity (increased response to forskolin-Mn2+) and on G-protein coupling (enhanced effect of fluoride and increased GTP dependence of basal activity). Isoproterenol pretreatment failed to cause beta-receptor down-regulation in 6-d-old animals, but by 15 d of age, down-regulation was detected along with slight desensitization of the cyclase response. However, at 25 d, neither effect was present. In adulthood, repeated isoproterenol administration failed to cause cyclase desensitization but did reduce beta-receptor numbers; the loss of receptors was still unusual in that beta-receptor down-regulation could be achieved with either isoproterenol or with methoxamine, an alpha-receptor agonist. The results indicate that, early in development, hepatic beta-receptor-mediated responses are enhanced, not desensitized, after chronic stimulation. These effects would foster responsiveness of hepatic gluconeogenesis in the face of the massive adrenergic stimulation associated with the transition from fetal to neonatal life. In adulthood, when receptor numbers are far lower than in the neonate, the inability to desensitize the signaling cascade despite receptor down-regulation would serve to maintain the response to catecholamines.

Beta-adrenoceptor control of cardiac adenylyl cyclase during development: agonist pretreatment in the neonate uniquely causes heterologous sensitization, not desensitization

In the adult, increased stimulation of postsynaptic receptor sites produces compensatory desensitization that reduces tissue responsiveness. During development, however, responses in most systems increase with age and with the maturation of neuronal inputs. In the current study, we examined whether agonist-induced desensitization of cardiac beta-adrenergic receptor signaling mediated through adenylyl cyclase could be elicited in 6-, 15- and 25-day-old rats, and in adults. In each case, animals were pretreated with isoproterenol daily for four days preceding the experiment, and on the fifth day, cardiac membrane preparations were examined. Fifteen and 25-day-old animals and adults all exhibited desensitization, as demonstrated by a diminished cyclase response to isoproterenol in vitro. However, in 6-day-old animals, the enzymatic response to isoproterenol was enhanced by chronic pretreatment. Measurements of the G-protein-sensitive component of cyclase (decrement in activity obtained with deletion of GTP from the reaction mixture, stimulatory response to fluoride) indicated heterologous desensitization in the older animals, evidenced by diminished dependence on GTP and reduced response to fluoride; the 6-day-old animals showed enhanced GTP dependence and augmentation of the fluoride response. Uniquely in 6-day-old animals, the total catalytic activity of adenylyl cyclase, measured with forskolin-Mn2+, was markedly elevated by chronic isoproterenol pretreatment, whereas it was unaffected in older animals. These data suggest that regulation of receptor signaling is completely different early in neonatal life. Instead of producing desensitization of responses, agonist exposure promotes receptor signaling by enhancing expression and/or catalytic efficiency of adenylyl cyclase. In older animals, the predominant effect is heterologous desensitization mediated at the level of G-proteins. These developmental differences are likely to be important in the maintenance of tissue responsiveness during the period in which innervation develops, as well as in the ability of neurotrophic input to 'program' the responsiveness of target tissues.

Neural input and the development of adrenergic intracellular signaling: neonatal denervation evokes neither receptor upregulation nor persistent supersensitivity of adenylate cyclase

In the adult, denervation of adrenergic target tissues leads to compensatory upregulation of receptor sites and to supersensitive responses. When 6-hydroxydopamine (6-OHDA) was given to neonatal rats, cardiac beta-receptors failed to show significant upregulation throughout the first five postnatal weeks and alpha 1-receptors were unchanged except at 35 days of age, despite 70-95% depletion of norepinephrine. The failure to upregulate could not be attributed to the high background level of receptor expression commensurate with ontogenetic increases in receptor numbers, since the same deficiency was seen in the liver, a tissue in which beta-receptors decline with development; liver alpha 1-receptors also failed to upregulate after neonatal denervation. Examination of the linkage of beta-receptors to adenylate cyclase indicated major differences from mature regulatory mechanisms, as denervation supersensitivity was completely absent (liver) or emerged only transiently several weeks after 6-OHDA treatment (heart). In the heart, there was evidence for a defect in the G-protein-dependent component of the receptor/cyclase linkage that could contribute to the delayed appearance of supersensitivity. Because the fundamental patterns of receptor ontogeny and of adenylate cyclase responsiveness are still present after neonatal denervation, it is unlikely that neural input provides the major impetus for basal development. However, adult-type regulation of receptors and responses did not emerge even after a prolonged period; thus, neural input during a critical developmental stage may be required for the cell to learn how to adjust receptor expression and the receptor/cyclase link in response to stimulation.

Intracerebroventricular injection of dibutyryl cyclic adenosine 3',5'-monophosphate increases hypothalamic levels of neuropeptide Y

This investigation examined in vivo the relationship between the nucleotide cAMP and hypothalamic levels of two peptides, neuropeptide Y (NPY) and galanin (GAL), which are known to potentiate feeding behavior. In brain-cannulated rats, third ventricular injections of N6,2'-O-dibutyryl cyclic adenosine 3',5'-monophosphate ((Bu)2cAMP, 25 micrograms), compared to saline, caused a significant increase in NPY levels in the arcuate nucleus (ARC) and medial parvocellular portion of the paraventricular nucleus (mPVN), while having no impact in other hypothalamic areas. These site-specific changes in NPY occurred in the absence of any alteration in circulating levels of insulin, corticosterone, aldosterone or glucose, or of changes in hypothalamic levels of GAL. These findings implicate cAMP as having regulatory functions within specific hypothalamic NPY-synthesizing neurons, projecting from the ARC to the mPVN, that are believed to be involved in energy homeostasis.