Ontogenetical variations of transcortin modulate glucocorticoid receptor function and corticotropic activity in the pituitary gland

Postnatal ontogeny of the glucocorticoid receptor in the hippocampus

Corticosteroid hormones are important intrinsic factors that not only mediate the response to stress but also largely contribute to the main physiological processes. The biological actions of these steroids involve, first of all, the activation of specific receptors, namely mineralocorticoid (MR) and glucocorticoid (GR) receptors. These two receptor types govern a flexible and well-balanced mechanism that leads to the often opposing changes in the cell. The hippocampus is the central part of the extrahypothalamic feedback loop in the control of the hypothalamic-pituitary-adrenal (HPA) axis activity. The coexpression of both MR and GR in the hippocampus serves a coordinated response to corticosteroids in the hippocampal neurons, thereby mediating the neuronal excitability, stress response, and behavioral adaptation. Each receptor type reveals distinct ontogenetic pattern over the postnatal period. This review addresses the issues relating to postnatal development of the HPA axis and especially the hippocampal expression of the GR proteins in intact and prenatally stressed rats.

Postnatal glucocorticoid excess due to pituitary glucocorticoid receptor deficiency: differential short- and long-term consequences

A tight regulation of hypothalamic-pituitary-adrenal (HPA) axis activity is essential for successful adaptation to stressful stimuli. Disruption of normal HPA axis development is a main risk factor for diseases such as posttraumatic stress disorder or depression, but the molecular mechanisms that lead to these long-term consequences are poorly understood. Here, we test the hypothesis that the pituitary glucocorticoid receptor (GR) is involved in regulating HPA axis function in neonatal and adult animals. Furthermore, we investigate whether postnatal hypercortisolism induced by pituitary GR deficiency is a main factor contributing to the persistent effects of early-life stress. Conditional knockout mice with a deletion of the GR at the pituitary (GR(POMCCre)) show excessive basal corticosterone levels during postnatal development, but not in adulthood. The hypercortisolemic state of neonatal GR(POMCCre) mice is accompanied by central gene expression changes of CRH and vasopressin in the paraventricular nucleus, but these alterations normalize at later ages. In adult mice, pituitary GR deficiency results in impaired glucocorticoid negative feedback. Furthermore, adult GR(POMCCre) mice display a more active coping strategy in the forced swim test, with no alterations in anxiety like behavior or cognitive functions. Postnatal GR antagonist treatment is able to prevent the long-term behavioral effects in GR(POMCCre) mice. In conclusion, we show that pituitary GRs are centrally involved in regulating HPA axis activity in neonates and mediate negative feedback regulation in adult animals. Postnatal glucocorticoid excess results in an altered stress-coping behavior in adult animals, with no effects on anxiety like behavior or cognition.

Hypothalamic-pituitary-adrenal axis activity of newborn mice rapidly desensitizes to repeated maternal absence but becomes highly responsive to novelty

In CD1 mice we investigated the hypothalamic-pituitary-adrenal (HPA) axis response to maternal separation for 8 h daily from postnatal d 3 to 5. At d 3 a slow separation-induced corticosterone response developed that peaked after 8 h, and the pups became responsive to stressors. On the second and third day, the response to 8 h separation rapidly attenuated, whereas the response to novelty did not, a pattern reflected by the hypothalamic c-fos mRNA response. If maternal separation and exposure to novelty were combined, then after the third such daily exposure, the sensitivity to the stressor was further enhanced. Meanwhile, basal corticosterone and ACTH levels were persistently suppressed 16 h after pups were reunited with their mothers. To explain the HPA axis desensitization after repeated separation, we found that circulating ghrelin levels increased and glucose levels decreased after all periods of maternal separation, ruling out a role of altered metabolism. Glucocorticoid feedback was not involved either because a glucocorticoid receptor antagonist amplified the corticosterone response after the first but became ineffective after the third separation. In contrast, a mineralocorticoid receptor antagonist decreased and increased corticosterone levels after the first and third period of separation, respectively. In conclusion, the newborn's HPA axis readily desensitizes to repeated daily maternal separation, but continues to respond to novelty in a manner influenced by a central mineralocorticoid receptor- rather than glucocorticoid receptor-mediated mechanism.

Metabolic signals modulate hypothalamic-pituitary-adrenal axis activation during maternal separation of the neonatal mouse

The postnatal development of the mouse is characterised by a period of hypo-responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to moderate stressors. Maternal separation disinhibits this blockade of the HPA axis, but the mechanism responsible is not clear. The present study examined the influence of metabolic signals on the central and peripheral components of the HPA axis in neonatal mice aged 8 days in absence or presence of the mother. Reductions in plasma glucose and leptin as well as rapid increases in plasma ghrelin were apparent in the neonate 4 h following maternal deprivation and maximal at 8 h. In addition, maternal separation induced an increase of neuropeptide Y (NPY) mRNA expression in the arcuate nucleus, a decrease of corticotrophin-releasing hormone (CRH) mRNA expression in the paraventricular nucleus and a rise in serum corticosterone. Pharmacological manipulation of the metabolic signals attenuated the HPA response to maternal separation. Thus, the rise in plasma corticosterone induced by maternal separation was ameliorated by prevention of reduction in blood glucose or blockade of the ghrelin signalling pathway, as were the hypothalamic changes in NPY and CRH mRNAs. By contrast, leptin treatment did not affect the HPA axis response to maternal separation. Together these results suggest that metabolic signals play an important role in triggering the HPA response of the neonate to maternal separation.

Stress, genes and the mechanism of programming the brain for later life

Adverse conditions during early life are a risk factor for stress-related diseases such as depression and post-traumatic stress disorder (PTSD). How this long-term effect of early adversity occurs is not known, although evidence accumulates that the action of stress hormones is an important determinant. In rodents after a variety of experiences, even minor ones, during postnatal life permanent changes in emotional and neuroendocrine reactivity have been observed. Also stressful events occurring prenatally and even the pre-implantation hormonal conditions can have permanent consequences. Here we will focus on evidence obtained from (i) the blastocyst implantation during conditions of ovarian hyperstimulation, which is commonly used in the generation of transgenic mice; (ii) the stress system activity in the newborn under various conditions of maternal care; (iii) the long-term consequences of maternal separation procedures. The results clearly demonstrate that early experiences trigger immediate changes in the stress system that may permanently alter brain and behaviour.

Glucocorticoid receptor blockade disinhibits pituitary-adrenal activity during the stress hyporesponsive period of the mouse

During postnatal development, mice undergo a period of reduced responsiveness of the pituitary-adrenal axis, the stress hyporesponsive period (SHRP), which is largely under control of maternal signals. The present study was designed to test the hypothesis that this quiescence in hypothalamic-pituitary-adrenal (HPA) activity is mediated by glucocorticoid feedback. For this purpose, the role of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in control of HPA activity was examined during the SHRP and in response to 24 h of maternal deprivation. Nondeprived or deprived (24 h) CD1 mice on postnatal d 8 were injected sc at 16 and 8 h before testing with the MR antagonist RU28318 or the GR antagonist RU38486. The results showed that, in nondeprived mice, blockade of GR rather than MR triggered a profound increase in anterior pituitary proopiomelanocortin mRNA, circulating ACTH, and corticosterone concentrations. In contrast, CRH mRNA in hypothalamus and GR mRNA in hippocampus and hypothalamus were decreased. Blockade of the GR during the deprivation period amplified the rise in corticosterone induced by maternal deprivation, whereas it reversed the deprivation effect on the other HPA markers, leading to profound increases in plasma ACTH, proopiomelanocortin mRNA expression in the anterior pituitary, CRH mRNA expression in the paraventricular nucleus, and MR mRNA expression in the hippocampus, but not in GR mRNA expression in the hippocampus and paraventricular nucleus. In conclusion, the data suggest that control of postnatal pituitary-adrenal activity during the SHRP involves GR-mediated feedback in the anterior pituitary, which is further potentiated in the absence of the mother.

Chronic leptin administration in developing rats reduces stress responsiveness partly through changes in maternal behavior

In adult rodents, leptin has been shown to significantly alter the activity of several neuroendocrine functions, including the activity of the hypothalamic-pituitary-adrenal (HPA) axis. Leptin is generally believed to be inhibitory to HPA activity in adults. Developing rat pups have high circulating levels of leptin, which begs the question of leptin's physiological role in controlling basal and stress-induced adrenocortical activity in neonatal rats. In this study, we treated rat pups daily from days 2-9 (or 6-10) of life with either vehicle or leptin (1 or 3 mg/kg body wt, ip) and determined the effects on body weight gain, fat pad deposits, and HPA activity in 10-day-old pups. We measured hypothalamic CRF mRNA levels in vehicle- and leptin-treated pups by in situ hybridization and determined plasma ACTH, corticosterone, and leptin concentrations under basal conditions or following exposure to a 3-min ether stress. Because leptin activates sympathetic activity and energy expenditure in adults and possibly also in rat pups, and because litter temperature is an important determinant of maternal behavior, we also investigated whether chronic leptin administration would modify aspects of maternal care that are important for the maintenance of HPA function. Chronic leptin treatment increased circulating levels of leptin and had significant dose-related metabolic effects, including reduced body weight gain and fat pad weight in 10-day-old pups. Basal expression of CRF mRNA in the PVN or secretion of ACTH and corticosterone was not modified by leptin treatment. In contrast, chronically elevated leptin concentrations during the neonatal period significantly lowered CRF expression in the PVN 60 min after stress and reduced the duration of the ACTH response to stress in pups, suggesting that glucocorticoid feedback on the HPA axis might be altered by this treatment. In addition, mothers caring for pups injected with leptin displayed longer bouts of anogenital licking of pups than mothers of vehicle-treated rats. Given that this particular type of pup stimulation has been shown to influence stress responsiveness, it is possible that the maternal response modulates the effects of exogenous leptin treatment. In conclusion, our results demonstrate that the leptin signal is functional during the early developmental period and that leptin can modulate the hormonal response to stress in young rats either by a direct effect on the HPA axis or indirectly through changing some aspects of maternal behavior.

Sex differences in corticosteroid binding in the rat brain: an in vitro autoradiographic study

Several previous studies have raised the possibility of sex differences in the distribution of corticosteroid receptors in the brain. The direction and magnitude of these differences have, however, remained controversial. In the present study, we have re-examined the concentrations of mineralocorticoid (MR) and glucocorticoid (GR) receptors in the brains of male and female rats at varying times (1 to 6 days) after combined gonadectomy (GDX) and adrenalectomy (ADX). Cytosol binding assays confirmed the presence of higher MR levels in short-term (3-day) GDX-ADX males. This difference disappeared by 6 days after surgery, as receptor levels in females rose to be equivalent to those in males. Using an improved in vitro autoradiographic method, the distribution of MR and GR was studied in males and females 3 days after GDX-ADX. The distribution of MR and GR in the brains of these rats was similar in the two sexes. MR binding in the male, however, was significantly greater than that in the female throughout the principal cell fields of the hippocampus. Measurements of circulating corticosterone levels at the time of GDX-ADX suggest that this sex difference may reflect a more rapid recovery of the MR system in males than in females following the stress-induced rise in corticosterone secretion occurring at the time of surgery.

Activation and inhibition of the hypothalamic-pituitary-adrenal axis of the neonatal rat: effects of maternal deprivation

These studies investigated the activation and inhibition (negative feedback) of the neonatal rat. The ACTH response of maternally deprived pups is persistently elevated for 30 min, suggesting a deficiency in the negative feedback system. In Experiment 1, we examined the time-course of corticosterone (CORT) and ACTH responses to a saline injection over a 120-min period during development. In deprived pups, CORT and ACTH were persistently elevated throughout the testing period, whereas only 15-day-old nondeprived pups showed ACTH and CORT elevations. Further nondeprived and deprived pups were exposed twice to ether (Experiment 2) or saline injections (Experiment 3) separated by a 1-h interval. Nondeprived pups showed an augmented ACTH response to double exposure to ether, but not to saline. No CORT response to either stimulus was observed. In response to one exposure of each stimulus, deprived pups showed increased ACTH and CORT values and no further elevation to repeated exposure. These results suggest the negative feedback system of neonates is immature, but partially functional in deprived pups. Moreover, nondeprived pups show a stressor-specific response to stress, whereas deprived animals show a similar response to different stimuli.

Hypothalamic-pituitary-adrenal activation following endotoxin administration in the developing rat: a CRH-mediated effect

The present studies assessed hypothalamic-pituitary-adrenal (HPA) responses following immune activation with endotoxin (i.p.) in three-day old Long Evans rats. Marked plasma corticosterone (B), adrenocorticotrophic hormone (ACTH) responses and biphasic fluctuations in plasma glucose were maximal at a dose of 0.05 mg/kg. HPA responses peaked between 3-5 h following immune challenge and plasma ACTH and B responses were greater in female than in male rat pups. Plasma levels of corticosterone binding globulin (CBG) were reduced in males and substantially increased in females during the peak HPA response. Changes in plasma glucose were biphasic with slight increases when ACTH and B levels were maximal, but hypoglycemia was evident once plasma B levels returned to resting values. Endotoxin challenge reduced median eminence corticotropin-releasing hormone (CRH) levels at times corresponding with elevated HPA activity, and prior i.c.v. injection of the CRH antagonist, alpha-helical CRH, significantly attenuated elevations in plasma ACTH and B. In addition, alpha-helical CRH pretreatment completely blocked endotoxin-induced changes in plasma CBG in both males and females. These findings support the view that endotoxin-induced HPA activation in the neonate may occur via CRH.

Maternal regulation of the hypothalamic-pituitary-adrenal axis in the infant rat: the roles of feeding and stroking

Twenty-four hours of maternal separation results in increased secretion of ACTH and corticosterone (CORT), suggesting the hypothalamic-pituitary-adrenal (HPA) axis is regulated by some aspect of maternal behavior. Previous results indicate that feeding plays a role in maintaining low levels of CORT in 12-day-old pups. In Experiment 1 basal and stress levels of CORT and ACTH were measured in maternally-deprived pups either provided or not with milk to determine whether: (1) feeding maintains ACTH secretion at low levels, and/or (2) feeding maintains the adrenal insensitive to ACTH. The results showed that, although ACTH levels were markedly low (compared to previous values reported by this laboratory) for both groups, only non-fed pups showed a robust increase in basal and stress CORT levels. During the deprivation period in Experiment 1, all pups were manually stroked to induce urination and defecation, suggesting an effect of stroking on ACTH secretion. Experiment 2 examined this hypothesis. Stroking suppressed stress-induced elevations of ACTH secretion due to maternal deprivation. CORT levels, however, were elevated in all deprived pups. The results indicate that maternal regulation of the infant's HPA axis occurs at multiple levels. Feeding appears to regulate adrenal sensitivity, whereas anogenital stroking inhibits the activation of centrally-controlled components of the axis.

Differential development of the stress response in congenital learned helplessness

Early in the development of the hypothalamic-pituitary-adrenal (HPA) axis, the rat undergoes a stress hyporesponsive period of blunted responses to several stressors including cold exposure (CE) and maternal deprivation (MD). We examined the development of the axis by monitoring adrenocorticotropin hormone (ACTH) plasma levels in an animal model of depression and/or anxiety characterized by learned helpless (LH) behavior and a dysfunctional HPA axis in adult life. On postnatal day 7 there was no significant difference in basal plasma ACTH levels between congenital (cLH) and controls, but cLH animals showed a blunted response to CE (P < 0.001). By postnatal day 14 there was a dramatic increase in ACTH response to CE (P < 0.005). On postnatal day 21 baseline ACTH and response to CE were again significantly suppressed in cLH rats. Stress responsiveness to MD was present in all groups and was insignificantly different for all ages of development between groups. These findings suggest that rats with congenital learned helplessness undergo a differential response in the development of the HPA axis in that the axis was hypersensitive at postnatal day 14 and became hyporesponsive beyond day 14, and this may, in part, account for the dysfunctional stress response observed during adulthood.

Maternal regulation of adrenocortical activity in the infant rat: effects of feeding

Basal and stress-induced corticosterone release in the infant rat has been shown to be inhibited by some aspect of maternal care. The following studies examined specific maternal cues that might be responsible for this regulation. In Experiments 1 and 2, 12-day-old pups remained with their dam but were either prevented or not from feeding; at the end of 24 hr, basal and stress-induced corticosterone levels were measured. Only those animals that were able to feed showed the hyporesponsiveness characteristic of nondeprived animals, suggesting that feeding rather than some other aspect of maternal care was the critical variable. In Experiment 3, all animals were maternally deprived, and some of them were fed via an intracheek cannula. Once again, feeding led to a pronounced diminution in both basal and stress-induced levels of corticosterone. Our results point to feeding as one of the critical features responsible for the inhibitory effect of the dam on the infant's adrenocortical activity.

Effects of repeated maternal separations on the adrenocortical response to stress of preweanling rats

Previous data indicate that the infant rat shows a marked increase in adrenocortical responsiveness to stress immediately following prolonged maternal separation. In Experiment 1 we studied the immediate effects of repeated maternal deprivation. Our results indicate that the increase in basal as well as stress-induced corticosterone levels is a direct function of the length of the deprivation period immediately preceding testing, and is not cumulative. In Experiment 2 we examined the long-term consequences of maternal deprivation on adrenal responsivity. Four days following a single 24-h period of maternal deprivation, pups remained hyperresponsive to stress, although their basal levels of corticosterone had returned to control values. Shorter periods of deprivation (which did result in increased responsivity immediately following deprivation) did not have persistent effects. Our data suggest: 1) short periods of deprivation do not have a cumulative effect, and 2) there is a critical length of deprivation beyond which persistent changes in adrenocortical responsivity ensue.

Multifactorial regulation of the hypothalamic-pituitary-adrenal axis during development

The hypothalamic-pituitary-adrenal system shows an overall diminished responsiveness throughout ontogeny. Thus, during this period, the sensitivity of the adrenal gland to ACTH is markedly reduced. Furthermore, basal and stress-induced concentrations of corticosterone (CORT), ACTH and hypothalamic secretagogues remain at very low levels. Both structural immaturity and active inhibitory processes appear to underlie this overall hyporesponsiveness. The available data indicate that the characteristic developmental pattern of the HPA system results from multiple regulatory factors acting in conjunction at various levels of the axis. The primary rate-limiting steps, however, are probably at the brain and adrenal levels. The ultimate "goal" appears to be to keep CORT levels within the narrow range of concentrations required for normal development.

Time course of the effect of maternal deprivation on the hypothalamic-pituitary-adrenal axis in the infant rat

Prolonged (i.e., 24-hr) maternal deprivation leads to a marked disinhibition of the infant rat's adrenocortical response to stress and/or ACTH. In the following study we examined the time course over which these effects develop. Pups were maternally deprived for varying lengths of time (i.e., 0, 2, 4, 8, & 24 hr); at the end of this period, corticosterone (CORT) secretion in response to stress (novelty or novelty plus saline injection) and ACTH injection was measured. Basal levels of CORT increased progressively over time in 7- and 11- (but not 3-) day-old pups. CORT release in response to stress followed a similar pattern. In contrast, ACTH injection resulted in marked increases in CORT levels regardless of the length of maternal deprivation in 3-day-old animals; at older ages, however, 24 hr of deprivation led to a much larger increase. These findings support the hypothesis that the hypothalamic-pituitary-adrenal axis of the neonatal rat is subject to maternal regulation.

Maternal regulation of the adrenocortical response in preweanling rats

In the following studies, we investigated the effects of 24-h maternal deprivation on the infant's hypothalamic-pituitary-adrenal system. Experiment 1 examined the effect of deprivation on the infant's corticosterone (CORT) response to adrenocorticotropin hormone (ACTH) injection. At all ages studied, deprivation resulted in a potentiation of the response. At some ages, deprived nontreated pups had higher CORT levels than nondeprived pups. Experiment 2 examined the ontogeny of the deprivation-induced stress response, and the capacity of the mother to inhibit it. From 8 days of age onwards, deprived animals showed a CORT response to saline injection that was either absent or far smaller in nondeprived pups. Saline-induced CORT secretion was diminished, or prevented, by returning the infant to its dam. Maternal reunion had no effect on ACTH-induced CORT elevations. Finally, Experiment 3 investigated the effects of deprivation over a more extended period of time. In maternally deprived pups, ACTH-induced CORT elevations persisted for at least 2 h following reunion, but by 6 h had returned to baseline. These data suggest that maternal factors are involved in the regulation of the responsiveness of the pup's hypothalamic-pituitary-adrenal system.

Cellular mechanisms underlying the development and expression of individual differences in the hypothalamic-pituitary-adrenal stress response

Several years ago Levine, Denenberg, Ader, and others described the effects of postnatal "handling" on the development of behavioral and endocrine responses to stress. As adults, handled rats exhibited attenuated fearfulness in novel environments and a less pronounced increase in the secretion of the adrenal glucocorticoids in response to a variety of stressors. These findings clearly demonstrated that the development of rudimentary, adaptive responses to stress could be modified by environmental events. We have followed these earlier studies, convinced that this paradigm provides a marvellous opportunity to examine how subtle variations in the early environment alter the development of specific neurochemical systems, leading to stable individual differences in biological responses to stimuli that threaten homeostasis. In this work we have shown how early handling influences the development of certain brain regions that regulate glucocorticoid negative-feedback inhibition over hypothalamic-pituitary-adrenal (HPA) activity. Specifically, handling increases glucocorticoid (type II corticosteroid) receptor density in the hippocampus and frontal cortex, enhancing the sensitivity of these structures to the negative-feedback effects of elevated circulating glucocorticoids, and increasing the efficacy of neural inhibition over ACTH secretion. These effects are reflected in the differential secretory pattern of ACTH and corticosterone in handled and nonhandled animals under conditions of stress. In more recent years, using a hippocampal cell culture system, we have provided evidence for the importance of serotonin-induced changes in cAMP levels in mediating the effect of postnatal handling on hippocampal glucocorticoid receptor density. The results of these studies are consistent with the idea that environmental events in early life can permanently alter glucocorticoid receptor gene expression in the hippocampus, providing evidence for a neural mechanism for the development of individual differences in HPA function.

The effects of neonatal handling on the development of the adrenocortical response to stress: implications for neuropathology and cognitive deficits in later life

Several years ago Levine, Denenberg, Weininger, Ader, and others described the effects of postnatal "handling" on the development of behavioral and endocrine responses to stress. The handling procedure usually involved removing rat pups from their cages, placing the animals together in small containers, and 15-20 min later, returning the animals to their cages and their mothers. The manipulation was performed daily for the first 21 days of life. As adults, handled (H) rats exhibited attenuated fearfulness (e.g., decreased freezing, increased exploration) in novel environments and a less pronounced increase in the secretion of adrenal glucocorticoids in response to a variety of stressors. These findings clearly demonstrated that the development of rudimentary, adaptive responses to stress could be modified by environmental events. We have followed on these earlier handling studies, convinced that this paradigm provides a marvelous opportunity to examine how subtle variations in the early environment alter the development of specific biochemical systems in the brain, leading to stable individual differences in biological responses to stimuli that threaten homeostasis. In this work we have shown how early handling influences the neurochemical development of certain brain regions that regulate the adrenocortical response to stress. Neonatal handling increases the efficiency of this endocrine response to stress, preventing excessive exposure to the highly catabolic adrenal steroids. In later life, this effect appears to protect the animal from potentially damaging effects of these steroids, ensuring the anatomical integrity of brain structures involved in cognitive functioning.

Postnatal handling attenuates certain neuroendocrine, anatomical, and cognitive dysfunctions associated with aging in female rats

Hippocampal degeneration with aging is associated with increased hypothalamic-pituitary-adrenal (HPA) activity and, in male rats, both are attenuated by postnatal handling. Considering the important sex differences in the effects of handling and in HPA responses to stress in older rats, we have examined the effects of postnatal handling on aging in females. Female, Long-Evans rats were handled (H) during the first 3 weeks of life and later compared with nonhandled (NH) controls at various ages. Handling resulted in permanently increased hippocampal type II, glucocorticoid receptor binding. Relative to H females, NH females showed increased basal corticosterone levels in later life and hypersecreted corticosterone following stress at all ages examined. Both effects are similar to those reported in males. However, unlike males, H and NH females did not differ in corticosterone levels achieved during stress, a finding that may be related to sex-dependent effects of handling on pituitary transcortin receptors. There were no differences in hippocampal neuron density in 6-month-old animals. However, the older NH animals showed considerable neuron loss in the CA1 and CA3 hippocampal cellfields. There was little or no neuron loss in the H animals. Finally, the NH animals exhibited age-related spatial memory impairments, such that by 24 months of age the performance of the NH females was profoundly worse than that of the younger NHs and same-aged H animals. These data suggest that early handling permanently alters CNS systems that regulate hypothalamic-pituitary-adrenal (HPA) function, although the effect may depend on the gender of the animal. In both males and females, however, handling appears to prevent (or minimize) increased adrenal secretion in later life and to attenuate hippocampal cell loss and spatial memory impairments.

Estrophilic 3 alpha,3 beta,17 beta,20 alpha-hydroxysteroid dehydrogenase from rabbit liver--I. Isolation and purification

A procedure for isolation of a highly-purified estrophilic hydroxysteroid dehydrogenase (EHSD) from rabbit liver, including ammonium sulphate fractionation, gel filtration, ion-exchange and affinity chromatography on estradiol-Sepharose, has been developed. The enzyme possesses NADP-dependent 3 alpha,3 beta,17 beta,20 alpha-HSD activities with a wide spectrum of androgenic, progestagenic, and estrogenic substrates. EHSD is a monomeric protein whose molecular mass determined by different methods is 35,000-39,000. The protein exhibits microheterogeneity due to the differences in molecular surface charge. The catalytic and hormone-binding properties and molecular sizes of the two protein fractions obtained by chromatography on DEAE-Toyopearl are close or identical. The enzymatic activity of EHSD is minor as compared to other HSDs from rabbit liver. However, the low values of Km, the high affinity for steroid ligands, and high tissue levels of EHSD suggest the protein to play a role in the biodynamics of sex hormones.

Ontogeny of mineralocorticoid (type 1) receptors in brain and pituitary: an in vivo autoradiographical study

The ontogeny of high affinity [3H]corticosterone uptake and retention in brain and pituitary of 24-h adrenalectomized rats was examined using autoradiography of in vivo labeled brain sections. Our data indicate: (1) There is specific uptake of radiolabeled steroid in both brain and pituitary already at 2 days of age, following administration of a tracer (2 microCi/g body wt.) dose of [3H]corticosterone. This uptake is maximum around 4-8 days of age and decreases towards adult values around postnatal day 16. (2) High affinity uptake, at least in the brain, probably represents mostly binding to the mineralocorticoid receptor (MR) and not to the glucocorticoid receptor (GR), as it was not displaced by an excess dose of a GR antagonist, RU 38486, and its location in the hippocampus resembled that of MRs in the adult animal. The tracer amounts of [3H]corticosterone circulating after injection in the rat pups resulted in steroid levels comparable to basal levels of non-adrenalectomized animals of equivalent age. Thus, MRs may be the receptors mainly responsible for mediating physiological effects of glucocorticoids during early ontogeny.

Sex difference in glucocorticoid binding in rat pituitary is estrogen dependent

Sex-dependent differences in corticosteroid binding were assessed in individual pituitaries from adult male and female rats that had been adrenalectomized 12 h before sacrifice. Soluble binding was assayed in duplicate on LH-20 columns. Gonadally intact females showed significantly less 3H-dexamethasone binding than did intact males (p less than 0.01). This difference was confirmed in a second study (p less than .001). However, when ovariectomized females were compared with gondadectomized males, there was no difference in receptor concentration. Estrogen was able to reverse the effect of ovariectomy: ovariectomized females receiving estrogen (10 micrograms/rat/day) had significantly fewer receptors than intact males; p less than 0.01). Progesterone (500 micrograms/rat/day) did not antagonize the effect of estrogen in the pituitary. A sex difference was also found in the Type I (mineralocorticoid) receptor subpopulation which comprised approximately 10% of the total receptors, with females having fewer receptors than males. These results demonstrate that in the pituitary, the level of functional corticosteroid receptors is subject to a 20% down-regulation by circulating levels of estrogen. This raises the possibility that the lower number of receptors in females may act to reduce their sensitivity to the negative feedback effects of glucocorticoids at the level of the pituitary.

Pituitary-adrenal response to bacterial endotoxin in developing rats

The neonatal rat is very sensitive to the lethal effects of bacterial endotoxin. Because of the adaptive importance of pituitary-adrenal secretions to stress, this study examined the ontogeny of the plasma corticosterone and adrenocorticotropic hormone (ACTH) responses to endotoxin. The lethal sensitivity of young rats to endotoxin ranged from 0.5 to 30 mg/kg (ip) in the 1- to 21-day-old rat. After endotoxin treatment, the 1- and 2-day-old rat showed marked elevations of corticosterone similar in magnitude to that seen in 21-day-old and adult rats; however, significantly depressed corticosterone increments were observed in the 5-, 10-, and 14-day-old rats. This age-related pattern of adrenocortical secretion was correlated with the developing rat's corticosterone response to exogenous ACTH. In contrast, endotoxin administered to 5-, 10-, and 14-day-old rats resulted in increments of plasma ACTH similar to those observed in the 21-day-old and adult rats. Although plasma ACTH levels increased by 84-127% in the 1- and 2-day-old rats, these increases were significantly less than those of rats at all other ages tested. Thus the newborn rat mounts an effective corticosterone response to endotoxin, loses this ability between ages 5-14 days, and regains this response at 21 days of age. Because the hyporesponsive ages exhibit a marked increase in ACTH secretion, the loss of the adrenocortical response to endotoxin appears to be a result of a depressed responsiveness of the adrenal cortex to ACTH.

The beta-endorphin response to stress during postnatal development in the rat

The plasma beta-endorphin and adrenocortical responses to ether and handling stress were examined in animals of various ages. At each age studied there was a significant, stress-induced elevation of plasma beta-endorphin-like immunoreactivity levels. Moreover, basal beta-endorphin-like immunoreactivity levels were higher in animals 3, 7, and 14 days of age than in adults. In contrast, plasma corticosterone levels in the Day 7 pups were not elevated by stress; a finding consistent with several previous reports on the absence of increased release of adrenocorticotropin and corticosterone during stress in the neonate. These data suggest that the release of adrenocorticotropin and beta-endorphin in response to stress differ in the developing animal.