Sexually dimorphic effects of maternal adrenalectomy on hypothalamic corticotrophin-releasing factor, glucocorticoid receptor and anterior pituitary POMC mRNA levels in rat neonates

Sex-biased transgenerational transmission of betaine-induced epigenetic modifications in glucocorticoid receptor gene and its down-stream BDNF/ERK pathway in rat hippocampus

Objectives: Glucocorticoid receptor (GR) expressed in hippocampus is critical for the homeostasis of stress responses and susceptible to epigenetic modulation caused by maternal factors. Here we show that maternal methyl nutrition causes sex-biased changes in hippocampal expression of GR exon 1 mRNA variants, associated with promoter DNA methylation, across two offspring generations in rats.Methods: Three-month-old female Sprague-Dawley rats (F0) were fed a diet supplemented with 1% betaine throughout the gestation and lactation. F0 dams and their F1 and F2 offspring of both sexes at weaning were used in the study.Results: A sex-specific transgenerational effect was observed. F2 females, but not males, followed the same pattern of their grand dams showing increased mRNA expression of total GR and its exons 1.4, 1.7, 1.10 and 1.11 variants coincided with promoter DNA hypomethylation in the hippocampus. However, F1 females, but not males, exhibited an opposite pattern, showing decreased expression of GR and its mRNA variants accompanied with promoter hypermethylation. The protein content of phospho-GR and BDNF/ERK in the hippocampus displayed the same sex and generation specificity.Discussion: These results indicate that maternal betaine exerts transgenerational effects on hippocampal GR expression and BDNF/ERK pathway in female rat offspring, with generation-dependent patterns of DNA methylation on alternative GR promoters.

The Effects of Acute Neonatal Pain on Expression of Corticotropin-Releasing Hormone and Juvenile Anxiety in a Rodent Model

Premature infants in the neonatal intensive care unit (NICU) may be subjected to numerous painful procedures without analgesics. One necessary, though acutely painful, procedure is the use of heel lances to monitor blood composition. The current study examined the acute effects of neonatal pain on maternal behavior as well as amygdalar and hypothalamic activation, and the long-term effects of neonatal pain on later-life anxiety-like behavior, using a rodent model. Neonatal manipulations consisted of either painful needle pricks or non-painful tactile stimulation in subjects’ left plantar paw surface which occurred four times daily during the first week of life [postnatal day (PND)1–PND7]. Additionally, maternal behaviors in manipulated litters were compared against undisturbed litters via scoring of videotaped interactions to examine the long-term effects of pain on dam-pup interactions. Select subjects underwent neonatal brain collection (PND6) and fluorescent in situ hybridization (FISH) for corticotropin-releasing hormone (CRH) and the immediate early gene c-fos. Other subjects were raised to juvenile age (PND24 and PND25) and underwent innate anxiety testing utilizing an elevated plus maze (EPM) protocol. FISH indicated that neonatal pain influenced amygdalar CRH and c-fos expression, predominately in males. No significant increase in c-fos or CRH expression was observed in the hypothalamus. Additionally, neonatal pain altered anxiety behaviors independent of sex, with neonatal pain subjects showing the highest frequency of exploratory behavior. Neonatal manipulations did not alter maternal behaviors. Overall, neonatal pain drives CRH expression and produces behavioral changes in anxiety that persist until the juvenile stage.

"Comfort-foods" chronic intake has different behavioral and neurobiological effects in male rats exposed or not to early-life stress

The ability of "comfort-food" (CF) diet to revert long-term effects of early-life stress (ELS) is less well known. The objective of this study was to verify if the chronic exposure to CF diet in animals submitted to ELS could relief the stress response at behavioral, neuroendocrine, and neurobiochemical levels, via differences in glucocorticoid receptors expression in brain areas involved in the stress response. From the second day of life, litters of Wistar rats and their mothers were submitted to the reduced nesting material protocol (ELS). In adult life, ELS and a control group were exposed chronically to two diet schemes: standard rat chow only or both "CF" diet, containing fat (34%) and sugar (20%) and a diet similar to the standard diet. Anxiety-like behavior, neuroendocrine response stress, leptin, GR, SOCS-3, pSTAT3, and the abdominal fat were evaluated. The anxiety-like behavior results showed that ELS group when exposed to comfort food were not different from the others groups. Chronic exposure to CF diet induced an anxiety-like behavior in the control group. Groups chronically exposed to CF diet had lower levels of corticosterone over time independent of the neonatal group. The ELS group exposed to the "CF" diet had higher levels of hippocampal GR, lower levels of hypothalamic SOCS-3 and greater accumulation of abdominal fat. Chronic CF diet consumption is able to reduce corticosterone levels independent of the neonatal history, but is associated with anxiety-like behavior in animals without previous history of trauma. Metabolic disturbances like increased adiposity and altered SOCS-3 seem to be a result of multiple insults (neonatal trauma followed by chronic CF diet). We highlight that the Control-chow and ELS-chow data were previously published, and are included in this study for comparative analysis.

A Single Postnatal Dose of Dexamethasone Enhances Memory of Rat Pups Later in Life

Postnatal dexamethasone (Dex) therapy is associated with adverse neurodevelopmental outcomes, which might be related to its timing of administration. We used time-dated pregnant Wistar albino rats, whose litters were divided into experimental (Dex) and control groups intraperitoneally administered one dose of Dex (0.5 mg/kg) or normal saline (NS), respectively, at either day 1 (P1) or 7 (P7). The magnitude of the contextual freezing response and performance on the Morris water maze were significantly higher in the Dex-P7 group than in those of the other groups at P56. Dendritic spine density, membranous expression of the N-methyl-d-aspartate receptor (NMDAR) subunit NR2A/2B, and postsynaptic density-95 (PSD-95) were significantly higher in the Dex-P7 group than in the other groups. Furthermore, cytosolic expression of nuclear factor kappa B (NF-κB) and phosphatidylinositol 3-kinase (PI3K) was significantly higher in the Dex group than in NS group. Moreover, Dex administration at P7 increased cell proliferation, neuronal differentiation, and the survival of newly born neurons in the dentate gyrus. These results suggest Dex at P7 enhances the acquisition of contextual fear and spatial memory later in life due to the modulation of the newly born neurons, increase in dendritic spine number, and NMDAR expression.

The corticotropin releasing factor system in cancer: expression and pathophysiological implications

Malignant tumors express multiple factors that have some role in the regulating networks supporting their ectopic growth. Recently, increased interest has been developing in the expression and biological role of the neuropeptides and receptors of the corticotropin releasing factor (CRF) system, the principal neuroendocrine mediator of the stress response, especially in the light of several R&D programs for small molecule antagonists that could present some anticancer therapeutic benefit. In the present article, we review the literature suggesting that the CRF system could be involved in the regulation of human cancer development. Potential implication in growth, metastasis, angiogenesis, or immune parameters via activation of locally expressed receptors could be clinically exploited by presenting targets of new therapeutic approaches.

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.

Effects of maternal corticosterone and stress on behavioral and hormonal indices of formalin pain in male and female offspring of different ages

In previous studies, we showed for the first time that prenatal stress in rats produces long-term alterations of formalin-induced pain behavior that are dependent on age and sex, and we demonstrated an important role of the serotonergic system in mechanisms of prenatal stress (Butkevich, I.P. and Vershinina, E.A., 2001; Butkevich, I.P. and Vershinina, E.A., 2003; Butkevich, I.P., Mikhailenko, V.A., Vershinina, E.A., Khozhai, L.I., Grigorev, I.P., Otellin, V.A., 2005; Butkevich, I.P., Mikhailenko, V.A., Khozhai, L.I., Otellin, V.A., 2006). In the present study, we focus on the influence of the maternal corticosterone milieu and its role in the effects of stress during pregnancy on formalin-induced pain and the corticosterone response to it in male and female offspring of different ages. For this purpose, we used adrenalectomy (AD) in female rats 3-4 weeks before mating (as distinct from AD typically performed at the beginning of pregnancy). Since AD is considered a reliable method to treat hypercortisolism, researches on the effects of long-term AD in dams on the systems responsible for adaptive behavior in offspring are important (such studies are not described in the literature). The results demonstrate that the differences in the corticosterone response to injection of formalin and saline are obvious in 90-day-old (adult) female offspring but masked in 25-day-old ones. AD promoted the corticosterone response to formalin-induced pain but not to injection of saline in prenatally non-stressed female offspring of both ages. Prenatal stress canceled the differences in corticosterone response to injection of formalin and saline in 25-day-old offspring of AD dams and in adult offspring of sham-operated (SH) dams but caused similar differences in adult offspring of AD dams. Sex differences were found in basal corticosterone levels in AD prenatally stressed rats of both age groups, with a higher level in females, and in the corticosterone response to formalin-induced pain in the adult rats of all groups investigated, with higher corticosterone levels in females. In regard to pain behavior, AD induced significant changes in flexing+shaking in prenatally non-stressed adult offspring and canceled the differences in this behavior between non-stressed and stressed 25-day-old offspring. There were sex differences in pain behavior of the adult rats: greater flexing+shaking in AD non-stressed males but in SH non-stressed females; greater licking in prenatally-stressed AD and SH females. These results indicate that the long-term influences of maternal corticosterone on formalin-induced pain and the corticosterone response to it are determined by the sex and age of the offspring and suggest that other mechanisms, including serotonergic ones revealed in our previous studies, are involved in the effects of prenatal stress on inflammatory pain behavior.

Novel role of adrenergic neurons in the brain stem in mediating the hypothalamic-pituitary axis hyperactivity caused by prenatal alcohol exposure

Exposure to alcohol during embryonic development leads to changes in the hypothalamic-pituitary-adrenal (HPA) axis such that adult offspring release more adrenocorticotrophic hormone (ACTH) than controls when exposed to stress. In the present work, we tested the hypothesis that changes in the activity of the catecholaminergic system modulate, at least in part, this upregulation of the HPA axis. Pregnant Sprague-Dawley rats were exposed to alcohol 6 h daily during gestation days 7-18 using the vapor chamber model, which generated mean blood alcohol levels of 188.6+/-10 mg/dl. All experiments were performed on 2 to 3-month-old offspring. We first measured the ACTH response to i.c.v. injection of adrenergic receptor agonists. In rats exposed to footshocks, we then investigated the activity of corticotrophin-releasing factor (CRF) as well as indexes of catecholamine ir, namely tyrosine hydroxylase (TH) immunopositive neurons in the paraventricular nucleus (PVN), TH immunopositive neurons in the locus coeruleus, and phenylethanolamine N-methyltransferase (PNMT) immunopositive neurons in the brain stem. While adult females exposed to alcohol during fetal development (FAE) displayed the expected enhanced ACTH response to stress, there were no significant differences in response to adrenergic receptor agonists or in shock-induced CRF/TH ir and neuronal activity, as determined by c-fos colocalization. In contrast, FAE female offspring exposed to footshocks showed a significant increase in the activity of adrenergic neurons in the C1 region of the brain stem, a population of cells that project to the PVN. Collectively, these results suggest that while FAE-induced hyperactivity of the HPA axis is not accompanied by significant changes in PVN CRF or TH-ir neurons, it is characterized by an upregulation of C1 adrenergic neurons of the brain stem. This novel finding should lead to the functional characterization of this brain region in the FAE model.

Effects of Prenatal Ethanol Exposure on Basal Limbic?Hypothalamic?Pituitary?Adrenal Regulation: Role of Corticosterone

BACKGROUND

Rats prenatally exposed to ethanol (E) exhibit hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness and changes in central HPA regulation following exposure to stressors. Whether ethanol-induced alterations in basal HPA regulation play a role in mediating HPA hyperresponsiveness remains unclear. We utilized adrenalectomy (ADX), with or without corticosterone (CORT) replacement, to investigate basal HPA function and the role of CORT in mediating ethanol-induced alterations.

METHODS

Adult males and females from prenatal E, pair-fed (PF), and ad lib-fed control (C) groups were terminated at the circadian peak, 7 days following sham surgery or ADX, with or without CORT replacement. Plasma levels of CORT and adrenocorticotropin (ACTH), and mRNA levels of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) in the paraventricular nucleus, CRH Type 1 receptor (CRH-R1) and pro-opiomelanocortin (POMC) in the anterior pituitary, and mineralocorticoid (MR) and glucocorticoid (GR) receptors in the dorsal hippocampus were determined.

RESULTS

Adrenalectomy resulted in significantly greater plasma ACTH elevations in E and PF males, and parallel CRH mRNA elevations in both E and PF males and females compared with their C counterparts. In contrast, pituitary CRH-R1 mRNA levels were lower in E compared with C males, with no differences in POMC. In addition, in response to ADX, E females showed a greater MR mRNA response, and E males showed a greater GR mRNA response compared with their C counterparts, and CORT replacement was ineffective in normalizing ADX-induced alterations in ACTH levels in E and PF females, hippocampal MR mRNA levels in E males, and AVP mRNA levels in PF males and females.

CONCLUSIONS

Together, these data indicate that the prenatal ethanol exposure induces HPA dysregulation under basal conditions at multiple levels of the axis, resulting in alterations in both HPA drive and feedback regulation and/or in the balance between drive and feedback. While some effects may be nutritionally mediated, it appears that the mechanisms underlying basal HPA dysregulation may differ between E and PF animals rather than occurring along a continuum of effects on the same pathway. Altered basal HPA tone may play a role in mediating the HPA hyperresponsiveness to stressors observed in E offspring.

Effects of neonatal dexamethasone treatment on hippocampal synaptic function

OBJECTIVE

Synthetic glucocorticoid dexamethasone (DEX) is frequently used as a therapeutic agent to lessen the morbidity of chronic lung disease in premature infants. Surprisingly, little is known about the long-term neurodevelopmental outcomes of this therapy.

METHODS

Using a schedule of tapering doses of DEX similar to that used in premature infants, we examined the consequences of neonatal DEX treatment on hippocampal synaptic plasticity of infants and associative memory later in their lives.

RESULTS

Neonatal DEX treatment changed the direction of synaptic plasticity, favoring low-frequency, stimulation-induced, long-term depression and opposing the induction of long-term potentiation by high-frequency stimulation in adolescent (5-week-old) rats, but these alterations disappeared in young adult (8-week-old) rats. The effects of DEX on long-term depression and long-term potentiation were found to correlate with an increase in the autophosphorylation of Ca(2+)/calmodulin-dependent protein kinase II and a decrease in the protein phosphatase 1 activity. Neonatal DEX treatment also disrupted memory retention in 5-week-old (but not 8-week-old) rats subjected to passive avoidance learning tasks.

INTERPRETATION

These results suggest that neonatal DEX treatment alters hippocampal synaptic plasticity and contextual fear memory formation in later life, but these impairments apparently are not permanent.

Sexually dimorphic effects of maternal asthma during pregnancy on placental glucocorticoid metabolism and fetal growth

Human pregnancy is associated with sexually dimorphic differences in mortality and morbidity of the fetus with the male fetus experiencing the poorest outcome following complications such as pre-eclampsia, pre-term delivery and infection. The physiological mechanisms that confer these differences have not been well characterised in the human. Work conducted on the effect of maternal asthma during pregnancy, combining data collected from the mother, placenta and fetus has found some significant sex-related mechanistic differences associated with fetal growth in both normal pregnancies and pregnancies complicated by asthma. Specifically, sexually dimorphic differences have been found in placental glucocorticoid metabolism in male and female fetuses of normal pregnancies. In response to the presence of maternal asthma, only the female fetus alters placental glucocorticoid metabolism resulting in decreased growth. The male fetus does not alter placental function or growth in response to maternal asthma. As a result of the alterations in glucocorticoid metabolism in the female, downstream changes occur in pathways regulated by glucocorticoids. These data suggest that the female fetus adjusts placental function and reduces growth to compensate for maternal disease. However, the male fetus continues to grow in response to maternal asthma with no changes in placental function. This response by the male fetus may partially contribute to the increased risk of morbidity and mortality in this sex.

Maternal adrenalectomy affects development of adrenal medulla

This work investigates the effects of maternal adrenalectomy (ADX) on the development of the adrenal medulla. Adrenal catecholamines (AC) were measured at postnatal day (PN) 1, 8, 12 and 22 in rat offspring of ADX dams and in pups of control dams. The pups of ADX rats showed a reduction in AC concentrations in the adrenal medulla at PN 1, 12 and 22, although these were higher than in the pups of sham dams at PN 8. Further, in the pups of control mothers, there was an increase in ACs during the first two weeks of life whereas pups of ADX mothers only showed increases in noradrenaline, dopamine and adrenaline levels at day 8. These results suggest that maternal absence of corticosterone affects the medulla catecholamine content during development. These data support the idea that a maternal glucocorticoids are involved in the differentiation or/and maturation of the adrenal medulla.

Sex-differences in adrenocortical responsiveness during development in rats

It is known that the stress hyporesponsive period (SHRP), which seems to be related to an immature hypothalamo-pituitary-adrenal (HPA) regulatory system, occurs during the first 2 weeks after birth in rats. In the present study, we investigated the effects of sex-steroid hormones on adrenocortical responsiveness to adrenocorticotropic hormone (ACTH) in neonatal rats. The levels of cyclic adenosine 3',5'-monophosphate (cAMP), corticosterone, and adenylate cyclase activity increased with the dose of ACTH in adrenal cells of males and females in vitro. The ACTH responsiveness in adrenal cells increased with age (7-35 days of age), that is, the loss in responsiveness to ACTH just after birth began to recover in 14-35-day-old rats, but the responsiveness in 14-day-old rats was attenuated in males compared with females. Although castration markedly augmented the responsiveness in male rats, testosterone-replacement in the castrated male rats inhibited the enhancement. Furthermore, the responsiveness in 14-day-intact female rats was suppressed by treatment with testosterone. Expression levels of ACTH receptor mRNA in adrenals increased with age in the female rat, but not in the male. Castration enhanced the level of ACTH receptor mRNA to three-fold of that in intact male rats at 14 days of age, but replacement treatment with testosterone in castrated male rats lowered the elevated levels. Testicular androgens are thought to evoke a gender-specific response in neonates, and the temporal decrease of adrenal ACTH-responsiveness might be due to the topically immature adrenal system as well as the central nervous system in mammals.

Maternal alcohol and adrenalectomy: asynchrony of stress response and forced swim behavior

Fetal alcohol-exposed (FAE) rats exhibit heightened hormonal and behavioral stress responses, strikingly similar to those caused by exposure to elevated maternal corticosterone (CORT). Since alcohol increases maternal CORT, this study examined the effect of maternal adrenalectomy (ADX) on the CORT stress response and forced swim test (FST) behavior of the adult FAE offspring. Maternal ADX alone dramatically enhanced the CORT stress response of the offspring of pair-fed (PF) mothers but had no effect on the exaggerated CORT response to restraint stress observed in the FAE female. In contrast, maternal ADX reversed the increased immobility of FAE offspring in the FST of depressive behavior. These findings provide original evidence that stress hyper-reactivity and depressive behavior in the FAE offspring are mediated by separate developmental mechanisms.

Effects of neonatal corticosterone treatment on maze performance and HPA axis in juvenile rats

Previous research has indicated that administering corticosterone to dams' drinking water for 21 days produced persistent alterations in physiology and behavior. We investigated whether 4 days of corticosterone exposure would have similar effects, and whether greater effects would be found when corticosterone was administered early in neonatal life than later in neonatal life. Sprague-Dawley dams were given either corticosterone (250 microg/ml) in their water bottles for postnatal days (PND) 5-9 (early corticosterone treatment: ECT), PND 13-17 (late corticosterone treatment: LCT) or no treatment (NT). At the end of treatment, corticosterone levels were higher in pups of corticosterone drinking dams. However, at weaning, ECT and LCT pups had lower basal corticosterone levels than NT pups. As juveniles, ECT pups learned to navigate to a visible and then to a nonvisible platform in a Morris water maze more quickly than did LCT and NT pups. Among females, ECT pups had higher corticosterone release in response to stress than LCT and NT pups. There were no differences in hippocampal corticosteroid receptor levels among the groups. The pattern of results is similar to, but not identical to, that found for pups exposed to corticosterone for 21 days. The results also suggest that there is a critical or sensitive period for corticosterone treatment in that early treatment was more effective than later treatment.

Effects of maternal separation during early postnatal development on male sexual behavior and female reproductive function

The endocrine response to stress is an important homoeostatic mechanism, and the secretion of glucocorticoids from the adrenal cortex is a central feature of this response. During early postnatal development, the neonatal rat displays a reduced hypothalamic-pituitary-adrenal (HPA) response to stress. This early period has been termed the 'stress hyporesponsive period' (SHRP). Maternal separation (Sep) of neonates from their mothers during early postnatal development alters the HPA response to stress. In this study, we report the effects of Sep during the SHRP. Female rats were time mated and randomly divided into control or Sep groups before birth. The Sep litters were removed from the mothers during the dark cycle for 6 h per day from postnatal day (PND) 2 to 10. On PND 28, the pups from both groups were weighed, the anogenital distance (AGD) was measured and the animals weaned. At 40 days of age, male and female animals from both groups were tested for open-field activity. As the animals matured, vaginal opening and estrous cycles were measured in females, and males were tested for male sexual behavior at adulthood. Basal, stress, and stress recovery serum corticosterone levels were measured from control and Sep male and female animals. Open-field activity was not significantly different between control or Sep male or female animals. Sep did not affect either vaginal opening or estrous cycles in female animals. Corticosterone secretion in response to stress was similar in control and Sep males and females; however, the recovery levels were significantly higher in Sep females than in Sep males or female control values. In male sexual behavior tests, Sep males had significantly longer mount latencies (time to the first mount), longer intromission latencies (time to the first intromission) and a significant reduction in the percent of animals ejaculating versus control values (controls 84 and Sep 50%). Therefore, Sep males as adults displayed altered reproductive behavior, whereas their stress recovery levels of corticosterone returned to near basal levels in a similar fashion to that observed for control non-handled males. In contrast, females displayed normal reproductive physiology, while their recovery levels of corticosterone remained high, unlike that observed with control females. Thus, significant gender differences in response to Sep (during the dark phase of the circadian cycle) were observed in the paradigm used in the present study.

Effects of neonatal RU486 on adult sexual, parental, and fearful behaviors in rats

Exposure to gonadal hormones during perinatal life influences later behavior. The finding that sex differences exist in progestin receptor expression in the perinatal rat brain suggests differential sensitivity of male and female brains to progesterone (C. K. Wagner, A. N. Nakayama, & G. J. De Vries, 1998). Because these sex differences are in neural sites that influence sexually differentiated sexual, parental, and fearful behaviors in adults, this study examined the effects of administering the progestin receptor antagonist RU486 for the first 10 days after birth on these behaviors in adulthood. Neonatal RU486 significantly reduced sexual behavior in males but did not impair reproduction in females. Neonatal RU486 did not affect parental responses of virgin rats exposed to pups (sensitization) but reduced fear in the elevated plus-maze in both sexes. Treatment of pups with RU486 affected neither mother-litter interactions nor plasma testosterone levels in males during or after treatment. These results suggest that neonatal exposure to progesterone, in addition to androgens and estrogens, influences behavioral development in rats.

Differential regulation of glucocorticoid receptor messenger RNA (GR-mRNA) by maternal deprivation in immature rat hypothalamus and limbic regions

Maternal deprivation (MDep) of neonatal rats significantly influences the hypothalamic-pituitary-adrenal (HPA) axis. This study hypothesized that GR-mRNA modulation constituted an early, critical mechanism for the acute effects of MDep on neuroendocrine stress-responses. GR-mRNA hybridization signal in hippocampal CA1, hypothalamic paraventricular nucleus (PVN) and frontal cortex was significantly reduced immediately following 24 h MDep. In amygdala, cingulate cortex, PVN and CA1, apparent gender-dependent MDep effects on GR-mRNA expression were observed, without significant differences in absolute levels. Thus, rapid, region-specific MDep effects on GR-mRNA expression in HPA-regulating areas are shown, consistent with involvement of GR-expression in mechanisms of MDep influence on HPA tone.

Long-term alterations in opiate antinociception resulting from infant fentanyl tolerance and dependence

Postnatal day-14 (P14) infant rats remained naive or were implanted with osmotic minipumps infusing saline or fentanyl (50 microg kg(-1) h(-1)). Fentanyl was administered 72 h later for measurement of antinociception in the tail-flick test. The potency of fentanyl was 3.0-fold lower in fentanyl-infused compared to saline-infused P17 rats. Fentanyl-infused P17 rats injected with naloxone underwent withdrawal characterized by increases in spontaneous activity, wall climbing, diarrhea, abdominal stretching, forepaw treading/tremors, wet-dog shakes, jumping, ptosis, rhinorrhea and hypothermia. Other naive, saline-infused and fentanyl-infused P17 rats not challenged with fentanyl or naloxone were housed until maturing into P42 juveniles. Fentanyl's potency was equal among each treatment group. However, morphine's potency was reduced in juveniles tolerant to fentanyl as infants. Morphine was also less potent in P90 adults tolerant to fentanyl as infants. Thus, chronic opiate exposure during infancy may affect the developing central nervous system, and desensitize animals and humans to opiate analgesia throughout life.