Prenatal ethanol exposure alters core body temperature and corticosterone rhythms in adult male rats

Sexually dimorphic role of circadian clock genes in alcohol drinking behavior

Sex differences in alcohol use and abuse are pervasive and carry important implications for the prevention and treatment of alcohol use disorder (AUD), yet insight into underlying sexually dimorphic mechanisms is limited. Growing experimental and clinical evidence points to an important influence of circadian rhythms and circadian clock genes in the control of alcohol drinking behavior and AUD. Sex differences in the expression of circadian rhythms and in the molecular circadian clock that drive these rhythms have been reported in humans and animals. While studying the role of striatal circadian clock gene expression in the control of affective and goal-directed behaviors, we uncovered a novel sexually dimorphic function of the clock genes Bmal1 and Per2 in the control of voluntary alcohol consumption in mice, which may contribute to sex differences in alcohol drinking behavior. In this mini review, we briefly discuss relevant literature on AUD, circadian rhythms and clock genes, and on sex differences in these domains, and describe our own findings on clock genes as sexually dimorphic regulators of alcohol drinking behavior in mice.

Chronotype in very low birth weight adults - a sibling study

Chronotype is the temporal preference for activity and sleep during the 24 h day and is linked to mental and physical health, quality of life, and mortality. Later chronotypes, so-called "night owls", consistently display poorer health outcomes than "larks". Previous studies have suggested that preterm birth (<37 weeks of gestation) is associated with an earlier chronotype in children, adolescents, and young adults, but studies beyond this age are absent. Our aim was to determine if adults born preterm at very low birth weight (VLBW, ≤1500 g) display different chronotypes than their siblings. We studied VLBW adults, aged 29.9 years (SD 2.8), matched with same-sex term-born siblings as controls. A total of 123 participants, consisting of 53 sibling pairs and 17 unmatched participants, provided actigraphy-derived data on the timing, duration, and quality of sleep from 1640 nights (mean 13.3 per participant, SD 2.7). Mixed effects models provided estimates and significance tests. Compared to their siblings, VLBW adults displayed 27 min earlier sleep midpoint during free days (95% CI: 3 to 51 min, p =.029). This was also reflected in the timing of falling asleep, waking up, and sleep-debt corrected sleep midpoint. The findings were emphasized in VLBW participants born small for gestational age. VLBW adults displayed an earlier chronotype than their siblings still at age 30, which suggests that the earlier chronotype is an enduring individual trait not explained by shared family factors. This preference could provide protection from risks associated with preterm birth.

ABBREVIATIONS

AGA: Appropriate for gestational age; ELBW: Extremely low birth weight, ≤ 1000 grams; FMBR: Finnish Medical Birth Registry; HeSVA: Helsinki Study of Very low birth weight Adults; MSFsc: Midsleep on free days, corrected for sleep debt; SGA: Small for gestational age, ≤ -2 SD; VLBW: Very low birth weight, ≤ 1500 grams; WASO: Wake after sleep onset.

Sleep in Infants and Children with Prenatal Alcohol Exposure

Prenatal exposure to alcohol can result in a range of neurobehavioral impairments and physical abnormalities. The term "fetal alcohol spectrum disorders (FASD)" encompasses the outcomes of prenatal alcohol exposure (PAE), the most severe of which is fetal alcohol syndrome. These effects have lifelong consequences, placing a significant burden on affected individuals, caregivers, and communities. Caregivers of affected children often report that their child has sleep problems, and many symptoms of sleep deprivation overlap with the cognitive and behavioral deficits characteristic of FASD. Alcohol-exposed infants and children demonstrate poor sleep quality based on measures of electroencephalography, actigraphy, and questionnaires. These sleep studies indicate a common theme of disrupted sleep pattern, more frequent awakenings, and reduced total sleep time. However, relatively little is known about circadian rhythm disruption and the neurobehavioral correlates of sleep disturbance in individuals with PAE. Furthermore, there is limited information available to healthcare providers about identification and treatment of sleep disorders in patients with FASD. This review consolidates the findings from studies of infant and pediatric sleep in this population, providing an overview of typical sleep characteristics, neurobehavioral correlates of sleep disruption, and potential avenues for intervention in the context of PAE.

Chronic ethanol exposure increases the non-dominant glucocorticoid, corticosterone, in the near-term pregnant guinea pig

Maternal-fetal signaling is critical for optimal fetal development and postnatal outcomes. Chronic ethanol exposure alters programming of the fetal hypothalamic-pituitary-adrenal (HPA) axis, resulting in a myriad of neurochemical and behavioral alterations in postnatal life. Based on a recent study which showed that human intra-partum fetal stress increased fetal secretion of corticosterone, the non-dominant glucocorticoid, this investigation tested the hypothesis that an established model of HPA axis programming, chronic maternal ethanol administration to the pregnant guinea pig, would result in preferential elevation of corticosterone, which is also the non-dominant glucocorticoid. Starting on gestational day (GD) 2, guinea pigs received oral administration of ethanol (4 g/kg maternal body weight/day) or isocaloric-sucrose/pair-feeding. Each treatment was administered daily and continued until GD 45, 55, or 65 (approximately 3 days pre-term), when pregnant animals were euthanized and fetuses delivered by Caesarean section. Maternal and fetal plasma samples were collected. After sample preparation (protein precipitation and C-18 solid phase extraction), plasma cortisol and corticosterone concentrations were determined simultaneously by liquid chromatography coupled to tandem mass spectrometry. As predicted, chronic ethanol exposure increased both fetal and maternal plasma corticosterone concentration in late gestation. In contrast, plasma cortisol did not differ across maternal treatments in maternal or fetal samples. The plasma concentration of both maternal glucocorticoids increased with gestational age. Thus, corticosterone, the non-dominant glucocorticoid, but not cortisol, was elevated by chronic ethanol exposure, which may have effects on HPA function in later life.

Effects of L-glutamine supplementation on maternal and fetal hemodynamics in gestating ewes exposed to alcohol

Not much is known about effects of gestational alcohol exposure on maternal and fetal cardiovascular adaptations. This study determined whether maternal binge alcohol exposure and L-glutamine supplementation could affect maternal-fetal hemodynamics and fetal regional brain blood flow during the brain growth spurt period. Pregnant sheep were randomly assigned to one of four groups: saline control, alcohol (1.75-2.5 g/kg body weight), glutamine (100 mg/kg body weight) or alcohol + glutamine. A chronic weekend binge drinking paradigm between gestational days (GD) 99 and 115 was utilized. Fetuses were surgically instrumented on GD 117 ± 1 and studied on GD 120 ± 1. Binge alcohol exposure caused maternal acidemia, hypercapnea, and hypoxemia. Fetuses were acidemic and hypercapnic, but not hypoxemic. Alcohol exposure increased fetal mean arterial pressure, whereas fetal heart rate was unaltered. Alcohol exposure resulted in ~40 % reduction in maternal uterine artery blood flow. Labeled microsphere analyses showed that alcohol induced >2-fold increases in fetal whole brain blood flow. The elevation in fetal brain blood flow was region-specific, particularly affecting the developing cerebellum, brain stem, and olfactory bulb. Maternal L-glutamine supplementation attenuated alcohol-induced maternal hypercapnea, fetal acidemia and increases in fetal brain blood flow. L-Glutamine supplementation did not affect uterine blood flow. Collectively, alcohol exposure alters maternal and fetal acid-base balance, decreases uterine blood flow, and alters fetal regional brain blood flow. Importantly, L-glutamine supplementation mitigates alcohol-induced acid-base imbalances and alterations in fetal regional brain blood flow. Further studies are warranted to elucidate mechanisms responsible for alcohol-induced programming of maternal uterine artery and fetal circulation adaptations in pregnancy.

Exposure to dexamethasone during late gestation causes female-specific decreases in core body temperature and prepro-thyrotropin-releasing hormone expression in the paraventricular nucleus of the hypothalamus in rats

Synthetic glucocorticoids (GC) have been used to promote lung development in preterm infants, thereby decreasing respiratory distress syndrome and mortality, yet, concern has arisen from reports that such treatment predisposes individuals to disease in adulthood. Given the variety of preclinical studies that show metabolic and behavioral abnormalities in adulthood following fetal exposure to synthetic GC, we examined the effect of in utero exposure to the synthetic GC, dexamethasone (DEX), on hypothalamic expression of thyrotropin-releasing hormone (TRH) a central neuropeptide involved in mediating behavior and metabolic balance. Pregnant Sprague-Dawley rats were administered 0.4mg/kg DEX on gestational days 18-21. As adults (postnatal day (PD) 60), the offspring were fitted with temperature sensing transmitters allowing real-time monitoring of core body temperature (CBT) across the 24h light dark period. This revealed a significant decrease in CBT throughout the day in prenatal DEX-treated females on estrus and diestrus, but not in male offspring. The reduction in CBT by prenatal DEX exposure was accompanied by a significant decrease in the expression of Trh transcript in the paraventricular nucleus of the hypothalamus (PVN) of female rats at PD 60 and this effect was also present on PD7. There was also a female-specific reduction in the number of preproTRH-immunoreactive (ir) neurons in the PVN, with ppTRH-ir nerve fibers decreases that were present in both male and female offspring. No changes in thyroid hormone (triiodothyronine, T3; thyroxine, T4) were observed in adult offspring, but during development, both males and females (PD14) had lower T3 and T4 levels. These data indicate abnormal expression of TRH results from fetal DEX exposure during late gestation, possibly explaining the decreased CBT observed in the female offspring.

Evidence for possible period 2 gene mediation of the effects of alcohol exposure during the postnatal period on genes associated with maintaining metabolic signaling in the mouse hypothalamus

BACKGROUND

Animals exposed to alcohol during the developmental period develop circadian disturbances and metabolic problems that often persist during their adult period. In order to study whether alcohol and the circadian clock interact to alter metabolic signaling in the hypothalamus, we determined whether postnatal alcohol feeding in mice permanently alters metabolic sensing in the hypothalamus. Furthermore, we evaluated whether the effect of circadian disruption via Period 2 (Per2) gene mutation prevents alcohol's effects on metabolic signaling in the hypothalamus.

METHODS

Per2 mutant and wild-type male and female mice of the same genetic background were given a milk formula containing ethanol (EtOH; 11.34% vol/vol) from postnatal day (PD) 2 to 7 and used for gene expression and peptide level determinations in the hypothalamus at PD7 and PD90.

RESULTS

We report here that postnatal alcohol feeding reduces the expression of proopiomelanocortin (Pomc) gene and production of β-endorphin and α-melanocyte stimulating hormone (α-MSH) in the hypothalamus that persists into adulthood. In addition, expressions of metabolic sensing genes in the hypothalamus were also reduced as a consequence of postnatal alcohol exposure. These effects were not sex-specific and were observed in both males and females. Mice carrying a mutation of the Per2 gene did not show any reductions in hypothalamic levels of Pomc and metabolic genes and β-endorphin and α-MSH peptides following alcohol exposure.

CONCLUSIONS

These data suggest that early-life exposure to alcohol alters metabolic sensing to the hypothalamus possibly via regulating Per2 gene and/or the cellular circadian clock mechanism.

Circadian genes, the stress axis, and alcoholism

The body's internal system to control the daily rhythm of the body's functions (i.e., the circadian system), the body's stress response, and the body's neurobiology are highly interconnected. Thus, the rhythm of the circadian system impacts alcohol use patterns; at the same time, alcohol drinking also can alter circadian functions. The sensitivity of the circadian system to alcohol may result from alcohol's effects on the expression of several of the clock genes that regulate circadian function. The stress response system involves the hypothalamus and pituitary gland in the brain and the adrenal glands, as well as the hormones they secrete, including corticotrophin-releasing hormone, adrenocorticotrophic hormone, and glucocorticoids. It is controlled by brain-signaling molecules, including endogenous opioids such as β-endorphin. Alcohol consumption influences the activity of this system and vice versa. Finally, interactions exist between the circadian system, the hypothalamic-pituitary-adrenal axis, and alcohol consumption. Thus, it seems that certain clock genes may control functions of the stress response system and that these interactions are affected by alcohol.

Period 2 gene deletion abolishes beta-endorphin neuronal response to ethanol

BACKGROUND

Ethanol exposure during early life has been shown to permanently alter the circadian expression of clock regulatory genes and the beta-endorphin precursor proopiomelanocortin (POMC) gene in the hypothalamus. Ethanol also alters the stress- and immune-regulatory functions of beta-endorphin neurons in laboratory rodents. Our aim was to determine whether the circadian clock regulatory Per2 gene modulates the action of ethanol on beta-endorphin neurons in mice.

METHODS

Per2 mutant (mPer2(Brdml)) and wild type (C57BL/6J) mice were used to determine the effect of Per2 mutation on ethanol-regulated beta-endorphin neuronal activity during neonatal period using an in vitro mediobasal hypothalamic (MBH) cell culture model and an in vivo milk formula feeding animal model. The beta-endorphin neuronal activity following acute and chronic ethanol treatments was evaluated by measuring the peptide released from cultured cells or peptide levels in the MBH tissues, using enzyme-linked immunosorbent assay (ELISA).

RESULTS

Per2 mutant mice showed a higher basal level of beta-endorphin release from cultured MBH cells and a moderate increase in the peptide content in the MBH in comparison with control mice. However, unlike wild type mice, Per2 mutant mice showed no stimulatory or inhibitory beta-endorphin-secretory responses to acute and chronic ethanol challenges in vitro. Furthermore, Per2 mutant mice, but not wild type mice, failed to show the stimulatory and inhibitory responses of MBH beta-endorphin levels to acute and chronic ethanol challenges in vivo.

CONCLUSIONS

These results suggest for the first time that the Per2 gene may be critically involved in regulating beta-endorphin neuronal function. Furthermore, the data revealed an involvement of the Per2 gene in regulating beta-endorphin neuronal responses to ethanol.

Prenatal alcohol exposure: implications for cardiovascular function in the fetus and beyond

1. The effects of heavy maternal alcohol consumption during pregnancy on cognitive and behavioural performance and craniofacial malformations in the offspring have been studied extensively. In contrast, the impact of maternal alcohol intake on the cardiovascular system of the offspring and the effects of more modest consumption have received very scant consideration. 2. Adverse conditions in the pre- and neonatal periods can have a profound legacy on offspring health, including the risk of cardiovascular disease. Prenatal alcohol exposure can modulate vascular reactivity, including endothelial and smooth muscle function. 3. Other effects of prenatal alcohol exposure are emerging, including impairment of nephrogenesis and kidney function and increased arterial stiffness. The impact of even modest prenatal alcohol exposure on cardiovascular health in the offspring remains to be determined. 4. It is envisaged that the culmination of reduced renal and vascular capacity will render the offspring more vulnerable to cardiovascular disease with ageing and exposure to additional insults and lifestyle factors.

Effects of neonatal alcohol exposure on vasoactive intestinal polypeptide neurons in the rat suprachiasmatic nucleus

Neonatal alcohol exposure produces long-term changes in the suprachiasmatic nucleus (SCN) that are presumably responsible for disturbances in the light-dark regulation of circadian behavior in adult rats, including the pattern of photoentrainment, rate of re-entrainment to shifted light-dark cycles, and phase-shifting responses to light. Because SCN neurons containing vasoactive intestinal polypeptide (VIP) receive direct photic input via the retinohypothalamic tract and thus play an important role in the circadian regulation of the SCN clock mechanism by light, the present study examined the long-term effects of neonatal alcohol exposure on VIP neuronal populations within the SCN of adult rats. Male Sprague-Dawley rat pups were exposed to alcohol (EtOH; 3.0, 4.5, or 6.0 g/kg/day) or isocaloric milk formula (gastrostomy control; GC) on postnatal days 4-9 using artificial-rearing methods. At 2-3 months of age, animals from the suckle control (SC), GC, and EtOH groups were exposed to constant darkness (DD) and SCN tissue was harvested for subsequent analysis of either VIP mRNA expression by quantitative polymerase chain reaction (PCR) and in situ hybridization or of VIP-immunoreactive (ir) neurons using stereological methods. Neonatal alcohol exposure had no impact on VIP mRNA expression but dramatically altered immunostaining of neurons containing this peptide within the SCN of adult rats. The relative abundance of VIP mRNA and anatomical distribution of neurons expressing this transcript were similar among all control- and EtOH-treated groups. However, the total number and density of VIP-ir neurons within the SCN were significantly decreased by about 35% in rats exposed to alcohol at a dose of 6.0 g/kg/day relative to that observed in both control groups. These results demonstrate that VIP neuronal populations in the SCN are vulnerable to EtOH-induced insult during brain development. The observed alterations in SCN neurons containing VIP may have an impact upon clock responses to light input and thus contribute to the long-term effects of neonatal alcohol exposure on the photic regulation of circadian behavior.

Organizational influence of the postnatal testosterone surge on the circadian rhythm of core body temperature of adult male rats

The suprachiasmatic nucleus (SCN) of the hypothalamus coordinates physiological and behavioral circadian rhythms such as activity, body temperature, and hormone secretion. Circadian rhythms coordinated by the SCN often show sex differences arising from both organizational and activational effects of gonadal hormones. In males, little is known about the organizational role of testosterone on the circadian regulation of core body temperature (CBT) in adulthood. To explore this, we castrated or sham-operated male rats on the day of birth, and at 4 months of age, implanted them with transmitters that measured CBT rhythms under a 12:12 light/dark cycle. This study revealed a significantly earlier rise in CBT during the light phase in neonatally castrated males. Subsequently, we found that treating neonatally castrated males with testosterone propionate (TP) in adulthood did not reverse the effect of neonatal castration, thus indicating an organizational role for testosterone. In contrast, a single injection of TP at the time of neonatal surgery, to mimic the postnatal surge of testosterone, coupled with TP treatment in adulthood, normalized the circadian rise in CBT. In a final study we examined CBT circadian rhythms in intact adult male and female rats and detected no differences in the rise of CBT during the light phase, although there was a greater overall elevation in female CBT. Together, results of these studies reveal an early organizational role of testosterone in males on the timing of the circadian rise of CBT, a difference that does not appear to reflect "defeminization".