Neonatal alcohol exposure permanently disrupts the circadian properties and photic entrainment of the activity rhythm in adult rats

Developmental alcohol exposure is exhausting: Sleep and the enduring consequences of alcohol exposure during development

Prenatal alcohol exposure is the leading nongenetic cause of human intellectual impairment. The long-term impacts of prenatal alcohol exposure on health and well-being are diverse, including neuropathology leading to behavioral, cognitive, and emotional impairments. Additionally negative effects also occur on the physiological level, such as the endocrine, cardiovascular, and immune systems. Among these diverse impacts is sleep disruption. In this review, we describe how prenatal alcohol exposure affects sleep, and potential mechanisms of those effects. Furthermore, we outline the evidence that sleep disruption across the lifespan may be a mediator of some cognitive and behavioral impacts of developmental alcohol exposure, and thus may represent a promising target for treatment.

Loss of circadian protection against influenza infection in adult mice exposed to hyperoxia as neonates

Adverse early-life exposures have a lasting negative impact on health. Neonatal hyperoxia that is a risk factor for bronchopulmonary dysplasia confers susceptibility to influenza A virus (IAV) infection later in life. Given our previous findings that the circadian clock protects against IAV, we asked if the long-term impact of neonatal hyperoxia vis-à-vis IAV infection includes circadian disruption. Here, we show that neonatal hyperoxia abolishes the clock-mediated time of day protection from IAV in mice, independent of viral burden through host tolerance pathways. We discovered that the lung intrinsic clock (and not the central or immune clocks) mediated this dysregulation. Loss of circadian protein, Bmal1, in alveolar type 2 (AT2) cells recapitulates the increased mortality, loss of temporal gating, and other key features of hyperoxia-exposed animals. Our data suggest a novel role for the circadian clock in AT2 cells in mediating long-term effects of early-life exposures to the lungs.

Understanding and managing sleep disruption in children with fetal alcohol spectrum disorder

Accumulating evidence has revealed high rates of sleep disruption among children with fetal alcohol spectrum disorder (FASD). Multiple animal and clinical studies have found a clear association between sleep problems and prenatal alcohol exposure, and recent research is beginning to characterize the types and extent of sleep disruption in FASD. Nevertheless, sleep disruption in children with FASD often goes unrecognized or is treated without referring to an evidence base. Children's disrupted sleep interferes with parental sleep and increases caregiver burden, which is of particular importance for families raising children with FASD, a group with very high levels of caregiving stress. The literature supporting an association between sleep problems and deficits in emotional, behavioral, and cognitive function in children is compelling, but needs further investigation in children with FASD. This paper will review the current state of knowledge on sleep in FASD and recommend a rational approach to sleep interventions for affected children and their families.

Developmental ethanol exposure-induced sleep fragmentation predicts adult cognitive impairment

Developmental ethanol (EtOH) exposure can lead to long-lasting cognitive impairment, hyperactivity, and emotional dysregulation among other problems. In healthy adults, sleep plays an important role in each of these behavioral manifestations. Here we explored circadian rhythms (activity, temperature) and slow-wave sleep (SWS) in adult mice that had received a single day of EtOH exposure on postnatal day 7 and saline littermate controls. We tested for correlations between slow-wave activity and both contextual fear conditioning and hyperactivity. Developmental EtOH resulted in adult hyperactivity within the home cage compared to controls but did not significantly modify circadian cycles in activity or temperature. It also resulted in reduced and fragmented SWS, including reduced slow-wave bout duration and increased slow-wave/fast-wave transitions over 24-h periods. In the same animals, developmental EtOH exposure also resulted in impaired contextual fear conditioning memory. The impairment in memory was significantly correlated with SWS fragmentation. Furthermore, EtOH-treated animals did not display a post-training modification in SWS which occurred in controls. In contrast to the memory impairment, sleep fragmentation was not correlated with the developmental EtOH-induced hyperactivity. Together these results suggest that disruption of SWS and its plasticity are a secondary contributor to a subset of developmental EtOH exposure's long-lasting consequences.

Circadian rhythms and addiction: mechanistic insights and future directions

Circadian rhythms are prominent in many physiological and behavioral functions. Circadian disruptions either by environmental or molecular perturbation can have profound health consequences, including the development and progression of addiction. Both animal and humans studies indicate extensive bidirectional relationships between the circadian system and drugs of abuse. Addicted individuals display disrupted rhythms, and chronic disruption or particular chronotypes may increase the risk for substance abuse and relapse. Moreover, polymorphisms in circadian genes and an evening chronotype have been linked to mood and addiction disorders, and recent efforts suggest an association with the function of reward neurocircuitry. Animal studies are beginning to determine how altered circadian gene function results in drug-induced neuroplasticity and behaviors. Many studies suggest a critical role for circadian rhythms in reward-related pathways in the brain and indicate that drugs of abuse directly affect the central circadian pacemaker. In this review, we highlight key findings demonstrating the importance of circadian rhythms in addiction and how future studies will reveal important mechanistic insights into the involvement of circadian rhythms in drug addiction.

Larval ethanol exposure alters free-running circadian rhythm and per Locus transcription in adult D. melanogaster period mutants

Alcohol consumption causes disruptions in a variety of daily rhythms, including the circadian free-running rhythm. A previous study conducted in our laboratories has shown that larval ethanol exposure alters the free-running period in adult Canton-S Drosophila melanogaster. Few studies, however, have explored the effect of alcohol exposure on organisms exhibiting circadian periods radically different than (normal) 24-h. We reared Canton-S, period long, and period short Drosophila melanogaster larvae on 10%-ethanol supplemented food, and assessed their adult free-running locomotor activity and period transcript at ZT 12. We demonstrate that in Canton-S larval ethanol exposure shortens the adult free-running locomotor activity but does not significantly alter period mRNA levels at ZT 12. Period long mutants exposed to larval ethanol had significantly shortened adult free-running locomotor activity rhythms and decreased period mRNA levels, while period short mutants lengthened their free-running rhythm and showed increased period mRNA levels at ZT 12 after being exposed to larval ethanol. These results indicate that the effects of ethanol on the circadian clock might depend upon the baseline circadian period of the organism or that period mutant gene expression is sensitive to developmental ethanol treatment.

Larval ethanol exposure alters adult circadian free-running locomotor activity rhythm in Drosophila melanogaster

Alcohol consumption causes disruptions in a variety of daily rhythms, including the sleep-wake cycle. Few studies have explored the effect of alcohol exposure only during developmental stages preceding maturation of the adult circadian clock, and none have examined the effects of alcohol on clock function in Drosophila. This study investigates developmental and behavioral correlates between larval ethanol exposure and the adult circadian clock in Drosophila melanogaster, a well-established model for studying circadian rhythms and effects of ethanol exposure. We reared Drosophila larvae on 0%, 10%, or 20% ethanol-supplemented food and assessed effects upon eclosion and the free-running period of the circadian rhythm of locomotor activity. We observed a dose-dependent effect of ethanol on period, with higher doses resulting in shorter periods. We also identified the third larval instar stage as a critical time for the developmental effects of 10% ethanol on circadian period. These results demonstrate that developmental ethanol exposure causes sustainable shortening of the adult free-running period in Drosophila melanogaster, even after adult exposure to ethanol is terminated, and suggests that the third instar is a sensitive time for this effect.

Lobeline attenuates neonatal ethanol-mediated changes in hyperactivity and dopamine transporter function in the prefrontal cortex in rats

Current therapies for attention deficit hyperactivity disorder (ADHD) have varying efficacy in individuals with fetal alcohol spectrum disorders (FASD), suggesting that alternative therapeutics are needed. Developmental exposure to ethanol produces changes in dopamine (DA) systems, and DA has also been implicated in ADHD pathology. In the current study, lobeline, which interacts with proteins in dopaminergic presynaptic terminals, was evaluated for its ability to attenuate neonatal ethanol-induced locomotor hyperactivity and alterations in dopamine transporter (DAT) function in striatum and prefrontal cortex (PFC). From postnatal days (PND) 1-7, male and female rat pups were intubated twice daily with either 3 g/kg ethanol or milk, or were not intubated (non-intubated control) as a model for "third trimester" ethanol exposure. On PND 21 and 22, pups received acute lobeline (0, 0.3, 1, or 3 mg/kg), and locomotor activity was assessed. On PND 23-25, pups again received an acute injection of lobeline (1 or 3 mg/kg), and DAT kinetic parameters (Km and V(max)) were determined. Results demonstrated that neonatal ethanol produced locomotor hyperactivity on PND 21 that was reversed by lobeline (1 and 3 mg/kg). Although striatal DAT function was not altered by neonatal ethanol or acute lobeline, neonatal ethanol exposure increased the V(max) for DAT in the PFC, suggesting an increase in DAT function in PFC. Lobeline ameliorated this effect on PFC V(max) at the same doses that decreased hyperactivity. Methylphenidate, the gold standard therapeutic for ADHD, was also evaluated for comparison with lobeline. Methylphenidate decreased DAT V(max) and Km in PFC from ethanol-treated pups. Thus, lobeline and methylphenidate differentially altered DAT function following neonatal ethanol exposure. Collectively, these findings provide support that lobeline may be a useful pharmacotherapy for some of the deficits associated with neonatal ethanol exposure.

Cardiac-specific mutation of Clock alters the quantitative measurements of physical activities without changing behavioral circadian rhythms

Even though peripheral circadian oscillators in the cardiovascular system are known to exist, the daily rhythms of the cardiovascular system are mainly attributed to autonomic or hormonal inputs under the control of the central oscillator, the suprachiasmatic nucleus (SCN). In order to examine the role of peripheral oscillators in the cardiovascular system, we used a transgenic mouse where the Clock gene is specifically disrupted in cardiomyocytes. In this cardiomyocyte-specific CLOCK mutant (CCM) mouse model, the circadian input from the SCN remains intact. Both CCM and wild-type (WT) littermates displayed circadian rhythms in wheel-running behavior. However, the overall wheel-running activities were significantly lower in CCM mice compared to WT over the course of 5 weeks, indicating that CCM mice either have lower baseline physical activities or they have lower physical adaptation abilities because daily wheel running, like routine exercise, induces physical adaptation over a period of time. Upon further biochemical analysis, it was revealed that the diurnal oscillations of phosphorylation states of several kinases and protein expression of the L-type voltage-gated calcium channel (L-VGCC) α1D subunit found in WT hearts were abolished in CCM hearts, indicating that in mammalian hearts, the daily oscillations of the activities of these kinases and L-VGCCs were downstream elements of the cardiac core oscillators. However, the phosphorylation of p38 MAPK exhibited robust diurnal rhythms in both WT and CCM hearts, indicating that cardiac p38 could be under the influence of the central clock through neurohormonal signals or be part of the circadian input pathway in cardiomyocytes. Taken together, these results indicate that the cardiac core oscillators have an impact in regulating circadian rhythmicities and cardiac function.

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.

Binge-like postnatal alcohol exposure triggers cortical gliogenesis in adolescent rats

The long-term effects of binge-like postnatal alcohol exposure on cell proliferation and differentiation in the adolescent rat neocortex were examined. Unlike the hippocampal dentate gyrus, where proliferation of progenitors results primarily in addition of granule cells in adulthood, the vast majority of newly generated cells in the intact mature rodent neocortex appear to be glial cells. The current study examined cytogenesis in the motor cortex of adolescent and adult rats that were exposed to 5.25 g/kg/day of alcohol on postnatal days (PD) 4-9 in a binge manner. Cytogenesis was examined at PD50 (through bromodeoxyuridine [BrdU] labeling) and survival of these newly generated cells was evaluated at PD80. At PD50, significantly more BrdU-positive cells were present in the motor cortex of alcohol-exposed rats than controls. Confocal analysis revealed that the majority (>60%) of these labeled cells also expressed NG2 chondroitin sulfate proteoglycan (NG2 glia). Additionally, survival of these newly generated cortical cells was affected by neonatal alcohol exposure, based on the greater reduction in the number of BrdU-labeled cells from PD50 to PD80 in the alcohol-exposed animals compared to controls. These findings demonstrate that neonatal alcohol exposure triggers an increase in gliogenesis in the adult motor cortex.

Neonatal alcohol exposure differentially alters clock gene oscillations within the suprachiasmatic nucleus, cerebellum, and liver of adult rats

BACKGROUND

In rats, alcohol exposure during the period of rapid brain growth produces long-term changes in the free-running period, photoentrainment and phase-shifting responses of the circadian rhythm in wheel-running behavior. To determine whether these alterations in circadian behavior are associated with permanent damage to the circadian timekeeping mechanism or reconfiguration of its molecular components, we examined the long-term effects of neonatal alcohol exposure on clock gene rhythms in the pacemaker located in the suprachiasmatic nucleus (SCN) and in other brain or peripheral tissues of adult rats.

METHODS

Artificially reared male rat pups were exposed to alcohol (4.5 g/kg/d) or isocaloric milk formula (gastrostomy control; GC) on postnatal days 4 to 9. At 3 months of age, animals were exposed to constant darkness and then SCN, cerebellum, and liver tissue were harvested at 6-hour intervals for subsequent analysis of Period1 (Per1), Per2, Cryptochrome1 (Cry1), Bmal1, and Rev-erbalpha mRNA levels by quantitative PCR.

RESULTS

In the SCN, cerebellum and liver, Per1, Per2, Cry1, Bmal1, and Rev-erbalpha expression oscillated with a similar amplitude (peak-to-trough differences of 2- to 9-fold) and phase in the suckle control (SC) and GC groups. These clock gene rhythms in control animals were marked by peak expression of Per1, Per2, Cry1, and Rev-erbalpha during the subjective day and of Bmal1 during the subjective night. The EtOH group was distinguished by altered rhythms in the expression of specific clock genes within the SCN, cerebellum and liver. In EtOH-treated rats, the SCN rhythm in Cry1 expression was strongly damped and the Per2 rhythms in the cerebellum and liver were phase-advanced such that peak expression occurred during the mid-subjective day.

CONCLUSIONS

These results demonstrate alcohol exposure during the brain growth spurt alters the circadian regulation of some molecular components of the clock mechanism in the rat SCN, cerebellum, and liver. The observed alterations in the temporal configuration of essential "gears" of the molecular clockworks may play a role in the long-term effects of neonatal alcohol exposure on the regulation of circadian behavior.

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

Ethanol's effects on the developing brain include alterations in morphology and biochemistry of the hypothalamus. To examine the potential functional consequences of ethanol's interference with hypothalamic differentiation, we studied the long-term effects of prenatal ethanol exposure on basal circadian rhythms of core body temperature (CBT) and heart rate (HR). We also examined the late afternoon surge in corticosterone (CORT). Core body temperature and HR rhythms were studied in separate groups of animals at 4, 8, and 20 months of age. The normal late afternoon rise in plasma CORT was examined in freely moving male rats at 6 months of age via an indwelling right atrial cannula. Results showed that the CBT circadian rhythm exhibited an earlier rise after the nadir of the rhythm in fetal alcohol-exposed (FAE) males at all ages compared to controls. At 8 months of age, the amplitude of the CBT circadian rhythm in FAE males was significantly reduced to the level observed in controls at 20 months. No significant effects of prenatal ethanol exposure were observed on basal HR rhythm at any age. The diurnal rise in CORT secretion was blunted and prolonged in 6-month-old FAE males compared to controls. Both control groups exhibited a robust surge in CORT secretion around the onset of the dark phase of the light cycle, which peaked at 7:30 p.m. Whereas FAE males exhibited a linear rise beginning in mid afternoon, which peaked at 9:30 p.m. These results indicate that exposure to ethanol during the period of hypothalamic development can alter the long-term regulation of circadian rhythms in specific physiological systems.

Meeting report: the role of environmental lighting and circadian disruption in cancer and other diseases

Light, including artificial light, has a range of effects on human physiology and behavior and can therefore alter human physiology when inappropriately timed. One example of potential light-induced disruption is the effect of light on circadian organization, including the production of several hormone rhythms. Changes in light-dark exposure (e.g., by nonday occupation or transmeridian travel) shift the timing of the circadian system such that internal rhythms can become desynchronized from both the external environment and internally with each other, impairing our ability to sleep and wake at the appropriate times and compromising physiologic and metabolic processes. Light can also have direct acute effects on neuroendocrine systems, for example, in suppressing melatonin synthesis or elevating cortisol production that may have untoward long-term consequences. For these reasons, the National Institute of Environmental Health Sciences convened a workshop of a diverse group of scientists to consider how best to conduct research on possible connections between lighting and health. According to the participants in the workshop, there are three broad areas of research effort that need to be addressed. First are the basic biophysical and molecular genetic mechanisms for phototransduction for circadian, neuroendocrine, and neurobehavioral regulation. Second are the possible physiologic consequences of disrupting these circadian regulatory processes such as on hormone production, particularly melatonin, and normal and neoplastic tissue growth dynamics. Third are effects of light-induced physiologic disruption on disease occurrence and prognosis, and how prevention and treatment could be improved by application of this knowledge.

Long-term effects of neonatal alcohol exposure on photic reentrainment and phase-shifting responses of the activity rhythm in adult rats

In rats, neonatal alcohol (EtOH) exposure coinciding with the period of rapid brain growth produces structural damage in some brain regions that often persists into adulthood and thus may have long-term consequences in the neural regulation of behavior. Because recent findings indicate that the circadian clock located in the rat suprachiasmatic nucleus is vulnerable to alcohol-induced insults during development, the present study examined the long-term effects of neonatal alcohol exposure on the photic regulation of circadian behavior in adult rats. Rat pups were exposed to alcohol (3.0, 4.5, or 6.0 g x kg(-1) x day(-1)) or isocaloric milk formula on postnatal days 4-9 using artificial-rearing methods. At 2 months of age, animals were housed individually and circadian wheel-running behavior was continuously analyzed to determine the effects of neonatal alcohol treatment on the rate of reentrainment to a 6-h advance in the 12-h light:12-h dark photoperiod and the phase-shifting properties of free-running rhythms in response to discrete light pulses on a background of constant darkness. For all doses, neonatal alcohol exposure had a significant effect in reducing the time for reentrainment such that EtOH-treated rats required four to five fewer days than control animals for stable realignment of the activity rhythm to the shifted light-dark cycle. Coupled with the accelerated rate of reentrainment, the amplitude of light-evoked phase delays at circadian time 14 and advances at circadian time 22 in the 4.5 and 6.0 g x kg(-1) x day(-1) EtOH groups was almost twofold greater than that observed in control animals. The present observations indicate that the mechanisms by which photic signals regulate circadian behavior are permanently altered following alcohol exposure during the period of rapid brain development. These long-term alterations in the photic regulation of circadian rhythms may account, at least partially, for some neurobehavioral consequences of prenatal alcohol exposure in humans such as depression.