Neurophysiologic consequences of neonatal ethanol exposure in the rat

Embryonic alcohol exposure impairs the dopaminergic system and social behavioral responses in adult zebrafish

BACKGROUND

The zebrafish is a powerful neurobehavioral genetics tool with which complex human brain disorders including alcohol abuse and fetal alcohol spectrum disorders may be modeled and investigated. Zebrafish innately form social groups called shoals. Previously, it has been demonstrated that a single bath exposure (24 hours postfertilization) to low doses of alcohol (0, 0.25, 0.50, 0.75, and 1% vol/vol) for a short duration (2 hours) leads to impaired group forming, or shoaling, in adult zebrafish.

METHODS

In the current study, we immersed zebrafish eggs in a low concentration of alcohol (0.5% or 1% vol/vol) for 2 hours at 24 hours postfertilization and let the fish grow and reach adulthood. In addition to quantifying the behavioral response of the adult fish to an animated shoal, we also measured the amount of dopamine and its metabolite 3,4-dihydroxyphenylacetic acid from whole brain extracts of these fish using high-pressure liquid chromatograph.

RESULTS

Here we confirm that embryonic alcohol exposure makes adult zebrafish increase their distance from the shoal stimulus in a dose-dependent manner. We also show that the shoal stimulus increases the amount of dopamine and 3,4-dihydroxyphenylacetic acid in the brain of control zebrafish but not in fish previously exposed to alcohol during their embryonic development.

CONCLUSIONS

We speculate that one of the mechanisms that may explain the embryonic alcohol-induced impaired shoaling response in zebrafish is dysfunction of reward mechanisms subserved by the dopaminergic system.

Pioglitazone blocks ethanol induction of microglial activation and immune responses in the hippocampus, cerebellum, and cerebral cortex in a mouse model of fetal alcohol spectrum disorders

BACKGROUND

Fetal alcohol spectrum disorders (FASD) result from fetal exposure to alcohol and are the leading cause of mental retardation in the United States. There is currently no effective treatment that targets the causes of these disorders. Thus, novel therapies are critically needed to limit the neurodevelopmental and neurodegenerative pathologies associated with FASD.

METHODS

A neonatal mouse FASD model was used to examine the role of the neuroimmune system in ethanol (EtOH)-induced neuropathology. Neonatal C57BL/6 mice were treated with EtOH, with or without pioglitazone, on postnatal days 4 through 9, and tissue was harvested 1 day post treatment. Pioglitazone is a peroxisome proliferator-activated receptor (PPAR)-γ agonist that exhibits anti-inflammatory activity and is neuroprotective. We compared the effects of EtOH with or without pioglitazone on cytokine and chemokine expression and microglial morphology in the hippocampus, cerebellum, and cerebral cortex.

RESULTS

In EtOH-treated animals compared with controls, cytokines interleukin-1β and tumor necrosis factor-α mRNA levels were increased significantly in the hippocampus, cerebellum, and cerebral cortex. Chemokine CCL2 mRNA was increased significantly in the hippocampus and cerebellum. Pioglitazone effectively blocked the EtOH-induced increase in the cytokines and chemokine in all tissues to the level expressed in handled-only and vehicle-treated control animals. EtOH also produced a change in microglial morphology in all brain regions that was indicative of microglial activation, and pioglitazone blocked this EtOH-induced morphological change.

CONCLUSIONS

These studies indicate that EtOH activates microglia to a pro-inflammatory stage and also increases the expression of neuroinflammatory cytokines and chemokines in diverse regions of the developing brain. Further, the anti-inflammatory and neuroprotective PPAR-γ agonist pioglitazone blocked these effects. It is proposed that microglial activation and inflammatory molecules expressed as a result of EtOH treatment during brain development contribute to the sequelae associated with FASD. Thus, pioglitazone and anti-inflammatory pharmaceuticals more broadly have potential as novel therapeutics for FASD.

Fetal alcohol spectrum disorders and neuroimmune changes

The behavioral consequences of fetal alcohol spectrum disorders (FASD) are serious and persist throughout life. The causative mechanisms underlying FASD are poorly understood. However, much has been learned about FASD from human structural and functional studies as well as from animal models, which have provided a greater understanding of the mechanisms underlying FASD. Using animal models of FASD, it has been recently discovered that ethanol induces neuroimmune activation in the developing brain. The resulting microglial activation, production of proinflammatory molecules, and alteration in expression of developmental genes are postulated to alter neuron survival and function and lead to long-term neuropathological and cognitive defects. It has also been discovered that microglial loss occurs, reducing microglia's ability to protect neurons and contribute to neuronal development. This is important, because emerging evidence demonstrates that microglial depletion during brain development leads to long-term neuropathological and cognitive defects. Interestingly, the behavioral consequences of microglial depletion and neuroimmune activation in the fetal brain are particularly relevant to FASD. This chapter reviews the neuropathological and behavioral abnormalities of FASD and delineates correlates in animal models. This serves as a foundation to discuss the role of the neuroimmune system in normal brain development, the consequences of microglial depletion and neuroinflammation, the evidence of ethanol induction of neuroinflammatory processes in animal models of FASD, and the development of anti-inflammatory therapies as a new strategy for prevention or treatment of FASD. Together, this knowledge provides a framework for discussion and further investigation of the role of neuroimmune processes in FASD.

Long-lasting neural circuit dysfunction following developmental ethanol exposure

Fetal Alcohol Spectrum Disorder (FASD) is a general diagnosis for those exhibiting long-lasting neurobehavioral and cognitive deficiencies as a result of fetal alcohol exposure. It is among the most common causes of mental deficits today. Those impacted are left to rely on advances in our understanding of the nature of early alcohol-induced disorders toward human therapies. Research findings over the last decade have developed a model where ethanol-induced neurodegeneration impacts early neural circuit development, thereby perpetuating subsequent integration and plasticity in vulnerable brain regions. Here we review our current knowledge of FASD neuropathology based on discoveries of long-lasting neurophysiological effects of acute developmental ethanol exposure in animal models. We discuss the important balance between synaptic excitation and inhibition in normal neural network function, and relate the significance of that balance to human FASD as well as related disease states. Finally, we postulate that excitation/inhibition imbalance caused by early ethanol-induced neurodegeneration results in perturbed local and regional network signaling and therefore neurobehavioral pathology.

Delays in auditory processing identified in preschool children with FASD

BACKGROUND

Both sensory and cognitive deficits have been associated with prenatal exposure to alcohol; however, very few studies have focused on sensory deficits in preschool-aged children. As sensory skills develop early, characterization of sensory deficits using novel imaging methods may reveal important neural markers of prenatal alcohol exposure.

METHODS

Participants in this study were 10 children with a fetal alcohol spectrum disorder (FASD) and 15 healthy control (HC) children aged 3 to 6 years. All participants had normal hearing as determined by clinical screens. We measured their neurophysiological responses to auditory stimuli (1,000 Hz, 72 dB tone) using magnetoencephalography (MEG). We used a multidipole spatio-temporal modeling technique to identify the location and timecourse of cortical activity in response to the auditory tones. The timing and amplitude of the left and right superior temporal gyrus sources associated with activation of left and right primary/secondary auditory cortices were compared across groups.

RESULTS

There was a significant delay in M100 and M200 latencies for the FASD children relative to the HC children (p = 0.01), when including age as a covariate. The within-subjects effect of hemisphere was not significant. A comparable delay in M100 and M200 latencies was observed in children across the FASD subtypes.

CONCLUSIONS

Auditory delay revealed by MEG in children with FASDs may prove to be a useful neural marker of information processing difficulties in young children with prenatal alcohol exposure. The fact that delayed auditory responses were observed across the FASD spectrum suggests that it may be a sensitive measure of alcohol-induced brain damage. Therefore, this measure in conjunction with other clinical tools may prove useful for early identification of alcohol affected children, particularly those without dysmorphia.

Lithium prevents long-term neural and behavioral pathology induced by early alcohol exposure

Fetal alcohol exposure can cause developmental defects in offspring known as fetal alcohol spectrum disorder (FASD). FASD symptoms range from obvious facial deformities to changes in neuroanatomy and neurophysiology that disrupt normal brain function and behavior. Ethanol exposure at postnatal day 7 in C57BL/6 mice induces neuronal cell death and long-lasting neurobehavioral dysfunction. Previous work has demonstrated that early ethanol exposure impairs spatial memory task performance into adulthood and perturbs local and interregional brain circuit integrity in the olfacto-hippocampal pathway. Here we pursue these findings to examine whether lithium prevents anatomical, neurophysiological, and behavioral pathologies that result from early ethanol exposure. Lithium has neuroprotective properties that have been shown to prevent ethanol-induced apoptosis. Here we show that mice co-treated with lithium on the same day as ethanol exposure exhibit dramatically reduced acute neurodegeneration in the hippocampus and retain hippocampal-dependent spatial memory as adults. Lithium co-treatment also blocked ethanol-induced disruption in synaptic plasticity in slice recordings of hippocampal CA1 in the adult mouse brain. Moreover, long-lasting dysfunctions caused by ethanol in olfacto-hippocampal networks, including sensory-evoked oscillations and resting state coherence, were prevented in mice co-treated with lithium. Together, these results provide behavioral and physiological evidence that lithium is capable of preventing or reducing immediate and long-term deleterious consequences of early ethanol exposure on brain function.

Acute administration of vinpocetine, a phosphodiesterase type 1 inhibitor, ameliorates hyperactivity in a mice model of fetal alcohol spectrum disorder

BACKGROUND

Maternal alcohol use during pregnancy causes a continuum of long-lasting disabilities in the offspring, commonly referred to as fetal alcohol spectrum disorder (FASD). Attention-deficit/hyperactivity disorder (ADHD) is possibly the most common behavioral problem in children with FASD and devising strategies that ameliorate this condition has great clinical relevance. Studies in rodent models of ADHD and FASD suggest that impairments in the cAMP signaling cascade contribute to the hyperactivity phenotype. In this work, we investigated whether the cAMP levels are affected in a long-lasting manner by ethanol exposure during the third trimester equivalent period of human gestation and whether the acute administration of the PDE1 inhibitor vinpocetine ameliorates the ethanol-induced hyperactivity.

METHODS

From postnatal day (P) 2 to P8, Swiss mice either received ethanol (5g/kg i.p.) or saline every other day. At P30, the animals either received vinpocetine (20mg/kg or 10mg/kg i.p.) or vehicle 4h before being tested in the open field. After the test, frontal cerebral cortices and hippocampi were dissected and collected for assessment of cAMP levels.

RESULTS

Early alcohol exposure significantly increased locomotor activity in the open field and reduced cAMP levels in the hippocampus. The acute treatment of ethanol-exposed animals with 20mg/kg of vinpocetine restored both their locomotor activity and cAMP levels to control levels.

CONCLUSIONS

These data lend support to the idea that cAMP signaling system contribute to the hyperactivity induced by developmental alcohol exposure and provide evidence for the potential therapeutic use of vinpocetine in FASD.

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.

Local and regional network function in behaviorally relevant cortical circuits of adult mice following postnatal alcohol exposure

BACKGROUND

Ethanol consumption during pregnancy can lead to fetal alcohol spectrum disorder (FASD), which consists of the complete spectrum of developmental deficits including neurological dysfunction. FASD is associated with a variety of neurobehavioral disturbances dependent on the age and duration of exposure. Ethanol exposure in neonatal rodents can also induce widespread apoptotic neurodegeneration and long-lasting behavioral abnormalities similar to FASD. The developmental stage of neonatal rodent brains that are at the peak of synaptogenesis is equivalent to the third trimester of human gestation.

METHODS

Male and female C57BL/6By mice were injected with ethanol (20%, 2.5 g/kg, 2 s.c. injections) or an equal volume of saline (controls) on postnatal day 7 (P7). Animals were allowed to mature and at 3 months were tested on an olfactory habituation task known to be dependent on piriform cortex function, a hippocampal-dependent object place memory task, and used for electrophysiological testing of spontaneous and odor-evoked local field potential (LFP) activity in the olfactory bulb, piriform cortex, and dorsal hippocampus.

RESULTS

P7 ethanol induced widespread cell death within 1 day of exposure, with highest levels in the neocortex, intermediate levels in the dorsal hippocampus, and relatively low levels in the primary olfactory system. No impairment of odor investigation or odor habituation was detected in P7 ethanol-exposed 3-month-old mice compared to saline controls. However, hippocampal-dependent object place memory was significantly impaired in the P7 ethanol-treated adult mice. Odor-evoked LFP activity was enhanced throughout the olfacto-hippocampal pathway, primarily within the theta frequency band, although the hippocampus also showed elevated evoked delta frequency activity. In addition, functional coherence between the piriform cortex and olfactory bulb and between the piriform cortex and dorsal hippocampus was enhanced in the beta frequency range in P7 ethanol-treated adult mice compared to controls.

CONCLUSIONS

P7 ethanol induces an immediate wave of regionally selective cell death followed by long-lasting changes in local circuit and regional network function that are accompanied by changes in neurobehavioral performance. The results suggest that both the activity of local neural circuits within a brain region and the flow of information between brain regions can be modified by early alcohol exposure, which may contribute to long-lasting behavioral abnormalities known to rely on those circuits.

The effects of prenatal alcohol exposure on behavior: rodent and primate studies

The use of alcohol by women during pregnancy is a continuing problem. In this review the behavioral effects of prenatal alcohol from animal models are described and related to studies of children and adults with FASD. Studies with monkeys and rodents show that prenatal alcohol exposure adversely affects neonatal orienting, attention and motor maturity, as well as activity level, executive function, response inhibition, and sensory processing later in life. The primate moderate dose behavioral findings fill an important gap between human correlational data and rodent mechanistic research. These animal findings are directly translatable to human findings. Moreover, primate studies that manipulated prenatal alcohol exposure and prenatal stress independently show that prenatal stress exacerbates prenatal alcohol-induced behavioral impairments, underscoring the need to consider stress-induced effects in fetal alcohol research. Studies in rodents and primates show long-term effects of prenatal and developmental alcohol exposure on dopamine system functioning, which could underpin the behavioral effects.

N-methyl-D-aspartate receptor subunit expression in adult and adolescent brain following chronic ethanol exposure

Substantial evidence suggests that glutamatergic neurotransmission is a critical mediator of the experience-dependent synaptic plasticity that may underlie alcohol dependence. Substance abuse typically begins in adolescence; therefore, the impact of alcohol on glutamatergic systems during this critical time in brain development is of particular importance. The N-methyl-d-aspartate receptor (NMDAR) is involved in developmental mechanisms underlying neuronal differentiation and synaptogenesis and as such may be a target system for alcohol effects during adolescence. In the present study quantitative biochemical determinations were made of the relative abundance of different protein expressions of NMDAR subunits in adolescents and adults after 2 weeks of ethanol vapor exposure, and 24 h and 2 weeks following withdrawal. After 2 weeks of ethanol vapor exposure N-methyl-d-aspartate receptor NR1 subunit (NR1), N-methyl-d-aspartate receptor NR2A subunit (NR2A), and N-methyl-d-aspartate receptor NR2B subunit (NR2B) subunit expression was found to be increased in hippocampus of the adults. In contrast, 2 weeks of ethanol exposure resulted in no significant changes in NR1 and NR2B subunits and a reduction NR2A subunit expression in hippocampus in adolescents. Twenty-four h and 2 weeks following withdrawal from ethanol vapor NR1 and NR2A subunit expression in hippocampus was decreased in adolescents, whereas in adults it had returned to control levels. In frontal cortex, 2 weeks of chronic ethanol exposure produced decreases in NR1 subunit expression in both adults and adolescents but also produced decreases in NR2A and NR2B subunit expression in adults that returned or exceeded control levels by 2 weeks following withdrawal from ethanol vapor. These results demonstrate that NMDAR subunit composition can be modulated differentially between adolescents and adults by chronic ethanol exposure and withdrawal. These developmental differences in NMDAR subunits composition may also be associated with the enhanced vulnerability of the adolescent brain to ethanol dependence.

Difluoromethylornithine (DFMO) reduces deficits in isolation-induced ultrasonic vocalizations and balance following neonatal ethanol exposure in rats

Neonatal ethanol (EtOH) exposure is associated with central nervous system dysfunction and neurotoxicity in rats. Increases in polyamine levels have been implicated as one underlying mechanism for some of EtOH's effects on the developing brain. In this study we addressed whether the inhibition of polyamine biosynthesis by alpha-difluoromethylornithine (DFMO) could reduce behavioral deficits induced by early EtOH exposure. Male and female rat pups received ethanol (6 g/kg/day EtOH i.g.), or isocaloric maltose (control) from postnatal days (PND) 1-8. On PND 8, animals were injected with either saline or DFMO (500 mg/kg, s.c.) immediately following the final neonatal treatment. Subjects were tested for isolation-induced ultrasonic vocalizations (USV) on PND 16; spontaneous activity in an open field apparatus on PND 20 and 21; and balance on PND 31. Animals exposed to EtOH neonatally displayed an increased latency to the first USV and reduced frequencies of USV, hyperactivity and preference for the center of the open field and poorer balance relative to controls. DFMO minimized these deficits in latency to the first USV and balance. These data provide further support that polyamines play a role in some of the functional deficits associated with EtOH exposure during early development and that reducing polyamine activity can improve outcome.

Artificial rearing

Prenatal alcohol exposure disrupts development, leading to a range of effects referred to as fetal alcohol spectrum disorders (FASD). FASDs include physical, central nervous system, and behavioral alterations. Animal model systems are used to study the relationship between alcohol-related central nervous system damage and behavioral alterations, risk factors for FASD, mechanisms of alcohol-induced damage, as well as treatments and interventions. When using a rodent model, it is important to recognize that the timing of brain development relative to birth differs between humans and rodents. Thus, to model alcohol exposure during the third trimester equivalent, rats must be exposed during early postnatal development (postnatal days 4-9). Artificial rearing is one experimental paradigm that is used to expose neonatal rats to alcohol during this period of brain development. Neonatal rat pups are housed in an artificial rearing environment and automatically fed a milk diet substitute via an intragastric cannula to ensure adequate growth during the treatment period. Alcohol is delivered in the milk diet. This chapter provides a description of the methods needed for this administrative technique, including preparation of the artificial rearing environment, gastrostomy surgery, and care of artificially reared rat pups.

Reversal learning after prenatal or early postnatal alcohol exposure in juvenile and adult rats

Learning tasks that require the reversal of a previously learned contingency are disrupted in animals and humans exposed to alcohol during the perinatal period. The current experiments examined how varying the time of alcohol exposure and the age at which subjects were tested would affect the expression of reversal deficits in a T-maze task. Groups of rats were exposed to alcohol from gestational day (GD) 8 to GD20 or from postnatal day (PN) 4 to PN9, and then tested in a spatial reversal task at either PN28 or PN63. Results indicate that exposure to alcohol during the prenatal period did not lead to substantial dose-dependent reversal learning deficits in males or females at either age tested. However, exposure to alcohol during the early postnatal period, a period that corresponds to the third trimester in human neural development, selectively disrupted reversal learning performance in male rats at PN28 but not PN63. Statistically significant sex differences were seen when subjects were tested at PN63. These results demonstrate how the timing of alcohol exposure leads to variability in the age-dependent expression of learning deficits associated with fetal alcohol effects.