A low chronic ethanol exposure induces morphological changes in the adolescent rat brain that are not fully recovered even after a long abstinence: An immunohistochemical study

Chronic ethanol consumption exacerbates future stress-enhanced fear learning, an effect mediated by dorsal hippocampal astrocytes

BACKGROUND

Alcohol use disorder (AUD) and post-traumatic stress disorder (PTSD) are highly comorbid, yet there is a lack of preclinical research investigating how prior ethanol (EtOH) dependence influences the development of a PTSD-like phenotype. Furthermore, the neuroimmune system has been implicated in the development of both AUD and PTSD, but the extent of glial involvement in this context remains unclear. A rodent model was developed to address this gap in the literature.

METHODS

We used a 15-day exposure to the 5% w/v EtOH low-fat Lieber-DeCarli liquid diet in combination with the stress-enhanced fear learning (SEFL) paradigm to investigate the effects of chronic EtOH consumption on the development of a PTSD-like phenotype. Next, we used a reverse transcription quantitative real-time polymerase chain reaction to quantify mRNA expression of glial cell markers GFAP (astrocytes) and CD68 (microglia) following severe footshock stress in EtOH-withdrawn rats. Finally, we tested the functional contribution of dorsal hippocampal (DH) astrocytes in the development of SEFL in EtOH-dependent rats using astrocyte-specific Gi designer receptors exclusively activated by designer drugs (Gi -DREADD).

RESULTS

Results demonstrate that chronic EtOH consumption and withdrawal exacerbate future SEFL. Additionally, we found significantly increased GFAP mRNA expression in the dorsal and ventral hippocampus and amygdalar complex following the severe stressor in EtOH-withdrawn animals. Finally, the stimulation of the astroglial Gi -DREADD during EtOH withdrawal prevented the EtOH-induced enhancement of SEFL.

CONCLUSIONS

Collectively, results indicate that prior EtOH dependence and withdrawal combined with a severe stressor potentiate future enhanced fear learning. Furthermore, DH astrocytes significantly contribute to this change in behavior. Overall, these studies provide insight into the comorbidity of AUD and PTSD and the potential neurobiological mechanisms behind increased susceptibility to a PTSD-like phenotype in individuals with AUD.

Behavioral alterations induced by intermittent ethanol intake and noise exposure in adolescent rats

Alcohol intake and exposure to noise are common activities of human adolescents performed in entertainment contexts worldwide that can induce behavioral disturbances. Therefore, the aim of the present work was to investigate in an experimental model of adolescent animals whether noise exposure and intermittent ethanol intake, when present individually or sequentially, might be able to modify different behaviors. Adolescent Wistar rats of both sexes were subjected to voluntary intermittent ethanol intake for 1 week followed by exposure to noise for 2 h and tested in a battery of behavioral tasks. Data show that males exposed to noise experienced a deficit in associative memory (AM), increase in anxiety-like behaviors (ALB) and altered reaction to novelty (RN) when compared with sham animals, whereas females also showed an increase in risk assessment behaviors (RAB) and a decrease in exploratory activity (EA). In contrast, ethanol intake induced an increase in RAB and RN in males and females, whereas females also showed a deficit in AM and EA as well as an increase in ALB. When ethanol was ingested before noise exposure, most parameters were counteracted both in male and females, but differed among sexes. In consequence, it could be hypothesized that an environmental acute stressor like noise might trigger a behavioral counteracting induced by a previous repeated exposure to a chemical agent such as ethanol, leading to a compensation of a non-adaptive behavior and reaching a better adjustment to the environment.

The role of sex in the persistent effects of adolescent alcohol exposure on behavior and neurobiology in rodents

Alcohol drinking is often initiated during adolescence, and this frequently escalates to binge drinking. As adolescence is also a period of dynamic neurodevelopment, preclinical evidence has highlighted that some of the consequences of binge drinking can be long lasting with deficits persisting into adulthood in a variety of cognitive-behavioral tasks. However, while the majority of preclinical work to date has been performed in male rodents, the rapid increase in binge drinking in adolescent female humans has re-emphasized the importance of addressing alcohol effects in the context of sex as a biological variable. Here we review several of the consequences of adolescent ethanol exposure in light of sex as a critical biological variable. While some alcohol-induced outcomes, such as non-social approach/avoidance behavior and sleep disruption, are generally consistent across sex, others are variable across sex, such as alcohol drinking, sensitivity to ethanol, social anxiety-like behavior, and induction of proinflammatory markers.

Rats exposed to intermittent ethanol during late adolescence exhibit enhanced habitual behavior following reward devaluation

The brain undergoes substantial maturation during adolescence, and repeated exposure to ethanol at this time has been shown to result in long-lasting behavioral and neural consequences. During the broad period of adolescence, different neuronal populations and circuits are refined between early and late adolescence, suggesting the possibility that ethanol exposure at these differing times may lead to differential outcomes. The goal of the current study was to evaluate the impact of adolescent intermittent ethanol (AIE) during early and late adolescence on the formation of goal-directed and habitual behavior in adulthood. Male and female Sprague-Dawley rats were exposed to ethanol via intragastric gavage (4.0 g/kg, 25% v/v) every other day from postnatal day (P) 25-45 or P45-65, considered early and late adolescence, respectively. In adulthood (~P70 early or ~ P90 late), rats were gradually food-restricted and began operant training on a fixed ratio 1 schedule. Rats were then transitioned onto random interval schedules and eventually underwent a sensory-specific satiation procedure as a model of reward devaluation. Few differences as a result of adolescent ethanol exposure were found during instrumental training. Following reward devaluation, rats exposed to water and ethanol during early adolescence exhibited reductions in lever pressing, suggestive of a goal-directed response pattern. In contrast, late AIE males and females demonstrated persistent responding following both devalued and non-devalued trials, findings representative of a habitual behavior pattern. The shifts from goal-directed to habitual behavior noted only following late AIE contribute to the growing literature identifying specific behavioral consequences as a result of ethanol exposure during distinct developmental periods within adolescence. More work is needed to determine whether the greater habit formation following late AIE is also associated with elevated habitual ethanol consumption.

Drug addiction co-morbidity with alcohol: Neurobiological insights

Addiction is a chronic disorder that consists of a three-stage cycle of binge/intoxication, withdrawal/negative affect, and preoccupation/anticipation. These stages involve, respectively, neuroadaptations in brain circuits involved in incentive salience and habit formation, stress surfeit and reward deficit, and executive function. Much research on addiction focuses on the neurobiology underlying single drug use. However, alcohol use disorder (AUD) can be co-morbid with substance use disorder (SUD), called dual dependence. The limited epidemiological data on dual dependence indicates that there is a large population of individuals suffering from addiction who are dependent on more than one drug and/or alcohol, yet dual dependence remains understudied in addiction research. Here, we review neurobiological data on neurotransmitter and neuropeptide systems that are known to contribute to addiction pathology and how the involvement of these systems is consistent or divergent across drug classes. In particular, we highlight the dopamine, opioid, corticotropin-releasing factor, norepinephrine, hypocretin/orexin, glucocorticoid, neuroimmune signaling, endocannabinoid, glutamate, and GABA systems. We also discuss the limited research on these systems in dual dependence. Collectively, these studies demonstrate that the use of multiple drugs can produce neuroadaptations that are distinct from single drug use. Further investigation into the neurobiology of dual dependence is necessary to develop effective treatments for addiction to multiple drugs.

Activation of Melanocortin-4 Receptor Inhibits Both Neuroinflammation Induced by Early Exposure to Ethanol and Subsequent Voluntary Alcohol Intake in Adulthood in Animal Models: Is BDNF the Key Mediator?

The concept that neuroinflammation induced by excessive alcohol intake in adolescence triggers brain mechanisms that perpetuate consumption has strengthened in recent years. The melanocortin system, composed of the melanocortin 4 receptor (MC4R) and its ligand α-melanocyte-stimulating hormone (α-MSH), has been implicated both in modulation of alcohol consumption and in ethanol-induced neuroinflammation decrease. Chronic alcohol consumption in adolescent rats causes a decrease in an α-MSH release by the hypothalamus, while the administration of synthetic agonists of MC4R causes a decrease in neuroinflammation and a decrease in voluntary alcohol consumption. However, the mechanism that connects the activation of MC4R with the decrease of both neuroinflammation and voluntary alcohol consumption has not been elucidated. Brain-derived neurotrophic factor (BDNF) has been implicated in alcohol drinking motivation, dependence and withdrawal, and its levels are reduced in alcoholics. Deficiencies in BDNF levels increased ethanol self-administration in rats. Further, BDNF triggers important anti-inflammatory effects in the brain, and this could be one of the mechanisms by which BDNF reduces chronic alcohol intake. Interestingly, MC4R signaling induces BDNF expression through the activation of the cAMP-responsive element-binding protein (CREB). We hypothesize that ethanol exposure during adolescence decreases the expression of α-MSH and hence MC4R signaling in the hippocampus, leading to a lower BDNF activity that causes dramatic changes in the brain (e.g., neuroinflammation and decreased neurogenesis) that predispose to maintain alcohol abuse until adulthood. The activation of MC4R either by α-MSH or by synthetic agonist peptides can induce the expression of BDNF, which would trigger several processes that lead to lower alcohol consumption.

Perineurial Barrier Glia Physically Respond to Alcohol in an Akap200-Dependent Manner to Promote Tolerance

Ethanol is the most common drug of abuse. It exerts its behavioral effects by acting on widespread neural circuits; however, its impact on glial cells is less understood. We show that Drosophila perineurial glia are critical for ethanol tolerance, a simple form of behavioral plasticity. The perineurial glia form the continuous outer cellular layer of the blood-brain barrier and are the interface between the brain and the circulation. Ethanol tolerance development requires the A kinase anchoring protein Akap200 specifically in perineurial glia. Akap200 tightly coordinates protein kinase A, actin, and calcium signaling at the membrane to control tolerance. Furthermore, ethanol causes a structural remodeling of the actin cytoskeleton and perineurial membrane topology in an Akap200-dependent manner, without disrupting classical barrier functions. Our findings reveal an active molecular signaling process in the cells at the blood-brain interface that permits a form of behavioral plasticity induced by ethanol.

Neuroimmune signaling in alcohol use disorder

Alcohol use disorder (AUD) is a widespread disease with limited treatment options. Targeting the neuroimmune system is a new avenue for developing or repurposing effective pharmacotherapies. Alcohol modulates innate immune signaling in different cell types in the brain by altering gene expression and the molecular pathways that regulate neuroinflammation. Chronic alcohol abuse may cause an imbalance in neuroimmune function, resulting in prolonged perturbations in brain function. Likewise, manipulating the neuroimmune system may change alcohol-related behaviors. Psychiatric disorders that are comorbid with AUD, such as post-traumatic stress disorder, major depressive disorder, and other substance use disorders, may also have underlying neuroimmune mechanisms; current evidence suggests that convergent immune pathways may be involved in AUD and in these comorbid disorders. In this review, we provide an overview of major neuroimmune cell-types and pathways involved in mediating alcohol behaviors, discuss potential mechanisms of alcohol-induced neuroimmune activation, and present recent clinical evidence for candidate immune-related drugs to treat AUD.

Astroglial correlates of neuropsychiatric disease: From astrocytopathy to astrogliosis

Complex roles for astrocytes in health and disease continue to emerge, highlighting this class of cells as integral to function and dysfunction of the nervous system. In particular, escalating evidence strongly implicates a range of changes in astrocyte structure and function associated with neuropsychiatric diseases including major depressive disorder, schizophrenia, and addiction. These changes can range from astrocytopathy, degeneration, and loss of function, to astrogliosis and hypertrophy, and can be either adaptive or maladaptive. Evidence from the literature indicates a myriad of changes observed in astrocytes from both human postmortem studies as well as preclinical animal models, including changes in expression of glial fibrillary protein, as well as changes in astrocyte morphology and astrocyte-mediated regulation of synaptic function. In this review, we seek to provide a comprehensive assessment of these findings and consequently evidence for common themes regarding adaptations in astrocytes associated with neuropsychiatric disease. While results are mixed across conditions and models, general findings indicate decreased astrocyte cellular features and gene expression in depression, chronic stress and anxiety, but increased inflammation in schizophrenia. Changes also vary widely in response to different drugs of abuse, with evidence reflective of features of astrocytopathy to astrogliosis, varying across drug classes, route of administration and length of withdrawal.

Retinal structure and function in monkeys with fetal alcohol exposure

Exposure to ethanol in utero leads to several brain development disorders including retinal abnormalities whose underlying cellular pathogenesis remains elusive. We recently reported that fetal alcohol exposure (FAE) in vervet monkeys induces anomalies of full-field electroretinogram (ERG) waveforms that suggest premature aging of the retina. The goal of this study is to characterize the anatomo-functional mechanisms underlying the retinal changes observed in fetal alcohol exposed (FAE) monkeys, and age- and sex-matched normals. First, we examined in vivo the fundus of the eyes, measured intraocular pressure (IOP) and assessed cone activity using flicker ERG. Second, we investigated ex vivo, protein expression and anatomical organization of the retina using Western blotting, classical histology and immunohistochemistry. Our results indicated that the fundus of the eyes showed both, increased vascularization (tessellated fundus) and IOP in FAE monkeys. Furthermore, light-adapted flicker responses above 15 Hz were also significantly higher in FAE monkeys. Although there were no obvious changes in the overall anatomy in the FAE retina, Glial Fibrillary Acidic Protein (GFAP, a potent marker of astrocytes) immunoreactivity was increased in the FAE retinal ganglion cell layer indicating a strong astrogliosis. These alterations were present in juvenile (2 years old) monkeys and persist in adults (8 years old). Moreover, using specific cell type markers, no significant modifications in the morphology of the photoreceptors, horizontal cells, bipolar cells, and amacrine cells were observed. Our data indicate that FAE does indeed induce anatomical changes within the retinal ganglion cell layer that are reflected in the increased photosensitivity of the cone photoreceptors.

Effects of adolescent alcohol exposure on stress-induced reward deficits, brain CRF, monoamines and glutamate in adult rats

BACKGROUND

Adolescent alcohol exposure may increase depression vulnerability in adulthood by increasing the anhedonic response to stress.

METHODS

Male Wistar rats (postnatal days 28-53) were exposed to binge-like adolescent intermittent ethanol (AIE) or water. In adulthood, rats were exposed to social defeat, consisting of daily confrontations with an aggressive conspecific, followed by testing of brain reward function in a discrete-trial current-intensity intracranial self-stimulation procedure for 10 consecutive days. Neurochemistry and corticotropin-releasing factor (CRF) and CRF receptor 1 (CRFR1) mRNA levels were assessed in corticolimbic brain areas on day 11 of social defeat stress.

RESULTS

Social defeat elevated reward thresholds in both AIE- and water-exposed rats indicating stress-induced anhedonia. However, AIE-exposed rats were more likely to show threshold elevations after repeated stress compared to water-exposed rats. AIE exposure decreased CRF mRNA levels in the nucleus accumbens and increased CRFR1 mRNA levels in the prefrontal cortex, while stress increased CRF mRNA levels in the central amygdala. In the caudate putamen, AIE exposure decreased dopamine turnover, while stress increased glutamate and serotonin metabolism and turnover.

CONCLUSIONS

These results demonstrate increased risk of repeated stress-induced anhedonia after AIE exposure, an effect that may be due to alterations in brain CRF and dopamine systems. These results suggest that the increased rates of depression reported in people with a history of adolescent alcohol exposure may be related to alterations in brain reward and stress systems that may contribute to increased stress-induced anhedonia.

Long-Term Effects of Intermittent Adolescent Alcohol Exposure in Male and Female Rats

Alcohol is a serious public health concern that has a differential impact on individuals depending upon age and sex. Patterns of alcohol consumption have recently changed: heavy episodic drinking—known as binge-drinking—has become most popular among the youth. Herein, we aimed to investigate the consequences of intermittent adolescent alcohol consumption in male and female animals. Thus, Wistar rats were given free access to ethanol (20% in drinking water) or tap water for 2-h sessions during 3 days, and for an additional 4-h session on the 4th day; every week during adolescence, from postnatal day (pnd) 28–52. During this period, animals consumed a moderate amount of alcohol despite blood ethanol concentration (BEC) did not achieve binge-drinking levels. No withdrawal signs were observed: no changes were observed regarding anxiety-like responses in the elevated plus-maze or plasma corticosterone levels (pnd 53–54). In the novel object recognition (NOR) test (pnd 63), a significant deficit in recognition memory was observed in both male and female rats. Western Blot analyses resulted in an increase in the expression of synaptophysin in the frontal cortex (FC) of male and female animals, together with a decrease in the expression of the CB2R in the same brain region. In addition, adolescent alcohol induced, exclusively among females, a decrease in several markers of dopaminergic and serotonergic neurotransmission, in which epigenetic mechanisms, i.e., histone acetylation, might be involved. Taken together, further research is still needed to specifically correlate sex-specific brain and behavioral consequences of adolescent alcohol exposure.

Voluntary alcohol intake after noise exposure in adolescent rats: Hippocampal-related behavioral alterations

Different physical or chemical agents, such as noise or alcohol, can induce diverse behavioral and biochemical alterations. Considering the high probability of young people to undergo consecutive or simultaneous exposures, the aim of the present work was to investigate in an animal model if noise exposure at early adolescence could induce hippocampal-related behavioral changes that might be modified after alcohol intake. Male Wistar rats (28-days-old) were exposed to noise (95-97 dB, 2 h). Afterwards, animals were allowed to voluntarily drink alcohol (10% ethanol in tap water) for three consecutive days, using the two-bottle free choice paradigm. After that, hippocampal-related memory and anxiety-like behavior tests were performed. Results show that whereas noise-exposed rats presented deficits in habituation memory, those who drank alcohol exhibited impairments in associative memory and anxiety-like behaviors. In contrast, exposure to noise followed by alcohol intake showed increases in exploratory and locomotor activities as well as in anxiety-like behaviors, unlike what was observed using each agent separately. Finally, lower levels of alcohol intake were measured in these animals when compared with those that drank alcohol and were not exposed to noise. Present findings demonstrate that exposure to physical and chemical challenges during early adolescence might induce behavioral alterations that could differ depending on the schedule used, suggesting a high vulnerability of rat developing brain to these socially relevant agents.

New Implications for the Melanocortin System in Alcohol Drinking Behavior in Adolescents: The Glial Dysfunction Hypothesis

Alcohol dependence causes physical, social, and moral harms and currently represents an important public health concern. According to the World Health Organization (WHO), alcoholism is the third leading cause of death worldwide, after tobacco consumption and hypertension. Recent epidemiologic studies have shown a growing trend in alcohol abuse among adolescents, characterized by the consumption of large doses of alcohol over a short time period. Since brain development is an ongoing process during adolescence, short- and long-term brain damage associated with drinking behavior could lead to serious consequences for health and wellbeing. Accumulating evidence indicates that alcohol impairs the function of different components of the melanocortin system, a major player involved in the consolidation of addictive behaviors during adolescence and adulthood. Here, we hypothesize the possible implications of melanocortins and glial cells in the onset and progression of alcohol addiction. In particular, we propose that alcohol-induced decrease in α-MSH levels may trigger a cascade of glial inflammatory pathways that culminate in altered gliotransmission in the ventral tegmental area and nucleus accumbens (NAc). The latter might potentiate dopaminergic drive in the NAc, contributing to increase the vulnerability to alcohol dependence and addiction in the adolescence and adulthood.

Adolescent intermittent ethanol reduces serotonin expression in the adult raphe nucleus and upregulates innate immune expression that is prevented by exercise

Serotonergic neurons of the raphe nucleus regulate sleep, mood, endocrine function, and other processes that mature during adolescence. Alcohol abuse and binge drinking are common during human adolescence. We tested the novel hypothesis that adolescent intermittent ethanol exposure would alter the serotonergic system that would persist into adulthood. Using a Wistar rat model of adolescent intermittent ethanol (AIE; 5.0g/kg, i.g., 2-day on/2-day off from postnatal day [P]25 to P55), we found a loss of dorsal raphe nucleus (DRN) serotonin (5-HT)-immunoreactive (+IR) neurons that persisted from late adolescence (P56) into adulthood (P220). Hypothalamic and amygdalar DRN serotonergic projections were reduced following AIE. Tryptophan hydroxylase 2, the rate-limiting 5-HT synthesizing enzyme, and vesicular monoamine transporter 2, which packages 5-HT into synaptic vesicles, were also reduced in the young adult midbrain following AIE treatment. Adolescent intermittent ethanol treatment increased expression of phosphorylated (activated) NF-κB p65 as well as markers of microglial activation (i.e., Iba-1 and CD11b) in the adult DRN. Administration of lipopolysaccharide to mimic AIE-induced innate immune activation reduced 5-HT+IR and increased phosphorylated NF-κB p65+IR similar to AIE treatment. Voluntary exercise during adolescence through young adulthood blunted microglial marker and phosphorylated NF-κB p65+IR, and prevented the AIE-induced loss of 5-HT+IR neurons in the DRN. Together, these novel data reveal that AIE reduces 5-HT+IR neurons in the adult DRN, possibly through an innate immune mechanism, which might impact adult cognition, arousal, or reward sensitivity. Further, exercise prevents the deleterious effects of AIE on the serotonergic system.

The neuroimmune transcriptome and alcohol dependence: potential for targeted therapies

Transcriptome profiling enables discovery of gene networks that are altered in alcoholic brains. This technique has revealed involvement of the brain's neuroimmune system in regulating alcohol abuse and dependence, and has provided potential therapeutic targets. In this review, we discuss Toll-like-receptor pathways, hypothesized to be key players in many stages of the alcohol addiction cycle. The growing appreciation of the neuroimmune system's involvement in alcoholism has also led to consideration of crucial roles for glial cells, including astrocytes and microglia, in the brain's response to alcohol abuse. We discuss current knowledge and hypotheses on the roles that specific neuroimmune cell types may play in addiction. Current strategies for repurposing US FDA-approved drugs for the treatment of alcohol use disorders are also discussed.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

Cannabinoid receptor type 1 agonist ACEA improves motor recovery and protects neurons in ischemic stroke in mice

Brain ischemia produces neuronal cell death and the recruitment of pro-inflammatory cells. In turn, the search for neuroprotection against this type of insult has rendered results involving a beneficial role of endocannabinoid receptor agonists in the Central Nervous System. In this work, to further elucidate the mechanisms associated to this neuroprotective effect, focal brain ischemia was generated by middle cerebral artery occlusion (MCAo) in C57Bl/6 mice. Three, 24 and 48 h after MCAo, animals received CB1R agonist ACEA (1 mg/kg), CB1R antagonist AM251 (1 mg/kg) or vehicle. To assess motor activity, neural deficit scores and motor tests were performed 1 day before and 3, 7, 14, 21, and 28 days after MCAo. At 7 and 28 days post lesion, cytoskeleton structure, astroglial and microglial reaction, and alterations in synapsis were studied in the cerebral cortex. ACEA treatment reduced astrocytic reaction, neuronal death, and dendritic loss. In contrast, AM251 treatment increased these parameters. Motor tests showed a progressive deterioration in motor activity in ischemic animals, which only ACEA treatment was able to counteract. Our results suggest that CB1R may be involved in neuronal survival and in the regulation of neuroprotection during focal cerebral ischemia in mice.

Prenatal ethanol exposure impairs spatial cognition and synaptic plasticity in female rats

Chronic prenatal ethanol exposure (CPEE) can impair long-term potentiation (LTP) in the male hippocampus. Sexually specific alterations were frequently reported in female animals that had been prenatally exposed to ethanol. This study aimed to examine the effects of CPEE on spatial learning and memory, as well as on hippocampal synaptic plasticity in female adolescent rats. Female offspring were selected from dams that had been exposed to 4 g/kg/day of ethanol throughout the gestational period. Subsequently, performance in the Morris water maze (MWM) was determined, while LTP and depotentiation were measured in the hippocampal CA3-CA1 pathway. In the behavioral test, the escape latencies in both initial and reversal training stages were significantly prolonged. Interestingly, LTP was considerably enhanced while depotentiation was significantly depressed. Our results suggest a critical role of synaptic plasticity balance, which may prominently contribute to the cognitive deficits present in CPEE offspring.

Chronic ethanol exposure during adolescence through early adulthood in female rats induces emotional and memory deficits associated with morphological and molecular alterations in hippocampus

There is increasing evidence that heavy ethanol exposure in early life may produce long-lasting neurobehavioral consequences, since brain structural maturation continues until adolescence. It is well established that females are more susceptible to alcohol-induced neurotoxicity and that ethanol consumption is increasing among women, especially during adolescence. In the present study, we investigated whether chronic ethanol exposure during adolescence through early adulthood in female rats may induce hippocampal histological damage and neurobehavioral impairments. Female rats were treated with distilled water or ethanol (6.5 g/kg/day, 22.5% w/v) by gavage from the 35(th)-90(th) day of life. Ethanol-exposed animals displayed reduced exploration of the central area and increased number of fecal boluses in the open field test indicative of anxiogenic responses. Moreover, chronic high ethanol exposure during adolescence induced marked impairments on short-term memory of female rats addressed on social recognition and step-down inhibitory avoidance tasks. These neurobehavioral deficits induced by ethanol exposure during adolescence through early adulthood were accompanied by the reduction of hippocampal formation volume as well as the loss of neurons, astrocytes and microglia cells in the hippocampus. These results indicate that chronic high ethanol exposure during adolescence through early adulthood in female rats induces long-lasting emotional and memory deficits associated with morphological and molecular alterations in the hippocampus.

Further Evidence for the Neuroplastic Role of Cannabinoids: A Study in Organotypic Hippocampal Slice Cultures

Endocannabinoid receptors CB1R and CB2R are present in the CNS and modulate synaptic activity. By using an in vitro model, two concentrations of CB1R agonist ACEA at 0.5 and 5 μM doses and CB1R antagonist AM251 at 1 and 10 μM doses were administered in organotypic slice cultures of mouse hippocampus, and their effects on neurons and glial cells were analyzed at different time points. Exposure to low concentrations of ACEA (0.5 μM) did not seem to affect tissue organization, neuronal morphology, or glial response. In contrast, at a higher concentration of ACEA, many neurons in the dentate gyrus exhibited strong caspase-3 immunoreactivity. After treatment with AM251, we observed an increase in caspase-3 immunoreactivity and a downregulation of CB1R expression. Results show that long-term hippocampal slice cultures respond to both CB1R activation and inactivation by changing neuronal protein expression patterns. In the present study, we demonstrate that CB1R agonist ACEA promotes alterations in the neuronal cytoskeleton as well as changes in CB1R expression in organotypic hippocampal slice cultures, and that CB1R antagonist AM251 promotes neuronal death and astroglial reaction.

nNOS is involved in cardiac remodeling induced by chronic ethanol consumption

Chronic ethanol consumption has deleterious effects on the cardiovascular system by directly damaging the myocardial structure and/or by neurohormonal activation. Moreover, nitric oxide (NO) derived from neuronal NO synthase (nNOS) seems to be important to balance the harmful effects of ethanol consumption, because it influences several aspects of cardiac physiology and attenuates pathological cardiac remodeling. However, the impact of chronic ethanol consumption on nNOS expression is unknown. We address this subject in the present study by evaluating whether chronic ethanol consumption induces cardiac remodeling and hypertension, and if these changes are associated with alterations in the expression of nNOS. Male Wistar rats were examined after ingesting a 20% alcohol solution for 6 months. Blood alcohol concentration and brain natriuretic peptide (BNP) levels were measured. The cardiac remodeling was assessed by histomorphometric analysis and the nNOS expression was evaluated by immunofluorescence and western blot analysis. Our results show that chronic ethanol consumption induces cardiac remodeling, namely thinning of left ventricular wall, cardiomyocyte hypertrophy and increased fibrosis, and elevations of arterial blood pressure. They also show that in rats fed with ethanol for 6 months, the circulating BNP levels had decreased as well as the expression of nNOS in left ventricle cardiomyocytes. These findings suggest that the effects of chronic ethanol consumption on BNP levels and/or on nNOS expression in cardiomyocytes may contribute to aggravate the cardiac remodeling and leads to progression of cardiomyopathy.

Gene expression changes in serotonin, GABA-A receptors, neuropeptides and ion channels in the dorsal raphe nucleus of adolescent alcohol-preferring (P) rats following binge-like alcohol drinking

Alcohol binge-drinking during adolescence is a serious public health concern with long-term consequences. We used RNA sequencing to assess the effects of excessive adolescent ethanol binge-drinking on gene expression in the dorsal raphe nucleus (DRN) of alcohol preferring (P) rats. Repeated binges across adolescence (three 1h sessions across the dark-cycle per day, 5 days per week for 3 weeks starting at 28 days of age; ethanol intakes of 2.5-3 g/kg/session) significantly altered the expression of approximately one-third of the detected genes. Multiple neurotransmitter systems were altered, with the largest changes in the serotonin system (21 of 23 serotonin-related genes showed decreased expression) and GABA-A receptors (8 decreased and 2 increased). Multiple neuropeptide systems were also altered, with changes in the neuropeptide Y and corticotropin-releasing hormone systems similar to those associated with increased drinking and decreased resistance to stress. There was increased expression of 21 of 32 genes for potassium channels. Expression of downstream targets of CREB signaling was increased. There were also changes in expression of genes involved in inflammatory processes, axonal guidance, growth factors, transcription factors, and several intracellular signaling pathways. These widespread changes indicate that excessive binge drinking during adolescence alters the functioning of the DRN and likely its modulation of many regions of the central nervous system, including the mesocorticolimbic system.

Alcohol and adult hippocampal neurogenesis: promiscuous drug, wanton effects

Adult neurogenesis is now widely accepted as an important contributor to hippocampal integrity and function but also dysfunction when adult neurogenesis is affected in neuropsychiatric diseases such as alcohol use disorders. Excessive alcohol consumption, the defining characteristic of alcohol use disorders, results in a variety of cognitive and behavioral impairments related wholly or in part to hippocampal structure and function. Recent preclinical work has shown that adult neurogenesis may be one route by which alcohol produces hippocampal neuropathology. Alcohol is a pharmacologically promiscuous drug capable of interfering with adult neurogenesis through multiple mechanisms. This review will discuss the primary mechanisms underlying alcohol-induced changes in adult hippocampal neurogenesis including alcohol's effects on neurotransmitters, CREB and its downstream effectors, and the neurogenic niche.

Further evidence for the neuroprotective role of oleanolic acid in a model of focal brain hypoxia in rats

Ischemic brain injury is a dynamic process involving oxidative stress, inflammation, cell death and the activation of endogenous adaptive and regenerative mechanisms depending on the activation of transcription factors such as hypoxia-inducible factor 1-alpha. Accordingly, we have previously described a new focal hypoxia model by direct intracerebral cobalt chloride injection. In turn, oleanolic acid, a plant-derived triterpenoid, has been extensively used in Asian countries for its anti-inflammatory and anti-tumor properties. A variety of novel pharmacological effects have been attributed to this triterpenoid, including beneficial effects on neurodegenerative disorders--including experimental autoimmune encephalomyelitis--due to its immunomodulatory activities at systemic level, as well as within the central nervous system. In this context, we hypothesize that this triterpenoid may be capable of exerting neuroprotective effects in ischemic brain, suppressing glial activities that contribute to neurotoxicity while promoting those that support neuronal survival. In order to test this hypothesis, we used the intraperitoneal administration of oleanoic acid in adult rats for seven days previous to focal cortical hypoxia induced by cobalt chloride brain injection. We analyzed the neuroprotective effect of oleanoic acid from a morphological point of view, focusing on neuronal survival and glial reaction.

Type 1 equilibrative nucleoside transporter regulates astrocyte-specific glial fibrillary acidic protein expression in the striatum

BACKGROUND

Adenosine signaling has been implicated in several neurological and psychiatric disorders. Previously, we found that astrocytic excitatory amino acid transporter 2 (EAAT2) and aquaporin 4 (AQP4) are downregulated in the striatum of mice lacking type 1 equilibrative nucleoside transporter (ENT1).

METHODS

To further investigate the gene expression profile in the striatum, we preformed Illumina Mouse Whole Genome BeadChip microarray analysis of the caudate-putamen (CPu) and nucleus accumbens (NAc) in ENT1 null mice. Gene expression was validated by RT-PCR, Western blot, and immunofluorescence. Using transgenic mice expressing enhanced green fluorescence protein (EGFP) under the control of the glial fibrillary acidic protein (GFAP) promoter, we examined EGFP expression in an ENT1 null background.

RESULTS

Glial fibrillary acidic protein was identified as a top candidate gene that was reduced in ENT1 null mice compared to wild-type littermates. Furthermore, EGFP expression was significantly reduced in GFAP-EGFP transgenic mice in an ENT1 null background in both the CPu and NAc. Finally, pharmacological inhibition or siRNA knockdown of ENT1 in cultured astrocytes also reduced GFAP mRNA levels.

CONCLUSIONS

Overall, our findings demonstrate that ENT1 regulates GFAP expression and possibly astrocyte function.

Effects of ethanol exposure on nervous system development in zebrafish

Alcohol (ethanol) is a teratogen that adversely affects nervous system development in a wide range of animal species. In humans numerous congenital abnormalities arise as a result of fetal alcohol exposure, leading to a spectrum of disorders referred to as fetal alcohol spectrum disorder (FASD). These abnormalities include craniofacial defects as well as neurological defects that affect a variety of behaviors. These human FASD phenotypes are reproduced in the rodent central nervous system (CNS) following prenatal ethanol exposure. While the study of ethanol effects on zebrafish development has been more limited, several studies have shown that different strains of zebrafish exhibit differential susceptibility to ethanol-induced cyclopia, as well as behavioral deficits. Molecular mechanisms underlying the effects of ethanol on CNS development also appear to be shared between rodent and zebrafish. Thus, zebrafish appear to recapitulate the observed effects of ethanol on human and mouse CNS development, indicating that zebrafish can serve as a complimentary developmental model system to study the molecular basis of FASD. Recent studies examining the effect of ethanol exposure on zebrafish nervous system development are reviewed, with an emphasis on attempts to elucidate possible molecular pathways that may be impacted by developmental ethanol exposure. Recent work from our laboratories supports a role for perturbed extracellular matrix function in the pathology of ethanol exposure during zebrafish CNS development. The use of the zebrafish model to assess the effects of ethanol exposure on adult nervous system function as manifested by changes in zebrafish behavior is also discussed.

Ethanol impairs microtubule formation via interactions at a microtubule associated protein-sensitive site

Prolonged ethanol abuse has been associated with brain injury caused by impaired synaptogenesis, cellular migration, neurogenesis, and cell signaling, all of which require proper microtubule functioning. However, the means by which ethanol may impair microtubule formation or function and the role that microtubule-associated proteins (MAPs) have in mediating such effects are not clear. In the present studies, purified MAP-deficient (2 mg/mL) and MAP-rich (pre-conjugated; 1 mg/mL) bovine α/β tubulin dimer was allowed to polymerize at 37 °C, forming microtubules in the presence or absence of ethanol (25-500 mM). Microtubule formation was assessed in a 96-well format using a turbidity assay, with absorption measured at 340 nm for 45 min. Additional studies co-exposed α/β tubulin dimers to 50 mM ethanol and purified MAPs (0.1 mg/mL) for 45 min. Polymerization of MAP-deficient tubulin was significantly decreased (at 15-45 min of polymerization) during exposure to ethanol (>25 mM). In contrast, ethanol exposure did not alter polymerization of α/β tubulin dimers pre-conjugated to MAPs, at any concentration. Concurrent exposure of MAP-deficient tubulin with purified MAPs and ethanol resulted in significant and time-dependent decreases in tubulin polymerization, with recovery from inhibition at later time points. The present results suggest that ethanol disrupts MAP-independent microtubule formation and MAP-dependent microtubule formation via direct actions at an MAP-sensitive microtubule residue, indicating that disruption of neuronal microtubule formation and function may contribute to the neurodegenerative effects of binge-like ethanol intake.

Changes in CNS cells in hyperammonemic portal hypertensive rats

Rats with pre-hepatic portal hypertension because of partial portal vein ligation develop minimal hepatic encephalopathy (MHE) with hyperammonemia, impaired blood-brain barrier, mild brain edema, and severe mitochondrial changes in the hippocampus. The aim of this study was to evaluate changes of different neural cells in the cerebral cortex and the hippocampus. Animals were divided into two groups, MHE and sham. Astrocytes were studied by immunostaining with glial fibrillary acidic protein and S100β protein; neurons were immunostained with neuronal nuclear marker, microtubule associated protein-2, and NF-200 and capillaries with Nestin. The hypoxia-inducible factor 1α (HIF-1α) and its downstream proteins, P-glycoprotein (P-gp) and erythropoietin receptor (Epo-R), were also evaluated. Astrocytes were increased in area and number only in the hippocampus, while S100β increased in both brain areas in MHE animals. Microtubule associated protein-2 and NF-200 immunoreactivities (-ir) were significantly reduced in both areas. Hippocampal Nestin-ir was increased in MHE animals. These cellular changes were similar to those described in ischemic conditions, thus HIF-1α, P-gp, and Epo-R were also evaluated. A high expression of HIF-1α in cortical neurons was observed in the MHE group. It is likely that this hypoxia-like state is triggered via ammonia occupying the binding domain of HIF-1α and thereby preventing its degradation and inducing its stabilization, leading to the over-expression of P-gp and the Epo-R.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

Determining the threshold for alcohol-induced brain damage: new evidence with gliosis markers

BACKGROUND

Chronic intake of ethanol (EtOH) has been linked to serious health consequences such as cardiac and liver problems, cognitive impairments, and brain damage. Alcohol's detrimental effects depend upon the dose, duration, and pattern of exposure with binge drinking as one of the most common, but most damaging, patterns of intake. Little is known about the threshold of the damaging effects of alcohol. Therefore, these experiments sought to determine a threshold for brain damage using various markers of neurodegeneration.

METHODS

Adult male Sprague-Dawley rats were administered nutritionally complete liquid diet containing either EtOH (25% w/v) or isocaloric dextrose every 8 hours for either 1 (mean dose, 13.4 ± 0.3 g/kg/d; mean blood EtOH concentration (BEC), 336.2 ± 18.8 mg/dl) or 2 days (mean dose, 10.9 ± 0.3 g/kg/d; mean BEC, 369.8 ± 18.1 mg/dl). On the basis of a known time course of various neurodegeneration-associated events, rats were perfused transcardially immediately following, 2 days after, or 7 days post EtOH exposure. To label actively dividing cells, some animals were injected with BromodeoxyUridine (BrdU) 2 hours prior to perfusion. Tissue was then analyzed for the presence of BrdU (cell proliferation), FluoroJade B (degenerative neurons), and vimentin (reactive astrogliosis) immunoreactivity.

RESULTS

One or 2 days of EtOH exposure failed to alter cell proliferation at any of the time points analyzed. However, significant 2- to 9-fold increases in neuronal degeneration in limbic cortex and clear evidence of reactive gliosis as indicated by a 2- to 8-fold upregulation in vimentin immunoreactivity in the hippocampus were observed following as little as 1 day of binge EtOH exposure.

CONCLUSIONS

These results indicate that as little as 1 day (24 hours) of high BEC, binge-like EtOH exposure is enough to elicit signs of alcohol-induced brain damage in adult rats. Further, reactive gliosis may be a more sensitive marker of alcohol-induced damage in the hippocampus.

Effects of ethanol during adolescence on the number of neurons and glia in the medial prefrontal cortex and basolateral amygdala of adult male and female rats

Human adolescents often consume alcohol in a binge-like manner at a time when changes are occurring within specific brain structures, such as the medial prefrontal cortex (mPFC) and the basolateral nucleus of the amygdala (BLN). In particular, the number of neurons and glia is changing in both of these areas in the rat between adolescence and adulthood (Markham et al., 2007; Rubinow and Juraska, 2009). The current study investigated the effects of ethanol exposure during adolescence on the number of neurons and glia in the adult mPFC and BLN in Long-Evans male and female rats. Saline or 3g/kg ethanol was administered between postnatal days (P) 35-45 in a binge-like pattern, with 2days of injections followed by 1 day without an injection. Stereological analyses of the ventral mPFC (prelimbic and infralimbic areas) and the BLN were performed on brains from rats at 100 days of age. Neuron and glia densities were assessed with the optical disector and then multiplied by the volume to calculate the total number of neurons and glia. In the adult mPFC, ethanol administration during adolescence resulted in a decreased number of glia in males, but not females, and had no effect on the number of neurons. Adolescent ethanol exposure had no effects on glia or neuron number in the BLN. These results suggest that glia cells in the prefrontal cortex are particularly sensitive to binge-like exposure to ethanol during adolescence in male rats only, potentially due to a decrease in proliferation in males or protective mechanisms in females.

Common transcriptional effects in the mouse striatum following chronic treatment with heroin and methamphetamine

The molecular alterations that underlie the long-lasting behavioural effects of drugs of abuse, such as psychomotor sensitization and physical dependence, are still not known. Moreover, it is not known which molecular effects are similar for addictive drugs from various pharmacological classes. In this study, we utilized whole-genome microarray profiling to evaluate the detailed time-course of transcriptional alterations in the mouse striatum during chronic treatment with heroin (HER) and methamphetamine (METH) and after period of spontaneous withdrawal. We identified 27 genes regulated by chronic drug administration. The overlap between lists of HER- and METH-induced genes was highly significant. The most substantial impact on the gene expression profile was observed for circadian genes (Per1, Per2 and Nr1d1). However, changing the treatment scheme from diurnal to nocturnal was sufficient to attenuate the drug-induced changes in circadian gene mRNA levels. Both of the drugs caused a dose-dependent induction in glucocorticoid-dependent genes with relatively long mRNA half-lives (Fkbp5, Sult1a1 and Plin4). The analysis also showed a drug-regulated group of transcripts enriched in the nucleus accumbens and includes well known (Pdyn, Cartpt and Rgs2) as well as new (Fam40b and Inmt) candidate genes. All identified alterations in the striatal transcriptome were transient and persisted up to 6 days after withdrawal. Behavioural sensitization, however, was maintained throughout the 12-day withdrawal period for both HER and METH. We suggest that transient gene expression alterations during drug treatment and in the early period of withdrawal are involved in the establishment of persistent neuroplastic alterations responsible for the development of drug addiction.

Repeated ethanol but not phencyclidine impairs spontaneous alternation behaviour in the Y-maze

Prolonged consumption of ethanol produces prefrontal cortex (PFC) dysfunction in patients, and this has been demonstrated using structural, physiological and psychological measurements. We therefore wanted to develop an animal model of PFC dysfunction to study whether this state changes sensitivity for ethanol or other behavioural/motivational measures. Adolescent Wistar rats were first screened in the novel object recognition task to establish a pre-treatment baseline measure of locomotor activity, anxiety-like behaviour and PFC function. Animals were divided into four treatment groups [saline, 5 mg/kg phencyclidine (PCP), 2.5g/kg ethanol, ethanol + PCP] and injected i.p. for 5 days followed by a 2-day washout. On the 8th day, animals were allowed to explore a Y-maze for 10 min. and spontaneous alternations were recorded using the ANY-maze tracking system. PCP, a classic drug used to induce PFC dysfunction in animals, did not significantly reduce the % correct alternations relative to the 70% level achieved by the saline group. Ethanol and the combination of Ethanol + PCP, however, significantly reduced alternations to approximately 30%. The combined dose was not additive in terms of Y-maze impairment, and these animals had less total distance travelled and greater time immobile relative to the other groups. We therefore concluded that injection of 2.5 g/kg ethanol for 5 days in Wistar rats produces a more substantial, consistent and valid PFC dysfunction than 5 mg/kg PCP.

Upregulated vimentin suggests new areas of neurodegeneration in a model of an alcohol use disorder

Excessive alcohol intake, characteristic of an alcohol use disorder (AUD), results in neurodegeneration as well as cognitive deficits that may recover in abstinence. Neurodegeneration in psychiatric disorders such as AUDs is due to various effects on tissue integrity. Several groups report that alcohol-induced neurodegeneration and recovery include a role for adult neurogenesis. Therefore, the initial purpose of this study was to investigate the effect of alcohol on the temporal profile of neural progenitor cells using the radial glia marker, vimentin, in a model of an AUD. However, striking vimentin expression throughout corticolimbic regions led, instead, to the discovery of a significant gliosis response in this model. Adult male rats were subjected to a 4-day binge model of an AUD and brains harvested for immunohistochemistry at 0, 2, 4, 7, 14, and 28 days following the last dose of ethanol. A prominent increase in vimentin immunoreactivity was apparent at 4 and 7 days post binge that returned to control levels by 14 days in the corticolimbic regions examined. Vimentin-positive cells co-labeled with glial fibrillary acidic protein (GFAP), which suggested that cells were reactive astrocytes. A second experiment supported that increased vimentin was not primarily due to alcohol withdrawal seizures and is more likely due to alcohol-induced cell death. As this gliosis was remarkably distinct in regions where cell death had not previously been reported in this model, adjacent tissue sections were processed for FluoroJade B staining for cell death. FluoroJade B-positive cells were evident immediately following the last ethanol dose as expected, but were significantly elevated in the hippocampal dentate gyrus and CA3 regions and corticolimbic regions from 2 to 7 days post binge. Intriguingly, vimentin labeling of astrogliosis is more widespread than FluoroJade B labeling of cell death, which suggests that 4-day binge ethanol consumption is more damaging than originally realized.

Immediate and prolonged effects of alcohol exposure on the activity of the hypothalamic-pituitary-adrenal axis in adult and adolescent rats

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis. Part of this influence is likely exerted directly at the level of the corticotropin-releasing factor (CRF) gene, but intermediates may also play a role. Here we review the effect of alcohol on this axis, provide new data on the effects of binge drinking during adolescence, and argue for a role of catecholaminergic circuits. Indeed, acute injection of this drug activates brain stem adrenergic and noradrenergic circuits, and their lesion, or blockade of α1 adrenergic receptors significantly blunts alcohol-induced ACTH release. As alcohol can influence the HPA axis even once discontinued, and alcohol consumption in young people is associated with increased adult drug abuse (a phenomenon possibly mediated by the HPA axis), we determined whether alcohol consumption during adolescence modified this axis. The number of CRF-immunoreactive (ir) cells/section was significantly decreased in the central nucleus of the amygdala of adolescent self-administering binge-drinking animals, compared to controls. When another group of adolescent binge-drinking rats was administered alcohol in adulthood, the number of colocalized c-fos-ir and PNMT-ir cells/brain stem section in the C3 area was significantly decreased, compared to controls. As the HPA axis response to alcohol is blunted in adult rats exposed to alcohol vapors during adolescence, a phenomenon which was not observed in our model of self-administration, it is possible that the blood alcohol levels achieved in various models play a role in the long-term consequences of exposure to alcohol early in life. Collectively, these results suggest an important role of brain catecholamines in modulating the short- and long-term consequences of alcohol administration.

Effects of prenatal ethanol exposure on rat brain radial glia and neuroblast migration

Prenatal ethanol exposure (PEE) induces morphologic and functional alterations in the developing central nervous system. The orderly migration of neuroblasts is a key process in the development of a layered structure such as the cerebral cortex (CC). From initial stages of corticogenesis, the transcription factor Pax6 is intensely expressed in neuroepithelial and radial glia cells (RGCs) and is involved in continual regulation of cell surface properties responsible for both cellular identity and radial migration. In the present work, one month before mating, during pregnancy and lactation, a group of female Wistar rats were fed a liquid diet with 5.9% (w/w) ethanol (EtOH), rendering moderate blood EtOH concentrations. Maternal gestational weight progression and fetal CC thickness were measured. CC from E12-P3 rats were examined for expression of vimentin, nestin, S-100b, Pax6 and doublecortin using immunohistochemical assays. RGCs expressing vimentin, nestin, S-100b and Pax6 had abnormal morphologies. The migration distance through the CC and the number of doublecortin-ir neuroblasts in germinative zones were decreased. We found significant morphologic defects on RGCs, a marked delay in neuronal migration, decreased numbers of neuroblasts, and decreased numbers of Pax6-ir cells in the CC as a consequence of exposure to ethanol during development. These observations suggest a sequence of toxic events that contribute to cortical dysplasia in offspring exposed to EtOH during gestation.

Adolescent alcohol exposure alters the central brain circuits known to regulate the stress response

Adolescent alcohol exposure (AAE) may exert long-term effects on the adult brain. Here, we tested the hypothesis that the brain regions affected include the rat hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined the consequences of AAE [postnatal days (PND) 28-42] on the HPA axis-related brain circuitry of male rats challenged with an intragastric (ig) administration of alcohol in young adulthood (PND 61-62). Adolescent rats were exposed to alcohol vapors, while controls did not receive the drug. The mean blood alcohol level in adolescence on PND 40 was 212.8±5.7 mg %. Using immunohistochemistry and in situ hybridization procedures, we measured signals for c-fos and corticotropin releasing factor (CRF) in the paraventricular nucleus (PVN) of the hypothalamus, as well as signals for c-fos and phenylethanolamine N-methyltransferase (PNMT) in the adrenergic brain stem regions (C1 and C2). PVN CRF mRNA expression was significantly blunted in AAE rats tested at PND 61-62, compared to their controls. These animals also displayed a significant increase in the mean number of PNMT-ir cells/brain stem section in the C2 area. Collectively, these results suggest that exposure to alcohol vapors during adolescence exerts long-term effects on the ability of the PVN to mount a response to an acute alcohol administration in young adulthood, possibly mediated by medullary catecholamine input to the PVN.

Glial and glutamatergic markers in depression, alcoholism, and their comorbidity

BACKGROUND

Alteration of glutamatergic neurotransmission in the prefrontal cortex (PFC) may contribute to the pathophysiology of alcoholism and major depressive disorder (MDD). Among glial cells, astrocytes are mostly responsible for recycling synaptic glutamate by uptake through excitatory amino acid transporters 1 and 2 (EAAT1 and EAAT2), and conversion to glutamine with glutamine synthetase (GS). Low density of astrocytes in the PFC of "uncomplicated' alcoholics and MDD subjects may parallel altered glutamate transporters and GS in the PFC.

METHODS

Immunohistochemistry and Western blotting for glutamate transporters, GS and glial fibrillary acidic protein (GFAP) were applied to postmortem tissue of the left orbitofrontal cortex from 13 subjects with MDD, 13 with alcoholism, 10 with comorbid alcoholism plus MDD (MDA), and 13 non-psychiatric controls. Area fraction of immunoreactivity was measured in sections, and protein levels in Western blots.

RESULTS

EAAT2 immunoreactivity was significantly lower in MDD and MDA subjects than in controls. EAAT1 levels were lower in MDA and MDD subjects as compared to controls, while GS levels in MDA were significantly lower than in alcoholics and controls, and lower in MDD subjects than in alcoholics. Area fraction of GFAP was lower in MDD, but not in MDA subjects as compared to controls or alcoholics.

LIMITATIONS

High variability of protein levels in some groups and effects of antidepressant treatment, although appearing to be limited, cannot be fully evaluated.

CONCLUSIONS

There are differential changes in the expression of glial glutamatergic markers in depression and alcoholism, suggesting a depletion of certain aspects of glutamatergic processing in depression.

Laboratory models available to study alcohol-induced organ damage and immune variations: choosing the appropriate model

The morbidity and mortality resulting from alcohol-related diseases globally impose a substantive cost to society. To minimize the financial burden on society and improve the quality of life for individuals suffering from the ill effects of alcohol abuse, substantial research in the alcohol field is focused on understanding the mechanisms by which alcohol-related diseases develop and progress. Since ethical concerns and inherent difficulties limit the amount of alcohol abuse research that can be performed in humans, most studies are performed in laboratory animals. This article summarizes the various laboratory models of alcohol abuse that are currently available and are used to study the mechanisms by which alcohol abuse induces organ damage and immune defects. The strengths and weaknesses of each of the models are discussed. Integrated into the review are the presentations that were made in the symposium "Methods of Ethanol Application in Alcohol Model-How Long is Long Enough" at the joint 2008 Research Society on Alcoholism (RSA) and International Society for Biomedical Research on Alcoholism (ISBRA) meeting, Washington, DC, emphasizing the importance not only of selecting the most appropriate laboratory alcohol model to address the specific goals of a project but also of ensuring that the findings can be extrapolated to alcohol-induced diseases in humans.

Alcohol inhibition of neurogenesis: a mechanism of hippocampal neurodegeneration in an adolescent alcohol abuse model

Adolescents diagnosed with an alcohol use disorder show neurodegeneration in the hippocampus, a region important for learning, memory, and mood regulation. This study examines a potential mechanism by which excessive alcohol intake, characteristic of an alcohol use disorder, produces neurodegeneration. As hippocampal neural stem cells underlie ongoing neurogenesis, a phenomenon that contributes to hippocampal structure and function, we investigated aspects of cell death and cell birth in an adolescent rat model of an alcohol use disorder. Immunohistochemistry of various markers along with Bromo-deoxy-Uridine (BrdU) injections were used to examine different aspects of neurogenesis. After 4 days of binge alcohol exposure, neurogenesis was decreased by 33 and 28% at 0 and 2 days after the last dose according to doublecortin expression. To determine whether this decrease in neurogenesis was due to effects on neural stem cell proliferation, quantification of BrdU-labeled cells revealed a 21% decrease in the dentate gyrus of alcohol-exposed brains. Cell survival and phenotype of BrdU-labeled cells were assessed 28 days after alcohol exposure and revealed a significant, 50% decrease in the number of surviving cells in the alcohol-exposed group. Reduced survival was supported by significant increases in the number of pyknotic-, FluoroJade B positive-, and TUNEL-positive cells. However, so few cells were TUNEL-positive that cell death is likely necrotic in this model. Although alcohol decreased the number of newborn cells, it did not affect the percentage of cells that matured into neurons (differentiation). Thus, our data support that in a model of an adolescent alcohol use disorder, neurogenesis is impaired by two mechanisms: alcohol-inhibition of neural stem cell proliferation and alcohol effects on new cell survival. Remarkably, alcohol inhibition of neurogenesis may outweigh the few dying cells per section, which implies that alcohol inhibition of neurogenesis contributes to hippocampal neurodegeneration in alcohol use disorders.

Effects of exogenous agents on brain development: stress, abuse and therapeutic compounds

The range of exogenous agents likely to affect, generally detrimentally, the normal development of the brain and central nervous system defies estimation although the amount of accumulated evidence is enormous. The present review is limited to certain types of chemotherapeutic and "use-and-abuse" compounds and environmental agents, exemplified by anesthetic, antiepileptic, sleep-inducing and anxiolytic compounds, nicotine and alcohol, and stress as well as agents of infection; each of these agents have been investigated quite extensively and have been shown to contribute to the etiopathogenesis of serious neuropsychiatric disorders. To greater or lesser extent, all of the exogenous agents discussed in the present treatise have been investigated for their influence upon neurodevelopmental processes during the period of the brain growth spurt and during other phases uptill adulthood, thereby maintaining the notion of critical phases for the outcome of treatment whether prenatal, postnatal, or adolescent. Several of these agents have contributed to the developmental disruptions underlying structural and functional brain abnormalities that are observed in the symptom and biomarker profiles of the schizophrenia spectrum disorders and the fetal alcohol spectrum disorders. In each case, the effects of the exogenous agents upon the status of the affected brain, within defined parameters and conditions, is generally permanent and irreversible.

Adolescence as a critical window for developing an alcohol use disorder: current findings in neuroscience

PURPOSE OF REVIEW

Alcohol consumption during adolescence greatly increases the likelihood that an alcohol use disorder will develop later in life. Elucidating how alcohol impacts the adolescent brain is paramount to understanding how alcohol use disorders arise. This review focuses on recent work addressing alcohol's unique effect on the adolescent brain.

RECENT FINDINGS

The unique and dynamic state of the developing adolescent brain is discussed with an emphasis on the developmentally distinct effect of alcohol on the dopaminergic reward system and corticolimbic structure and function. Reward neurocircuitry undergoes significant developmental shifts during adolescence, making it particularly sensitive to alcohol in ways that could promote excessive consumption. In addition, developing corticolimbic systems, including the prefrontal cortex and hippocampus, exhibit enhanced vulnerability to alcohol-induced damage. Disruption of white matter integrity, neurotoxicity and inhibition of adult neurogenesis may underlie alcohol-mediated cognitive dysfunction and lead to decreased behavioral control over consumption.

SUMMARY

In adolescents, alcohol interacts extensively with reward neurocircuitry and corticolimbic structure and function in ways that promote maladaptive behaviors that lead to addiction. Future work is needed to further understand the mechanisms involved in these interactions. Therapeutic strategies that restore proper reward neurochemistry or reverse alcohol-induced neurodegeneration could prove useful in preventing emergence of alcohol use disorders.

Roles of neural stem cells and adult neurogenesis in adolescent alcohol use disorders

This review discusses the contributions of a newly considered form of plasticity, the ongoing production of new neurons from neural stem cells, or adult neurogenesis, within the context of neuropathologies that occur with excessive alcohol intake in the adolescents. Neural stem cells and adult neurogenesis are now thought to contribute to the structural integrity of the hippocampus, a limbic system region involved in learning, memory, behavioral control, and mood. In adolescents with alcohol use disorders (AUDs), the hippocampus appears to be particularly vulnerable to the neurodegenerative effects of alcohol, but the role of neural stem cells and adult neurogenesis in alcoholic neuropathology has only recently been considered. This review encompasses a brief overview of neural stem cells and the processes involved in adult neurogenesis, how neural stem cells are affected by alcohol, and possible differences in the neurogenic niche between adults and adolescents. Specifically, what is known about developmental differences in adult neurogenesis between the adult and adolescent is gleaned from the literature, as well as how alcohol affects this process differently among the age groups. Finally, this review suggests differences that may exist in the neurogenic niche between adults and adolescents and how these differences may contribute to the susceptibility of the adolescent hippocampus to damage. However, many more studies are needed to discern whether these developmental differences contribute to the vulnerability of the adolescent to developing an AUD.