Paternal alcohol consumption in the rat impairs spatial learning performance in male offspring

Neurological Disorders Induced by Drug Use: Effects of Adolescent and Embryonic Drug Exposure on Behavioral Neurodevelopment

Clinical studies demonstrate that the risk of developing neurological disorders is increased by overconsumption of the commonly used drugs, alcohol, nicotine and cannabis. These drug-induced neurological disorders, which include substance use disorder (SUD) and its co-occurring emotional conditions such as anxiety and depression, are observed not only in adults but also with drug use during adolescence and after prenatal exposure to these drugs, and they are accompanied by long-lasting disturbances in brain development. This report provides overviews of clinical and preclinical studies, which confirm these adverse effects in adolescents and the offspring prenatally exposed to the drugs and include a more in-depth description of specific neuronal systems, their neurocircuitry and molecular mechanisms, affected by drug exposure and of specific techniques used to determine if these effects in the brain are causally related to the behavioral disturbances. With analysis of further studies, this review then addresses four specific questions that are important for fully understanding the impact that drug use in young individuals can have on future pregnancies and their offspring. Evidence demonstrates that the adverse effects on their brain and behavior can occur: (1) at low doses with short periods of drug exposure during pregnancy; (2) after pre-conception drug use by both females and males; (3) in subsequent generations following the initial drug exposure; and (4) in a sex-dependent manner, with drug use producing a greater risk in females than males of developing SUDs with emotional conditions and female offspring after prenatal drug exposure responding more adversely than male offspring. With the recent rise in drug use by adolescents and pregnant women that has occurred in association with the legalization of cannabis and increased availability of vaping tools, these conclusions from the clinical and preclinical literature are particularly alarming and underscore the urgent need to educate young women and men about the possible harmful effects of early drug use and to seek novel therapeutic strategies that might help to limit drug use in young individuals.

Preconception ethanol exposure changes anxiety, depressive and checking-like behavior and alter the expression levels of MAO-B in male offspring

Alcohol use, which alters the epigenome, increases the probability that it could affect subsequent generations, even if they were never directly exposed to ethanol or even in utero. We explored the effects of parental ethanol exposure before conception on behavioral changes in the offspring. Considering the role of Monoamine oxidase-B (MAO-B) in dopamine turnover in the prefrontal cortex (PFC) and its influence on behavior, and taking into account that ethanol exposure could alter MAO-B, we assessed the protein levels in the offspring. Male and female rats were exposed to ethanol for 30 days and then allowed ten days of abstinence. Afterward, they were mated with either control or ethanol-exposed rats. The F1 and F2 male offspring underwent tests to assess behavioral changes. Additionally, the levels of MAO-B in the PFC were evaluated. Results revealed that in the F1, anxiety increased only in the bi-parental ethanol-exposed male offspring in the elevated plus maze test (p < 0.05), while depressive-like behavior rose only in maternal and bi-parental ethanol-exposed offspring (p < 0.01). However, compulsive-like behavior increased in all ethanol-exposed offspring (p < 0.01). No significant phenotypic changes were observed in the F2. The levels of MAO-B in the PFC increased in the maternal (p < 0.05) and bi-parental ethanol-exposed offspring (p < 0.01). Our study demonstrates that parental ethanol exposure, even in the days preceding mating, adversely affects behaviors and induces molecular changes in the brain. Given these findings, it becomes imperative to monitor children exposed to parental (especially maternal) ethanol for the prevention of mental disorders.

Alcohol: Epigenome alteration and inter/transgenerational effect

While DNA serves as the fundamental genetic blueprint for an organism, it is not a static entity. Gene expression, the process by which genetic information is utilized to create functional products like proteins, can be modulated by a diverse range of environmental factors. Epigenetic mechanisms, including DNA methylation, histone modification, and microRNAs, play a pivotal role in mediating the intricate interplay between the environment and gene expression. Intriguingly, alterations in the epigenome have the potential to be inherited across generations. Alcohol use disorder (AUD) poses significant health issues worldwide. Alcohol has the capability to induce changes in the epigenome, which can be inherited by offspring, thus impacting them even in the absence of direct alcohol exposure. This review delves into the impact of alcohol on the epigenome, examining how its effects vary based on factors such as the age of exposure (adolescence or adulthood), the duration of exposure (chronic or acute), and the specific sample collected (brain, blood, or sperm). The literature underscores that alcohol exposure can elicit diverse effects on the epigenome during different life stages. Furthermore, compelling evidence from human and animal studies demonstrates that alcohol induces alterations in epigenome content, affecting both the brain and blood. Notably, rodent studies suggest that these epigenetic changes can result in lasting phenotype alterations that extend across at least two generations. In conclusion, the comprehensive literature analysis supports the notion that alcohol exposure induces lasting epigenetic alterations, influencing the behavior and health of future generations. This knowledge emphasizes the significance of addressing the potential transgenerational effects of alcohol and highlights the importance of preventive measures to minimize the adverse impact on offspring.

Trans-generational effects of parental exposure to drugs of abuse on offspring memory functions

Recent evidence reported that parental-derived phenotypes can be passed on to the next generations. Within the inheritance of epigenetic characteristics allowing the transmission of information related to the ancestral environment to the offspring, the specific case of the trans-generational effects of parental drug addiction has been extensively studied. Drug addiction is a chronic disorder resulting from complex interactions among environmental, genetic, and drug-related factors. Repeated exposures to drugs induce epigenetic changes in the reward circuitry that in turn mediate enduring changes in brain function. Addictive drugs can exert their effects trans-generally and influence the offspring of addicted parents. Although there is growing evidence that shows a wide range of behavioral, physiological, and molecular phenotypes in inter-, multi-, and trans-generational studies, transmitted phenotypes often vary widely even within similar protocols. Given the breadth of literature findings, in the present review, we restricted our investigation to learning and memory performances, as examples of the offspring's complex behavioral outcomes following parental exposure to drugs of abuse, including morphine, cocaine, cannabinoids, nicotine, heroin, and alcohol.

Inter- and transgenerational heritability of preconception chronic stress or alcohol exposure: Translational outcomes in brain and behavior

Chronic stress and alcohol (ethanol) use are highly interrelated and can change an individual's behavior through molecular adaptations that do not change the DNA sequence, but instead change gene expression. A recent wealth of research has found that these nongenomic changes can be transmitted across generations, which could partially account for the "missing heritability" observed in genome-wide association studies of alcohol use disorder and other stress-related neuropsychiatric disorders. In this review, we summarize the molecular and behavioral outcomes of nongenomic inheritance of chronic stress and ethanol exposure and the germline mechanisms that could give rise to this heritability. In doing so, we outline the need for further research to: (1) Investigate individual germline mechanisms of paternal, maternal, and biparental nongenomic chronic stress- and ethanol-related inheritance; (2) Synthesize and dissect cross-generational chronic stress and ethanol exposure; (3) Determine cross-generational molecular outcomes of preconception ethanol exposure that contribute to alcohol-related disease risk, using cancer as an example. A detailed understanding of the cross-generational nongenomic effects of stress and/or ethanol will yield novel insight into the impact of ancestral perturbations on disease risk across generations and uncover actionable targets to improve human health.

Paternal alcohol exposure attenuates maintenance and reinstated operant responding for alcohol in the offspring of rats

BACKGROUND

The heritability of alcohol use disorder is close to 50%, yet common genetic variants account for less than 5% of risk. The missing heritability may reflect environmental exposure in the parents prior to conception. Indeed, paternal alcohol exposure has many behavioral and biological consequences for rodent offspring. We recently found that paternal alcohol exposure attenuated the acquisition of operant alcohol self-administration in offspring of rats of both sexes. Here we test whether this effect extends to other phases of operant self-administration thought to model motivation, craving, and relapse.

METHODS

Wistar male rats exposed to alcohol vapors or air for 6 weeks were mated with alcohol-naïve females 8 weeks later. The adult offspring were trained to lever press for alcohol and tested under several conditions: (1) maintenance responding under a progressive ratio schedule, (2) extinction responding due to removal of the alcohol delivery contingency, (3) reinstatement of extinguished responding in the presence of alcohol-associated cues, and (4) reinitiation of lever press responding for alcohol delivery under fixed and progressive ratio schedules.

RESULTS

Alcohol-sired offspring showed reduced responding under the progressive ratio schedule and blunted cue-induced reinstatement of extinguished responding. Alcohol-sired offspring also emitted fewer responses during extinction sessions and did not reinitiate responding to the same extent as control-sired rats after alcohol delivery was restored.

CONCLUSIONS

Across all conditions, paternal alcohol exposure led to a reduction in the reinforcing effects of alcohol in offspring. These results are consistent with studies conducted with paternal cocaine exposure except that here we find effects in rats of both sexes.

Intergenerational consequences of adolescent morphine exposure on learning and memory

Drug addiction is a worldwide social and medical disorder. More than 50 percent of drug abusers start their substance abuse in adolescence between the ages of 15-19. Adolescence is a sensitive and crucial period for the development and maturity of the brain. Chronic exposure to morphine, particularly during this period, lead to long-lasting effects, including effects that extend to the next generation. The current study examined the intergenerational effects of paternal morphine exposure during adolescence on learning and memory. In this study, male Wistar rats were exposed to increasing doses of morphine (5-25 mg/kg, s.c.) or saline for 10 days at postnatal days (PND) 30-39 during adolescence. Following a 20-day drug-free period, the treated male rats were mated with naïve females. Adult male offspring (PND 60-80) were tested for working memory, novel object recognition memory, spatial memory, and passive avoidance memory using the Y-Maze, novel object recognition, Morris water maze, and shuttle box tests, respectively. The spontaneous alternation (as measured in the Y-Maze test) was significantly less in the morphine-sired group compared to the saline-sired one. The offspring showed significantly less discrimination index in the novel object recognition test when compared to the control group. Morphine-sired offspring tended to spend significantly more time in the target quadrant and less escape latency in the Morris water maze on probe day when compared to the saline-sired ones. The offspring showed significantly less step-through latency to enter the dark compartment compared to the control group when measured in the shuttle box test. Paternal exposure to morphine during adolescence impaired working, novel object recognition, and passive avoidance memory in male offspring. Spatial memory changed in the morphine-sired group compared to the saline-sired one.

Paternal alcohol exposure has task- and sex-dependent behavioral effect in offspring

BACKGROUND

Endophenotypes for alcohol use disorder are well known and may reflect paternal exposure effects passed down to offspring via epigenetic mechanisms. Previously, we showed that paternal alcohol exposure prior to conception attenuates the acquisition of operant alcohol self-administration. We now test whether paternal alcohol exposure alters their offsprings' behavioral responses to alcohol (endophenotypes) and global DNA methylation levels in reward-related brain regions.

METHODS

Adult male rats were exposed to alcohol vapors or air for 6 weeks and mated with alcohol-naïve females 8 weeks later. Adult male and female offspring of the alcohol- and control-sired litters were tested on three behaviors 30 m after gavage with water or alcohol (1.5 g/kg): open field, elevated plus maze, and accelerating rotarod. Global DNA methylation levels in sperm, nucleus accumbens, and prefrontal cortex were examined in male sires and in another group of offspring.

RESULTS

Alcohol-sired males showed less anxiety-like behavior in the elevated plus maze that was not affected by alcohol administration. By contrast, alcohol had anxiolytic effects in the open field in male offspring only with no paternal alcohol effect. Neither paternal alcohol exposure nor alcohol administration altered locomotor activity in either sex. Sex-specific effects of paternal alcohol exposure were seen in the rotarod test. Alcohol-sired male offspring showed blunted sensitivity to the alcohol's motor-impairing effects, whereas alcohol-sired female offspring showed enhanced sensitivity. Global DNA methylation was altered in the sperm of alcohol-exposed males, but no changes were seen in their offspring.

CONCLUSIONS

Paternal alcohol exposure prior to conception has sex- and task-dependent effects on unconditioned behaviors in their offspring.

Paternal and/or maternal preconception-induced neurobehavioral teratogenicity in animal and human models

Prenatal insult exposure effects on the offspring, have and are still considered the main interest of most teratological studies, while paternal and maternal preconception effects have received relatively little interest. Once thought to be a myth, paternal exposure to insults leading to numerous detrimental effects in the offspring, has been confirmed on several occasions and is gaining increased attention. These effects could be demonstrated molecularly, biochemically and/or behaviorally. Different epigenetic mechanisms have been proposed for these effects to occur, including DNA methylation, histone modification and sperm RNA transmission. Paternal insult exposure has been shown to cause several neurobehavioral and developmental defects in the offspring. Findings on parental insult exposure effects on the progeny will be discussed in this review, with the main focus being on neurobehavioral effects after parental preconceptional exposure. The exposure to the insults induced long-lasting, mostly marked, defects. A few pioneering, prevention and reversal studies were published. Interestingly, most studies were conducted on paternal exposure and, at the present state of this field, on animal models. Clinical translation remains the subsequent challenge.

Paternal exposure to exercise and/or caffeine and alcohol modify offspring behavioral and pathophysiological recovery from repetitive mild traumatic brain injury in adolescence

Only recently has the scope of parental research expanded to include the paternal sphere with epidemiological studies implicating stress, nutrition and alcohol consumption in the neurobiological and behavioral characteristics of offspring. This study was designed to determine if paternal exposure to caffeine, alcohol and exercise prior to conception would improve or exacerbate offspring recovery from adolescent repetitive mild traumatic brain injury (RmTBI). Sires received 7 weeks of standard drinking water, or caffeine and ethanol and were housed in regular cages or cages with running wheels, prior to being mated to control females. At postnatal day 40, offspring were administered RmTBI or sham injuries and were assessed for post concussive symptomology. Post-mortem quantitative real-time polymerase chain reaction (qRT-PCR) was used to assess gene expression in the prefrontal cortex (PFC), nucleus accumbens (NAc) and changes in telomere length. Additionally, enzyme-linked immunosorbent assay (ELISA's) were run on serum to detect levels of cytokines, chemokines and sex hormones. Paternal experience did not improve or exacerbate RmTBI behavioral outcomes. However, female and male offspring displayed unique responses to RmTBI and paternal experience, resulting in changes in physical, behavioral and molecular outcomes. Injury and paternal exercise modified changes in female offspring, whereas male offspring were affected by paternal exercise, caffeine and alcohol treatment. Additionally, paternal experience and RmTBI modified expression of many genes in the PFC, NAc, telomere length and levels of sex hormones. Although further exploration is required to understand the heterogeneity that exists in disease risk and resiliency, this study provides corroborating evidence that paternal experiences prior to conception influences offspring development.

Exposure to drugs of abuse induce effects that persist across generations

Substance use disorders are highly prevalent and continue to be one of the leading causes of disability in the world. Notably, not all people who use addictive drugs develop a substance use disorder. Although substance use disorders are highly heritable, patterns of inheritance cannot be explained purely by Mendelian genetic mechanisms. Vulnerability to developing drug addiction depends on the interplay between genetics and environment. Additionally, evidence from the past decade has pointed to the role of epigenetic inheritance in drug addiction. This emerging field focuses on how environmental perturbations, including exposure to addictive drugs, induce epigenetic modifications that are transmitted to the embryo at fertilization and modify developmental gene expression programs to ultimately impact subsequent generations. This chapter highlights intergenerational and transgenerational phenotypes in offspring following a history of parental drug exposure. Special attention is paid to parental preconception exposure studies of five drugs of abuse (alcohol, cocaine, nicotine, cannabinoids, and opiates) and associated behavioral and physiological outcomes in offspring. The highlighted studies demonstrate that parental exposure to drugs of abuse has enduring effects that persist into subsequent generations. Understanding the contribution of epigenetic inheritance in drug addiction may provide clues for better treatments and therapies for substance use disorders.

Effects of Paternal Preconception Vapor Alcohol Exposure Paradigms on Behavioral Responses in Offspring

We and others previously reported that paternal preconception chronic ethanol exposure leads to molecular, physiological, and behavioral changes in offspring including reduced ethanol consumption and preference relative to controls. The goal of the present study was to further explore the impact of paternal ethanol exposure on a wide variety of basal and drug-induced behavioral responses in first generation offspring. Adult male mice were exposed to chronic intermittent vapor ethanol or control conditions for 5-6 weeks before being mated with ethanol-naïve females to produce ethanol (E)- and control (C)-sired offspring. E-sired male offspring showed stress hyporesponsivity in a stress-induced hyperthermia assay and E-sired female offspring had reduced binge-like ethanol consumption in a drinking in the dark assay compared to C-sired offspring. E-sired offspring also showed altered sensitivity to a sedative/hypnotic dose of the GABAergic drug midazolam, but not ketamine or ethanol, in a loss of the righting response assay. E-sired offspring did not differ from controls in marble burying, novel object location, novel object recognition, social interaction, bottle-brush, novelty suppressed feeding, prepulse inhibition, every-other-day ethanol drinking, or home cage activity assays. This study adds to a growing body of literature suggesting that like in utero alcohol exposure, paternal preconception alcohol exposure can also have effects that persist and impact behavior of offspring.

Impact of nicotine, alcohol, and cocaine exposure on germline integrity and epigenome

Converging evidence suggests that parental exposure to drugs of abuse can affect offspring phenotypes. The impacts of drug abuse on germ cell quality may mediate multigenerational and transgenerational inheritance, although biological pathways underlying this mode of inheritance are not yet characterized. Germline epigenetic marks are modified by drug exposure and have emerged as promising mechanistic candidates in recent work. Drug exposure also impacts overall germline integrity and reproductive functioning, although the role of these consequences in multi/transgenerational inheritance is unclear. This review synthesizes literature on effects of exposure to alcohol, cocaine, and nicotine on the germline with a focus on epigenetic modifications following drug exposure and broader impacts on germline integrity and reproductive functioning. We discuss potential interactions between reproductive functioning, germline integrity, and germline epigenome/transcriptome in pathways underlying multi/transgenerational inheritance. We find that existing data may support independent or interactive contributions of these germline impacts on offspring phenotypes in a manner that may mediate multi/transgenerational inheritance.

Multi-, Inter-, and Transgenerational Effects of Drugs of Abuse on Behavior

Transgenerational epigenetic inheritance is a burgeoning field that has recently garnered much attention. A growing body of evidence identifies behavioral phenotypes associated with inter-, multi-, and transgenerational studies following a wide variety of parental exposures. This chapter in current topics in behavioral neurogenomics examines the evidence for the presence of behavioral phenotypes and, in particular, the varied and often opposite behavioral responses observed with protocol shifts. Effects following parental exposure to drugs of abuse are used as an example of the wide range of behavioral outcomes and the variability associated with these multiple generation studies. The behavioral phenotypes associated with drug exposure are reviewed in depth.

The Impact of Paternal Alcohol Consumption on Offspring Brain and Behavioral Development

BACKGROUND

Fetal alcohol spectrum disorders (FASD) describe the wide array of long-lasting developmental abnormalities in offspring due to prenatal alcohol (ethanol [EtOH]) exposure via maternal gestational drinking. Although the teratogenic consequences of prenatal EtOH exposure, are apparent, the effects of preconception paternal EtOH exposure (PatEE) are still unclear. Previous research suggests that PatEE can induce molecular changes and abnormal behavior in the offspring. However, it is not known whether PatEE impacts the development of the neocortex and behavior in offspring as demonstrated in maternal consumption models of FASD (J Neurosci, 33, 2013, 18893).

METHODS

In this study, we utilized a novel mouse model of PatEE where male mice self-administered 25% EtOH for an extended period prior to conception, generating indirect exposure to the offspring through the paternal germline. Following mating, we examined the effects of PatEE on offspring neocortical development at postnatal day (P) 0 and evaluated several aspects of behavior at both P20 and P30 using a battery of behavioral assays.

RESULTS

PatEE resulted in significant impact on neocortical development, including abnormal patterns of gene expression within the neocortex at P0 and subtle alterations in patterns of intraneocortical connections. Additionally, PatEE mice exhibited a sex-specific increase in activity and sensorimotor integration deficits at P20, and decreased balance, coordination, and short-term motor learning at P30. This suggests that PatEE may generate long-lasting, sex-specific effects on offspring behavior.

CONCLUSIONS

These results demonstrate that the developmental impact of preconception PatEE is more harmful than previously thought and provide additional insights into the biological mechanisms that may underlie atypical behavior observed in children of alcoholic fathers.

Who's your daddy? Behavioral and epigenetic consequences of paternal drug exposure

Substance use disorders (SUDs) reflect genetic and environmental factors. While identifying reliable genetic variants that predispose individuals to developing SUDs has been challenging, epigenetic factors may also contribute to the heritability of SUDs. Familial drug use associates with a wide range of problems in children, including an increased risk for developing a SUD. The implications of maternal drug use on offspring development are a well-studied area; however, paternal drug use prior to conception has received relatively little attention. Paternal exposure to several environmental stimuli (i.e. stress or diet manipulations) results in behavioral and epigenetic changes in offspring. The purpose of this review is to determine the state of the preclinical literature on the behavioral and epigenetic consequences of paternal drug exposure. Drug-sired offspring show several developmental and physiological abnormalities. These offspring also show deficits in cognitive and emotional domains. Examining sensitivity to drugs in offspring is a growing area of research. Drug-sired offspring are resistant to the rewarding and reinforcing properties of drugs. However, greater paternal motivation for the drug, combined with high drug intake, can result in addiction-like behaviors in offspring. Drug-sired offspring also show altered histone modifications and DNA methylation levels of imprinted genes and microRNAs; epigenetic-mediated changes were also noted in genes related to glutamatergic and neurotrophic factor signaling. In some instances, drug use resulted in aberrant epigenetic modifications in sire sperm, and these changes were maintained in the brains of offspring. Thus, paternal drug exposure has long-lasting consequences that include altered drug sensitivity in subsequent generations. We discuss factors (i.e. maternal behaviors) that may moderate these paternal drug-induced effects as well as ideas for future directions.

Intergenerational Effects of Alcohol: A Review of Paternal Preconception Ethanol Exposure Studies and Epigenetic Mechanisms in the Male Germline

While alcohol use disorder (AUD) is a highly heritable psychiatric disease, efforts to elucidate that heritability by examining genetic variation (e.g., single nucleotide polymorphisms) have been insufficient to fully account for familial AUD risk. Perhaps not coincidently, there has been a burgeoning interest in novel nongenomic mechanisms of inheritance (i.e., epigenetics) that are shaped in the male or female germ cells by significant lifetime experiences such as exposure to chronic stress, malnutrition, or drugs of abuse. While many epidemiological and preclinical studies have long pointed to a role for the parental preconception environment in offspring behavior, over the last decade many studies have implicated a causal relationship between the environmentally sensitive sperm epigenome and intergenerational phenotypes. This critical review will detail the heritable effects of alcohol and the potential role for epigenetics.

Offspring of male rats exposed to binge alcohol exhibit heightened ethanol intake at infancy and alterations in T-maze performance

Alcohol use is associated with a variety of negative consequences, including heightened likelihood of cognitive impairment, proclivity to alcohol use disorders (AUD), and alterations in the drinker's offspring. Children and rodents exposed to alcohol during pregnancy, or those whose fathers consumed alcohol prior to mating, often exhibit neurodevelopmental, physiological, and behavioral deficits. The present study assessed cognitive function and alcohol intake in male and female rats that were offspring of alcohol-exposed fathers. Adult male rats were exposed to alcohol or vehicle (0.0 or 2.0 g/kg, respectively; twice daily for 2 days followed by a rest day, for a total of eight alcohol or vehicle exposure days), or were left untreated and then mated with non-manipulated females. The offspring were assessed for alcohol intake, via intraoral infusion, followed by cognitive assessment via an alternating T-maze task. The results indicated that paternal ethanol exposure, prior to breeding, resulted in offspring that consumed significantly more ethanol than vehicle or untreated controls. Furthermore, the offspring of alcohol-exposed fathers exhibited a significant failure to initiate and complete the T-maze performance tests. Although, when they did engage in the tests they performed at the level of controls (i.e., 80% correct). The present results add to a growing body of literature suggesting that paternal pre-conception alcohol exposure can have deleterious effects on the offspring.

Epigenetic effects of paternal cocaine on reward stimulus behavior and accumbens gene expression in mice

Paternal cocaine use causes phenotypic alterations in offspring behavior and associated neural processing. In rodents, changes in first generation (F1) offspring include drug reward behavior, circadian timing, and anxiety responses. This study, utilizing a murine (C57BL/6J) oral cocaine model, examines the effects of paternal cocaine exposure on fundamental characteristics of offspring reward responses, including: 1) the extent of cocaine-induced effects after different durations of sire drug withdrawal; 2) sex- and drug-dependent differences in F1 reward preference; 3) effects on second generation (F2) cocaine preference; and 4) corresponding changes in reward area (nucleus accumbens) mRNA expression. We demonstrate that paternal cocaine intake over a single ˜40-day spermatogenic cycle significantly decreased cocaine (but not ethanol or sucrose) preference in a sex-specific manner in F1 mice from sires mated 24 h after drug withdrawal. However, F1 offspring of sires bred 4 months after withdrawal did not exhibit altered cocaine preference. Altered cocaine preference also was not observed in F2's. RNASeq analyses of F1 accumbens tissue revealed changes in gene expression in male offspring of cocaine-exposed sires, including many genes not previously linked to cocaine addiction. Enrichment analyses highlight genes linked to CNS development, synaptic signaling, extracellular matrix, and immune function. Expression correlation analyses identified a novel target, Fam19a4, that may negatively regulate many genes in the accumbens, including genes already identified in addiction. Collectively, these results reveal that paternal cocaine effects in F1 offspring may involve temporally limited epigenetic germline effects and identify new genetic targets for addiction research.

NGF and BDNF Alterations by Prenatal Alcohol Exposure

BACKGROUND

It is now widely established that the devastating effects of prenatal alcohol exposure on the embryo and fetus development cause marked cognitive and neurobiological deficits in the newborns. The negative effects of the gestational alcohol use have been well documented and known for some time. However, also the subtle role of alcohol consumption by fathers prior to mating is drawing special attention.

OBJECTIVE

Both paternal and maternal alcohol exposure has been shown to affect the neurotrophins' signalling pathways in the brain and in target organs of ethanol intoxication. Neurotrophins, in particular nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), are molecules playing a pivotal role in the survival, development and function of the peripheral and central nervous systems but also in the pathogenesis of developmental defects caused by alcohol exposure.

METHODS

New researches from the available literature and experimental data from our laboratory are presented in this review to offer the most recent findings regarding the effects of maternal and paternal prenatal ethanol exposure especially on the neurotrophins' signalling pathways.

RESULTS

NGF and BDNF changes play a subtle role in short- and long-lasting effects of alcohol in ethanol target tissues, including neuronal cell death and severe cognitive and physiological deficits in the newborns.

CONCLUSION

The review suggests a possible therapeutic intervention based on the use of specific molecules with antioxidant properties in order to induce a potential prevention of the harmful effects of the paternal and/or maternal alcohol exposure.

Multigenerational and transgenerational effects of paternal exposure to drugs of abuse on behavioral and neural function

Addictions are highly heritable disorders, with heritability estimates ranging from 39% to 72%. Multiple studies suggest a link between paternal drug abuse and addiction in their children. However, patterns of inheritance cannot be explained purely by Mendelian genetic mechanisms. Exposure to drugs of abuse results in epigenetic changes that may be passed on through the germline. This mechanism of epigenetic transgenerational inheritance may provide a link between paternal drug exposure and addiction susceptibility in the offspring. Recent studies have begun to investigate the effect of paternal drug exposure on behavioral and neurobiological phenotypes in offspring of drug-exposed fathers in rodent models. This review aims to discuss behavioral and neural effects of paternal exposure to alcohol, cocaine, opioids, and nicotine. Although a special focus will be on addiction-relevant behaviors, additional behavioral effects including cognition, anxiety, and depressive-like behaviors will be discussed.

Alcohol effects on the epigenome in the germline: Role in the inheritance of alcohol-related pathology

Excessive alcohol exposure has severe health consequences, and clinical and animal studies have demonstrated that disruptions in the epigenome of somatic cells, such as those in brain, are an important factor in the development of alcohol-related pathologies, such as alcohol-use disorders (AUDs) and fetal alcohol spectrum disorders (FASDs). It is also well known that alcohol-related health problems are passed down across generations in human populations, but the complete mechanisms for this phenomenon are currently unknown. Recent studies in animal models have suggested that epigenetic factors are also responsible for the transmission of alcohol-related pathologies across generations. Alcohol exposure has been shown to induce changes in the epigenome of sperm of exposed male animals, and these epimutations are inherited in the offspring. This paper reviews evidence for multigenerational and transgenerational epigenetic inheritance of alcohol-related pathology through the germline. We also review the literature on the epigenetic effects of alcohol exposure on somatic cells in brain, and its contribution to AUDs and FASDs. We note gaps in knowledge in this field, such as the lack of clinical studies in human populations and the lack of data on epigenetic inheritance via the female germline, and we suggest future research directions.

Strain-specific programming of prenatal ethanol exposure across generations

Behavioral consequences of prenatal alcohol exposure (PAE) can be transmitted from in utero-exposed F1 generation to their F2 offspring. This type of transmission is modulated by genetic and epigenetic mechanisms. This study investigated the intergenerational consequences of prenatal exposure to a low ethanol dose (1 g/kg) during gestational days 17-20, on ethanol-induced hypnosis in adolescent male F1 and F2 generations, in two strains of rats. Adolescent Long-Evans and Sprague-Dawley male rats were tested for sensitivity to ethanol-induced hypnosis at a 3.5-g/kg or 4.5-g/kg ethanol dose using the loss of righting reflex (LORR) paradigm. We hypothesized that PAE would attenuate sensitivity to ethanol-induced hypnosis in the ethanol-exposed animals in these two strains and in both generations. Interestingly, we only found this effect in Sprague-Dawley rats. Lastly, we investigated PAE related changes in expression of GABA_A receptor α1, α4, and δ subunits in the cerebral cortex of the PAE sensitive Sprague-Dawley strain. We hypothesized a reduction in the cerebral cortex GABA_A receptor subunits' expression in the F1 and F2 PAE groups compared to control animals. GABA_A receptor α1, α4, and δ subunits protein expressions were quantified in the cerebral cortex of F1 and F2 male adolescents by western blotting. PAE did not alter cerebral cortical GABA_A receptor subunit expressions in the F1 generation, but it decreased GABA_A receptor α4 and δ subunits' expressions in the F2 generation, and had a tendency to decrease α1 subunit expression. We also found correlations between some of the subunits in both generations. These strain-dependent vulnerabilities to ethanol sensitivity, and intergenerational PAE-mediated changes in sensitivity to alcohol indicate that genetic and epigenetic factors interact to determine the outcomes of PAE animals and their offspring.

Paternal alcohol exposure in mice alters brain NGF and BDNF and increases ethanol-elicited preference in male offspring

Ethanol (EtOH) exposure during pregnancy induces cognitive and physiological deficits in the offspring. However, the role of paternal alcohol exposure (PAE) on offspring EtOH sensitivity and neurotrophins has not received much attention. The present study examined whether PAE may disrupt nerve growth factor (NGF) and/or brain-derived neurotrophic factor (BDNF) and affect EtOH preference/rewarding properties in the male offspring. CD1 sire mice were chronically addicted for EtOH or administered with sucrose. Their male offsprings when adult were assessed for EtOH preference by a conditioned place preference paradigm. NGF and BDNF, their receptors (p75(NTR) , TrkA and TrkB), dopamine active transporter (DAT), dopamine receptors D1 and D2, pro-NGF and pro-BDNF were also evaluated in brain areas. PAE affected NGF levels in frontal cortex, striatum, olfactory lobes, hippocampus and hypothalamus. BDNF alterations in frontal cortex, striatum and olfactory lobes were found. PAE induced a higher susceptibility to the EtOH rewarding effects mostly evident at the lower concentration (0.5 g/kg) that was ineffective in non-PAE offsprings. Moreover, higher ethanol concentrations (1.5 g/kg) produced an aversive response in PAE animals and a significant preference in non-PAE offspring. PAE affected also TrkA in the hippocampus and p75(NTR) in the frontal cortex. DAT was affected in the olfactory lobes in PAE animals treated with 0.5 g/kg of ethanol while no differences were found on D1/D2 receptors and for pro-NGF or pro-BDNF. In conclusion, this study shows that: PAE affects NGF and BDNF expression in the mouse brain; PAE may induce ethanol intake preference in the male offspring.

Drinking beyond a lifetime: New and emerging insights into paternal alcohol exposure on subsequent generations

Alcohol-use disorder (AUD) is prevalent and associated with substantial socioeconomic costs. While heritability estimates of AUD are ∼50%, identifying specific gene variants associated with risk for AUD has proven challenging despite considerable investment. Emerging research into heritability of complex diseases has implicated transmission of epigenetic variants in the development of behavioral phenotypes, including drug preference and drug-induced behavior. Several recent rodent studies have specifically focused on paternal transmission of epigenetic variants, which is especially relevant because sires are not present for offspring rearing and changes to offspring phenotype are assumed to result from modifications to the sperm epigenome. While considerable interest in paternal transmission of epigenetic variants has emerged recently, paternal alcohol exposures have been studied for 30+ years with interesting behavioral and physiologic effects noted on offspring. However, only recently, with improvements in technology to identify epigenetic modifications in germ cells, has it been possible to identify mechanisms by which paternal ethanol exposure alters offspring behavior. This review presents an overview of epigenetic inheritance in the context of paternal ethanol exposure and suggests future studies to identify specific effects of paternal ethanol exposure on offspring behavior and response to ethanol.

Multigenerational and transgenerational inheritance of drug exposure: The effects of alcohol, opiates, cocaine, marijuana, and nicotine

Familial inheritance of drug abuse is composed of both genetic and environmental factors. Additionally, epigenetic transgenerational inheritance may provide a means by which parental drug use can influence several generations of offspring. Recent evidence suggests that parental drug exposure produces behavioral, biochemical, and neuroanatomical changes in future generations. The focus of this review is to discuss these multigenerational and transgenerational phenotypes in the offspring of animals exposed to drugs of abuse. Specifically, changes found following the administration of alcohol, opioids, cocaine, marijuana, and nicotine will be discussed. In addition, epigenetic modifications to the genome following administration of these drugs will be detailed as well as their potential for transmission to the next generation.

Paternal alcohol exposure reduces alcohol drinking and increases behavioral sensitivity to alcohol selectively in male offspring

Alcohol use disorder (AUD) is heritable, but the genetic basis for this disease remains poorly understood. Although numerous gene variants have been associated with AUD, these variants account for only a small fraction of the total risk. The idea of inheritance of acquired characteristics, i.e. “epigenetic inheritance,” is re-emerging as a proven adjunct to traditional modes of genetic inheritance. We hypothesized that alcohol drinking and neurobiological sensitivity to alcohol are influenced by ancestral alcohol exposure. To test this hypothesis, we exposed male mice to chronic vapor ethanol or control conditions, mated them to ethanol-naïve females, and tested adult offspring for ethanol drinking, ethanol-induced behaviors, gene expression, and DNA methylation. We found that ethanol-sired male offspring had reduced ethanol preference and consumption, enhanced sensitivity to the anxiolytic and motor-enhancing effects of ethanol, and increased Bdnf expression in the ventral tegmental area (VTA) compared to control-sired male offspring. There were no differences among ethanol- and control-sired female offspring on these assays. Ethanol exposure also decreased DNA methylation at the BdnfÆpromoter of sire's germ cells and hypomethylation was maintained in the VTA of both male and female ethanol-sired offspring. Our findings show that paternal alcohol exposure is a previously unrecognized regulator of alcohol drinking and behavioral sensitivity to alcohol in male, but not female, offspring. Paternal alcohol exposure also induces epigenetic alterations (DNA hypomethylation) and gene expression changes that persist in the VTA of offspring. These results provide new insight into the inheritance and development of alcohol drinking behaviors.

Paternal ethanol exposure and behavioral abnormities in offspring: associated alterations in imprinted gene methylation

Research confirms that maternal ethanol (EtOH) exposure can induce physical and mental disorders in offspring, yet the effect of paternal ethanol exposure on offspring is unclear. Methylation alterations in imprinted genes may be related to the well-documented teratogenic effects of ethanol. Here, we report that ethanol (0, 1.1, 3.3 g/kg) was administered intragastrically to male mice and a behavioral study was performed on their F1 generation. Data show that F1 mice with fathers exposed to the highest dose of ethanol had delayed cognitive performance and increased anxiety and depression. A specific circling behavior was observed in the offspring of the paternally ethanol-exposed group. The degree of methylation and mRNA expression of H19, Peg3, Ndn and Snrpn were assessed in paternal sperm and in the cerebral cortices of each offspring. It did affect methylation in paternal sperm (H19 and Peg3) and in the offspring's cerebral cortices (CpG7 and CpG11 in Peg3 and Snrpn), but the level of mRNA expression has not changed. In the circling mice, the highest ethanol exposure increase in methylation (CpG 1, 2, 7 and 11) and decreases in mRNA of Peg3.Thus, chronic paternal ethanol exposure can affect the methylation of imprinted genes in sire sperm that may be passed on to offspring, giving rise to mental deficits.

The impact of exposure to addictive drugs on future generations: Physiological and behavioral effects

It is clear that both genetic and environmental factors contribute to drug addiction. Recent evidence indicating trans-generational influences of drug abuse highlight potential epigenetic factors as well. Specifically, mounting evidence suggests that parental ingestion of abused drugs influence the physiology and behavior of future generations even in the absence of prenatal exposure. The goal of this review is to describe the trans-generational consequences of preconception exposure to drugs of abuse for five major classes of drugs: alcohol, nicotine, marijuana, opioids, and cocaine. The potential epigenetic mechanisms underlying the transmission of these phenotypes across generations also are detailed. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Subtle biobehavioral effects produced by paternal cocaine exposure

Despite the increased prevalence of cocaine use and abuse in males when compared with females, possible effects of paternal cocaine exposure on biobehavioral development have received little attention. We therefore exposed male mice to cocaine (20 mg/kg, i.p.) or vehicle for 10 weeks and then used those mice as sires. We then behaviorally phenotyped the F1 offspring to assess the consequences of paternal cocaine exposure on brain function. We report the presence of a subtle but significant increase in immobility in the tail suspension test, a measure of behavioral depression, following paternal cocaine. Body weight was also significantly decreased in paternal cocaine-exposed offspring. Other aspects of neurobehavioral function, including locomotor activity, anxiety, and learning and memory, were not affected by paternal cocaine history. These data suggest alterations in brain systems and/or circuitry underlying mood regulation in the offspring of cocaine-using fathers. Synapse 2012. © 2012 Wiley Periodicals, Inc.

Epigenetics and the origins of paternal effects

Though there are multiple routes through which parents can influence their offspring, recent studies of environmentally induced epigenetic variation have highlighted the role of non-genomic pathways. In addition to the experience-dependent modification of DNA methylation that can be achieved via mother-infant interactions, there has been increasing interest in the epigenetic mechanisms through which paternal influences on offspring development can be achieved. Epidemiological and laboratory studies suggest that paternal nutritional and toxicological exposures as well as paternal age and phenotypic variation can lead to variations in offspring and, in some cases, grand-offspring development. These findings suggest a potential epigenetic germline inheritance of paternal effects. However, it may be important to consider the interplay between maternal and paternal influences as well as the experimental dissociation between experience-dependent and germline transmission when exploring the role of epigenetic variation within the germline as a mediator of these effects. In this review, we will explore these issues, with a particular focus on the potential role of paternally induced maternal investment, highlight the literature illustrating the transgenerational impact of paternal experiences, and discuss the evidence supporting the role of epigenetic mechanisms in maintaining paternal effects both within and across generations.

Parent-of-origin and trans-generational germline influences on behavioral development: the interacting roles of mothers, fathers, and grandparents

Mothers and fathers do not contribute equally to the development of their offspring. In addition to the differential investment of mothers versus fathers in the rearing of offspring, there are also a number of germline factors that are transmitted unequally from one parent or the other that contribute significantly to offspring development. This article shall review four major sources of such parent-of-origin effects. Firstly, there is increasing evidence that genes inherited on the sex chromosomes including the nonpseudoautosomal part of the Y chromosome that is only inherited from fathers to sons, contribute to brain development and behavior independently of the organizing effects of sex hormones. Secondly, recent work has demonstrated that mitochondrial DNA that is primarily inherited only from mothers may play a much greater than anticipated role in neurobehavioral development. Thirdly, there exists a class of genes known as imprinted genes that are epigenetically silenced when passed on in a parent-of-origin specific manner and have been shown to regulate brain development and a variety of behaviors. Finally, there is converging evidence from several disciplines that environmental variations experienced by mothers and fathers may lead to plasticity in the development and behavior of offspring and that this phenotypic inheritance can be solely transmitted through the germline. Mechanistically, this may be achieved through altered programming within germ cells of the epigenetic status of particular genes such as retrotransposons and imprinted genes or potentially through altered expression of RNAs within gametes.

Acute paternal alcohol use affects offspring development and adult behavior

Swiss Webster pups were fathered by sires given either an acute dose of alcohol (alcohol-sired) or saline (saline-sired) 12-24 h before mating. The same sires were used to father both groups of pups. Alcohol-sired pups were significantly lighter at birth and for the following three weeks than were saline-sired pups. Significantly more pups were fathered by saline-exposed sires, and dams carrying those pups had significantly longer gestations than those carrying pups of alcohol-using sires. More runts were born to the alcohol-sired group, and more pups in that group died over the next three weeks than in the saline-sired group. Significantly more pups in the saline-sired group achieved such developmental milestones as surface righting, clinging, the tail-pull reflex, rotation, linear movement and climbing an inclined surface earlier than did alcohol-sired pups. As adults, animals from the alcohol-sired group showed significantly less risk assessment behavior and longer latencies to such behaviors as stretched attention, flatback, freezing and defensive burying than did the saline-sired animals. Alcohol-sired animals contacted the stimulus object in the risk assessment test significantly sooner and more often than did the saline-sired group. In tests of aggression, alcohol-sired male offspring showed more frequent aggressive behaviors such as on-top, lateral attacks and jump-attacks, and significantly fewer defensive/fearful behaviors such as piloerection, tail rattling and jump-escape. This pattern of results suggests that exposure of the sire to one acute dose of alcohol before insemination caused some early developmental delays and that alcohol-sired animals are less fearful and more aggressive as adults than saline-sired animals.

Characterizing learning deficits and hippocampal neuron loss following transient global cerebral ischemia in rats

The 2-vessel-occlusion + hypotension (2VO + H) model of transient global cerebral ischemia results in neurodegeneration within the CA1 field of the hippocampus, but previous research has failed to demonstrate robust or reliable learning/memory deficits in rats subjected to this treatment. In the present study, sensitive behavioral protocols were developed in an effort to characterize the cognitive impairments following 2VO + H more precisely. Adult rats were exposed to 10 min of bilateral carotid occlusion with simultaneous hypotension. Following recovery, 2VO + H and control rats were subjected to a series of behavioral tests (locomotor activity, sensorimotor battery, water maze [cued, place, learning set], object recognition, and radial arm maze) over an extended recovery period followed by an assessment of neuronal loss in the dorsal hippocampus. The 2VO + H treatment was associated with long-lasting spatial learning deficits in the absence of other behavioral impairments and with neurodegeneration in dorsal hippocampal CA1. Water maze protocols that placed higher memory demands upon the rats (relatively "hard" vs. "easy") were more sensitive for detecting ischemia-induced deficits. We have shown that the use of appropriate behavioral tests (e.g., a relatively difficult place learning task) allowed for the observation of robust spatial learning deficits in a model previously shown to induce relatively subtle behavioral effects. Thus, the 2VO + H model induces both hippocampal neuronal loss and long-term learning deficits in rats, providing a potentially useful model for evaluating therapeutic efficacy.

Paternal contribution to fetal alcohol syndrome

Maternal alcohol use during pregnancy is associated with a wide range of adverse outcomes for the child. Many women who drink during pregnancy also have male partners who abuse alcohol. Existing data on paternal effects of alcohol abuse during the preconceptual period and at the time of conception are reviewed. Epidemiological data offer some support for a paternal influence on birth weight, congenital heart defects, and some evidence of mild cognitive impairments. Animal data have demonstrated decreased litter size, increased prevalence of low birth weight fetuses and mixed data on risk of malformations. Increased susceptibility to Pseudomonas bacterial infection has been reported. Cognitive and behavioral findings are the most robust effects. These include learning and memory deficits, hyperactivity, and poor stress tolerance. Multiple causal mechanisms for a paternal effect have been suggested, but none seems satisfactory to explain all findings. Further research is needed on paternal effects in animals and human populations. The results of this research may influence prevention activities.

Neurobehavioral effects in rat pups whose sires were exposed to alcohol

Developmental neurobehavioral effects associated with maternal exposure to alcohol during pregnancy are well described, but little is known about the effects of paternal exposure prior to conception. Using a quasi-experimental, within-subjects design, neurobehavioral outcomes (reflex acquisition, activity, gait) and cerebral cortical layer thickness were assessed in Sprague-Dawley rat pups from breeding pairs where the sires were exposed to alcohol. Comparisons were made on the basis of the timing of conception relative to alcohol exposure: phase 1 (controls), prior to initiation of alcohol exposure; phase 2, during the period of treatment with 20% alcohol; and phase 3, following cessation of alcohol exposure. Phase 2 and 3 pups were noted to attain negative geotaxis and reflex suspension benchmarks earlier than control pups and to have more difficulty with balance. Phase 3 pups were noted to attain righting reflex earlier than controls. In addition, phase 3 pups demonstrated increased levels of reverse maze activity and a shorter and narrower gait. Brain morphometry revealed thickening of cortical sections I-IV and V-VI resulting in overall cortical enlargement in both phase 2 and 3 pups. Further analysis of phase 2 and 3 subphases based on the presumed stages of the spermatogenic cycle during which sires were exposed to alcohol revealed significant differences in maze activity, reflex acquisition, and gait length. These findings suggest pre-conception male exposure to alcohol may have an effect on the offspring and the extent of the effects may vary with the timing of alcohol exposure relative to conception.

Early exposure to common anesthetic agents causes widespread neurodegeneration in the developing rat brain and persistent learning deficits

Recently it was demonstrated that exposure of the developing brain during the period of synaptogenesis to drugs that block NMDA glutamate receptors or drugs that potentiate GABA(A) receptors can trigger widespread apoptotic neurodegeneration. All currently used general anesthetic agents have either NMDA receptor-blocking or GABA(A) receptor-enhancing properties. To induce or maintain a surgical plane of anesthesia, it is common practice in pediatric or obstetrical medicine to use agents from these two classes in combination. Therefore, the question arises whether this practice entails significant risk of inducing apoptotic neurodegeneration in the developing human brain. To begin to address this problem, we have administered to 7-d-old infant rats a combination of drugs commonly used in pediatric anesthesia (midazolam, nitrous oxide, and isoflurane) in doses sufficient to maintain a surgical plane of anesthesia for 6 hr, and have observed that this causes widespread apoptotic neurodegeneration in the developing brain, deficits in hippocampal synaptic function, and persistent memory/learning impairments.

Second generation effects of maternal alcohol consumption during pregnancy in rats

1. Previous studies have shown that when female rats are administered alcohol during pregnancy there are adverse effects on their progeny, including decreased birth weight and delayed neuromotor development. Evidence from several sources suggests alcohol exposure may contribute to cytogenetic abnormalities, suggesting the possibility of cross generational effects from prenatal exposure. 2. On day 1 of gestation female rats were randomly allocated to the Alcohol group, which received a liquid diet containing 5% (v/v) ethanol solution until parturition, the Sucrose control group, which received an identical diet, except that sucrose had been isocalorically substituted for ethanol, or the Chow control, which received standard laboratory chow. 3. When the offspring of these rats reached adulthood they were mated with drug-free rats and the development of their offspring was monitored. 4. In comparison with female pups whose sires had been exposed to alcohol in utero, the weight of pups descended from fetally-exposed dams increased more slowly from day 1 to day 7. 5. At five days of age, significant differences favouring the two control groups were found in latency to right for pups descended from fetally-exposed dams. 6. These data suggest that the effects of prenatal exposure to alcohol are more pervasive than previously thought and affect female pups to a greater extent than males.

Paternal alcohol exposure: developmental and behavioral effects on the offspring of rats

The effect of paternal alcohol exposure on neurochemical and behavioral parameters was investigated using as a model system glial cells derived from newborn rat brain and cultured for 4 weeks. The total brain neurochemical parameters from rats born to mothers sired by an alcohol treated father were also investigated. Enzymatic markers of nerve cell development (enolase isoenzymes and glutamine synthetase) and the defense system (superoxide dismutase) against free radicals formed during alcohol degradation were measured in order to evaluate nerve cell damage. Behavioral locomotor tests (open-field, novelty-seeking, light/dark) were carried out to show long-lasting effects of paternal alcoholization on the offspring. Behavioral and developmental alterations were found until 1 year of age in the offspring and a significant growth retardation was observed in the males. Our results suggest that paternal alcohol exposure produces developmental and behavioral effects in the offspring. The consequence of either alcohol withdrawal during stage one spermatogenesis, or maternal diet supplementation with manganese during pregnancy were investigated. It was observed that some of the effects of paternal alcohol exposure on the offspring may be reversed by these treatments.

Clonidine potentiates the neuropathic pain-relieving action of MK-801 while preventing its neurotoxic and hyperactivity side effects

Antagonists of NMDA glutamate receptors have been shown to alleviate neuropathic pain in rats and humans. However, NMDA antagonists can cause significant side effects ranging from behavioral disturbances to injury of neurons in the posterior cingulate/retrosplenial (PC/RS) cortex. We have found that alpha-2 adrenergic agonists prevent the PC/RS neurotoxic side effects of NMDA antagonists. In the present study of adult female rats subjected to sciatic nerve ligation (Bennett neuropathic pain model) and tested for paw withdrawal latency (PWL) following a thermal stimulus, we evaluated the ability of the NMDA antagonist, MK-801, to alleviate neuropathic pain either by itself or when administered together with the alpha-2 adrenergic agonist, clonidine. We found that MK-801, at a dose (0.05 mg/kg s.c.) that is known to cause mild hyperactivity but is subthreshold for producing PC/RS neurotoxic changes, relieved the neuropathic pain state associated with sciatic nerve ligation. However, the relief at this dose was very transient, and no neuropathic pain-relieving effect was observed at a lower dose (0. 025 mg/kg s.c.) of MK-801. Clonidine, at a dose (0.05 mg/kg s.c.) that prevents the cerebrocortical neurotoxic effects of MK-801, decreased sensitivity to the thermal stimulus equally under all conditions (ligated, sham ligated, unoperated), but did not specifically relieve neuropathic pain in the ligated limb. Combining this dose of clonidine with an ineffective dose (0.025 mg/kg s.c.) of MK-801 provided specific, complete and long lasting (up to 4 h) relief from neuropathic pain. Rats receiving this drug combination did not display hyperactivity or any other behavioral disturbance typically associated with MK-801 treatment, nor show neurotoxic changes in cerebrocortical neurons. In separate experiments on normal unoperated rats, we found that clonidine (0.05 mg/kg s.c.) counteracted the hyperactivity induced by MK-801 (0.05 mg/kg s.c.) and returned activity levels to a normal range. These findings signify that clonidine, which does not specifically relieve neuropathic pain, can potentiate the neuropathic pain-relieving action of MK-801, while also protecting against neurotoxicity and hyperactivity side effects of MK-801. The potentiation is of a sufficient magnitude that it permits cutting the MK-801 dose requirement in half, thereby achieving prolonged neuropathic pain relief while doubling the margin of safety against any type of side effect that might be mediated by blockade of NMDA receptors.

Paternal exposures: impact on reproductive and developmental outcome. An overview

Experimental and epidemiologic investigations document the adverse consequences of an array of paternal exposures on the development of subsequent offspring. Male-mediated abnormalities have been reported after exposure to therapeutic and recreational drugs, to chemicals in the workplace and environment and to ionizing radiation. The impact on progeny outcome includes: an increase in congenital malformations, spontaneous abortions, fetal resorptions; low birth weight; increase in childhood cancers; developmental, neurobehavioral, neuroendocrine, neurochemical abnormalities; effects in F2 generation progeny. Fertility is often unaffected. The comparative influence of genetic, epigenetic and nongenetic mechanisms in the etiology of paternally-mediated adverse outcomes is unknown. There is no a priori reason to assume that male-mediated effects are limited to the agents studied to date. The broad spectrum of alterations recorded after exposure to a variety of unrelated agents suggests the need for a more focused effort and multidisciplinary exploration of the potential impact of the male parent on reproductive outcome.

Acute alcohol exposure markedly influences male fertility and fetal outcome in the male rat

Although it is recognized that drugs ingested by pregnant females produce marked cognitive and physiological deficits in their offspring, the possibility that paternal exposure to drugs prior to mating may have adverse effects on fertility and fetal outcome has not received much attention. The purpose of the present studies was to examine whether a single, acute exposure to alcohol influences the subsequent ability of adult male rats to mate and produce healthy and viable litters. Our results showed that a relatively large dose of alcohol 24 hours prior to breeding had little effect on the mating behavior of male rats, but there were markedly fewer pregnancies in females mated with alcohol-exposed male rats than in controls. Of equal importance, we found that, even when conception occurred and live births were produced, there were striking differences in fetal outcome. Alcohol-treated males sired many fewer pups than control males and there was a markedly enhanced mortality rate in their offspring. Collectively, these data suggest that acute paternal alcohol administration 24 hours prior to breeding does not affect mating behavior, but results in a greatly diminished fertility rate and fewer and less viable offspring. These studies suggest that paternal alcohol use may be as important as maternal alcohol abuse as a negative variable in pregnancy and fetal outcome.

Paternal alcohol exposure and hyperactivity in rat offspring: effects of amphetamine

Locomotor activity of rat offspring sired by fathers treated with 0, 2 or 3 g/kg of alcohol twice daily was assessed at 21, 42 and 90 days of age. Fathers treated with the two lower doses were pair-fed to those treated with the highest dose. Offspring of nontreated ad-lib fed fathers were also evaluated to determine the possible role of paternal stress associated with intubation and pair-feeding. The behavioral response to amphetamine was also examined in 90-day-old male offspring. Paternal alcohol treatment resulted in increased activity at each age for 3 g/kg offspring compared to pair-fed controls. Ad-lib offspring did not differ from 0 g/kg controls at 21 and 42 days of age. The significant effect of paternal alcohol treatment on offspring activity at 90 days, including a significant linear paternal effect, occurred when all amphetamine-treated groups were pooled. The alcohol x amphetamine interaction was not significant, but a significant linear paternal alcohol x linear amphetamine interaction indicated that the paternal alcohol effect on activity was differentially responsive to amphetamine. Subsequent analysis of this interaction indicated a significant linear paternal alcohol trend only at the high dose of amphetamine. These results corroborate a previous report of increased activity on the part of offspring sired by fathers treated with alcohol. The presence of a differential effect of amphetamine suggests that the paternal effect on activity may be mediated by catecholaminergic activity. The absence of significant differences between ad lib and 0 g/kg pair-fed controls indicates that paternal stress/undernutrition does not significantly affect offspring activity.

Scopolamine does not differentially affect Morris maze performance in adult rats exposed prenatally to alcohol

Rats exposed prenatally to alcohol have shown deficits in spatial learning in radial-arm and Morris mazes. Prenatal exposure to alcohol in rats has also been shown to alter central nervous system (CNS) cholinergic function. Since cholinergic dysfunction disrupts spatial learning in normal rats, the present experiment assessed the role of putative prenatal alcohol-induced cholinergic dysfunction in spatial learning in rats. Pregnant rats were fed alcohol via liquid diet from gestation day 6 to 20. Control dams were pair-fed liquid diet without alcohol or fed ad lib lab chow and water. Group housed adult male and female offspring (postnatal days 110 to 135) were given scopolamine-HCl (0, 0.5, or 1.0 mg/kg/day) and tested in a Morris maze, with four trials per day for four days. A 15-s probe trial preceded testing on days 2-4. On day 5, the rats were given four trials to learn a new platform location. Scopolamine produced dose-dependent increases in latency to find the platform for all groups. There were no significant differences among prenatal treatment groups in scopolamine-induced shifts in performance. The results did not support the hypothesis that prenatal alcohol-induced CNS cholinergic dysfunction is related to spatial learning performance in these rats.

Rat offspring sired by males treated with alcohol

Male rats were intubated twice daily with either 2 or 3 g/kg of alcohol for nine weeks and were then bred to untreated females. Control animals were intubated with vehicle (distilled water). Controls and 2-g/kg males were pair-fed to 3-g/kg males. A fourth group served as a nonintubated, ad lib control. Male fertility was not affected by alcohol. Mean birth weights were not affected by paternal alcohol treatment, but there was a significant increase in the number of "runts" (< 5.5 g at birth) in the 3-g/kg paternal group. There was also a decrease in the percent of males per litter sired by alcohol-treated fathers. Adrenal weights were increased at birth and spleen weights were decreased at 21 days of age in these offspring as well. These results indicate the potential of paternal alcohol consumption for significantly altering stature and organs in offspring.

Genomic imprinting: implications for behavioral genetics

In recent years it has become apparent that the parental origin of genetic material has an impact on gene expression and this effect has become known as genomic imprinting. The evidence for the influence of genomic imprinting on behavior and in the etiology of certain neurobehavioral disorders is discussed. The possibilities for a role for genomic imprinting in the inheritance of behaviors related to alcohol abuse and alcoholism and in the paternal alcohol syndrome are also explored.