Development of anxiety-like behavior via hippocampal IGF-2 signaling in the offspring of parental morphine exposure: effect of enriched environment

Paternal heroin self-administration in rats increases drug-seeking behavior in male offspring via miR-19b downregulation in the nucleus accumbens

Accumulating evidence indicates that drug addiction may lead to adaptive behavioral changes in offspring, potentially due to epigenetic modifications in parental germline. However, the underlying mechanisms remain inadequately understood. In this study, we show that paternal heroin self-administration (SA) increased heroin-seeking behavior in the F1 generation, when compared with offspring sired by yoke-infused control males, indicating cross-generational impact of paternal voluntary heroin seeking behavior. Notably, the increase of heroin seeking behavior in offspring was replicated by zygotic microinjection of sperm RNAs derived from sperm of heroin-SA-experienced rats. Analysis of non-coding RNAs in spermatozoa revealed coordinated changes in miRNA content between the nucleus accumbens and spermatozoa. We validated that restoration of miR-19b downregulation in sperm RNA from self-administration-experienced rats, in parallel with its overexpression in the nucleus accumbens of F1 offspring sired by heroin-SA-experienced fathers, reversed the increased heroin SA observed in these F1 offspring. Taken together, our findings suggest in rats that paternal heroin self-administration induces epigenetic changes in both brain and sperm miRNA, with miR-19b downregulation playing a critical role in mediating the epigenetic inheritance of increased heroin self-administration behavior in the F1 generation.

Adrenomedullin 2 attenuates anxiety-like behaviors by increasing IGF-II in amygdala and re-establishing blood-brain barrier

Anxiety disorder, a prevalent mental health issue, is one of the leading causes of disability worldwide. Damage to the blood-brain barrier (BBB) is implicated in anxiety, but its regulatory mechanisms remain unclear. Herein, we show that adrenomedullin 2 (ADM2), a novel angiogenic growth factor, alleviates autistic and anxiety-like behaviors in mice. Based on transcriptome analysis and biochemical analyses, we found that ADM2 facilitates the expression of insulin-like growth factor 2 (IGF-II), which then triggers the activation of the AKT-GSK3β-mTOR signaling pathway via the IGF-II receptor (IGF-IIR), rather than the IGF-I receptor (IGF-IR). Furthermore, as evidenced by increased Evans blue staining and decreased VE-cadherin levels, the BBB exhibited dysfunction in ADM2 knockout mice with anxiety-like behaviors. In in vitro studies, ADM2 administration promoted the expression of VE-cadherin and decreased IGF-II leakage through the endothelial barrier in a BBB model. Taken together, ADM2 may alleviate anxiety-like behavior and social deficits by enhancing BBB integrity and increasing IGF-II levels in the brain. These findings highlight the potential of ADM2 as a therapeutic target for anxiety and related mental disorders.

Paternal cocaine-seeking motivation defines offspring's vulnerability to addiction by down-regulating GABAergic GABRG3 in the ventral tegmental area

Epidemiological investigations indicate that parental drug abuse experiences significantly influenced the addiction vulnerability of offspring. Studies using animal models have shown that paternal cocaine use and highly motivated drug-seeking behavior are important determinants of offspring addiction susceptibility. However, the key molecules contributing to offspring addiction susceptibility are currently unclear. The motivation for cocaine-seeking behavior in offspring of male rats was compared between those whose fathers self-administered cocaine (SA) and those who were yoked with them and received non-contingent cocaine administrations (Yoke). We found that paternal experience with cocaine-seeking behavior, but not direct cocaine exposure, could lead to increased lever-pressing behavior in male F1 offspring. This effect was observed without significant changes to the dose-response relationship. The transcriptomes of ventral tegmental area (VTA) in offspring were analyzed under both naive state and after self-administration training. Specific transcriptomic changes in response to paternal cocaine-seeking experiences were found, which mainly affected biological processes such as synaptic connections and receptor signaling pathways. Through joint analysis of these candidate genes and parental drug-seeking motivation scores, we found that gamma-aminobutyric acid receptor subunit gamma-3 (Gabrg3) was in the hub position of the drug-seeking motivation-related module network and highly correlated with parental drug-seeking motivation scores. The downregulation of Gabrg3 expression, caused by paternal motivational cocaine-seeking, mainly occurred in GABAergic neurons in the VTA. Furthermore, down-regulating GABAergic Gabrg3 in VTA resulted in an increase in cocaine-seeking behavior in the Yoke F1 group. This down-regulation also reduced transcriptome differences between the Yoke and SA groups, affecting processes related to synaptic formation and neurotransmitter transmission. Taken together, we propose that paternal cocaine-seeking behavior, rather than direct drug exposure, significantly influences offspring addiction susceptibility through the downregulation of Gabrg3 in GABAergic neurons of the VTA, highlighting the importance of understanding specific molecular pathways in the intergenerational inheritance of addiction vulnerability.

Subchronic Arsenic Exposure Induces Behavioral Impairments and Hippocampal Damage in Rats

This study investigated the effects of subchronic arsenic exposure on behavior, neurological function, and hippocampal damage in rats. Thirty-two male Wistar rats were divided into four groups and exposed to different concentrations of arsenic in their drinking water for 12 weeks, while weekly water intake and body weight were recorded. Various neurobehavioral tests were conducted, evaluating overall activity levels, exploratory behavior, short-term memory, spatial learning and memory, anxiety-like behavior, and depressive-like states. Arsenic levels in urine, serum, and brain tissue were measured, and histopathological analysis assessed hippocampal damage using hematoxylin and eosin staining. The results demonstrated that arsenic exposure did not significantly affect overall activity or exploratory behavior. However, it impaired short-term memory and spatial learning and memory functions. Arsenic-exposed rats exhibited increased anxiety-like behavior and a depressive-like state. Arsenic levels increased dose-dependently in urine, serum, and brain tissue. The histopathological examinations revealed significant hippocampal damage, including neuronal shrinkage, cell proliferation, irregular structure, disordered arrangement, and vacuolation. These findings emphasize the importance of understanding the impact of arsenic exposure on behavior and brain health, highlighting its potential neurological consequences.

Does Morphine Exposure Before Gestation Change Anxiety-Like Behavior During Morphine Dependence in Male Wistar Rats?

Background

Anxiety is one of the comorbid disorders of opioid addiction, which leads to opioid abuse or persuades people to engage in opioid abuse. Evidence revealed that morphine exposure before conception changes the offspring's phenotype. The current study aimed to investigate the influence of morphine dependence and abstinence on anxiety-like behavior in morphine-exposed and drug-naïve offspring.

Methods

Adult male and female rats were treated with morphine or vehicle for 21 days. Then, all rats were left without drug treatment for 10 days. A morphine-exposed female rat was mated with either a vehicle-exposed or morphine-abstinent male. According to parental morphine exposure, the offspring were categorized into four distinct groups: (1) control (both drug-naïve parents), (2) paternal morphine-exposed, (3) maternal morphine-exposed, and (4) biparental morphine-exposed. The anxiety-like behavior was measured in adult male offspring using open field and elevated plus-maze tests before morphine exposure (naïve), 21 days after morphine exposure (dependence), and ten days after the last morphine exposure (abstinence).

Findings

The results indicated that anxiety-like behavior increased before morphine exposure in maternal and biparental morphine-exposed offspring (P<0.05). However, after morphine exposure, the anxiety level did not change among the groups. Ten days after the last morphine exposure, anxiety-like behavior increased only in biparental morphine-exposed offspring (P<0.05).

Conclusion

The offspring of morphine-abstinent parents exhibited an anxious phenotype. Disruption of the HPA axis was seen in the progeny of maternal and biparental morphine-exposed rats. Indeed, morphine exposure for 21 days did not change anxiety-like behavior in these offspring which might be correlated to disruption of HPA axis in them.

High glucose induces tau hyperphosphorylation in hippocampal neurons via inhibition of ALKBH5-mediated Dgkh m6A demethylation: a potential mechanism for diabetic cognitive dysfunction

Tau hyperphosphorylation in hippocampal neurons has an important pathogenetic role in the development of diabetic cognitive dysfunction. N6-methyladenosine (m6A) methylation is the most common modification of eukaryotic mRNA and is involved in regulating diverse biological processes. However, the role of m6A alteration in tau hyperphosphorylation of hippocampus neurons has not been reported. We found lower ALKBH5 expression in the hippocampus of diabetic rats and in HN-h cells with high-glucose intervention, accompanied by tau hyperphosphorylation. ALKBH5 overexpression significantly reversed tau hyperphosphorylation in high-glucose-stimulated HN-h cells. Furthermore, we found and confirmed by m6A-mRNA epitope transcriptome microarray and transcriptome RNA sequencing coupled with methylated RNA immunoprecipitation that ALKBH5 regulates the m6A modification of Dgkh mRNA. High glucose inhibited the demethylation modification of Dgkh by ALKBH5, resulting in decreases in Dgkh mRNA and protein levels. Overexpression of Dgkh reversed tau hyperphosphorylation in HN-h cells after high-glucose stimulation. Overexpression of Dgkh by adenovirus suspension injection into the bilateral hippocampus of diabetic rats significantly ameliorated tau hyperphosphorylation and diabetic cognitive dysfunction. In addition, ALKBH5 targeted Dgkh to activate PKC-α, leading to tau hyperphosphorylation under high-glucose conditions. The results of this study reveal that high glucose suppresses the demethylation modification of Dgkh by ALKBH5, which downregulates Dgkh and leads to tau hyperphosphorylation through activation of PKC-α in hippocampal neurons. These findings may indicate a new mechanism and a novel therapeutic target for diabetic cognitive dysfunction.

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.

An epigenetic synopsis of parental substance use

The rate of substance use is rising, especially among reproductive-age individuals. Emerging evidence suggests that paternal pre-conception and maternal prenatal substance use may alter offspring epigenetic regulation (changes to gene expression without modifying DNA) and outcomes later in life, including neurodevelopment and mental health. However, relatively little is known due to the complexities and limitations of existing studies, making causal interpretations challenging. This review examines the contributions and influence of parental substance use on the gametes and potential transmissibility to the offspring's epigenome as possible areas to target public health warnings and healthcare provider counseling of individuals or couples in the pre-conception and prenatal periods to ultimately mitigate short- and long-term offspring morbidity and mortality.

IGF2 inhibits hippocampal over-activated microglia and alleviates depression-like behavior in LPS- treated male mice

Over-activated microglia and inflammatory mediators are found in patients with depression, while manipulation of the microglia function might represent a potential therapeutic strategy. Insulin-like growth factor 2 (IGF2) has been implicated in bacterial infections and autoimmune disorders, but the role of IGF2 on the active phenotype of microglia and neuroinflammation has not been well established. IGF2 influences in modulating microglia responding to neuroinflammation induced by lipopolysaccharide（LPS）challenge will be carefully examined. In the current study, we verified that systemic IGF2 treatment could produce an anti-depression effect in LPS-treated mice. Particularly, we found that systemic IGF2 treatment inhibited microglia over-activation and prevented its transformation to a pro-inflammatory phenotype, thereby protecting hippocampal neurogenesis. Since microglia reactive to neuroinflammation is a common feature of neuropsychiatric disorders, the discoveries from the present study may provide therapeutic innovation for these diseases.

Distinct effect of exercise modes on mood-related behavior in mice

Exercise can afford several benefits to combat mood disorders in both rodents and humans. Engagement in various physical activities upregulates levels of neurotrophic factors in several brain regions and improves mental health. However, the type of exercise that regulates mood and the underlying mechanisms in the brain remain elusive. Herein, we performed two distinct types of exercise and RNA sequencing analyses to investigate the effect of exercise on mood-related behaviors and explain the distinct patterns of gene expression. Specifically, resistance exercise exhibited reduced immobility time in the forced swim test when compared with both no exercise and treadmill exercise (in the aerobic training [AT] group). Interestingly, anxiety-like behaviors in the open field and nest-building tests were ameliorated in the AT group when compared with those in the control group; however, this was not observed in the RT group. To elucidate the mechanism underlying these different behavioral changes caused by distinct exercise types, we examined the shift in the gene expression pattern in the hippocampus, a brain region that plays a critical role in regulating mood. We discovered that 38 and 40 genes were altered in the AT and RT groups, respectively, compared with the control group. Both exercises regulated 16 common genes. Compared with the control group, mitogen-activated protein kinase (MAPK) was enriched in the AT group and phosphatidylinositol-3-kinase (PI3K)/AKT and neurotrophin signaling pathways were enriched in the RT group, as determined by bioinformatics pathway analysis. PCR results revealed that Cebpβ expression was increased in AT group, and Dcx expression was upregulated in both groups. Our findings indicate that different exercise types may exert substantially distinct effects on mood-like behaviors. Accordingly, appropriate types of exercise can be undertaken based on the mood disorder to be regulated.

Inter/Transgenerational Effects of Drugs of Abuse: A Scoping Review

Drug addiction is a chronic relapsing disorder that makes it a global problem. Genetics and environmental factors are the two most important factors that make someone vulnerable to drug addiction. Investigations in the past decade highlighted the role of epigenetics in the inter/transgenerational inheritance of drug addiction. A growing body of evidence showed that parental (paternal, maternal, and biparental) drug exposure before conception changes the phenotype of the offspring, which is correlated with neurochemical and neurostructural changes in the brain. The current paper reviews the effects of parental (maternal, paternal, and biparental) exposure to drugs of abuse (opioids, cocaine, nicotine, alcohol, and cannabis) before gestation in animal models.

Anxiety and hippocampal neuronal activity: Relationship and potential mechanisms

The hippocampus has been implicated in modulating anxiety. It interacts with a variety of brain regions, both cortical and subcortical areas regulating emotion and stress responses, including prefrontal cortex, amygdala, hypothalamus, and the nucleus accumbens, to adjust anxiety levels in response to a variety of stressful conditions. Growing evidence indicates that anxiety is associated with increased neuronal excitability in the hippocampus, and alterations in local regulation of hippocampal excitability have been suggested to underlie behavioral disruptions characteristic of certain anxiety disorders. Furthermore, studies have shown that some anxiolytics can treat anxiety by altering the excitability and plasticity of hippocampal neurons. Hence, identifying cellular and molecular mechanisms and neural circuits that regulate hippocampal excitability in anxiety may be beneficial for developing targeted interventions for treatment of anxiety disorders particularly for the treatment-resistant cases. We first briefly review a role of the hippocampus in fear. We then review the evidence indicating a relationship between the hippocampal activity and fear/anxiety and discuss some possible mechanisms underlying stress-induced hippocampal excitability and anxiety-related behavior.

The placenta as a target of opioid drugs†

Opioid drugs are analgesics increasingly being prescribed to control pain associated with a wide range of causes. Usage of pregnant women has dramatically increased in the past decades. Neonates born to these women are at risk for neonatal abstinence syndrome (also referred to as neonatal opioid withdrawal syndrome). Negative birth outcomes linked with maternal opioid use disorder include compromised fetal growth, premature birth, reduced birthweight, and congenital defects. Such infants require lengthier hospital stays necessitating rising health care costs, and they are at greater risk for neurobehavioral and other diseases. Thus, it is essential to understand the genesis of such disorders. As the primary communication organ between mother and conceptus, the placenta itself is susceptible to opioid effects but may be key to understanding how these drugs affect long-term offspring health and potential avenue to prevent later diseases. In this review, we will consider the evidence that placental responses are regulated through an endogenous opioid system. However, maternal consumption of opioid drugs can also bind and act through opioid receptors express by trophoblast cells of the placenta. Thus, we will also discuss the current human and rodent studies that have examined the effects of opioids on the placenta. These drugs might affect placental hormones associated with maternal recognition of pregnancy, including placental lactogens and human chorionic gonadotropin in rodents and humans, respectively. A further understanding of how such drugs affect the placenta may open up new avenues for early diagnostic and remediation approaches.

HPA axis dysfunction during morphine withdrawal in offspring of female rats exposed to opioids preconception

Opioid use and abuse remain a significant public health problem, particularly in the United States. Indeed, it is estimated that up to 10% of youths (age 12-18) have taken opioids illicitly. A growing body of evidence suggests that this level of widespread opioid exposure can have effects that extend to subsequent generations. Utilizing a well-established rodent model of preconception adolescent opioid exposure in females, we found decreased opioid self-administration coupled with increased cocaine self-administration in adult offspring. This bidirectional effect may be related to negative affect associated with opioid withdrawal, including enhanced stress reactivity. In this study, we tested the hypothesis that the adult offspring of females exposed to morphine during adolescence will demonstrate increased signs of opioid withdrawal when compared to offspring of saline controls. Females were administered increasing doses of morphine (5-25 mg/kg s.c.) or saline (1 ml/kg) from postnatal day 30 (PND30)-PND39. They were then maintained drug free for a minimum of 4 weeks and mated with drug-naïve males on or after PND70. As adults, their male and female offspring (referred to as Mor-F1 or Sal-F1) were administered morphine (10 mg/kg s.c.) twice a day for 5 days. They were then tested for spontaneous withdrawal behaviors for the next 4 days (∼PND70). Levels of corticotropin releasing hormone (Crh) and urocortin 3 (Ucn3) were examined in the amygdala at 48 h and 96 h of withdrawal. Circulating corticosterone was measured at 48 h. Results indicate that Mor-F1 males are heavier than Sal-F1 males with no baseline differences in females. However, Mor-F1 females did not gain weight at the same rate as Sal-F1 females during withdrawal. While there were no differences in somatic withdrawal signs, gene expression data revealed a sex-specific and time-dependent effect on Crh as well as increased Ucn3 and corticosterone in females at 48hrs withdrawal. Overall, these data point to differences in withdrawal and stress reactivity in Mor-F1 animals that may contribute to observed differences in addiction-like behaviors.

Environmental enrichment ameliorates high-fat diet induced olfactory deficit and decrease of parvalbumin neurons in the olfactory bulb in mice

Overweight induced by high-fat diet (HFD) represents one of the major health concerns in modern societies, which can cause lasting peripheral and central metabolic disorders in all age groups. Specifically, childhood obesity could lead to life-long impact on brain development and functioning. On the other hand, environmental enrichment (EE) has been demonstrated to be beneficial for learning and memory. Here, we explored the impact of high-fat diet on olfaction and organization of olfactory bulb cells in adolescent mice, and the effect of EE intervention thereon. Puberty mice (3-week-old) fed with HFD for 10 weeks exhibited poorer odor sensitivity and olfactory memory relative to controls consuming standard chows. The behavioral deficits were rescued in the HFD group with EE intervention. Neuroanatomically, parvalbumin (PV) interneurons in the olfactory bulb (OB) were reduced in the HFD-fed animals relative to control, while EE intervention also normalized this alteration. In contrast, cells expressing calbindin (CB), doublecortin (DCX) in the OB were not altered. Our findings suggest that PV interneurons may play a crucial role in mediating the HFD-induced olfactory deficit in adolescent mice, and can also serve a protective effect of EE against the functional deficit.

Consequences of Parental Opioid Exposure on Neurophysiology, Behavior, and Health in the Next Generations

Substance abuse and the ongoing opioid epidemic represents a large societal burden. This review will consider the long-term impact of opioid exposure on future generations. Prenatal, perinatal, and preconception exposure are reviewed with discussion of both maternal and paternal influences. Opioid exposure can have long-lasting effects on reproductive function, gametogenesis, and germline epigenetic programming, which can influence embryogenesis and alter the developmental trajectory of progeny. The potential mechanisms by which preconception maternal and paternal opioid exposure produce deleterious consequences on the health, behavior, and physiology of offspring that have been identified by clinical and animal studies will be discussed. The timing, nature, dosing, and duration of prenatal opioid exposure combined with other important environmental considerations influence the extent to which these manipulations affect parents and their progeny. Epigenetic inheritance refers to the transmission of environmental insults across generations via mechanisms independent of the DNA sequence. This topic will be further explored in the context of prenatal, perinatal, and preconception opioid exposure for both the maternal and paternal lineage.

Maternal Oxycodone Treatment Results in Neurobehavioral Disruptions in Mice Offspring

Opioid drugs are increasingly being prescribed to pregnant women. Such compounds can also bind and activate opioid receptors in the fetal brain, which could lead to long-term brain and behavioral disruptions. We hypothesized that maternal treatment with oxycodone (OXY), the primary opioid at the center of the current crisis, leads to later neurobehavioral disorders and gene expression changes in the hypothalamus and hippocampus of resulting offspring. Female mice were treated daily with 5 mg OXY/kg or saline solution (control; CTL) for two weeks before breeding and then throughout gestation. Male and female offspring from both groups were tested with a battery of behavioral and metabolic tests to measure cognition, exploratory-like, anxiety-like, voluntary physical activity, and socio-communication behaviors. qPCR analyses were performed for candidate gene expression patterns in the hypothalamus and hippocampus of OXY and CTL derived offspring. Developmental exposure to OXY caused socio-communication changes that persisted from weaning through adulthood. Such offspring also showed cognitive impairments, reduced voluntary physical activity, and weighed more than CTL counterparts. In the hippocampus, prenatal exposure to OXY caused sex-dependent differences in expression of genes encoding opioid receptors and those involved in serotonin signaling. OXY exposure induced changes in neuropeptide hormone expression and the epigenetic modulator, Dnmt3a, in the hypothalamus, which could result in epigenetic changes in this brain region. The findings suggest cause for concern that consumption of OXY by pregnant mothers may result in permanent neurobehavioral changes in their offspring. Further work is needed to determine the potential underpinning epigenetic mechanisms.

Differential behavioral functioning in the offspring of rats with high vs. low self-administration of the opioid agonist remifentanil

Opioid use disorder (OUD) has a variety of adverse effects on both the users and their offspring. In the current study, a random group of Sprague-Dawley rats (25 females and 15 males) were tested for intravenous self-administration of the opioid agonist remifentanil to determine the range of acquisition for opioid. One-month after the end of self-administration of remifentanil, rats with the highest intake were mated together and rats with lowest intake were mated together. Then, the offspring of the two groups were tested for anxiety-like behavior, locomotor activity, nociception and intravenous remifentanil self-administration. The parents showed a range of remifentanil self-administration, especially in the female rats. The offspring of the parents with low and high remifentanil self-administration showed significant differences in specific behavioral functions. On the hotplate test of nociception, the female offspring parents with high remifentanil self-administration had significantly longer hotplate latencies, indicating reduced nociception, than the female offspring of parents with low remifentanil-self-administration, whereas there was no difference in the male offspring of low and high responding parents. In the elevated plus maze test of anxiety-like behavior, the offspring of the parents with high remifentanil intake showed more anxiety-like behavior than the offspring of the parents with low remifentanil intake regardless of sex. Locomotor activity was not significantly different. Interestingly, no significant differences in remifentanil self-administration in the offspring of parents with low and high remifentanil self-administration were detected. Overall, our data suggest a considerable range in remifentanil self-administration in rats and the offspring of rats with high opioid self-administration exhibit different behaviors vs offspring of rats with low opioid self-administration.

Sex-specific transgenerational effects of adolescent morphine exposure on short-term memory and anxiety behavior: Male linage

Current estimates indicate that opioid use and misuse are a rising epidemic, which presents a substantial socioeconomic burden around the world. Chronic opioid consumption, specifically during the critical period of adolescence, can lead to enduring effects not only in individuals but also in future generations. Utilizing rodent model, we have previously reported the impacts of paternal exposure to chronic morphine during adolescence on neurobehavioral features in progenies. Currently, the potential transgenerational effects of paternal morphine exposure during adolescence on anxiety-like behavior and short-term memory remains unknown. Male Wistar rats were exposed to increasing doses of morphine for ten days in adolescence (PND 30-39). Thereafter, following a 30-days drug-free period, the treated male rats mated with naïve females. The anxiety-like behavior and short-term memory performance were assessed in adult male and female offspring (PND 60) using open field and Y-maze tests. Both male and female progenies of morphine-treated sires revealed a significant reduction in the movement velocity compared to progenies of saline-treated sires as measured by open field test. Morphine-sired male but not female offspring also showed a non-significant large decreasing effect on time spent in the center and frequency of entries to the center of open field box. Moreover, a significant reduction in the number of entries and percent of time spent in the novel arm was observed in male and female morphine-sired offspring, as measured using Y-maze test. Growth outcomes also did not demonstrate any difference in the number of dam's fertility, pups birth, and death between morphine-sired and saline-sired groups in both sexes. Collectively, paternal exposure to morphine during adolescence induces sex-specific and selective disturbances in short-term memory while anxiety-like behavior was slightly disturbed.

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.

Enriched environment and social isolation differentially modulate addiction-related behaviors in male offspring of morphine-addicted dams: The possible role of μ-opioid receptors and ΔFosB in the brain reward pathway

Prenatal opioids exposure negatively affects the neurobehavioral abilities of children born from dependence dams. Adolescent housing conditions can buffer the detrimental impacts of early life experiences or contradictory can worsen individual psychosocial functions. The present study investigated the effects of maternal morphine dependence and different rearing conditions on behaviors and protein expression in brain reward circuits of male pups. Female Wistar rats a week before conception, during pregnancy and lactation were injected twice daily with escalating doses of morphine or saline. On a postnatal day 21, male pups were weaned and subjected to three different environments for two months: standard (STD), isolated (ISO), or enriched environment (EE). The anxiety and drug-related reward were measured using elevated plus maze, open field test, and conditioned place preference. Western blotting was used to determine the protein level of ΔFosB and μ-opioid receptor proteins in the striatum and the midbrain of male offspring, respectively. Results showed that maternal morphine administration dramatically increased anxiety-like and morphine place preference behaviors in offspring. Also, ISO condition aggravated these behavioral outcomes. While, rearing in EE could attenuate anxiety and morphine conditioning in pups. At molecular levels, maternal morphine exposure and social isolation markedly increased both of ΔFosB and μ-opioid receptor proteins expression. However, rearing in the EE declined ΔFosB protein expression. Together, these findings help to elucidate long lasting impacts of early life morphine exposure and rearing environment on the behavioral and molecular profile of addicted individuals.

Generational Effects of Opioid Exposure

The inheritance of substance abuse, including opioid abuse, may be influenced by genetic and non-genetic factors related to the environment, such as stress and socioeconomic status. These non-genetic influences on the heritability of a trait can be attributed to epigenetics. Epigenetic inheritance can result from modifications passed down from the mother, father, or both, resulting in either maternal, paternal, or parental epigenetic inheritance, respectively. These epigenetic modifications can be passed to the offspring to result in multigenerational, intergenerational, or transgenerational inheritance. Human and animal models of opioid exposure have shown generational effects that result in molecular, developmental, and behavioral alterations in future generations.

Paternal nicotine enhances fear memory, reduces nicotine administration, and alters hippocampal genetic and neural function in offspring

Nicotine use remains highly prevalent with tobacco and e-cigarette products consumed worldwide. However, increasing evidence of transgenerational epigenetic inheritance suggests that nicotine use may alter behavior and neurobiology in subsequent generations. We tested the effects of chronic paternal nicotine exposure in C57BL6/J mice on fear conditioning in F1 and F2 offspring, as well as conditioned fear extinction and spontaneous recovery, nicotine self-administration, hippocampal cholinergic functioning, RNA expression, and DNA methylation in F1 offspring. Paternal nicotine exposure was associated with enhanced contextual and cued fear conditioning and spontaneous recovery of extinguished fear memories. Further, nicotine reinforcement was reduced in nicotine-sired mice, as assessed in a self-administration paradigm. These behavioral phenotypes were coupled with altered response to nicotine, upregulated hippocampal nicotinic acetylcholine receptor binding, reduced evoked hippocampal cholinergic currents, and altered methylation and expression of hippocampal genes related to neural development and plasticity. Gene expression analysis suggests multigenerational effects on broader gene networks potentially involved in neuroplasticity and mental disorders. The changes in fear conditioning similarly suggest phenotypes analogous to anxiety disorders similar to post-traumatic stress.

Mapping the past, present and future research landscape of paternal effects

BACKGROUND

Although in all sexually reproducing organisms an individual has a mother and a father, non-genetic inheritance has been predominantly studied in mothers. Paternal effects have been far less frequently studied, until recently. In the last 5 years, research on environmentally induced paternal effects has grown rapidly in the number of publications and diversity of topics. Here, we provide an overview of this field using synthesis of evidence (systematic map) and influence (bibliometric analyses).

RESULTS

We find that motivations for studies into paternal effects are diverse. For example, from the ecological and evolutionary perspective, paternal effects are of interest as facilitators of response to environmental change and mediators of extended heredity. Medical researchers track how paternal pre-fertilization exposures to factors, such as diet or trauma, influence offspring health. Toxicologists look at the effects of toxins. We compare how these three research guilds design experiments in relation to objects of their studies: fathers, mothers and offspring. We highlight examples of research gaps, which, in turn, lead to future avenues of research.

CONCLUSIONS

The literature on paternal effects is large and disparate. Our study helps in fostering connections between areas of knowledge that develop in parallel, but which could benefit from the lateral transfer of concepts and methods.

Hippocampal LASP1 ameliorates chronic stress-mediated behavioral responses in a mouse model of unpredictable chronic mild stress

Substantial evidence has revealed that abnormalities in synaptic plasticity play important roles during the process of depression. LASP1 (LIM and SH3 domain protein 1), a member of actin-binding proteins, has been shown to be associated with the regulation of synaptic plasticity. However, the role of LASP1 in the regulation of mood is still unclear. Here, using an unpredictable chronic mild stress (UCMS) paradigm, we found that the mRNA and protein levels of LASP1 were decreased in the hippocampus of stressed mice and that UCMS-induced down-regulation of LASP1 was abolished by chronic administration of fluoxetine. Adenosine-associated virus-mediated hippocampal LASP1 overexpression alleviated the UCMS-induced behavioral results of forced swimming test and sucrose preference test in stressed mice. It also restored the dendritic spine density, elevated the levels of AKT (a serine/threonine protein kinase), phosphorylated-AKT, insulin-like growth factor 2, and postsynaptic density protein 95. These findings suggest that LASP1 alleviates UCMS-provoked behavioral defects, which may be mediated by an enhanced dendritic spine density and more activated AKT-dependent LASP1 signaling, pointing to the antidepressant role of LASP1.

The epigenetic alterations of human sperm cells caused by heroin use disorder

The molecular mechanisms of drug use on sexual health are largely unknown. We investigated, the relationship between heroin use disorder and epigenetic factors influencing histone acetylation in sperm cells. The volunteers included twenty-four 20- to 50-year-old men with a normal spermogram who did not consume any drugs and twenty-four age- to BMI-matched men who consume only the drug heroin for more than last four months. HDAC1 and HDAC11 mRNA expression levels in spermatozoa and miR-34c-5p and miR-125b-5p expression levels in seminal plasma were measured. The heroin-user group showed significantly increased white blood cell counts and decreased sperm motility and survival rates (8.61 ± 1.73, 21.50 ± 3.11, 69.90 ± 4.69 respectively) as compared to the control group (1.49 ± 0.32, 38.82 ± 3.05, 87.50 ± 0.99 respectively) (p ≤ .001). An increase in DNA fragmentation index (DFI) (heroin-user group: 41.93 ± 6.59% and control group: 10.14 ± 1.43%, p = .003), a change in frequency of HDAC1 (heroin-user group: 1.69 ± 0.55 and control group: 0.45 ± 0.14, p = .045) and HDAC11 (heroin-user group: 0.29 ± 0.13 and control group: 2.36 ± 0.76, p = .019) in spermatozoa and a significant decrease in seminal miR-125b-5p abundance (heroin-user group: 0.37 ± 0.11 and control group: 1.59 ± 0.47, p = .028) were reported in heroin consumers. Heroin use can lead to male infertility by causing leukocytospermia, asthenozoospermia, DFI elevation in sperm cells and alterations in seminal RNA profile.

Swimming exercise during morphine abstinence in parents-to-be attenuated morphine-induced conditioned place preference and locomotor sensitization only in male rat offspring

This study was designed to examine the effects of swimming exercise during morphine abstinence in parents-to-be before mating on morphine-induced conditioned place preference (CPP) and locomotor sensitization in the pubertal male and female rat offspring. Male and female Wistar rats were injected with bi-daily doses (10 mg/kg, 12 h intervals) of morphine for 14 days. The exercising rats exposed to a regular swimming exercise (45 min/d, five days per a week) during 30 days of morphine abstinence before mating. Then, the pubertal male and female rat offspring were tested for morphine-induced CPP and locomotor sensitization (using the open field). The results showed that the pubertal male offspring of the morphine-abstinent parents-to-be exhibited an increase in CPP to morphine and locomotor activity after morphine challenge than the offspring from the control group. While, swimming exercise in morphine-abstinent parents-to-be decreased CPP score and locomotor activity in the pubertal male offspring than control offspring. Thus, exposure to swimming exercise in morphine-abstinent parents-to-be before mating may exert a protective effect against morphine-induced reward and locomotor sensitization in their pubertal offspring which may prevent the vulnerability of the first generation to drug abuse following opiate-addicted parents before mating.

Sex-specific transgenerational effects of morphine exposure on reward and affective behaviors

Current estimates indicate that millions of people in the United States abuse opioid drugs, which may also affect their offspring. To determine whether parental exposure to morphine alters reward and affective behaviors in subsequent generations we exposed male and female C57BL/6NTac mice to morphine (75 mg) or placebo pellets for 4 weeks. Naïve mice were used as mating partners to create subsequent generations (F1 and F2). Adult male and female F1 and F2 mice were tested in the morphine conditioned place preference paradigm (CPP), marble burying (MB), acoustic startle response (ASR), and open field tests (OFT). Paternal morphine exposure resulted in significantly attenuated preference scores amongst F1 male offspring, but significantly higher preference scores amongst F1 female offspring at the lowest CPP dose tested (5 mg/kg). In contrast, maternal exposure to morphine did not affect morphine reward in the F1 generation; however, the F2 male offspring of morphine-exposed F0 females displayed significantly higher CPP preference scores. Preference scores in F2 females were not affected by F0 male or female morphine exposure. Sex-specific alterations in affective behaviors were observed only in the offspring of F0 males exposed to morphine with F1 males spending less time in the center of the open field and F1 females spending more time in the center of the open field. One generation later, affective behaviors were no longer altered in F2 males but F2 females from the F0 male morphine exposure buried more marbles in the MB test. In summary, early exposure to morphine in males and females causes lineage-specific inheritance of reward and affective behaviors.

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.

Paternal morphine self-administration produces object recognition memory deficits in female, but not male offspring

RATIONALE

Parental drug use around or before conception can have adverse consequences for offspring. Historically, this research has focused on the effects of maternal substance use on future generations but less is known about the influence of the paternal lineage. This study focused on the impact of chronic paternal morphine exposure prior to conception on behavioral outcomes in male and female progeny.

OBJECTIVES

This study sought to investigate the impact of paternal morphine self-administration on anxiety-like behavior, the stress response, and memory in male and female offspring.

METHODS

Adult, drug-naïve male and female progeny of morphine-treated sires and controls were evaluated for anxiety-like behavior using defensive probe burying and novelty-induced hypophagia paradigms. Hypothalamic-pituitary-adrenal (HPA) axis function was assessed by measuring plasma corticosterone levels following a restraint stressor in male and female progeny. Memory was probed using a battery of tests including object location memory, novel object recognition, and contextual fear conditioning.

RESULTS

Paternal morphine exposure did not alter anxiety-like behavior or stress-induced HPA axis activation in male or female offspring. Morphine-sired male and female offspring showed intact hippocampus-dependent memory: they performed normally on the long-term fear conditioning and object location memory tests. In contrast, paternal morphine exposure selectively disrupted novel object recognition in female, but not male, progeny.

CONCLUSIONS

Our findings demonstrate that paternal morphine taking produces sex-specific and selective impairments in object recognition memory while leaving hippocampal function largely intact.

Transgenerational Inheritance of Betaine-Induced Epigenetic Alterations in Estrogen-Responsive IGF-2/IGFBP2 Genes in Rat Hippocampus

SCOPE

Betaine serves as a methyl donor for DNA methylation. Here, the effects of betaine on hippocampal expression of neurogenesis genes and their DNA methylation status across three generations are investigated.

METHODS AND RESULTS

Pregnant rats (F0) are fed control and betaine-supplemented diets throughout gestation and lactation. Female F1 and F2 offspring at weaning, together with the F0 dams, are used in the study. Hippocampal expression of aromatase, estrogen receptor α, and estrogen-related receptor β is downregulated in F1, together with the estrogen-responsive insulin-like growth factor 2/insulin-like growth factor binding protein 2 (IGF-2/IGFBP2) genes. However, all these genes are upregulated in F2, which follows the same pattern of F0. In agreement with changes in mRNA expression, the imprinting control region (ICR) of IGF-2 gene is hypomethylated in F1 but hypermethylated in F2 and F0. In contrast, the promoter DNA methylation status of all the affected genes is hypermethylated in F1 but hypomethylated in F2 and F0. Methyl transfer enzymes, such as betaine homocysteine methyltransferase and DNA methyltransferase 1, follow the same pattern of transgenerational inheritance.

CONCLUSION

These results indicate that betaine exerts a transgenerational effect on hippocampal expression of estrogen-responsive genes in rat offspring, which is associated with corresponding alterations in DNA methylation on ICR of IGF-2 gene and the promoter of affected genes.

Correlation among the Behavioral Features in the Offspring of Morphine-Abstinent Rats

BACKGROUND

Critical analysis of new evidence in medical sciences relies on statistics in terms of correlation. The aim of the present study was to evaluate the correlation coefficients among the behavioral features in the offspring of morphine-abstinent parent(s).

METHODS

The offspring of rats with various parental morphine-exposure were divided into four groups including offspring with healthy parents (CTL), offspring with paternal morphine-abstinent (PMA) parent, offspring with maternal morphine-abstinent (MMA) parent, and offspring with both morphine-abstinent (BMA) parents. Pain perception, depression-like behavior and avoidance-memory in the offspring were quantified. The association between variables was measured using Pearson correlation analysis.

FINDINGS

A strong correlation was observed between pain and depressive-like behavior in female and male offspring of healthy parents. Moreover, in the male and female offspring of healthy parents and BMA, no significant correlation was observed between avoidance memory and pain behavior or depressive-like behavior. However, in the offspring of MMA, a strong correlation was observed between avoidance memory and depressive-like behavior.

CONCLUSION

The results revealed that in comparison with the offspring with CTL, the correlation among the behavioral futures in the offspring with MMA or PMA parents is significantly different.

HPA axis regulation and stress response is subject to intergenerational modification by paternal trauma and stress

There is increasing evidence that one's risk for psychiatric disturbances and metabolic syndromes is influenced by their parents' own health history, lifestyle and living environment. For example, paternal high fat diet is strongly linked to neuroendocrine dysregulation in offspring and increased risk for diabetes. The potential intergenerational impact of paternal stress has only just begun to emerge, with the initial evidence suggestive of greater risk for anxiety-related disorders. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signalling system involved in physiological homeostasis and stress response. In individuals, dysregulation of this system is closely associated with behavioral deficits and mood disorders. Various preclinical models of paternal stress have demonstrated robust behavioral shifts but little is known about the intergenerational modification of HPA axis function. This review will present evidence drawn from a range of laboratory mouse and rat models that the intergenerational influence of paternal stress on offspring behavioral phenotypes involve some level of HPA axis dysregulation. It makes the case that further investigations to comprehensively profile HPA axis function in offspring generations is warranted.

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.

Exposure to opiates in male adolescent rats alters pain perception in the male offspring

During the past decades, the use/misuse of opioids has increased dramatically among adolescent population. It is now well acknowledged that various morphological and physiological changes occur in the brain during adolescence. During this critical period, brain development and maturation could be affected by several factors including stress, drug abuse, nutritional status, etc. Although studies on transgenerational effects of substances such as alcohol, nicotine, and cocaine have focused on both paternal and maternal drug exposure, most reports on transgenerational effects of morphine are restricted to maternal exposure. Thus, in this study, we aimed to investigate the transgenerational effect of paternal morphine exposure during adolescence on pain perception and antinociceptive effect of morphine in rat offspring. Male rats received escalating doses of morphine for 10 days during postnatal days 31-40. Twenty days after the last morphine injection, male rats were mated with intact female rats, and then behavioral tests were conducted on the male offspring on postnatal day 60. Pain perception and morphine antinociception were evaluated using the formalin test. Our results demonstrated that morphine-sired and saline-sired animals differed in the interphase and phase 2 of the formalin test. These findings indicate a significant transgenerational effect of paternal morphine exposure on pain-related behaviors in rat 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.

Sex differences in neural mechanisms mediating reward and addiction

There is increasing evidence in humans and laboratory animals for biologically based sex differences in every phase of drug addiction: acute reinforcing effects, transition from occasional to compulsive use, withdrawal-associated negative affective states, craving, and relapse. There is also evidence that many qualitative aspects of the addiction phases do not differ significantly between males and females, but one sex may be more likely to exhibit a trait than the other, resulting in population differences. The conceptual framework of this review is to focus on hormonal, chromosomal, and epigenetic organizational and contingent, sex-dependent mechanisms of four neural systems that are known-primarily in males-to be key players in addiction: dopamine, mu-opioid receptors (MOR), kappa opioid receptors (KOR), and brain-derived neurotrophic factor (BDNF). We highlight data demonstrating sex differences in development, expression, and function of these neural systems as they relate-directly or indirectly-to processes of reward and addictive behavior, with a focus on psychostimulants and opioids. We identify gaps in knowledge about how these neural systems interact with sex to influence addictive behavior, emphasizing throughout that the impact of sex can be highly nuanced and male/female data should be reported regardless of the outcome.

Insulin Peptides as Mediators of the Impact of Life Style in Alzheimer's disease

The search for the cause of Alzheimer's disease (AD), that affects millions of people worldwide, is currently one of the most important scientific endeavors from a clinical perspective. There are so many mechanisms proposed, and so disparate changes observed, that it is becoming a challenging task to provide a comprehensive view of possible pathogenic processes in AD. Tauopathy (intracellular neurofibrillary tangles) and amyloidosis (extracellular amyloid plaques) are the anatomical hallmarks of the disease, and the formation of these proteinaceous aggregates in specific brain areas is widely held as the ultimate pathogenic mechanism. However, the triggers of this dysproteostasis process remain unknown. Further, neurofibrillary tangles and plaques may only constitute the last stages of a process of still uncertain origin. Thus, without an established knowledge of its etiology, and no cure in the horizon, prevention - or merely delaying its development, has become a last-resort goal in AD research. As with other success stories in preventive medicine, epidemiological studies have provided basic knowledge of risk factors in AD that may contribute to understand its etiology. Disregarding old age, gender, and ApoE4 genotype as non preventable risk factors, there are diverse life-style traits - many of them closely related to cardiovascular health, that have been associated to AD risk. Most prominent among them are diet, physical and mental activity, exposure to stress, and sleep/wake patterns. We argue that all these life-style factors engage insulinergic pathways that affect brain function, providing a potentially unifying thread for life-style and AD risk. Although further studies are needed to firmly establish a link between faulty insulinergic function and AD, we herein summarize the evidence that this link should be thoroughly considered.

The Role of miR-150 in Stress-Induced Anxiety-Like Behavior in Mice

Stress plays a crucial role in several psychiatric disorders, including anxiety. However, the underlying mechanisms remain poorly understood. Here, we used acute stress (AS) and chronic restraint stress (CRS) models to develop anxiety-like behavior and investigate the role of miR-150 in the hippocampi of mice. Corticosterone levels as well as glutamate receptors in the hippocampus were evaluated. We found that anxiety-like behavior was induced after either AS or CRS, as determined by the open-field test (OFT) and elevated plus-maze test (EPM). Increased corticosterone levels were observed in the blood of AS and CRS groups, while the expression of miR-150 mRNA in the hippocampus was significantly decreased. The expressions of GluN2A, GluR1, GluR2, and V-Glut2 in the hippocampus were decreased after either AS or CRS. Hippocampal GAD67 expression was increased by AS but not CRS, and GluN2B expression was decreased by CRS but not AS. Adult miR-150 knockout mice showed anxiety-like behavior, as assessed by the OFT and EPM. The expressions of GluN2A, GluN2B, GluR1, and GluR2 were also downregulated, but the expression of V-Glut2 was upregulated in the hippocampi of miR-150 knockout mice compared with wild-type mice. Interestingly, we found that the miR-150 knockout mice showed decreased dendrite lengths, dendrite branchings, and numbers of dendrite spines in the hippocampus compared with wild-type mice. These results suggest that miR-150 may influence the synaptic plasticity of the hippocampus and play a significant role in stress-induced anxiety-like behavior in adult mice.

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.

Is the Nociception Mechanism Altered in Offspring of Morphine-Abstinent Rats?

To investigate the effect of parental drug abuse on children, nociception, electrophysiological alteration, mRNA expression of opioid receptors, and expression of certain intracellular proteins in offspring of morphine-abstinent rats were studied. Adult male and female animals received water-soluble morphine for 21 days. Ten days after the last morphine administration, animals were placed for mating in 4 groups as follows: healthy (drug naive) female and male, morphine-abstinent female and healthy male, morphine-abstinent male and healthy female, morphine-abstinent male and morphine-abstinent female. Their adult male offspring were tested for nociception, neuronal discharge in nucleus accumbens (NAC) and prefrontal cortex (PFC). Our results showed that nociception in male offspring of all morphine-abstinent parent(s) groups was significantly reduced, compared with the control group. In the offspring of morphine-abstinent parent(s) groups, sensitivity to the antinociceptive effect of morphine was enhanced in chronic as well as in acute phases of the formalin test. Neuronal electrical activity reduced in the offspring of the morphine-exposed parent(s) in NAC as well as PFC regions. Moreover, our findings show that opioid receptors' expressions (µ, κ, and δ) increased in NAC of the litter of morphine-abstinent parent(s), compared with the control group. In addition, the expression of κ receptors was remarkably increased in the PFC in morphine-abstinent parent group, relative to the control group. The phosphorylated levels of extracellular regulated kinase 1/2 and cyclic adenosine monophosphate responsive element binding protein were significantly higher in the offspring of the morphine-abstinent parent(s) than the control group in the NAC. Our results indicated that endogenous opioid is altered in offspring of the morphine-exposed parent(s) and that heritage has a major role.

PERSPECTIVE

This study showed that nociception was reduced in offspring of morphine-abstinent rat(s) and also these litters had a low level of neuronal firing rate, and enhanced opioid receptors expression, especially in the NAC. Because these offspring are more sensitive to the analgesic effect of morphine, clinicians should consider this issue to manage the dosage of morphine for treating pain in children with an abstinent parent(s).

Role of early environmental enrichment on the social dominance tube test at adulthood in the rat

RATIONALE

Environmental enrichment (EE) could influence brain plasticity and behavior in rodents. Whether the early EE may predispose individuals to a particular social hierarchy in the social dominance tube test (SDTT) at adulthood is still unknown.

OBJECTIVE

The present study directly investigated the influence of EE on competitive success in the SDTT among adult rats.

METHODS

Male rats were maintained in EE from postnatal days 21 to 35. Social dominance behavior was determined by SDTT, competitive food foraging test, and mate preference test at adulthood. IBA-1 expression in the hypothalamus was examined using immunohistochemistry and western blot.

RESULTS

EE rats were prone to become submissive during a social encounter with standard environment (SE) rats in the SDTT. No difference was found in food foraging in the competitive food foraging test between SE and EE rats. Male EE rats were more attractive than the SE to the female rats in the mate preference test. IBA-1 expression was found to be decreased in the hypothalamus of EE rats compared to SE group. Infusion of a microglia inhibitor reduced percentage of forward in SE rats in the SDTT. Infusion of DNA methyltransferase inhibitor prevented the development of subordinate status in EE rats and restored the expression of IBA-1 in the hypothalamus.

CONCLUSIONS

The results suggest that early EE did not lead to reduced social hierarchy in the male rat. However, EE caused a reduction in the percentage of forward in the SDTT, which might be associated with reduced number of microglia in the hypothalamus.

Effects of environmental enrichment during abstinence in morphine dependent parents on anxiety, depressive-like behaviors and voluntary morphine consumption in rat offspring

Chronic morphine exposure during puberty increased morphine-induced rewarding effects and sensitization in the next generation. Given the well-known beneficial effects of environmental enrichment on the severity of physical and psychological dependence on morphine, we examined effects of enriched environment during morphine abstinence in morphine dependent parental rats before mating on the anxiety and depressive-like behaviors, and voluntary morphine consumption in their offspring. Paternal and/or maternal rats were injected with bi-daily doses (10mg/kg, 12h intervals) of morphine for 14days followed by rearing in a standard environment (SE) or enriched environment (EE) during 30days of morphine abstinence before mating. The pubertal male and female rat offspring were tested for anxiety (the elevated plus maze- EPM) and depression (sucrose preference test-SPT), and voluntary morphine consumption using a two-bottle choice (TBC) paradigm. The results showed that EE experience in morphine-dependent both parents result in an increase in the percentage of time spent into open arms/time spent on both arms using EPM in male offspring, higher levels of sucrose preference in female offspring and lower levels of voluntary morphine consumption in male and female offspring. Thus, EE experience in morphine-dependent both parents reduced anxiety, depressive-like behavior and also the voluntary morphine consumption in their offspring during puberty which may prevent the vulnerability of the next generation to drug abuse.

Endogenous Opiates and Behavior: 2015

This paper is the thirty-eighth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2015 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Early-Life Social Isolation-Induced Depressive-Like Behavior in Rats Results in Microglial Activation and Neuronal Histone Methylation that Are Mitigated by Minocycline

Early-life stress is a potent risk factor for development of psychiatric conditions such as depression. The underlying mechanisms remain poorly understood. Here, we used the early-life social isolation (ESI) model of early-life stress in rats to characterize development of depressive-like behavior, the role of microglia, levels of histone methylation, as well as expression of glutamate receptor subunits in the hippocampus. We found that depressive-like behavior was induced after ESI as determined by sucrose preference and forced swimming tests. Increased expression of microglial activation marker, Iba1, was observed in the hippocampus of the ESI group, while expression of the microglial CD200 receptor, which promotes microglial quiescence, significantly decreased. In addition, increased levels of proinflammatory cytokines, interleukin 1β (IL-1β), interleukin 6 (IL-6), and tumor necrosis factor-alpha (TNF-α) were observed in the hippocampus of the ESI group. Moreover, ESI increased levels of neuronal H3K9me2 (a repressive marker of transcription) and its associated "writer" enzymes, G9a and G9a-like protein, in the hippocampus. ESI also decreased expression of hippocampal NMDA receptor subunits, NR1, and AMPA receptor subunits, GluR1 and GluR2, which are involved in synaptic plasticity, but it did not affect expression of PSD95 and NR2B. Interestingly, treatment with minocycline to block microglial activation induced by ESI inhibited increases in hippocampal microglia and prevented ESI-induced depressive-like behavior as well as increases in IL-1β, IL-6, and TNF-α. Notably, minocycline also triggered downregulation of H3K9me2 expression and restored expression of NR1, GluR1, and GluR2. These results suggest that ESI induces depressive-like behavior, which may be mediated by microglial signaling.