Behavior and drug measurements in Long-Evans and Sprague-Dawley rats after ethanol-cocaine exposure

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.

URB597 induces subtle changes to aggression in adult Lister Hooded rats

The endocannabinoid system has been implicated in both social and cognitive processing. The endocannabinoid metabolism inhibitor, URB597, dose-dependently improves non-social memory in adult Wistar and Sprague Dawley rats, whereas its effect on social interaction (SI) is affected by both rat strain and drug dose. Lister Hooded rats consistently respond differently to drug treatment in general compared with albino strains. This study sought to investigate the effects of different doses of URB597 on social and non-social memory in Lister Hooded rats, as well as analyzing the behavioral composition of the SI. Males were tested for novel object recognition (NOR), social preference (between an object and an unfamiliar rat), social novelty recognition (for a familiar vs. unfamiliar rat) and SI with an unfamiliar rat. URB597 (0.1 or 0.3 mg/kg) or vehicle was given 30 min before testing. During SI testing, total interaction time was assessed along with time spent on aggressive and explorative behaviors. Lister Hooded rats displayed expected non-social and social memory and social preference, which was not affected by URB597. During SI, URB597 did not affect total interaction time. However, the high dose increased aggression, compared to vehicle, and decreased anogenital sniffing, compared to the low dose of URB597. In summary, URB597 did not affect NOR, social preference or social recognition memory but did have subtle behavioral effects during SI in Lister hooded rats. Based on our findings we argue for the importance of considering strain as well as the detailed composition of behavior when investigating drug effects on social behavior.

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.

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.

Acute prenatal exposure to ethanol on gestational day 12 elicits opposing deficits in social behaviors and anxiety-like behaviors in Sprague Dawley rats

Our previous research has shown that in Long Evans rats acute prenatal exposure to a high dose of ethanol on gestational day (G) 12 produces social deficits in male offspring and elicits substantial decreases in social preference relative to controls, in late adolescents and adults regardless of sex. In order to generalize the observed detrimental effects of ethanol exposure on G12, pregnant female Sprague Dawley rats were exposed to ethanol or saline and their offspring were assessed in a modified social interaction (SI) test as early adolescents, late adolescents, or young adults. Anxiety-like behavior was also assessed in adults using the elevated plus maze (EPM) or the light/dark box (LDB) test. Age- and sex-dependent social alterations were evident in ethanol-exposed animals. Ethanol-exposed males showed deficits in social investigation at all ages and age-dependent alterations in social preference. Play fighting was not affected in males. In contrast, ethanol-exposed early adolescent females showed no changes in social interactions, whereas older females demonstrated social deficits and social indifference. In adulthood, anxiety-like behavior was decreased in males and females prenatally exposed to ethanol in the EPM, but not the LDB. These findings suggest that social alterations associated with acute exposure to ethanol on G12 are not strain-specific, although they are more pronounced in Long Evans males and Sprague Dawley females. Furthermore, given that anxiety-like behaviors were attenuated in a test-specific manner, this study indicates that early ethanol exposure can have differential effects on different forms of anxiety.

Drugs of abuse and brain gene expression

Addictive drugs like cocaine, ethanol, and morphine activate signal transduction pathways that regulate brain gene expression. Such regulation is modulated by the presence of certain transcription factor proteins present in a given neuron. This article summarizes the effects of several addictive drugs on transcriptional processes contributing to the development of a drug-dependent state. The characterization of drug-induced changes in gene expression shows promise for improving our understanding of drug-addiction phenomena and cellular modes of cocaine, ethanol, and morphine action.

Cocaethylene: effects on brain systems and behavior

Cocaethylene is a psychoactive metabolite formed during the combined consumption of cocaine and ethanol. In this brief review, we discuss several well-characterized effects of this metabolite with an emphasis on the neurobiological and behavioral correlates of polydrug addiction. Included herein are the descriptions of some of the changes in trans-synaptic transmission and their relationship to pathological behaviors associated with a chronic, drug-dependent state that may be altered by the spatial or temporal dynamics of cocaethylene.