Adolescent intermittent alcohol exposure produces strain-specific cross-sensitization to nicotine and other behavioral adaptations in adulthood in C57BL/6J and DBA/2J mice

Adolescent alcohol exposure is associated with lasting behavioral changes in humans and in mice. Prior work from our laboratory and others have demonstrated that C57BL/6J and DBA/2J mice differ in sensitivity to some effects of acute alcohol exposure during adolescence and adulthood. However, it is unknown if these strains differ in cognitive, anxiety-related, and addiction-related long-term consequences of adolescent intermittent alcohol exposure. This study examined the impact of a previously validated adolescent alcohol exposure paradigm (2-3 g/kg, i.p., every other day PND 30-44) in C57BL/6J and DBA/2J male and female mice on adult fear conditioning, anxiety-related behavior (elevated plus maze), and addiction-related phenotypes including nicotine sensitivity (hypothermia and locomotor depression) and alcohol sensitivity (loss of righting reflex; LORR). Both shared and strain-specific long-term consequences of adolescent alcohol exposure were found. Most notably, we found a strain-specific alcohol-induced increase in sensitivity to nicotine's hypothermic effects during adulthood in the DBA/2J strain but not in the C57BL/6J strain. Conversely, both strains demonstrated a robust increased latency to LORR during adulthood after adolescent alcohol exposure. Thus, we observed strain-dependent cross-sensitization to nicotine and strain-independent tolerance to alcohol due to adolescent alcohol exposure. Several strain and sex differences independent of adolescent alcohol treatment were also observed. These include increased sensitivity to nicotine-induced hypothermia in the C57BL/6J strain relative to the DBA/2J strain, in addition to DBA/2J mice showing more anxiety-like behaviors in the elevated plus maze relative to the C57BL/6J strain. Overall, these results suggest that adolescent alcohol exposure results in altered adult sensitivity to nicotine and alcohol with some phenotypes mediated by genetic background.

Propofol anesthesia concentration rather than abrupt behavioral unresponsiveness linearly degrades responses in the rat primary auditory cortex

Despite extensive knowledge of its molecular and cellular effects, how anesthesia affects sensory processing remains poorly understood. In particular, it remains unclear whether anesthesia modestly or robustly degrades activity in primary sensory regions, and whether such changes are linked to anesthesia drug concentration versus behavioral unresponsiveness, which are typically confounded. Here, we used slow gradual intravenous propofol anesthesia induction together with auditory stimulation and intermittent assessment of behavioral responsiveness while recording epidural electroencephalogram, and neuronal spiking activity in primary auditory cortex (PAC) of eight rats. We found that all main components of neuronal activity including spontaneous firing rates, onset response magnitudes, onset response latencies, postonset neuronal silence duration, late-locking to 40 Hz click-trains, and offset responses, gradually changed in a dose-dependent manner with increasing anesthesia levels without showing abrupt shifts around loss of righting reflex or other time-points. Thus, the dominant factor affecting PAC responses is the anesthesia drug concentration rather than any sudden, dichotomous behavioral state changes. Our findings explain a wide array of seemingly conflicting results in the literature that, depending on the precise definition of wakefulness (vigilant vs. drowsy) and anesthesia (light vs. deep/surgical), report a spectrum of effects in primary regions ranging from minimal to dramatic differences.

Chronic knockdown of the tetraspanin gene CD81 in the mouse nucleus accumbens modulates anxiety and ethanol-related behaviors

CD81, a member of the tetraspanin family, plays important roles in many physiological processes, such as cell motility, attachment, and entry. Yet, CD81 functions in the brain remain unclear. In this study, we investigated the effects of CD81 knockdown, using lentiviral vectors (LV), on anxiety- and ethanol-related behaviors. For this purpose, mice were stereotaxically injected with CD81 shRNA-expressing LV into the nucleus accumbens (Nacc) and were assessed for anxiety-like behavior using the elevated plus maze (EPM) and open field (OF) tests. Alcohol's sedative effects were studied using loss-of-righting-reflex (LORR) and voluntary ethanol intake was assessed using a two-bottle choice (TBC) procedure. Results showed that mice depleted of CD81 exhibited an anxiolytic-like response in the EPM and OF tests with no effect on locomotor activity. In addition, genetic reduction of CD81 in the Nacc increased mice' sensitivity to alcohol's sedative effects in the LORR test, although plasma alcohol concentrations were unaffected. Interestingly, CD81 loss-of-function-induced anxiolysis was accompanied by a significant decrease in ethanol, but not saccharin nor quinine, intake in the TBC procedure. Finally, and following CD81 mRNA quantification, Pearson's correlations showed a significant positive relationship between accumbal CD81 mRNA with anxiety and ethanol-related behaviors. Our data indicate that CD81 is implicated in the pathogenesis of anxiety and alcoholism. Indeed the targeted disruption of CD81, with the resultant decrease in CD81 mRNA in the Nacc, converted ethanol-"preferring" mice into ethanol "non-preferring" mice. Collectively, these findings demonstrate that future CD81-targeted pharmacotherapies may be beneficial for the treatment of anxiety and alcoholism.

Chronic Ethanol Exposure during Adolescence Increases Voluntary Ethanol Consumption in Adulthood in Female Sprague Dawley Rats

Early alcohol use is a major concern due to the dramatic rise in alcohol use during adolescence. In humans, adolescent males and females consume alcohol at equivalent rates; however, in adulthood males are more likely to consume harmful levels of alcohol. In animal models, the long-term dose-dependent and sex-dependent effects of alcohol exposure during adolescence have not been readily assessed relative to exposure that is initiated in adulthood. The purpose of the present set of experiments was to determine if adolescent exposure to chronic ethanol would predispose male and female rats to greater ethanol intake in adulthood when compared to animals that were not exposed to chronic ethanol exposure until early adulthood. Male and female rats were chronically administered 0.75 g/kg or 1.5 g/kg ethanol or saline for 21 days during adolescence (postnatal day (PND) 30–50) or adulthood (PND 60–80). All rats subsequently underwent 14-days of abstinence (PND 51–64 or PND 81–94, respectively). Finally, all rats were given 30-min daily access to saccharin-sweetened ethanol or saccharin alone from PND 65–80 for adolescent-exposed rats and PND 95–110 for adult-exposed rats. Exposure to 0.75 g/kg ethanol did not alter ethanol or saccharin intake in adolescent-exposed or adult-exposed rats, regardless of sex. In contrast, chronic exposure to the higher 1.5 g/kg dose during adolescence increased ethanol intake in adulthood in female rats. However, there was no change in saccharin intake in animals exposed to 1.5 g/kg ethanol during adolescence or adulthood, regardless of sex. Additionally, there were no clear age- and ethanol-dependent changes in duration of loss of righting reflex and blood ethanol concentrations to a challenge administration of a higher dose of ethanol. The results of the present set of experiments indicate chronic exposure to a high dose of ethanol during adolescence in female rats did indeed predispose rats to consume more ethanol in adulthood. Given that these effects were only observed in adolescent-exposed female rats, these results support a unique vulnerability to the long-term consequences of adolescent ethanol exposure in female rats, an effect that is not merely mediated by the sweetener used in the ethanol solution.

Lentiviral-mediated up-regulation of let-7d microRNA decreases alcohol intake through down-regulating the dopamine D3 receptor

Recent studies have shown that Lethal-7 (let-7) microRNA (miRNA) is involved in a wide range of psychiatric disorders such as anxiety, depression, schizophrenia, and cocaine addiction. However, the exact role of let-7d miRNA in regulating ethanol intake and preference remains to be elucidated. The aim of the present study was to clarify the role of accumbal let-7d in controlling ethanol-related behaviors in adult rats. For this purpose, stereotaxic injections of let-7d-overexpressing lentiviral vectors (LV) were administered bilaterally into the nucleus accumbens (Nacc) of Wistar rats. The ethanol-related behaviors were investigated using the two-bottle choice (TBC) access paradigm, in which the rats had access to 2.5, 5, and 10% ethanol solutions, the grid hanging test (GHT) and ethanol-induced loss-of-righting-reflex (LORR) test. The results showed that intra-accumbally administered let-7d-overexpressing LV significantly decreased ethanol intake and preference without having significant effects on body weight, consumption or preference for tastants (saccharin and quinine) or ethanol metabolism. Furthermore, accumbal let-7d increased resistance to ethanol-induced sedation in the GHT and LORR test. Most importantly, the data showed that the dopamine D3 receptor (D3R) was a candidate target of let-7d In fact, and using real time PCR, let-7d was found to directly target D3R mRNA to decrease its expression. Further analyses proved that D3R expression was negatively correlated with the levels of let-7d and ethanol-related behaviors parameters. Taken together, the data indicating that let-7d impaired ethanol-related behaviors by targeting D3R will open up new exciting possibilities and might provide potential therapeutic evidence for alcoholism.

Late aging alters behavioral sensitivity to ethanol in a sex-specific manner in Fischer 344 rats

Responsiveness to ethanol (EtOH) differs as a function of age. Adolescent rodents are less sensitive than adults to the sedative effects of EtOH, whereas they show enhanced sensitivity to EtOH-induced social facilitation. Late aging is associated with a natural decline in social behavior and aging-related peculiarities in sensitivity to EtOH have been largely unexplored. Whether there are sex differences in the behavioral response to EtOH during late aging remains unknown. Thus, behavioral responses to EtOH in male and female Fischer (F) 344 rats aged 4-5 months (adult) and 19-20 months (aging) were examined. First, the effects of saline and EtOH (0.5 and 0.75 g/kg) on social interaction were assessed. Social investigation and contact behavior were lower in aging animals and higher in females. Interestingly, in aged females, social contact behavior was increased following a 0.5 g/kg EtOH dose, whereas the same dose suppressed social contact in aged males. Behavioral sensitivity to the sedative effects of 3.0 and 3.5 g/kg EtOH was assessed with the loss of righting reflex (LORR) test. Although latency to LORR did not differ as a function of age or sex, aged rats showed significantly greater LORR duration and significantly lower blood ethanol concentrations (BECs) at regaining of the righting reflex relative to adults. In addition, females had a lower LORR duration, regardless of age; no sex differences were evident in BECs at awakening. In a second experiment, blood ethanol concentrations (BECs) over time were assessed following 0.75, 1.5, and 3.0 g/kg EtOH in 3-, 12-, and 18-month-old male and female F344 rats. Aged rats had higher peak BECs following 3.0 g/kg EtOH, whereas few age or sex differences were apparent at lower doses. Taken together, these data indicate that late aging is associated with altered sensitivity to the social facilitating effects and sedative effects of EtOH.

Nucleus accumbens lentiviral-mediated gain of function of the oxytocin receptor regulates anxiety- and ethanol-related behaviors in adult mice

Anxiety is believed to influence ethanol use human in alcoholics. Studies using laboratory animals suggested an interaction between oxytocin and the behavioral effects of ethanol. Our previous study implicated a potential role for the oxytocin receptor (OxtR) in regulating ethanol-conditioned place preference. Here, we examined anxiety and the behavioral responses to ethanol in C57BL/6 mice stereotaxically injected in the nucleus accumbens (NAcc) with lentiviral vectors expressing an empty vector (Mock) or the OxtR cDNA. For anxiety we used the elevated-plus maze, the open-field and the marble-burying tests and for ethanol we used the two-bottle choice paradigm, the wire-hanging and ethanol-induced loss-of-righting-reflex tests. We found that, compared to Mock, OxtR overexpression led to anxiolytic-like behavior without altering spontaneous locomotor activity. Most importantly, we found that, relative to Mock controls, increased expression of the OxtR in the NAcc led to decreased ethanol consumption and preference in the two-bottle choice protocol and increased resistance to ethanol-induced sedation. We also compared the consequence of OxtR modulation on the consumption and preference of saccharin and quinine and found that the two experimental groups did not differ for any tastant. These results provide further evidence that the oxytocin system contributes to the regulation of ethanol drinking and sensitivity and position OxtR as a central molecular mediator of ethanol's effects within the mesolimbic system. Taken together, the current findings suggest that OxtR manipulation may be a relevant strategy to address ethanol use disorders.