Estrogen Modulates Ethanol‐Induced Memory Deficit in Postpubertal Adolescent Rats

Assessment of Hippocampal-Related Behavioral Changes in Adolescent Rats of both Sexes Following Voluntary Intermittent Ethanol Intake and Noise Exposure: A Putative Underlying Mechanism and Implementation of a Non-pharmacological Preventive Strategy

Ethanol (EtOH) intake and noise exposure are particularly concerning among human adolescents because the potential to harm brain. Unfortunately, putative underlying mechanisms remain to be elucidated. Moreover, implementing non-pharmacological strategies, such as enriched environments (EE), would be pertinent in the field of neuroprotection. This study aims to explore possible underlying triggering mechanism of hippocampus-dependent behaviors in adolescent animals of both sexes following ethanol intake, noise exposure, or a combination of both, as well as the impact of EE. Adolescent Wistar rats of both sexes were subjected to an intermittent voluntary EtOH intake paradigm for one week. A subgroup of animals was exposed to white noise for two hours after the last session of EtOH intake. Some animals of both groups were housed in EE cages. Hippocampal-dependent behavioral assessment and hippocampal oxidative state evaluation were performed. Results show that different hippocampal-dependent behavioral alterations might be induced in animals of both sexes after EtOH intake and sequential noise exposure, that in some cases are sex-specific. Moreover, hippocampal oxidative imbalance seems to be one of the potential underlying mechanisms. Additionally, most behavioral and oxidative alterations were prevented by EE. These findings suggest that two frequently found environmental agents may impact behavior and oxidative pathways in both sexes in an animal model. In addition, EE resulted a partially effective neuroprotective strategy. Therefore, it could be suggested that the implementation of a non-pharmacological approach might also potentially provide neuroprotective advantages against other challenges. Finally, considering its potential for translational human benefit might be worth.

Behavioral changes and dendritic remodeling of hippocampal neurons in adolescent alcohol-treated rats

Objective: Earlier, we and others have reported that alcohol exposure in adolescent rat impaired performance of a spatial memory task in the Morris water maze. The goal of the present study was to investigate the effects of acute adolescent alcohol treatment on the hippocampus-dependent (contextual fear conditioning) and hippocampus-independent (cued fear) memories. The study also looked at the structural changes in anterior CA1 hippocampal neurons in adolescent alcohol-treated rats. Methods: Adolescent female rats were administered with a single dose of alcohol (1.0, 1.5, or 2.0 g/kg) or vehicle either before training (pre-training) or after training (pre-testing). Experimental and control rats were trained in the fear conditioning paradigm, and 24 h later tested for both contextual fear conditioning as well as cued fear memory. Separate groups of rats were treated with either alcohol (2 g/kg) or vehicle and sacrificed 24 h later. Their brains were harvested and processed for rapid Golgi staining. Randomly selected CA1 pyramidal neurons were analyzed for dendritic branching and dendritic spine density. Results: Pre-training alcohol dose-dependently attenuated acquisition of hippocampus-dependent contextual fear conditioning but had no effect on the acquisition of amygdala-associated cued fear. When administered following training (pre-testing), alcohol did not alter either contextual conditioning or cued fear memory. Golgi stained CA1 pyramidal neurons in alcohol treated female rats had reduced basilar tree branching and less complex dendritic arborization. Conclusion: Alcohol specifically impaired hippocampal learning in adolescent rats but not amygdala-associated cued fear memory. Compared to vehicle-treated rats, CA1 hippocampal pyramidal neurons in alcohol-treated rats had less complex dendritic morphology. Together, these data suggest that adolescent alcohol exposure produces changes in the neuronal organization of the hippocampus, and these changes may be related to impairments in hippocampus-dependent memory formation.

Lithium promotes recovery after spinal cord injury

Lithium is associated with oxidative stress and apoptosis, but the mechanism by which lithium protects against spinal cord injury remains poorly understood. In this study, we found that intraperitoneal administration of lithium chloride (LiCl) in a rat model of spinal cord injury alleviated pathological spinal cord injury and inhibited expression of tumor necrosis factor α, interleukin-6, and interleukin 1 β. Lithium inhibited pyroptosis and reduced inflammation by inhibiting Caspase-1 expression, reducing the oxidative stress response, and inhibiting activation of the Nod-like receptor protein 3 inflammasome. We also investigated the neuroprotective effects of lithium intervention on oxygen/glucose-deprived PC12 cells. We found that lithium reduced inflammation, oxidative damage, apoptosis, and necrosis and up-regulated nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 in PC12 cells. All-trans retinoic acid, an Nrf2 inhibitor, reversed the effects of lithium. These results suggest that lithium exerts anti-inflammatory, anti-oxidant, and anti-pyroptotic effects through the Nrf2/heme oxygenase-1 pathway to promote recovery after spinal cord injury. This study was approved by the Animal Ethics Committee of Xi’an Jiaotong University (approval No. 2018-2053) on October 23, 2018.

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

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

Sex difference in the vulnerability to hippocampus plasticity impairment after binge-like ethanol exposure in adolescent rat: Is estrogen the key?

Binge drinking during adolescence induces memory impairments, and evidences suggest that females are more vulnerable than males. However, the reason for such a difference is unclear, whereas preclinical studies addressing this question are lacking. Here we tested the hypothesis that endogenous estrogen level (E2) may explain sex differences in the effects of ethanol on hippocampus plasticity, the cellular mechanism of memory. Long-term depression (LTD) in hippocampus slice of pubertal female rats was recorded 24 h after two ethanol binges (3 g/kg, i.p., 9 h apart). Neither the estrous cycle nor ethanol altered LTD. However, if ethanol was administered during proestrus (i.e., at endogenous E2 peak), LTD was abolished 24 h later, whereas NMDA-fEPSPs response to a GluN2B antagonist increased. The abolition of LTD was not observed in adult female rats. Exogenous E2 combined with ethanol replicated LTD abolition in pubertal, prepubertal female, and in pubertal male rats without changes in ethanol metabolism. In male rats, a higher dose of ethanol was required to abolish LTD at 24-h delay. In pubertal female rats, tamoxifen, an antagonist of estrogen receptors, blocked the impairing effects of endogenous and exogenous E2 on LTD, suggesting estrogen interacts with ethanol through changes in gene expression. In addition, tamoxifen prevented LTD abolition at 24 h but not at 48-h delay. In conclusion, estrogen may explain the increased vulnerability to ethanol-induced plasticity impairment seen in females compared with males. This increased vulnerability of female rats is likely due to changes in the GluN2B subunit that represent a common target between ethanol and estrogen.

Adolescent alcohol exposure produces sex differences in negative affect-like behavior and group I mGluR BNST plasticity

Adolescent alcohol exposure increases the risk of developing alcohol use disorders (AUDs), yet the mechanisms responsible for this vulnerability remain largely unknown. One potential target for alcohol-induced changes is the circuitry that modulates negative affect and stress, two sexually dependent drivers of alcohol relapse. The bed nucleus of the stria terminalis (BNST) is a sexually dimorphic region that critically regulates negative affective- and stress-induced relapse. Group I metabotropic glutamate receptors (mGluR) are a target of interest due to their regulation of stress, anxiety behaviors, and BNST plasticity. The current studies investigate sex-dependent sensitivity to the effects of adolescent intermittent ethanol vapor exposure (AIE) on negative affect during acute and protracted alcohol withdrawal and following stress in adulthood. This work also assessed whether BNST group I mGluR-mediated long-term depression (LTD) was disrupted at these timepoints. During acute withdrawal, AIE altered LTD induced by the group I mGluR antagonist DHPG in females, but not males. During adulthood, stress unmasked persistent changes in DHPG-induced LTD and behavior that were not present under basal conditions. Females with an AIE history demonstrated enhanced negative affective-like behavior in the novelty-induced hypophagia test following restraint stress-a phenotype that could be blocked with systemic mGluR5 allosteric antagonism via MTEP. Conversely, males with an AIE history demonstrated elevated freezing in a contextual fear conditioning paradigm. These studies demonstrate long-lasting, sex-dependent phenotypes produced by AIE and suggest pharmaceutical interventions for alcohol use and comorbid disorders may be more effective if designed with sex differences in mind.