Voluntary alcohol intake after noise exposure in adolescent rats: Hippocampal-related behavioral alterations

Sex-dependent effects of short-term ethanol, energy drinks and acute noise exposure on hippocampal oxidative balance and glutamate transporter EAAT-1 during rat adolescence

It is known that human adolescents often consume ethanol (EtOH) alone or mixed with energy drinks (ED), especially in noisy environments. Although these agents impact the developing brain, their effects after brief exposure or when presented together remain unclear. Given that few animal studies in this subject are available, this research aimed to study the effects of a brief exposure to these stimuli on the oxidative state and EAAT-1 glutamate transporter levels in the developing rat hippocampus (HC). Adolescent Wistar rats were subjected to a two-bottle choice, limited access to drinking in the dark paradigm, for EtOH and EtOH+ED intake, for 4 days, and subsequent acute noise exposure. Next, hippocampal catalase activity, reactive oxygen species (ROS), glutaredoxin-1 (Grx-1) and glutamate transporter EAAT-1 levels were assessed. Results showed sex-dependent alterations after exposure to these stimuli: Females consuming EtOH had higher hippocampal ROS levels, which decreased when combined with noise; males showed reduced ROS levels only after noise exposure. No significant changes occurred in catalase activity, Grx-1, or EAAT-1 levels with EtOH and noise exposure in neither sex. Additionally, ED raised EtOH consumption in both sexes, normalizing ROS levels only in females when combined with EtOH. Finally, ED consumption altered Grx-1 and EAAT-1 levels in both sexes. In summary, brief exposure to these stimuli induced sex-dependent alterations, suggesting differentiated coping strategies between sexes. Whereas ED consumption may have antioxidant effects in some cases, it could also increase excitotoxicity risk. These novel findings raise questions for future research on the underlying corresponding mechanisms.

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 alterations induced by intermittent ethanol intake and noise exposure in adolescent rats

Alcohol intake and exposure to noise are common activities of human adolescents performed in entertainment contexts worldwide that can induce behavioral disturbances. Therefore, the aim of the present work was to investigate in an experimental model of adolescent animals whether noise exposure and intermittent ethanol intake, when present individually or sequentially, might be able to modify different behaviors. Adolescent Wistar rats of both sexes were subjected to voluntary intermittent ethanol intake for 1 week followed by exposure to noise for 2 h and tested in a battery of behavioral tasks. Data show that males exposed to noise experienced a deficit in associative memory (AM), increase in anxiety-like behaviors (ALB) and altered reaction to novelty (RN) when compared with sham animals, whereas females also showed an increase in risk assessment behaviors (RAB) and a decrease in exploratory activity (EA). In contrast, ethanol intake induced an increase in RAB and RN in males and females, whereas females also showed a deficit in AM and EA as well as an increase in ALB. When ethanol was ingested before noise exposure, most parameters were counteracted both in male and females, but differed among sexes. In consequence, it could be hypothesized that an environmental acute stressor like noise might trigger a behavioral counteracting induced by a previous repeated exposure to a chemical agent such as ethanol, leading to a compensation of a non-adaptive behavior and reaching a better adjustment to the environment.

Oxidative Stress-Induced Brain Damage Triggered by Voluntary Ethanol Consumption during Adolescence: A Potential Target for Neuroprotection?

Alcohol consumption, in particular ethanol (EtOH), typically begins in human adolescence, often in a "binge like" manner. However, although EtOH abuse has a high prevalence at this stage, the effects of exposure during adolescence have been less explored than prenatal or adult age exposure. Several authors have reported that EtOH intake during specific periods of development might induce brain damage. Although the mechanisms are poorly understood, it has been postulated that oxidative stress may play a role. In fact, some of these studies revealed a decrease in brain antioxidant enzymes' level and/or an increase in reactive oxygen species (ROS) production. Nevertheless, although existing literature shows a number of studies in which ROS were measured in developing animals, fewer reported the measurement of ROS levels after EtOH exposure in adolescence. Importantly, neuroprotective agents aimed to these potential targets may be relevant tools useful to reduce EtOH-induced neurodegeneration, restore cognitive function and improve treatment outcomes for alcohol use disorders (AUDs). The present paper reviews significant evidences about the mechanisms involved in EtOH-induced brain damage, as well as the effect of different potential neuroprotectants that have shown to be able to prevent EtOH-induced oxidative stress. A selective inhibitor of the endocannabinoid anandamide metabolism, a flavonol present in different fruits (quercetin), an antibiotic with known neuroprotective properties (minocycline), a SOD/catalase mimetic, a potent antioxidant and anti-inflammatory molecule (resveratrol), a powerful ROS scavenger (melatonin), an isoquinoline alkaloid (berberine), are some of the therapeutic strategies that could have some clinical relevance in the treatment of AUDs. As most of these works were performed in adult animal models and using EtOH-forced paradigms, the finding of neuroprotective tools that could be effective in adolescent animal models of voluntary EtOH intake should be encouraged.

Exposure of Developing Male Rats to One or Multiple Noise Sessions and Different Housing Conditions: Hippocampal Thioredoxin Changes and Behavioral Alterations

Exposure of developing rats to noise has shown to induce hippocampal-related behavioral alterations that were prevented after a week of housing in an enriched environment. However, neither the effect of repeated exposures nor its impact on key endogenous antioxidants had been studied yet. Thus, the aim of the present work was to reveal novel data about hippocampal oxidative state through the measurement of possible age-related differences in the levels of hippocampal thioredoxins in rats exposed to noise at different developmental ages and subjected to different schemes and housing conditions. In addition, the possibility that oxidative changes could underlie hippocampal-related behavioral changes was also analyzed. Developing male Wistar rats were exposed to noise for 2 h, either once or for 5 days. Upon weaning, some animals were transferred to an enriched cage for 1 week, whereas others were kept in standard cages. One week later, auditory and behavioral assessments, as well as measurement of hippocampal thioredoxin, were performed. Whereas no changes in the auditory function were observed, significant behavioral differences were found, that varied according to the age, scheme of exposure and housing condition. In addition, a significant increase in Trx-1 levels was found in all noise-exposed groups housed in standard cages. Housing animals in an enriched environment for 1 week was effective in preventing most of these changes. These findings suggest that animals become less susceptible to undergo behavioral alterations after repeated exposure to an environmental challenge, probably due to the ability of adaptation to an unfavorable condition. Moreover, it could be hypothesized that damage to younger individuals could be more easily prevented by a housing manipulation.