Behavioural 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 behavioural 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 behaviours. 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 behavioural tasks. Data show that males exposed to noise experienced a deficit in associative memory (AM), increase in anxiety-like behaviours (ALB) and altered reaction to novelty (RN) when compared with sham animals, whereas females also showed an increase in risk assessment behaviours (RABs) 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 behavioural counteracting induced by a previous repeated exposure to a chemical agent such as ethanol, leading to a compensation of a non-adaptive behaviour and reaching a better adjustment to the environment.

Effects of early noise exposure on hippocampal-dependent behaviors during adolescence in male rats: influence of different housing conditions.

Central nervous system (CNS) development is a very complex process that can be altered by environmental stimuli such as noise, which can generate long-term auditory and/or extra-auditory impairments. We have previously reported that early noise exposure can induce hippocampus-related behavioral alterations in postnatal day (PND) 28 adolescent rats. Furthermore, we recently found biochemical modifications in the hippocampus (HC) of these animals that seemed to endure even in more mature animals (i.e. PND35) and that have not been studied along with behavioral correlates. Thus, the aim of this work was to reveal novel data about the effects of early noise exposure on hippocampal-dependent behaviors in more mature animals. Additionally, extended enriched environment (EE) housing was evaluated to determine its capacity to induce behavioral modifications, either by its neuroprotective ability or the greater stimulation that it generates. Male Wistar rats were exposed to different noise schemes at PND7 or PND15. Upon weaning, some animals were transferred to EE whereas others were kept in standard cages. At PND35, different hippocampal-dependent behavioral assessments were performed. Results showed noise-induced behavioral changes that differed according to the scheme and age of exposure used. In addition, housing in an EE was effective either in preventing some of these changes or in inducing the appearance of new behavioral modifications. These findings suggest that CNS development would be sensitive to the effects of different type of environmental stimuli such as noise or enriched housing, leading to maladaptive behavioral changes that last even until adolescence.

Noise-induced hippocampal oxidative imbalance and aminoacidergic neurotransmitters alterations in developing male rats: Influence of enriched environment during adolescence.

Living in big cities might involuntarily expose people to high levels of noise causing auditory and/or extra-auditory impairments, including adverse effects on central nervous system (CNS) areas such as the hippocampus. In particular, CNS development is a very complex process that can be altered by environmental stimuli. We have previously shown that noise exposure of developing rats can induce hippocampal-related behavioral alterations. However, noise-induced biochemical alterations had not been studied yet. Thus, the aim of this work was to assess whether early noise exposure can affect rat hippocampal oxidative state and aminoacidergic neurotransmission tone. Additionally, the effectiveness of an enriched environment (EE) as a neuroprotective strategy was evaluated. Male Wistar rats were exposed to different noise schemes at 7 or 15 days after birth. Upon weaning, some animals were transferred to an EE whereas others were kept in standard cages. Short- and long-term measurements were performed to evaluate reactive oxygen species, thioredoxins levels and catalase activity as indicators of hippocampal oxidative status as well as glutamic acid decarboxylase and a subtype of glutamate transporter to evaluate aminoacidergic neurotransmission tone. Results showed noise-induced changes in hippocampal oxidative state and aminoacidergic neurotransmission markers that lasted until adolescence and differed according to the scheme and the age of exposure. Finally, EE housing was effective in preventing some of these changes. These findings suggest that CNS development seems to be sensitive to the effects of stressors such as noise, as well as those of an environmental stimulation, favoring prompt and lasting molecular changes.

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.