Commentary
Overcrowding is a growing problem that prevails in the urban areas of both developing and developed countries. It is considered as psycho-social stress that affects the behavior and physiology of individuals and societies [1].
Scientific awareness of overcrowding stress systematically started in the 1960s with the early experiments of John B. Calhoun using the so-called “rat utopia” and the theory of “behavioral sink” [2]. Depending on Calhoun’s experiments, connections between the model of rodent colonies and the arising problems of crowded cities were extrapolated [3]. However, the implementation of rodent models of overcrowding on human societies was always a matter of controversy [4]. In fact, in the light of the vast complexity of physiological and behavioral variables that alter the “average man” behavior and even the differences in social organization, an animal model of human overcrowding could be virtually impossible [5].
The consequences of overcrowding on animals include, among others, higher anxiety [6], diminished sociability [7] and raised cortisol and adrenocorticotrophic hormone (ACTH) [8]. When accompanied by noise, it causes degradation of performance in complex tasks as well as deterioration of cognition [9].
The findings that overcrowding results in modulatory effects on both central and systemic effects of various drugs [10-14] raised questions about the possible conditions in case of adolescence.
As the most recognized personality traits of adolescents are impulsivity, novelty seeking and low-risk assessment [15], then, a major issue of interest emerged, whether overcrowding during adolescence will affect neurobehavioral pharmacological actions of a widely used xenobiotic, which is alcohol.
In our study [16], we clearly revealed the modulatory potential of overcrowding of adolescent rats on the neurobehavioral profile of alcohol. Administration of alcohol to male adolescent rats significantly increased dopamine, the main player in the brain reward circuits, in the hippocampus. Moreover, a similar effect was observed in female animals (unpublished data). Overcrowded animals received alcohol expressed a lower, although statistically insignificant, dopamine content in the same brain region. Regarding the behavioral level, alcohol abolished locomotor activity in the open field while failed to alter sociability. However, co-exposure to overcrowding and alcohol significantly decreased social interaction, impaired motor activity and exploratory behavior as well as abolishing active fear response.
A recent study [17] extrapolated the neurobehavioral impact of adolescent alcohol exposure (AAE) to adulthood. Their findings concerning the behavioral effect of alcohol exposure during late adolescence interestingly agree with our observations.
A worth noting issue about AAE is being gender-specific with remarkable differences between males and females. Adolescent females suffered from higher levels of anxiety [18] and expressed an elevated level of blood corticosterone in response to ethanol intake [19]. Moreover, females exclusively demonstrated reduced molecular markers of serotoninergic, dopaminergic and glutamatergic signaling in various brain regions that was accompanied by declined histone acetylation [20]. This fact attracted our interest to further investigate the possible modulatory effect of overcrowding on female adolescents received alcohol as compared to males (under preparation for publication). However, extensive efforts are required to elucidate the underlying mechanisms that regulate such effects.
The consideration that the overcrowding condition, as a socioeconomic problematic issue, has a relatively higher weight in many societies of the south countries, as compared to the northern ones, may invite for a more focused concern in the southern countries regarding the possible pharmacological impacts of such conditions [16,17].
In general, certain distinctive local health and social concerns, especially in societies of the south, may be able to modulate the drug pharmacological effects. Explicitly, experimentally induced protein malnutrition was found to exert its impact on inflammation induction [21], testicular dysfunction [22] teratogenic potential of each of acetyl salicylic acid and paracetamol [23,24] and the neurobehavioral effect of caffeine [25].
References
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