MicroRNA Regulation of the Environmental Impact on Adolescent Neurobehavioral Development: A Systematic Review

Adolescence is a late developmental period marked by pronounced reorganization of brain networks in which epigenetic mechanisms play a fundamental role. This brain remodeling is associated with a peculiar behavior characterized by novelty seeking and risky activities such as alcohol and drug abuse, which is associated with increased susceptibility to stress. Hence, adolescence is a vulnerable postnatal period since short- and long-term deleterious effects of alcohol drinking and drug abuse are a serious worldwide public health concern. Among several other consequences, it has been proposed that exposure to stress, alcohol, or other drugs disrupts epigenetic mechanisms mediated by small non-coding microRNAs (miRNAs). During adolescence, this modifies the expression of a variety of genes involved in neurodevelopmental processes such as proliferation, differentiation, synaptogenesis, neural plasticity, and apoptosis. Hence, the effect of miRNAs dysregulation during adolescence might contribute to a long-term impact on brain function. This systematic review focuses on the miRNA expression patterns in the adolescent rodent brain with special interest in the impact of stress and drugs such as amphetamine, cocaine, nicotine, cannabis, and ketamine. The results point to a relevant and complex role of miRNAs in the regulation of the molecular processes involved in adolescent brain development as part of a dynamic epigenetic network sensitive to environmental events with distinctive changes across adolescence. Several miRNAs have been assessed evidencing changing expression profiles during the adolescent transition which are altered by exposure to stress and drug abuse. Since this is an emerging rapidly growing field, updating the present knowledge will contribute to improving our understanding of the epigenetic regulation mechanisms involved in the neurodevelopmental changes responsible for adolescent behavior. It can be expected that increased knowledge of themolecularmechanismsmediating the effect of environmental threats during the adolescent critical developmental period will improve understanding of psychiatric and addictive disorders emerging at this stage.Spanish Government PID2020-114269GB-I00FEDER, Junta de Andalucia, Spain BSEJ.514.UGR20MIU, Spain FPU18/0501

Neofobia Gustativa, Inhibición Latente de la Aversión Gustativa y Memoria de Reconocimiento de Objetos en Ratas Adolescentes

This research was supported by project PID2020-v114269GB-I00 of the research project funded by MCIN/AEI/10.13039/501100011033, Junta de Andalucía (B.SEJ.514.UGR20. Spain) and a predoctoral fellowship to A. Navarro-Expósito of the Ministerio de Educación y Deportes (BES-2015-072307).Background: Adolescence in mammals is a period marked by increased novelty-seeking and enhanced responsiveness to the stressful properties of novel stimuli. Despite the need to taste potentially toxic novel foods during the adolescent growth spurt, there has been little study of taste neophobia and its attenuation. Method: Four experiments were carried out to compare taste neophobia and related memory processes in male and female adolescent (PND28) and adult (PND70) Wistar rats. Experiments 1 and 2 evaluated attenuation of taste neophobia to cider vinegar (3%) and sodium saccharin (0.1%) solutions were evaluated. Additionally, to test the role of memory in neophobia during adolescence, latent inhibition of taste aversion and object recognition memory were assessed in Experiment 3 and Experiment 4, respectively. Results: Adolescent and adult rats exhibited taste neophobia to the saccharin solution but adolescent rats required more exposure trials than adults to recognize the vinegar solution as safe. Both groups exhibited similar latent inhibition of taste aversion and object recognition memory. No sex effect was significant. Conclusions: Contrary to the accepted view associating adolescence with reduced neophobia, adolescent rats exhibited taste neophobia which even increased when sour tastes were encountered.Antecedentes: La adolescencia está marcada por búsqueda de la novedad y acentuada sensibilidad a las propiedades estresantes de los estímulos novedosos. A pesar de la necesidad de probar nuevos alimentos potencialmente tóxicos durante el periodo de crecimiento adolescente, la neofobia gustativa y su atenuación durante este periodo apenas ha sido estudiada. Método: Se evaluaron la neofobia gustativa y los procesos de memoria relacionados en ratas Wistar macho y hembra adolescentes (PND28) y adultas (PND70). En los Experimentos 1 y 2 Se exploró la atenuación de la neofobia gustativa a soluciones de vinagre de sidra (3%) y sacarina sódica (0,1%), respectivamente. En los experimentos 3 y 4, se evaluó también la inhibición latente de aversiones gustativas y la memoria de reconocimiento de objetos. Resultados: Adolescentes y adultos mostraron neofobia gustativa a la sacarina, pero las ratas adolescentes requirieron más exposiciones a la solución de vinagre para reconocerla como segura. No hubo diferencias entre los grupos en los Experimentos 3 and 4. No se hallaron efectos significativos del sexo. Conclusiones: A pesar de la ampliamente aceptada asociación entre adolescencia y reducida neofobia, las ratas adolescentes muestran neofobia al sabor que resulta incluso incrementada cuando se trata de sabores ácidos.MCIN/AEI/10.13039/50110001103: PID2020-v114269GB-I00Junta de Andalucía (B.SEJ.514.UGR20. Spain)Ministerio de Educación y Deportes (BES-2015-072307

Caloric Restriction in Group-Housed Mice: Littermate and Sex Influence on Behavioral and Hormonal Data

This study was partially funded by the Master's program in Basic and Applied Neuroscience and Pain, University of Granada, the Junta de Andalucia (grants CTS109 and B-CTS-422-UGR18) and the Spanish Ministry of Health (National Drug Plan grant 2020I049). AV-A was recipient of a predoctoral fellowship (Grant/Award number: FPU18/05012) of the Ministerio de Universidades, Spain. LR-L has a research contract under the grant B-CTS-422-UGR18 (Programa Operativo FEDER Andalucia 2014-2020).We acknowledge the technical assistance of Ms. Ana Fernández Ibáñez, who helped with the ACTH hormone analysis, and of Mr. Daniel González Fernández, who edited the final English version of this document.Much of the research done on aging, oxidative stress, anxiety, and cognitive and social behavior in rodents has focused on caloric restriction (CR). This often involves several days of single housing, which can cause numerous logistical problems, as well as cognitive and social dysfunctions. Previous results in our laboratory showed the viability of long-term CR in grouped rats. Our research has studied the possibility of CR in grouped female and male littermates and unrelated CB6F1/J (C57BL/6J x BALBc/J hybrid strain) mice, measuring: (i) possible differences in body mass proportions between mice in ad libitum and CR conditions (at 70% of ad libitum), (ii) aggressive behavior, using the number of pushes and chasing behavior time as an indicator and social behavior using the time under the feeder as indicator, and (iii) difference in serum adrenocorticotropic hormone (ACTH) concentrations (stress biomarker), under ad libitum and CR conditions. Results showed the impossibility of implementing CR in unrelated male mice. In all other groups, CR was possible, with a less aggressive behavior (measured only with the number of pushes) observed in the unrelated female mice under CR conditions. In that sense, the ACTH levels measured on the last day of CR showed no difference in stress levels. These results indicate that implementantion of long-term CR in mice can be optimized technically and also related to their well-being by grouping animals, in particular, related mice.Master's program in Basic and Applied Neuroscience and Pain, University of GranadaJunta de Andalucia CTS109 B-CTS-422-UGR18Spanish Ministry of Health (National Drug Plan grant) 2020I049Ministerio de Universidades, Spain FPU18/05012Programa Operativo FEDER Andalucia B-CTS-422-UGR1

Identification of Differentially Expressed MicroRNAs in the Rat Hippocampus during Adolescence through an Epigenome-Wide Analysis

This study was funded by the research projects PID2020-114269GB-I00 (MCIN/AEI/10.13039/501100011033), BSEJ.514.UGR20 (FEDER, Junta de Andalucía, Spain), “Instituto de Salud Carlos III,” project PI18/00467 (co-funded by European Regional Development Fund/European Social Fund “A way to make Europe”/“Investing in your future”), and a predoctoral fellowship to AV-Á (FPU18/05012, MIU, Spain).Introduction: Epigenetic mechanisms involving microRNAs (miRNAs) play a fundamental role in many biological processes, particularly during prenatal and early postnatal development. Their role in adolescent brain development, however, has been poorly described. The present study aimed to explore miRNA expression in the hippocampus during adolescence compared to adulthood in rats. Method: The brains of female and male Wistar rats were extracted, and the hippocampus was freshly dissected at postnatal day 41 (adolescence) and postnatal day 98 (adulthood). An epigenome-wide analysis was conducted to identify the miRNAs significantly expressed in adolescence compared to adulthood. Additionally, target genes of such miRNAs were considered to perform an exploratory Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis. Results: We identified 16 differentially expressed miRNAs in adolescent male rats compared with adult male rats and 4 differentially expressed miRNAs in adolescent females compared with adult females. Enrichment analysis reinforced that the target genes found are related to neurodevelopmental processes such as cell proliferation, cell migration, and nervous system development. Conclusion: Our findings suggest a complex pattern of miRNA expression during adolescence, which differs from that in adulthood. The differential expression of miRNA in the hippocampus during adolescence may be associated with the late developmental changes occurring in this brain region. Furthermore, the observed sex differences in miRNA expression patterns indicate potential sexual differentiation in hippocampal development. Further comprehensive investigations are needed to elucidate the roles of miRNA in normal brain development.MCIN/AEI/10.13039/501100011033 PID2020-114269GB-I00FEDER BSEJ.514.UGR20Junta de Andalucía, SpainEuropean Regional Development Fund “Instituto de Salud Carlos III” PI18/00467FPU18/05012, MIU, SpainUniversity of Granad

Adolescent alcohol exposure modifies adult anxiety-like behavior and amygdala sensitivity to alcohol in rats: Increased c-Fos activity and sex-dependent microRNA-182 expression

Adolescent binge alcohol drinking is a serious health concern contributing to adult alcohol abuse often associated with anxiety disorders. We have used adolescent intermittent ethanol (AIE) administration as a model of binge drinking in rats in order to explore its long-term effect on the basolateral amygdala (BLA) responsiveness to alcohol and anxiety-like behavior. AIE increased the number of BLA c-Fos positive cells in adult Wistar rats and anxiety-like behavior assessed by the open field test (OFT). Additionally, in adult female rats receiving AIE BLA over expression of miR-182 was found. Therefore, our results indicate that alcohol consumption during adolescence can lead to enduring changes in anxiety-like behavior and BLA susceptibility to alcohol that may be mediated by sex-dependent epigenetic changes. These results contribute to understanding the mechanisms involved in the development of alcohol use disorders (AUD) and anxiety-related disorders.Project PID2020-114269GBI00 funded by MCIN/AEI/10.13039/501100011033 (MICIU, Spain)Project BSEJ.514.UGR20 (FEDER, Junta de Andalucía, Spain)Predoctoral fellowship FPU18/05012 to AV-Á (MIU, Spain)Funding for open access charge: Universidad de Granada/CBUA

Adolescent alcohol exposure modifies adult anxiety-like behavior and amygdala sensitivity to alcohol in rats: Increased c-Fos activity and sex-dependent microRNA-182 expression

Adolescent binge alcohol drinking is a serious health concern contributing to adult alcohol abuse often associated with anxiety disorders. We have used adolescent intermittent ethanol (AIE) administration as a model of binge drinking in rats in order to explore its long-term effect on the basolateral amygdala (BLA) responsiveness to alcohol and anxiety-like behavior. AIE increased the number of BLA c-Fos positive cells in adult Wistar rats and anxiety-like behavior assessed by the open field test (OFT). Additionally, in adult female rats receiving AIE BLA over expression of miR-182 was found. Therefore, our results indicate that alcohol consumption during adolescence can lead to enduring changes in anxiety-like behavior and BLA susceptibility to alcohol that may be mediated by sex-dependent epigenetic changes. These results contribute to understanding the mechanisms involved in the development of alcohol use disorders (AUD) and anxiety-related disorders.This study was funded by the research projects PID2020-114269GB-I00 funded by MCIN/AEI/10.13039/501100011033 (MICIU, Spain), BSEJ.514.UGR20 (FEDER, Junta de Andalucía, Spain) and a pre-doctoral fellowship FPU18/05012 to AV-Á (MIU, Spain)