ABBREVIATION BDNFBrain-derived neurotrophic factorThe developing brain in utero and during the first years of life is highly vulnerable to environmental influences. Experiences occurring during this period permanently modify brain structure and function through epigenetic modifications (alterations of the DNA structure and chromatin function) and consequently affect the susceptibility to mental disorders. In this review, we describe evidence linking adverse environmental variation during early life (from the fetal period to childhood) and long-term changes in brain volume, microstructure, and connectivity, especially in amygdala and hippocampal regions. We also describe genetic variations that moderate the impact of adverse environmental conditions on child neurodevelopment, such as polymorphisms in brain-derived neurotrophic factor and catechol-Omethyltransferase genes, as well as genetic pathways related to glutamate and monoaminergic signaling. Lastly, we have depicted positive early life experiences that could benefit childhood neurodevelopment and reverse some detrimental effects of adversity in the offspring.

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Hypoxia-ischemia (HI) is the main cause of mortality in the perinatal period and morbidity, in survivors, which is characterized by neurological disabilities. The immature brain is highly susceptible to hypoxic-ischemic insult and is responsive to environmental stimuli, such as environmental enrichment (EE). Previous results indicate that EE recovered memory deficits in adult rats without reversing hippocampal atrophy related to HI. The aim of this study was to investigate behavioral performance in the open field and rota-rod apparatuses, in object recognition and inhibitory avoidance tasks, as well as dendritic spine density in the hippocampus, in rats undergoing HI and exposed to EE. Seven-day old male rats were submitted to the HI procedure and divided into 4 groups: control maintained in standard environment (CTSE), controls submitted to EE (CTEE), HI in standard environment (HISE) and HI in EE (HIEE). Behavioral and morphological parameters were evaluated 9 weeks after the environmental stimulation. Results indicate impairment in the object recognition task after HI that was recovered by enrichment; however the aversive memory impairment in the inhibitory avoidance task shown by hypoxic-ischemic rats was independent of the environment condition. Hypoxic-ischemic groups showed more crossing responses during the first minute in the open field, when compared to controls, but no differences were found between experimental groups in the rota-rod test. Dendritic spine density in the CA1 subfield of the right hippocampus (ipsilateral to the artery occlusion) was decreased after the HI insult, and increased in enriched controls; interestingly enriched HI rats did not differ from CTSE. In conclusion, EE was effective in recovering declarative memory impairment in object recognition and preserved hippocampal dendritic spine density loss after neonatal HI injury.

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Attention-deficit hyperactivity disorder (ADHD) may be caused by genetic or environmental factors. Among environmental factors, perinatal complications are related, such as neonatal hypoxia-ischemia (HI). Thus, the aim of this study was to investigate whether HI contributes to the development of characteristics related to ADHD in adult rats, and to correlate the behavioral results with brain damage volume. Male Wistar rats were divided into 2 groups: HI and control. The HI procedure consisted of a permanent occlusion of the right common carotid artery followed by a period of hypoxia (90 min; 8% O₂ and 92% N₂) on the 7th postnatal day. Two months later, animals were evaluated in the open field test during a single 5-min session, and in the 5-choice serial reaction time task (5-CSRTT), over 25 weeks. Our results demonstrated that animals submitted to HI manifest cognitive impairments in task acquisition, deficits in sustained attention, and increases in impulsivity and compulsivity in response to task manipulation in the 5-CSRTT. Locomotor activity observed in open field did not differ between groups. Moreover, brain volume loss in the total hemisphere, cerebral cortex, white matter, hippocampus, and striatum were observed in HI animals, especially on the side ipsilateral to the lesion. From these results, we can infer that neonatal HI is an environmental factor that could contribute to the development of behavioral characteristics observed in ADHD that are associated with general brain atrophy.

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