Abstract
The influence of exposure to impoverished environments on brain development is unexplored since most studies investigated how environmental impoverishment affects adult brain. To shed light on the impact of early impoverishment on developmental trajectories of the nervous system, we developed a protocol of environmental impoverishment in which dams and pups lived from birth in a condition of reduced sensory-motor stimulation. Focusing on visual system, we measured two indexes of functional development, that is visual acuity, assessed by using Visual Evoked Potentials (VEPs), and VEP latency. In addition, we assessed in the visual cortex levels of Insulin-Like Growth Factor 1 (IGF-1) and myelin maturation, together with the expression of the GABA biosynthetic enzyme GAD67. We found that early impoverishment strongly delays visual acuity and VEP latency development. These functional changes were accompanied by a significant reduction of IGF-1 protein and GAD67 expression, as well as by delayed myelination of nerve fibers, in the visual cortex of impoverished pups. Thus, exposure to impoverished living conditions causes a significant alteration of developmental trajectories leading to a prominent delay of brain maturation. These results underscore the significance of adequate levels of environmental stimulation for the maturation of central nervous system.
Highlights
The complexity of early stimulation can modulate brain developmental trajectories and can induce long-term changes in neural circuits that underlie enduring modifications in brain structure and function[1,2]
Since myelination is closely associated with axon maturation and is essential for establishing an efficient neuronal signaling network[75,76,77], we investigated the developmental pattern of myelin basic protein (MBP) staining in the visual cortex of standard rearing conditions (SC) and impoverished environment (IE) rats
We demonstrated that rearing rats from birth in an impoverished environment characterized by a reduction of sensorimotor stimulation leads to a marked delay of functional properties of visual system development, including visual acuity and the latency of visual cortical responses to the sensory input
Summary
The complexity of early stimulation can modulate brain developmental trajectories and can induce long-term changes in neural circuits that underlie enduring modifications in brain structure and function[1,2]. Despite the number of experiments showing the effect of single sensory deprivation on the development of central processing[21,22], direct evidence that impoverished living conditions can affect the functional and structural development of the nervous system is still lacking since most studies on the effects of impoverished environment (IE) were focused on adult animals. These studies showed that IE is able to modify animals’ behavior leading to impairments of cognitive functions[23,24,25,26,27] paralleled by anatomical[1,24,28,29,30,31,32,33] and molecular changes in the brain[1,26,34]. IGF-1 seems to be upstream of BDNF and inhibitory GABAergic circuit development[12,13,50] and mediates EE effects on visual development and the effects of an early enriched experience provided by massage, which recapitulates key features of maternal care in rat pups and in human babies[17]
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