Abstract
aim of the present study was to analyze the influence of enriched environment on the distribution of perineuronal nets (PNNs) using a stereogically based unbiased protocol and visual acuity in adult Swiss albino mice that underwent monocular deprivation during the critical period of postnatal development. Eight female Swiss albino mice were monocular deprived on postnatal day 10 and divided into two groups at weaning: standard environment (SE group, n = 4) and enriched environment (EE group, n = 4). After 3 months, all of the mice were subjected to grating visual acuity tests, sacrificed, and perfused with aldehyde fixative. The brains were removed and cut at 70 µm thickness in a vibratome and processed for lectin histochemical staining with Wisteria floribunda agglutinin (WFA). Architectonic limits of area 17 were conspicuously defined by WFA histochemical staining, and the optical fractionator stereological method was applied to estimate the total number of PNNs in the supragranular, granular, and infragranular layers. All groups were compared using Student's t-test at a 95% confidence level. Comparative analysis of the average PNN estimations revealed that the EE group had higher PNNs in the supragranular layer (2726.33 ± 405.416, mean ± standard deviation) compared with the SE group (1543.535 ± 260.686; Student's t-test, p = .0495). No differences were found in the other layers. Visual acuity was significantly lower in the SE group (0.55 cycles/degree) than in the EE group (1.06 cycles/ degree). Our results suggest that the integrity of the specialized extracellular matrix PNNs of the supragranular layer may be essential for normal visual acuity development. Keywords: monocular deprivation, critical period, visual cortex, perineuronal nets, visual acuity, stereology.
Highlights
Critical periods are associated with experiencedependent plasticity in various species and sensory systems and are related to an extreme form of more generalized sensitivity, in which the nervous system is able to respond and modulate its activity and connections based on natural experience, during the postnatal period (Hensch, 2004)
To determine whether perineuronal nets (PNNs) maturation is associated with improved performance in the visual acuity test, Figure 1
We quantified the number of PNNs stained by Wisteria floribunda lectin in the contralateral primary visual cortex using stereological procedures
Summary
Critical periods are associated with experiencedependent plasticity in various species and sensory systems and are related to an extreme form of more generalized sensitivity, in which the nervous system is able to respond and modulate its activity and connections based on natural experience, during the postnatal period (Hensch, 2004). The postnatal critical period window has been most extensively studied with regard to the visual system using classic experiments that typically comprise manipulations of sensory inputs, such as monocular deprivation in rodents, mammals, This manipulation of the visual experience results in an imbalance of inputs between the two eyes, and a shift of ocular dominance occurs in favor of the opened eye. The deprived eye experiences a loss of visual acuity, termed amblyopia. After the closure of the critical period and consequent reduction of cortical plasticity, achieving modifications in cortical circuitry and recovery of visual deficits induced by amblyopia is difficult. An enriched environment (EE), previously defined as “a combination of complex inanimate and social stimulation,” In an EE, animals are maintained in large cages with numerous other animals and a complex environment that provides them the opportunity to increase exploratory behavior, sensorymotor stimulation, and complex social interactions
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