Reviewer 2's Review (Fabiana Mesquita Carvalho)

“The manuscript arises two main questions: (1) whether IGF-1 is involved in mediating EE effects on the postnatal visual cortex development, and (2 - if the first answer is YES) whether a possible mechanism of IGF-1 action is exerted through the modulation of intracortical GABA circuitry and PNN development.

The authors covered everything promised in the introduction by properly placing and grounding the two main claims in the context of the previous literature. The authors made reference to the most appropriate work. Indeed, the authors themselves have already contributed to the research subject "EE and postnatal visual cortical development" with others relevant research articles. The authors were able to show in the present manuscript, for the first time, that IGF-1 affects both GAD-65 immunoreactivity and PNN development. These results suggest that IGF-1 is a mediator of EE effects on visual cortical development via GABA system and PNN development. The methodology is well described and detailed, and the authors corroborate the methodology by making references to previous works in which the methods have already been employed. In this way, the methods could be reproduced. The authors confirm their results by means of well-controlled experiments (the manuscript is scientifically rigorous). The results are clearly described both in the text and in the figures. The discussion is fully understandable and all topics are carefully discussed. In spite of authors are not native English speakers, their ideas are expressed clearly and concisely. The manuscript has a good overall balance and structure; the sections were neither neglected nor protracted and were written in a clear and logical flow.

The subjects carried on by the present manuscript are of interest to any research group involved in the study of the Central Nervous System development. IGF-1 is well known to be a key growth factor in several pre and postnatal developmental events in the CNS (although the possible mechanisms of action are not understood). More specifically, this manuscript would be of great validity and utility to researches interested in the visual system development and in the influence of an enriched environment on the CNS development and functioning.

Considering the further directions to the current research, it would be interesting and challenging trying to conciliate structural (developmental) and functional approaches. It is important to wonder whether structural changes (such as neurogenesis, synaptogenesis or cell differentiation) engendered by molecular processes (such as gene expression responsible for up and down regulations of cellular proteins) is related to functional (or behavioral) changes. Do the molecular changes related by the manuscript could lead to behavioral changes? The visual function (visual acuity and visual field) might be tested in the future by means of simple experiments like "place and cued learning" in an Open Field, in a Radial Maze or in a Morris Water Maze.

In my opinion, both the subject approached by the manuscript and how this approach was achieved make the present manuscript appropriate for the PLoS ONE journal.”

n.b. These are the general comments made by the reviewer when reviewing this paper. Specific points addressed during revision of the paper are not shown.