Mammalian visual cortex is immature at birth and develops gradually during defined postnatal temporal windows. Cell-cell and cellmatrix interactions play critical roles in all phases of developmental tissue
remodeling. A substantial amount of brain volume consists of extracellular space interposed between brain cells. This space is filled with a matrix of molecules that are linked between them.These interactions are
key determinants of the mechanical properties of brain tissue and are also able to activate intracellular signaling pathways. Here, we were studied the general histological background of the primary visual cortex by using Nissl's stain and investigated the expression of Matrix Metalloproteinases-2 (MMP-2), Tissue Inhibitors of Matrix metalloproteinases-2 (TIMP-2), Integrin alpha M (Integrin-_M) and mRNA of Transforming Growth Factor beta one (TGF-_1) in the developing rat primary visual cortex using immunohistochemistry and In situ hybridization technique of formalin-fixed and paraffin-embedded tissue. The development of the cortex was studied in (165) rats from postnatal day one (P1) to postnatal day twenty one (P21). MMP-2 is considered as a marker of undifferentiated primary visual cortex with no detectable activity in adult visual cortex. MMP-2 is acting as a marker for active migration throughout developmental stages, an intricate balance between extracellular matrix synthesis and degradation is preserved by the opposing actions of matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases (TIMPs). In addition, TIMPs exert diverse cell biological functions distinct from their MMP-inhibitory activities. In aggregate, MMPs together with their endogenous inhibitors are expected to play a significant role in neuronal functions, including synaptic reorganization. It is up to forthcoming study and other studies to verify this hypothesis. The spatiotemporal regulation of TIMP-2 may be crucial not only in neuron cell migration by counterbalance MMP-2, but it plays a major role in cellular maturation and differentiation by exit from the cell cycle, more generally, in brain maturation and plasticity. In addition to that, TIMP-2 will have an important role in maintaining tissue integrity in adult visual cortex. Integrin alpha (M) is the major marker of myeloid-cell-specific and it is principle for adhesion and migration of the monocytes through the blood brain barrier into extracellular space of the CNS, followed by differentiation of monocytes into microglial cells. These cells
(mesodermal in origin) will increase in population with increasing age of the rat and they migrate in groups. Integrin alpha M has important roles in regulating many immunologic functions such as phagocytosis and
apoptosis. Phosphorylation of integrin cytoplasmic domains is emerging as an important mechanism of regulating integrin functions causes directional migration of microglia that induces phenotypic changes and
hence microglia were shown in different sizes irrespective of their postnatal age. The cell migration is the main action during the first week of postnatal development; it was altered by TGF- 1 in a concentrationdependent manner: at low concentrations in superficial laminae, cell migration was promoted whereas at high concentrations in deep laminae, migration was impeded. While during the second week of postnatal development till P(15), a second wave of activity of the TGF- 1 mRNA was appeared from deep to superficial laminae. This wave was designed for cellular maturation and differentiation which are consider as the main actions during the second week of postnatal development till the time of the eye opening.