Postnatal maturation of the vascularisation of the suprasylvian gyrus of the cat.

Vascular growth in the median suprasylvian gyrus of the cat has been analysed quantitatively with respect to mitoses, vascular density, vascular diameters, vascular coefficient and preferential vascular orientation. After correction for shrinkage and growth, four maturation periods were identified: (i) Immature period (first postnatal week), when the tissue exhibited numerous vascular mitoses, a low but constant vascular density and vascular coefficient, preferentially radiate vessels and immature (small) vascular diameters. (ii) Premature period (second to fourth week), with few mitoses, a rapidly increasing vascular density, immature (small) vascular diameters, an increase in the number of vessels more than 10 microns in diameter, and a preferential orientation of tangential vessels. (iii) Pre-adult period (fifth to sixth week), without mitoses. The vascular density increased greatly, the vascular diameters reached adult profile, the number of vessels over 10 microns in diameter decreased, the vascular orientations were both tangential and radiate and the vascular coefficient remained slight. (iv) Adult period, when the vascular density and the vascular coefficient were maximal, the vessel diameters were of adult type, and the orientation was tangential. From six weeks, the vessels increased only in length. Vascular maturation proceeded from the depth toward the surface of the cerebral cortex. Layers II-IV were those most highly vascularised, regardless of age. This is discussed in relation to synaptic growth. There was no direct relation between vasculogenesis and myelination. The white matter had a typically radiate vascularisation. A transitional zone between cortex and white matter was identified. It had a loose mesh vascular network and corresponded to the area in which dendrites of inverted pyramidal cells were found. The role of immature vascularisation in the nutrition of the neuropil is discussed.