[Effects of chronic hypoxia on microcirculation of the central nervous system during embryonic development].

In the attempt to know the factors influencing the vasculogenesis and to verify whether the vessel formation and growth are influenced, during different ontogenetic periods, by oxygen deficiency, the intraneural vascular network has been morphometrically analyzed in chicken embryo optic tectum under conditions of aerogenic hypoxia. Chicken eggs, incubated under routine conditions, have been half-painted with melted wax at the 2nd incubation day (i.d.). Fragments of optic tectum, isolated from living embryos at the 8th, 14th and 17th i.d., have been fixed and embedded according to the usual E/M procedures. A parallel series of normally developed embryos of 8, 14 and 17 incubation days has been likewise prepared. On semithin sections from the hypoxic specimens and normal control embryos the area occupied by vessels (Av), the number of vessels (Nv) and the diameter of the radially directed ones (Dv) have been evaluated. The preliminary results indicate that hypoxia evokes, from the 8th to the 17th i.d., an increment of the Av parameter, due first to microvessel neoformation and enlargement from the 8th to the 14th i.d., then from the 14th to the 17th i.d. only to a growth of new capillary branches. The response of the vascular network to the hypoxic condition is more marked from the 8th to the 14th i.d., t.i. when, in relation to the differentiation and the stratification of the neurons, the metabolic requirements of the developing tectum are presumably increased. O2 deficiency causes severe developmental disorders of the cyto- and mieloarchitecture of the tectum: the vascular response can apparently prevent actual damages only when the hypoxic condition lasts for a relatively short time.