The growth of the feline brain from late fetal into adult life I. A morphometric study of the neocortex and white matter

We measured the growth of the neocortex (NCx) and telencephalic white matte r (WM) in the brain of 64 cats allocated to the following 11 age-groups: fe tal (E) 59 days (birth is at E63-65), postnatal (P) days 1, 7, 15, 30, 45, 60, 90, 120, 180, and adult. There were six subjects per group (except for E59, n = 4). Using a projection microscope and cytochrome oxidase-stained c oronal sections, a total of 4300 and 4325 sections at left and of 4282 and 4264 sections at right were drawn for the NCx and for the WM, respectively. With computer assistance, the drawings were digitized to calculate mean cr oss-sectional area and then the mean volume of each structure per age-group . The two structures grew heterochronously. In terms of percentage of the a dult volume, for the left side (both side grew at a similar rate), the size of the NCx grew very fast from a 15.7% at E59 to an adult-range value of 9 3.7% at P30. In contrast, the WM grew slowly. Starting at a larger volume o f 55%, the WM was only 72.5% of the adult size at P30 reaching an adult-ran ge value only by P180 (94.7%). After P30, both structures showed a small, a lbeit consistent, left versus right asymmetry with the right size been larg er at all (but fetal) ages by a margin ranging between 0.4 and 4.1%. In add ition, after P30 the NCx tended to overgrow with all groups showing higher values relative to adult cats, and reaching significance at P60 (volume hig her by 19.2%, P<0.01) and at P180 (higher by 14.5%, P<0.05). For the NCx th en were no within group correlations between volume of the structures and t he subjects' body weight, while a positive correlation was present for four of the WM postnatal groups. There were no correlations between the size of the structures and the sex of the cats. The data is discussed in the conte xt of the extant human and animal literature and, in the ensuing paper, als o within the context of growth of subcortical structures. (C) 2000 Elsevier Science B.V. All rights reserved.