A CRITICAL PERIOD FOR REDUCED BRAIN VULNERABILITY TO DEVELOPMENTAL INJURY II - VOLUMETRIC STUDY OF THE NEOCORTEX AND THALAMUS IN CATS

Groups of young adult cats with a left hemineodecortication at postnat al (P) ages (in days) 5-15 (P10), 30 (P30), 60 (P60), 90 (P90), 120 (P 120) and in adulthood, were used to measure the volume of the thalamus , bilaterally, and of the remaining neocortex (right hemisphere). The same subjects were employed for the behavioral studies reported in the preceding paper. There was a bilateral, age-dependent, thalamic volum e decrease. Ipsilateral to the resection, the thalamic shrinkage was t he largest for the adult-lesioned cats (by 56.7%) and it was the small est for the P30 group (43.3%), with a tendency towards a greater atrop hy as the age at lesion increased. A similar pattern of atrophy was se en for the contralateral thalamus but the volume reduction was much le ss pronounced such that it was significant only for the four older age -at-lesion groups (ranging from 18.2% to 11.2% for the P120 and P90 gr oups respectively). Once again, the shrinkage was the smallest for the P30 group (5.3%). The remaining neocortex also shrunk in these animal s, but the volume decrease was significant only for the adult-lesioned (17.8%) and the P120 group (15.4%), while the P30 group had practical ly no shrinkage (2.4%). The frontal cortex had no atrophy or it was mi nimal but the shrinkage gradually increased caudally such that all les ioned groups had some size reduction of the occipital cortex. The pres ent results, together with the main conclusion of the preceding paper, indicate that there is a critical maturation period (CMP) of reduced forebrain vulnerability to neocortical injury which, in cats, tends to end between 30 to 60 days postnatally. The implications for developme ntal brain damage in other higher mammal species as well as the possib le morphological ontogenetical underpinnings of this period are discus sed. (C) 1998 Elsevier Science B.V.