MORPHOLOGICAL-CHANGES IN THE THALAMUS AND NEOCORTEX OF THE CAT BRAIN AFTER A RESTRICTED UNILATERAL FETAL NEOCORTICAL LESION

In order to study the response of the brain to injury during early dev elopment, the neocortex of ten fetal kittens was lesioned at age E43-4 8, in either the frontal (n = 8) or parieto-occipital (n = 2) areas. T he thalamus and neocortex of the lesioned animals were analyzed using quantitative morphometry and compared to intact control cats (n = 10). Ipsilaterally, the volumes of the remaining neocortex and of the thal amus were 26.5% and 25.7% smaller, respectively (P < 0.05). Contralate rally, the neocortex did not change in volume, whereas the thalamus te nded to be smaller by a mean of 11.1%, Ipsilaterally, in all four thal amic nuclei studied, the neuronal and glial cell packing densities (NC PD and GCPD) and the cross sectional area of neuronal somata did not d iffer between lesioned and intact animals except for the principal ven tromedial nucleus, where the GCPD was significantly lower (P < 0.05) i n lesioned animals. Contralaterally, the NCPD and GCPD did not show an y differences between groups, except for the principal ventromedial nu cleus, in which the GCPD was lower in lesioned cats (P < 0.05). Furthe rmore, in the contralateral basal ventromedial nucleus, the cross sect ional area of the neuronal somata was smaller in lesioned than in inta ct animals (P < 0.01). These results indicate loss of neurons and glia in the ipsilateral thalamus and probably in the neocortex. Since, at the time of the cortical resection, transient reciprocal thalamosubpla te connections have been established in the cat, the lesion-induced de privation of subplate target neurons and cortical inputs probably prec luded the survival of a substantial number of developing thalamic neur ons. In the cortex the hypothetical loss of neurons may, at least part ly, be attributed to lesion-induced elimination of target neurons befo re establishment of corticocortical connections.