THE EFFECT OF NEOCORTICAL LESIONS ON THE NUMBER OF CELLS IN NEONATAL OR ADULT FELINE CAUDATE-NUCLEUS - COMPARISON TO FETAL LESIONS

After a unilateral resection of the frontal cortex in fetal cats the v olume of the caudate nucleus increases while the packing density of ne uronal and glial cells does not change. In the present report we addre ss the questions of whether a similar lesion sustained neonatally or a more extensive neodecortication sustained neonatally or in adulthood may have the same unusual effect. Stereological methods were used to d etermine bilaterally the volume of the caudate nucleus as well as to e stimate the total number and packing density of neurons and glial cell s in the caudate nucleus ipsilateral to the lesion. Comparisons betwee n each of three experimental groups and intact animals were made at a time when all animals were young adults. In cats with a unilateral fro ntal cortical lesion performed between postnatal days 8 and 14, none o f the measured parameters changed significantly compared to intact con trols. In cats with removal of the entire left neocortex in adulthood, the ipsilateral caudate nucleus volume decreased by 18.1% and by 21.5 % relative to intact and to neonatal hemidecorticated cats respectivel y (P<0.05), with no change in the contralateral caudate. In the ipsila teral caudate the total number of neurons decreased by 21.8% (P<0.05) compared to controls while the number of glial cells did not change si gnificantly. In the same caudate the packing density of neurons did no t change significantly (except for a 17.1% decrease, P<0.05, relative to frontal-lesioned cats) while that of glial cells increased by 19.9% and by 24.7% compared to intact and neonatal neodecorticated cats res pectively (P<0.05). In adult cats in which a similar hemineodecorticat ion was performed between postnatal days 8 and 13, the only significan t changes were a 25.8% (P<0.05) and a 30.6% (P<0.05) decrease in neuro n packing density compared to intact and frontal-lesioned cats, respec tively. In summary, a restricted unilateral neocortical resection in n eonatal cats did not induce any morphological changes in the caudate n ucleus that we could detect with the methods employed. In contrast, an extensive neodecortication sustained in adulthood produced ipsilatera l caudate shrinkage with substantial neuron loss and increase in packi ng density of glial cells, while a similar lesion but sustained neonat ally only altered substantially the packing density of glial cells (de creased). Therefore, we concluded that (i) the caudate nucleus hypertr ophy which we reported after a unilateral discrete cortical removal du ring the prenatal period is a unique phenomenon which is peculiar to t he cat brain during the last third of gestation; (ii) the caudate nucl eus changes seen in the cats with hemineodecortication in adulthood ar e degenerative in nature and closely resemble those which we reported for other subcortical nuclei following a similar lesion; and (iii) the animals with neonatal hemidecortication are relatively spared from th ese degenerative effects. Overall, these results indicate that; as for other structures, the morphological changes of the caudate nucleus fo llowing neocortical damage depend on the maturational stale of the bra in al the time of the injury and on the size of the lesion, and suppor t the notion that the consequences of cerebral cortex lesions upon sub cortical brain nuclei are of a different nature when sustained in pren atal as compared to postnatal cats. (C) 1997 IBRO.