INNERVATION OF THE CAUDATE-NUCLEUS, THALAMUS AND RED NUCLEUS BY THE REMAINING SENSORIMOTOR CORTEX IN CATS WITH FETAL OR NEONATAL UNILATERALFRONTAL-CORTEX REMOVAL

We studied the projections to the caudate nuclei, thalami and red nucl ei from the remaining sensorimotor cortex in adult cats that had susta ined a unilateral frontal cortex resection prenatally or neonatally. F our cats had the lesion at age E 50-55 and six animals sustained the a blation at age P 8-14 (seven cats were intact controls). All cats grew to young adulthood and then received injections of tritiated leucine- proline in the remaining sensorimotor cortex. Injection sites and axon terminal fields were reconstructed using autoradiography-processed ti ssue. In all cats the label filled a similar extent of the right peric ruciate cortex. Terminal field densities in the subcortical nuclei wer e estimated using computer-based video software. Three medial-lateral sectors at five coronal levels were examined in the caudate nucleus. T hree nuclear groups were analyzed in the thalamus (intralaminary, vent ralis lateralis and ventrobasal complex). For the red nucleus, the fou r quadrants were examined at four coronal levels. The main goal of the study was to assess possible changes in the cortical innervation of t he nuclei ipsilateral to the lesion. Therefore, the mean particle coun ts per nucleus (and per area or sector of nuclei) and per animal group were used to calculate percentage values for the decussated (crossed, or contralateral to the injection site) as a function of the non-decu ssated (uncrossed, or ipsilateral to the injection site) innervation. The percentage values for the crossed projections were: (a) for the en tire caudate nucleus, 61.3% for the intact, 56.7% for the fetal-lesion ed and 42.7% for the neonatal-lesioned cats, with no statistical diffe rences between groups; (b) for the thalamus the proportion of crossed projections was minimal fluctuating between a low 0.06-0.16% for the n ucleus ventralis lateralis and a high of 2.01-3.46% for the intralamin ary nuclei, with the highest values belonging to the lesioned groups b ut with no significant differences between groups; (c) for the entire red nucleus, 1.98%, 12.74% (P < 0.05) and 6.76% for the intact, fetal- and neonatal-lesioned cats respectively. In the lesioned cats, the to pography of the distribution of the axon terminals was bilaterally the same as in the controls. In conclusion, only the red nucleus of the f rontal-lesioned cats showed an increased crossed innervation from the remaining sensorimotor cortex but this was relatively weak and statist ically significant only for the fetal-lesioned animals. These results as well as the literature suggest that: (a) the crossed corticorubral projections in fetal cats may represent true reinnervation (i.e., newl y originated, no preexisting terminals); (b) the relative paucity of t he crossed projections in the present cats as compared to the extensiv e reorganization of subcortical terminals seen after cerebral hemisphe rectomy (our original postnatal lesion model) may be due to the much s maller size of the present cortical lesion which presumably induced on ly a limited amount of subcortical nuclear deafferentation.