Stereological evaluation of substantia nigra cell number in normal and hemispherectomized monkeys

The assessment of the anatomical consequences of cortical lesions on subcor tical visual relays is necessary to further understand residual visual capa cities. Unbiased stereological techniques were used to evaluate cell number s in the substantia nigra (SN), a structure involved in the control of sacc adic eye movements. Cell numbers were very similar in the ipsi- and contral ateral SN of the hemispherectomized animal (329,926 vs. 310,248). These num bers are close to what was observed in the normal monkey (300,130 and 320,8 59). In one case, part of the striatum was lesioned in addition to the cere bral hemisphere. Noticeable effects were observed in the SN ipsilateral to the cortical lesion: volume was reduced by 30.5% while the number of neuron s, compared to the contralateral side, dropped by 43.2% (186,644 vs. 328,75 7). These results suggest that due to its anatomical sparing following hemi spherectomy the SN, in addition to other subcortical structures, is in a pr ime position to modulate the spared saccadic behaviors seen after massive c ortical injuries. (C) 1999 Elsevier Science B.V. All rights reserved.