The effects of unilateral neonatal removal of visual cortex on transmitter parameters in the adult superior colliculus and lateral geniculate body.

High affinity glutamate uptake was reduced in the ipsilateral lateral geniculate body by 75% and in the ipsilateral superior colliculus by 50% one week after ablation of the visual cortex in the adult rat. Six days after neonatal removal of visual cortex, there were no effects on the high affinity glutamate uptake in these regions indicating that there were few functionally corticofugal fibres established at birth. Seventy-five days after unilateral neonatal ablation of visual cortex, the glutamate uptake in both ipsi- and contralateral superior colliculus was reduced 50% compared to unoperated controls. The glutamate uptake in the lateral geniculate body was reduced 55% ipsilateral to and 38% contralateral to the lesion. The neonatal lesion had therefore affected the development of glutamate nerve terminals bilaterally in these target regions. Destruction of the visual cortex on the unoperated side caused in these adults an additional bilateral decrease of the glutamate uptake in the superior colliculus, showing the presence of aberrant glutamatergic fibres crossing from the unoperated visual cortex. In the lateral geniculate body, a similar lesion was accompanied only by a reduction in glutamate uptake on the ipsilateral side. The neonatal ablation of visual cortex also induced small changes in glutamate decarboxylase and GABA uptake in superior colliculus 75 days after the operation.