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.

Development of neurotransmitter parameters in lateral geniculate body, superior colliculus and visual cortex of the albino rat.

The postnatal development of some neurotransmitter parameters was measured in lateral geniculate body, superior colliculus and visual cortex of the rat. The following parameters were studied: (i) high-affinity uptake of L-glutamate or D-aspartate as markers for glutamergic neurons; (ii) high-affinity uptake of GABA, which reflects both glial and neuronal uptake of GABA; (iii) HA beta-alanine uptake as a marker for accumulation of GABA in glial structures; (iv) activity of glutamic acid decarboxylase which reflects GABAergic neurons; and (v) activity of choline acetyltransferase as a cholinergic marker. Km and Vmax were determined for high-affinity uptake of glutamate and GABA in newborn and adult animals. The possible glial influence on the uptake during development is discussed. In lateral geniculate body and visual cortex the HA glutamate uptake showed increasing activity from birth to adulthood, whereas in superior colliculus, the uptake was higher at birth, reaching a small significant peak after 12 days of age, and was then reduced to adult level. Km showed no such change between neonatal and adult animals. At birth, high-affinity GABA-uptake was similar to the adult level in superior colliculus and lateral geniculate body. In visual cortex, the uptake of GABA was 50% of adults. However, on day 15, the GABA uptake showed 2 to 3-fold higher activity in all regions when compared to adult level. Km for GABA uptake in neonatals and adults differed only in lateral geniculate body. High affinity uptake of beta-alanine was 50-80% lower in adults than in newborn rats. Glutamate decarboxylase activity, however, increased continuously in all 3 regions examined. This was true also for choline acetyltransferase.

The effect of dark adaptation on some transmitter functions in the visual pathways.

1. The high affinity uptake of GABA in optic tectum was found to be about 40% higher in frogs kept in complete darkness for 3 weeks, than in frogs in the normal condition. 2. No effects were obtained in uptake of glutamate and activity of GAD in the optic tectum. 3. The isoenzyme composition of cholinesterases in frog optic tectum and retina was not affected by dark adaptation either.