Postnatal development of the excitatory amino acid system in visual cortex of the rat. Changes in uptake and levels of aspartate and glutamate

The postnatal changes of aspartate (Asp) and glutamate (Glu) levels, as well as the development of the high-affinity uptake of [3H]D-Asp were examined in the visual cortex of rats, aged 2-360 days. Perinatal (day 2) levels of Asp were relatively lower than those of Glu, i.e. about 30 and 60% of the respective values for adults (day 180). Both Asp and Glu levels showed a rapid increase during the second and third postnatal weeks. Asp reached its maximal concentration (day 20) a few days earlier than Glu (day 25). Thereafter, both Asp and Glu levels slowly declined to the adult values which were reached by day 90 and remained unchanged up to day 360. The uptake of D-Asp was low in newborns (5% of that in adult) and progressively increased with age up to about day 20, when adult values were attained. The increase of Asp and Glu levels showed a close correlation with the maturation of uptake capacity. Our findings indicate that the developmental increase of Asp and Glu levels is associated with the maturation of excitatory innervation in the visual cortex, but they do not support the concept of a transient Asp/Gluergic innervation of the immature visual cortex.