Postnatal development of the excitatory amino acid system in visual cortex of the rat. Changes in ligand binding to NMDA, quisqualate and kainate receptors

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Abstract
The postnatal development of the ligand binding to N‐methyl‐d‐aspartate (NMDA), quisqualate and kainate receptor sites was examined in whole homogenates of the visual cortex of rats, aged 2–360 days. As selective ligands, [3H]CPP (3‐(2‐carboxypyperazine‐4‐yl)‐propyl‐1‐phosphonic acid, [3H]AMPA (RS‐alpha‐amino‐3‐hydroxy‐5‐methyl‐isoxazole‐4‐propionic acid) and [3H]KA (kainic acid) were used, respectively. The binding of CPP was low in newborns, rapidly increased from the second postnatal week, reached its maximum between weeks 2 and 3, then slowly declined up to the age of 1 year. In contrast, the binding of AMPA and kainate was high perinatally, increased rapidly up to day 6 after birth to reach an early maximum value, then gradually decreased to adult values which were attained at an age of 3–4 weeks. These age‐related changes were derived from alterations in the density of binding sites, which, in the case of AMPA, was accompanied by an increase in binding affinity. The results, compared with the developmental time‐course of excitatory synapses, indicate that, in the immature cerebral cortex, NMDA receptors may be primarily involved in synaptic transmission, whereas quisqualate and kainate receptors may play some other (e.g. trophic) roles.