Age‐Related Loss of GABA‐Positive and GABA‐Negative Neurons in Neocortical Transplants

The numerical density of GABA immunopositive and GABA immunonegative neurons was quantitatively determined in 0, 12, 30 and 90 day-old neocortical transplants, derived from E17 rat embryos and transplanted into adult hosts. It was found that the original, very high neuronal density in the fetal transplant declined steadily after transplantation to the somatosensory cortex of adult rat. The decline in numerical density of GABA-positive neurons, however, was disproportionately larger than that of GABA-negative nerve cells: At 90 days the proportion of GABA-positive cells was 2.3% (in contrast to the 11.8% in the adult host cortex). The density of GABA-negative neurons, on the other hand, remained slightly higher than comparable values in the control cortex. The decline in density of GABA-positive neurons was continuous until the 90th post-transplantation day, while final, close to normal density values of GABA-negative nerve cells were already reached in 30 day-old grafts, with no significant change afterwards.