Distribution of GAP-43-immunoreactive structures in the human fetal amygdala

The growth-associated protein GAP-43 is a developmentally regulated protein which is involved in the formation of neuronal contacts. In immunohistoche mical studies, GAP-43 is detected within axons during their elongation; thu s a fibrous immunoreactivity is visible. After axonal growth is completed t here is a shift from a fibrous to a punctate immunoreactivity. The latter h as been shown to correlate with synaptogenesis. In the amygdala of the 5(th ) gestational month, a fibrous GAP-43-immunoreactivity is seen in the basol ateral nuclei, whereas the corticomedial nuclei exclusively show a punctate immunoreactivity. in the 7(th) month, all amygdaloid nuclei display immuno reactive puncta, but no fibers. In the 9(th) month GAP-43-immunoreactivity is no longer visible within the amygdala. The results demonstrate the diffe rential distribution of GAP-43-immunoreactive structures in the amygdaloid nuclei. The nuclear specific immunostaining and its changes may indicate th e Sequential appearance of the monoaminergic innervation of the amygdala, a s GAP-43 is known to occur in monoaminergic systems. Nuclei involved in hig h levels of the cortical processing hierarchy such as the lateral or basal nucleus display a late occurrence of GAP-43-immunoreactivity. In general, a nti-GAP-43 has been shown to be an appropriate tool to investigate axonal g rowth and synaptogenesis in the developing human brain.