Light and electron microscopic studies of postnatal developmentof the rat amygdala by Timm's sulphide silver method

The distribution of zinc and postnatal development of the rat amygdala were investigated by light and electron microscopy with Timm's sulphide silver method.By Timm's reaction and toluidine blue staining, the rat amygdala could be divided into cortical(CO), lateral(L), basolateral(ABL), basomedial(ABM), central(C), medial(M) and intercated(I) nuclear regions. CO was the most strongly positive to Timm's reaction, L, ABM and C were strongly positive, ABL was also positive, and I and M were weakly positive. In newborns, no positive Timm's reaction could be observed, but a very weakly positive reaction was observed from the 5th postnatal day. The reaction became stronger with development, and reached the strength of that of the adult on the 30th postnatal day.Electron microscopically, the deposits of silver grains were only located in the nerve fiber endings containing many small clear vesicles. This finding is quite similar to that described in the mossy fiber endings in the hippocampal formation. Deposits of silver grains could not be found in newborns, and only very few could be observed after the 5th postnatal day. The number of deposits increased with age, and reached that of the adult from the 20th to the 30th postnatal days.It was elucidated that a significant increase in the number of silver grains per square 10(-8) centimeter of Timm's positive nerve fiber endings occurred between the 10th and 20th postnatal days.These findings suggest that zinc exists in the nerve fiber endings in the rat amygdala and the amount of zinc increases with age. Zinc may play an important role in synaptic transmission.