Distribution of synaptic zinc in the macaque monkey amygdala.

We have mapped the macaque amygdala for the distribution of synaptic zinc (Zn), a co-factor of glutamate implicated in plasticity, as well as in several excitotoxic and other pathophysiological conditions. In brief, we found that the amygdala is Zn enriched in all nuclear groups (i.e., basolateral and cortical groups, as well as central and medial nuclei) but with marked differences in density. By comparing parallel tissue series histologically reacted for Zn and parvalbumin (PV), we further found that regions high in Zn are typically low in PV neuropil. In the basolateral group, there is a particularly distinct dorsoventral gradation such that Zn levels are most dense ventrally, i.e., in the paralaminar nucleus, the ventral division of the lateral nucleus, and the parvicellular divisions of both the basal nucleus and the accessory basal nucleus. PV levels are least dense in these same regions. For the central and medial nuclei, there is a slight mediolateral gradient, with Zn levels being higher medially. PV is low overall in these nuclei. Electron microscopic results confirmed that Zn is contained in synaptic boutons. These form asymmetrical, presumably excitatory, synapses, and the postsynaptic targets are mainly spines of projection neurons. The inhomogeneous distribution of Zn in the monkey amygdala may be related to different types or degrees of plasticity among the amygdaloid subnuclei. The complementary distribution with PV parallels that of several other substances and is interesting in the context of subnuclear vulnerability for human neuronal disease, such as seizure and Alzheimer's disease.