Monoaminergic innervation of the macaque extended amygdala

The extended amygdala is a group of structures including the central and medial amygdaloid nuclei, bed nucleus of the stria terminalis, and sublenticular substantia innominata. This group of structures is thought to be important in a variety of psychiatric disorders, many of which are linked in one way or another to monoamines and their transporters. However, not much is known about the distribution of these molecules in the primate extended amygdala. Thus, we mapped the distribution of fibers immunoreactive for tyrosine hydroxylase, dopamine beta-hydroxylase, serotonin, dopamine transporter, and serotonin transporter in the brains of macaque monkeys. Tyrosine hydroxylase-, serotonin-, and serotonin transporter-immunoreactive fibers were found in highest concentrations in the lateral division of the central nucleus and lateral dorsal part of the bed nucleus of the stria terminalis. Dopamine beta-hydroxylase-immunoreactive fibers were found in the highest concentration in the lateral ventral bed nucleus of the stria terminalis. Dopamine transporter-immunoreactive fibers were found in the highest concentrations in the lateral juxtacapsular and lateral dorsal capsular subnuclei of the bed nucleus and lateral capsular subnucleus of the central amygdaloid nucleus, though in much lower amounts than was present in the striatum. These results suggest prominent roles for these transmitters, particularly in the lateral dorsal bed nucleus and lateral part of the central nucleus. The relative absence of dopamine transporter in the extended amygdala suggests that this transmitter acts more through volume transmission while serotonin, which is generally accompanied by proportionate amounts of transporter, may act more like a classical neurotransmitter. In addition, the finding of heavy concentrations of dopamine- and serotonin-immunoreactive fibers in the lateral central nucleus and lateral dorsal bed nucleus lends further support to the idea of these areas as parallels in some respects to the striatum.