Light and electron microscopic study of cholinergic and noradrenergic elements in the basolateral nucleus of the rat amygdala: Evidence for interactions between the two systems

Pharmacological studies have suggested that the cholinergic (ACh) and norad renergic (NA) systems in the amygdala (AM) play an important role in learni ng and memory storage and that the two systems interact to modulate memory storage. To obtain anatomical evidence for the interaction, the organizatio n of the ACh and NA fibers in rat AM was investigated by immunocytochemistr y for choline acetyltransferase (ChAT) and dopamine-beta -hydroxylase (DBH) in conjunction with light, confocal laser scanning, and electron microscop y (LM, CLSM, and TEM, respectively). LM showed that the ChAT immunoreactivi ty was densest in the basolateral nucleus (BL), whereas the DBH immunoreact ivity was densest in the posterior BL. CLSM demonstrated that the ChAT-immu noreactive profiles in the BL were frequently located in juxtaposition to t he DBH-immunoreactive axons. The TEM observations were as follows: The majo rity of the synapses formed by ChAT-immunoreactive terminals were symmetric , but DBH-immunoreactive axons formed both asymmetric and symmetric synapse s. The ChAT-immunoreactive terminals usually established the symmetric syna ptic contacts with the DBH-immunoreactive terminals and varicosities. The D BH-immunoreactive terminals. formed the asymmetric synapses with the ChAT-i mmunoreactive dendrites of the intrinsic neurons within the AM. The results provide anatomical substrates for mnemonic functions of the ACh and NA sys tems and for the interactions between the two systems in the AM. (C) 2001 W iley-Liss,Inc.