Evidence that dopaminergic axons provide a dense innervation of specific neuronal subpopulations in the rat basolateral amygdala

Dopaminergic inputs from the ventral tegmental area and substantia nigra are involved in numerous emotional and behavioral functions mediated by the amygdala. Previous studies have shown that some dopaminergic axons selectively innervate subpopulations of neurons in the rat basolateral amygdala by forming dense pericellular arrays (baskets) that envelope the perikarya of these neurons. Because of the obvious functional significance of this innervation, a sequential two-color immunoperoxidase technique was used in the present study to determine which neuronal subpopulations are targeted. Pericellular baskets were seen in sections stained for tyrosine hydroxylase, but not for dopamine-beta-hydroxylase, suggesting that these axonal arrays are dopaminergic. Most baskets enveloped small ovoid or piriform perikarya, although a few in the anteroventral part of the basolateral nucleus were associated with larger pyramidal cells. Double-labeling immunohistochemistry revealed that all of the smaller baskets enveloped a subpopulation of parvalbumin-immunoreactive nonpyramidal neurons, but not nonpyramidal neurons containing vasoactive intestinal polypeptide or neuropeptide Y. Since these parvalbumin containing neurons are known to be GABAergic interneurons, the results of this study suggest that the actions of dopamine in the basolateral amygdala are mediated, in part, by a subpopulation of inhibitory interneurons. (C) 1999 Elsevier Science B.V. All rights reserved.