Interrelationships between tyrosine hydroxylase-immunoreactive dopaminergic afferents and somatostatinergic neurons in the rat central amygdaloid nucleus

Abstract

Interrelationships between dopaminergic afferents and somatostatinergic neurons of the rat central amygdaloid nucleus were studied using tyrosine hydroxylase/somatostatin double immunolabeling for light and electron microscopy. Additionally, morphological features of somatostatin neurons in different subnuclei of the central nucleus were studied, and the results were complemented by codistribution studies of somatostatin and D1 and D2 dopamine receptor mRNA expression. Dense axonal immunolabeling for tyrosine hydroxylase was colocalized with somatostatin-immunoreactive or somatostatin mRNA-reactive neurons in the medial and the central lateral part of the central nucleus. The number of somatostatinergic neurons detected was higher using in situ hybridization than using immunolabeling. Somatostatin-immunoreactive neurons of the medial central nucleus possessed deeply indented nuclei, and immunoreaction product was confined to the Golgi apparatus and its vicinity. On the other hand, those in the central lateral subnucleus possessed nuclei without indentations and showed diffuse staining of the cytoplasm and/or in large vesicles. Double labeling showed that in the central lateral central nucleus, somatostatin-immunoreactive neurons were contacted by tyrosine hydroxylase-immunoreactive terminals, and on the electron microscopic level synaptic contacts between differently labeled structures were observed. D1 and D2 receptor mRNA-reactive neurons were differentially distributed in central nucleus subnuclei. D1 receptor mRNA-expressing neurons were found only in the medial subnucleus, while D2 receptor mRNA was expressed by a number of neurons in the lateral central and a few in the medial one. Thus, the study proves that somatostatin-immunoreactive neurons of the central lateral central nucleus are directly innervated by dopaminergic afferents and may express the D2 dopamine receptor.