Histamine synthesizing afferents within the amygdaloid complex and bed nucleus of the stria terminalis of the rat.

The regional distribution of histidine decarboxylase (HD) activity has been studied in the amygdaloid complex and the bed nucleus of the stria terminalis (BST) of the rat. The central and medial nuclei of the amygdala had 2-fold higher HD activity levels than the remaining nuclei of the complex. HD activity was exceptionally high in the BST, particularly in its ventral part. A lesion of the stria terminalis had no effect on this distribution whereas a combined lesion of the stria terminalis and the so-called ventral pathway induced a decrease of approximately 60% in all the amygdaloid nuclei, but not in the BST. On the other hand, a lesion of the medial forebrain bundle (MFB) induced a similar decrease in both the amygdaloid nuclei and the BST. These results confirm that HD-containing fibres are present in the MFB. On the one hand these project massively to the BST and on the other penetrate in the amygdala ventromedially along the ansa peduncularis and preferentially innervate the more medially located nuclei.