Contributions of different afferent pathways to the catecholamine and 5-hydroxytryptamine-innervation of the amygdala: A neurochemical and histochemical study

Abstract

The contributions of different afferent pathways to the monoaminergic innervation of the rat amygdala was investigated using fluorescent histochemical and radiochemical techniques. The amounts of dopamine, noradrenaline and 5-hydroxytryptamine in dissected amygdaloid nuclei were determined, as well as the activities of the associated biosynthetic enzymes, tyrosine hydroxylase and tryptophan hydroxylase in the same nuclei from control rats and rats with lesions of afferent pathways. Three different lesions were used: the ventral pathway was cut by a lesion of the lateral medial forebrain bundle; the piriform cortex was undercut; and a hemisection of the stria terminalis was performed. The results indicated that the ventral pathway to the amygdala carries between 50 and 75% of monoamine-containing fibres projecting to the rat amygdala. This was confirmed by fluorescent histochemical studies of rats with afferent pathway lesions which showed a qualitatively similar depletion of catecholamine-positive fibres from the amygdala and piriform cortex after ventral pathway lesions. The histochemical and radiochemical assay data have been used to draw up a proposed scheme showing the catecholaminergic innervation of the amygdala, in which noradrenergic fibres from cells in the medulla oblongata and locus coeruleus, and dopaminergic fibres from cells in the substantia nigra and ventral tegmental area ascend via the medial forebrain bundle.