[Distribution of horseradish peroxidase-labeled neurons, sources of descending fiber systems, in subcortical brain structures and the hypothalamus of cats].

Location of neurons which initiate different descending fibre systems from amygdaloid nuclei, basal ganglia and hypothalamus to brain stem was studied using the method of horse-radish peroxidase retrograde axonal transport. It was shown that neurons from magnocellular part of the basal amygdaloid nucleus and medial part of central amygdaloid nucleus send their axons to the dorsal hypothalamus, substantia nigra, lateral area of the mesencephalic central grey and midbrain reticular formation at the level of inferior olives. The central amygdaloid nucleus is the main source of projections to the hypothalamus and brain stem structures. It also sends projections to the nucleus of solitary tract and to the dorsal motor nucleus of the vagus. Uncrossed descending fibre systems from the basal ganglia terminate at the pons level, while the uncrossed and crossed fibre systems from dorsolateral and ventromedial areas of hypothalamus descend into the spinal cord. A possible role of the amygdaloid nuclei, basal ganglia, hypothalamus and their different pathways in regulation of somatic and autonomic functions and complex behavioural and emotional responses is discussed.