Descending projections of the rostral septal region: An electrophysiological-histological study in the cat

Abstract

Descending connections from a specifically delineated region of the medial forebrain, named the rostral septal region, are described in the cat. Extensive studies of its function in cats, rhesus monkeys, and man led to the original demarcation of this region. In the present study, monosynaptic connections are demonstrated to numerous sensory relay nuclei and to nuclei containing noradrenergic, dopaminergic, and serotonergic cells, as well as to other precise nuclei in the brain stem, more caudal than those previously described in anatomic reports of septal region efferents, by use of electrophysiological (evoked potential) and histological (Fink-Heimer) techniques. Fibers descend through four rostral—caudal thoroughfares—the medial forebrain bundle, the inferior thalamic peduncle, the stria medullaris thalami, and the ventromedial sector of the internal capsule. These findings, together with those of earlier anatomical studies of this region, help to clarify the neural substrate underlying some basic behavioral phenomena.