Efferent connections of the septal area in the rat: an analysis utilizing retrograde and anterograde transport methods.

Experiments were performed by either retrograde (horseradish peroxidase histochemistry) or anterograde ([3H]leucine radioautography) transport methods to determine the efferent connections of the septum in the rat. It was observed that the dorsal septum projects to the lateral preoptic area, lateral hypothalamus, periventricular hypothalamus and midline thalamus. Fibers from the ventral half of the septum project topographically to the hippocampal formation, thalamus, hypothalamus and midbrain. Specifically, neurons located along the midline in the vertical limb of the diagonal band project through the dorsal fornix to all CA fields of the dorsal hippo campus and adjacent subicular cortex. Other fibers from this region project through the stria medullaris to the medial habenular nucleus and anteromedial nuclhe pars posterior of the medial mammillary nucleus. Cells located immediately lateral to the midline in the vertical limb of the diagonal band project through the medial part of the fimbria to all CA fields of the posterior hippocampus and adjacent subicular cortex. Other fibers which originate from this region project through the stria medullaris to both the medial and lateral habenular nuclei and the paratenial nucleus of the thalamus, and through the medial forebrain bundle to the pars posterior of the medial mammillary nucleus. Cells located in the intermediolateral septum project through the lateral part of the fimbria to all CA fields of the ventral hippocampus and adjacent subicular and entorhinal cortices. These cells also send fibers through the stria medullaris to the lateral habenular nucleus and mediodorsal thalamic nucleus. Other axons arising from these cells descend through the medial forebrain bundle to terminate in a region dorsal to the interpeduncular nucleus. Fibers from the most lateral part of the ventrl septum (i.e., bed nucleus of the anterior commissure) project through the stria terminalis to the ventral subiculum. In addition, cells located in the horizontal limb of the diagonal band project massively to the pars posterior of the medial mammillary nucleus and the ventral tegmental area, and amygdala.