Morphological evidence for a substance P projection from medial septum to hippocampus.

The medial septal nucleus provides one of the major afferents to the hippocampal formation. The two major types of neurons present in the medial septum are cholinergic and GABAergic, but other types of neurons are also present. A small population of substance P-containing neurons is present along the border between the medial and lateral septum, but it is unclear whether these project to the hippocampus. The present study, by employing both anterograde and retrograde tracing techniques, combined with immunocytochemistry for substance P, provides direct morphological evidence for a substance P projection from the lateral region of medial septum to a portion of CA2/3a, which is restricted to the mid-septotemporal portion of the hippocampus.