Corticotropin regulates transsynaptically the activity of septo-hippocampal cholinergic neurones.

The activity of septo-hippocampal neurones is affected by the action on cholinergic perikarya in the septum of a variety of putative neurotransmitters, including substance P and beta-endorphin. (The latter is released in the septal region from neurones which originate in the medial basal hypothalamus.) It has also been reported that two other neuropeptides, corticotropin (ACTH1-24) and alpha-melanotropin (alpha-MSH), affect acetylcholine turnover in septo-hippocampal neurones in a manner that is not blocked by transection of the afferents to the hippocampus, from which it has been inferred that the neurotransmitters act directly on the hippocampus. We now describe experiments with corticotropin which show that the effect is rather the influence on septo-hippocampal cholinergic neurones of peptidergic neurones within the septum.