Modulation of the turnover rate of hippocampal acetylcholine by neuropeptides: possible site of action of alpha-melanocyte-stimulating hormone, adrenocorticotrophic hormone and somatostatin.

The intraventricular injection of alpha-melanocyte-stimulating hormone (alpha-MSH), adrenocorticotrophic hormone (ACTH1--24) or somatostatin increases the acetylcholine turnover rate (TRACh) in the hippocampus of rats. Two to 3 weeks after surgical transection of the projections from the cingulum of the entorhinal cortex to the hippocampus the injections of these peptides can still activate hippocampal TRACh. alpha-MSH, ACTH1--24 and somatostatin also increase hippocampal TRACh when injected two to 3 hr after section of the fimbria. In contrast, the intraseptal administration of these peptides fails to change the hippocampal TRACh. The results suggest that the increase in hippocampal TRACh elicited by the three polypeptides may be caused by their interaction with receptors located in the hippocampus. Moreover, the data exclude the possibility that these peptide receptors may be located in septum or in other telencephalic areas that contain neurons projecting to the hippocampus. In addition, this study shows that the septal-hippocampal cholinergic pathway is necessary to elicit a specific stretching-yawning syndrome described by Ferrari et al. (Ann. N.Y. Acad. Sci. 104: 330--345, 1963) after injection of alpha-MSH or ACTH1--24.