Modulation of acetylcholine metabolism in the hippocampal cholinergic pathway by intraseptally injected substance P.

Intraventricular injection of substance P induced a dose-dependent decrease of acetylcholine (ACh) turnover rate (TRACh) in the hippocampus of rats. The highest dose used (20 nmol) decreased the hippocampal TRACh to 40% of the control value. No changes in the ACh or choline content were detected in the various brain areas 40 minutes after injection, but after 70 minutes an increase in ACh content in diencephalon was significant. Local injection of substance P into the medial nuclei of the septum decreased significantly the hippocampal TRACh. Neither intraventricular injection nor injection into the periaqueductal grey of high doses of substance P (30 nmol) induced analgesia, whereas beta-endorphin (1 nmol) and morphine (15 nmol) were effective. No specific change in the electroencephalograph pattern recorded from either cortex or hippocampus could be detected within the first 2 hours after intraventricular injection of substance P.