This study is designed to characterize the central and peripheral actions of drugs on intestinal motility and intestinal propulsion. Drugs known to produce constipation, diarrhea or vomiting will be tested. Intestinal motility will be determined in intact, unanesthetized animals surgically implanted with monopolar, surface electrodes along the small intestine. Intestinal propulsion will be determined in rats by measuring the progression of a radioactive marker along the small intestine. Drugs will be administered either by peripheral or by intracerebroventricular injection. A peripheral or central site of action for a drug effect on the small intestine may be determined by several means: (1) relative potency of the drug when administered centrally or peripherally, (2) relative effects of pharmacological receptor antagonists given centrally or peripherally, (3) effects of pharmacological agents which alter neurotransmitter synthesis, storage and release on the central and peripheral actions of the drugs, (4) the effects of surgical transection of the extrinsic nerve supply to the small intestine and (5) alterations in brain and intestinal biochemistry associated with the drug response. The results will improve our understanding of drugs which affect intestinal function therapeutically or as a side-effect, and increase our knowledge of the central nervous system control of intestinal function.