The positive feedback effects originate primarily in the mouth and stimulate the central nervous system to continue eating. The central dopamine and opioid systems appear to be important for this positive feedback effect and are under intensive study at the present time. The negative feedback effects on ingested food originate primarily from the stomach and the small intestine and they act to slow eating. The major mechanisms of the negative feedback effects include cholecystokinin released from the small intestine and visceral afferent mechanisms monitoring mechanical and chemical stimuli in the stomach. The meal ends when the potency of the negative and positive feedback effects are judged to be equal by a comparator mechanism in the central nervous system, parts of which are represented in the caudal brain stem.
Current research involves a variety of neuroscientific and behavioral techniques.
These include the measurement of lick patterns and oral movements during ingestion, chronic gastrointestinal preparations for the isolated delivery and stimulation of specific receptor populations in the gastrointestinal tract, intracerebral cannulation techniques for the delivery of synaptic agents and drugs in specific central neural sites, and microdialysis of dopamine and its metabolites from specific brain sites during eating behavior. Although adult rats are the usual subjects of these experiments, the ontogeny of these controls are also being studied in preweanling rat pups. Estradiol interacts with gastric or postgastric food stimuli to decrease sucrose ingestion in ovariectomized rats. Raclopride reduces sucrose preference in rats. Weill Medical College of Cornell University.