Neuropeptides and appetite: contribution of neuropharmacological modeling

It is now clear that a variety of neuropeptides interact with the more classically defined neurotransmitters to stimulate or inhibit feeding. An extensive peripheral peptide satiety system has been identified. Peptides involved in this system include cholecystokinin, bombesin, gastrin-releasing peptide, glucagon, somatostatin, and possibly thyrotropin-releasing hormone and calcitonin. Some of these peptides appear to inhibit feeding by activating ascending fibers in the vagus, whereas others exert their actions independent of the vagus. In addition, neuropeptides appear to play a role in producing the neuromodulatory effects of taste on appetite, and hormones from the endocrine system modulate neuropeptide effects on feeding. The central appetite regulatory system appears to be arranged in a cascade, with an interaction between dynorphin and dopamine producing a part of the feeding drive. This drive is held in check by a variety of neuropeptides including calcitonin, corticotropin-releasing factor, and bombesin. In turn, these peptides are modulated by a norepinephrine-alpha-aminobutyric acid (GABA) system. Neurotensin, serotonin, cyclohistidyl proline diketopiperazine, and the peripheral satiety system appear to modulate the norepinephrine-GABA disinhibitory system. By the judicious use of neuropharmacological modeling we have developed a model of the neurotransmitter interactions involved in appetite regulation that can act as a springboard for the design of future experiments to unravel the mysteries of appetite regulation.