title: Reduction of food intake by cholecystokinin requires activation of hindbrain NMDA-type glutamate receptors.
abstract: Intraperitoneal injection of CCK reduces food intake and triggers a behavioral pattern similar to natural satiation. Reduction of food intake by CCK is mediated by vagal afferents that innervate the stomach and small intestine. These afferents synapse in the hindbrain nucleus of the solitary tract (NTS) where gastrointestinal satiation signals are processed. Previously, we demonstrated that intraperitoneal (IP) administration of either competitive or noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonists attenuates reduction of food intake by CCK. However, because vagal afferents themselves express NMDA receptors at both central and peripheral endings, our results did not speak to the question of whether NMDA receptors in the brain play an essential role in reduction of feeding by CCK. We hypothesized that activation of NMDA receptors in the NTS is necessary for reduction of food intake by CCK. To test this hypothesis, we measured food intake following IP CCK, subsequent to NMDA receptor antagonist injections into the fourth ventricle, directly into the NTS or subcutaneously. We found that either fourth-ventricle or NTS injection of the noncompetitive NMDA receptor antagonist MK-801 was sufficient to inhibit CCK-induced reduction of feeding, while the same antagonist doses injected subcutaneously did not. Similarly fourth ventricle injection of d-3-(2-carboxypiperazin-4-yl)-1-propenyl-1-phosphoric acid (d-CPPene), a competitive NMDA receptor antagonist, also blocked reduction of food intake following IP CCK. Finally, d-CPPene injected into the fourth ventricle attenuated CCK-induced expression of nuclear c-Fos immunoreactivity in the dorsal vagal complex. We conclude that activation of NMDA receptors in the hindbrain is necessary for the reduction of food intake by CCK. Hindbrain NMDA receptors could comprise a critical avenue for control and modulation of satiation signals to influence food intake and energy balance.
authors.affiliation: Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology and Programs in Neuroscience, College of Veterinary Medicine, Washington State University, Pullman, Washington 99164-6520, USA.
authors.forename: Jason
authors.initials: J
authors.lastname: Wright
authors.forename: Carlos
authors.initials: C
authors.lastname: Campos
authors.forename: Thiebaut
authors.initials: T
authors.lastname: Herzog
authors.forename: Mihai
authors.initials: M
authors.lastname: Covasa
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Czaja
authors.forename: Robert C
authors.initials: RC
authors.lastname: Ritter
mesh_terms: D000818:Animals; D002766:Cholecystokinin / Q000494:pharmacology*; D016291:Dizocilpine Maleate / Q000008:administration & dosage / Q000494:pharmacology; D004435:Eating / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000502:physiology; D016762:Genes, fos / Q000502:physiology; D007276:Injections, Intraventricular; D008297:Male; D010879:Piperazines / Q000008:administration & dosage / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000145:classification / Q000378:metabolism*; D012249:Rhombencephalon / Q000187:drug effects* / Q000502:physiology; D012527:Satiation
chemical_list: D010879:Piperazines; D017470:Receptors, Glutamate; C065286:SDZ EAA 494; D016291:Dizocilpine Maleate; D002766:Cholecystokinin