title: Presynaptically mediated effects of cholecystokinin-8 on the excitability of area postrema neurons in rat brain slices.
abstract: Cholecystokinin (CCK) is a well-known gut hormone that shows anorexigenic effects via action at peripheral and central receptors. CCK is also widely distributed throughout the mammalian brain and appears to function as a neurotransmitter and neuromodulator. The area postrema is one of the circumventricular organs, located on the dorsal surface of the medulla oblongata at the caudal end of the fourth ventricle. Blood vessels in the area postrema lack a blood brain barrier, offering specific central neural elements unique access to circulating substances. Immunohistochemical studies show CCK-A receptors in the area postrema, and we reported CCK-sensitive area postrema neurons. However, the receptive mechanism of CCK in area postrema neurons still remains unexplained. We investigated the responses of area postrema neurons to agonists and antagonists of CCK receptors using whole cell and perforated patch-clamp recordings in rat brain slices. The application of CCK-8 elicited excitatory responses, such as increases in the frequency of mEPSCs (miniature excitatory postsynaptic currents), a shift toward larger amplitude mEPSCs, and increases in the frequency of action potentials. These changes were found mostly in cells not displaying the hyperpolarization-activated cation current (Ih), except for small excitatory changes in a minority of Ih-positive neurons. Tonic inward currents or an inhibitory response to CCK-8 were never seen. Analysis of the amplitude of mEPSCs before and after the administration of CCK-8 indicated the responses mediated via the presynaptic receptors. The effect of CCK-8 was abolished in the presence of CNQX (AMPA type glutamate receptor antagonist). In the presence of lorglumide (a selective CCK-A receptor antagonist), CCK-8-induced excitatory responses were inhibited. No cells responded to the administration of non-sulfated CCK-8 (CCK-8NS, a selective CCK-B receptor agonist). We conclude that CCK-8 exerts its action via presynaptic CCK-A receptors to facilitate glutamate release onto Ih-negative area postrema cells.
authors.affiliation: Department of Gerodontology, Division of Oral Health Science, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan; Department of Oral Physiology, Division of Oral Functional Sciences, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: sugeta@den.hokudai.ac.jp.
authors.forename: Shingo
authors.initials: S
authors.lastname: Sugeta
authors.affiliation: Department of Oral Physiology, Division of Oral Functional Sciences, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: hirai@den.hokudai.ac.jp.
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Hirai
authors.affiliation: Department of Oral Physiology, Division of Oral Functional Sciences, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: maezawa@den.hokudai.ac.jp.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Maezawa
authors.affiliation: Department of Gerodontology, Division of Oral Health Science, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: nobu@den.hokudai.ac.jp.
authors.forename: Nobuo
authors.initials: N
authors.lastname: Inoue
authors.affiliation: Department of Gerodontology, Division of Oral Health Science, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: yutaka8@den.hokudai.ac.jp.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Yamazaki
authors.affiliation: Department of Oral Physiology, Division of Oral Functional Sciences, Hokkaido University Graduate School of Dental Medicine, Kita 13, Nishi 7, Kita-ku, Sapporo 060-8586, Japan. Electronic address: mfuna@den.hokudai.ac.jp.
authors.forename: Makoto
authors.initials: M
authors.lastname: Funahashi
mesh_terms: D018750:6-Cyano-7-nitroquinoxaline-2,3-dione / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D031608:Area Postrema / Q000166:cytology*; D001703:Biophysics; D002766:Cholecystokinin / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D066298:In Vitro Techniques; D009474:Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D010446:Peptide Fragments / Q000494:pharmacology*; D017729:Presynaptic Terminals / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology; D018709:Statistics, Nonparametric; D013779:Tetrodotoxin / Q000494:pharmacology
chemical_list: D018691:Excitatory Amino Acid Antagonists; D010446:Peptide Fragments; D026941:Sodium Channel Blockers; C410885:cholecystokinin 8; D013779:Tetrodotoxin; D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D002766:Cholecystokinin
keywords: Area postrema; Brain slices; CCK-8; Neurons; Patch-clamp recording; Rats