Sugeta Shingo, Hirai Yoshiyuki, Maezawa Hitoshi, Inoue Nobuo, Yamazaki Yutaka, Funahashi Makoto
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.
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.
Brain Res. 2015 Aug 27;1618:83-90. doi: 10.1016/j.brainres.2015.05.018. Epub 2015 May 22.
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.
胆囊收缩素（CCK）是一种著名的肠道激素，通过作用于外周和中枢受体发挥厌食作用。CCK在整个哺乳动物大脑中也广泛分布，似乎起着神经递质和神经调质的作用。最后区是室周器官之一，位于第四脑室尾端延髓的背表面。最后区的血管缺乏血脑屏障，使特定的中枢神经元件能够独特地接触循环物质。免疫组织化学研究显示最后区存在CCK-A受体，并且我们报道了对CCK敏感的最后区神经元。然而，CCK在最后区神经元中的感受机制仍未得到解释。我们使用大鼠脑片的全细胞和穿孔膜片钳记录，研究了最后区神经元对CCK受体激动剂和拮抗剂的反应。应用CCK-8引发了兴奋性反应，如微小兴奋性突触后电流（mEPSCs）频率增加、mEPSCs向更大幅度转变以及动作电位频率增加。这些变化大多出现在不显示超极化激活阳离子电流（Ih）的细胞中，少数Ih阳性神经元有小的兴奋性变化除外。从未观察到持续性内向电流或对CCK-8的抑制反应。对给予CCK-8前后mEPSCs幅度的分析表明，这些反应是通过突触前受体介导的。在存在CNQX（AMPA型谷氨酸受体拮抗剂）的情况下，CCK-8的作用被消除。在存在洛谷胺（一种选择性CCK-A受体拮抗剂）的情况下，CCK-8诱导的兴奋性反应受到抑制。没有细胞对非硫酸化CCK-8（CCK-8NS，一种选择性CCK-B受体激动剂）的给药产生反应。我们得出结论，CCK-8通过突触前CCK-A受体发挥作用，促进谷氨酸释放到Ih阴性的最后区细胞上。
