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Ohtani S, Fujita S, Hasegawa K, Tsuda H, Tonogi M, Kobayashi M. Relationship between the fluorescence intensity of rhodamine-labeled orexin A and the calcium responses in cortical neurons: An in vivo two-photon calcium imaging study. J Pharmacol Sci 2018; 138:76-82. [PMID: 30293961 DOI: 10.1016/j.jphs.2018.09.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2018] [Revised: 08/24/2018] [Accepted: 09/12/2018] [Indexed: 10/28/2022] Open
Abstract
Neural responses to a ligand vary widely between neurons; however, the mechanisms underlying this variation remain unclear. One possible mechanism is a variation in the number of receptors expressed in each neural membrane. Here, we synthesized a rhodamine-labeled orexin A compound, enabling us to quantify the amount of orexin binding to its receptors, OX1 and OX2, which principally couple to the Gq/11 protein. The rhodamine intensity and calcium response were measured under tetrodotoxin application from insular cortical glutamatergic neurons in Thy1-GCaMP6s transgenic mice using an in vivo two-photon microscope. Applying rhodamine-labeled orexin A (10 μM) to the cortical surface gradually and heterogeneously increased both the intensity of the rhodamine fluorescence and [Ca2+]i. Calcium responses started simultaneously with the increase in rhodamine-labeled orexin fluorescence and reached a plateau within several minutes. We classified neurons as high- and low-responding neurons based on the peak amplitude of the [Ca2+]i increase. The rhodamine fluorescence intensity was larger in the high-responding neurons than the low-responding neurons. Preapplication of SB334867 and TCS-OX2-29, OX1 and OX2 antagonists, respectively, decreased the proportion of high-responding neurons. These results suggest that the diverse receptor expression level in neural membranes is involved in mechanisms underlying varied neural responses, including [Ca2+]i increases.
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Affiliation(s)
- Saori Ohtani
- Department of Pharmacology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
| | - Satoshi Fujita
- Department of Pharmacology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Division of Oral and Craniomaxillofacial Research, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan.
| | - Koki Hasegawa
- Center for Instrumental Analysis, Kyoto Pharmaceutical University, Misasagi-Shichonocho 1, Yamashina-ku, Kyoto 607-8412, Japan
| | - Hiromasa Tsuda
- Department of Biochemistry, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Division of Functional Morphology, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
| | - Morio Tonogi
- Department of Oral and Maxillofacial Surgery, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan
| | - Masayuki Kobayashi
- Department of Pharmacology, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Division of Oral and Craniomaxillofacial Research, Dental Research Center, Nihon University School of Dentistry, 1-8-13 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-8310, Japan; Molecular Dynamics Imaging Unit, RIKEN Center for Life Science Technologies, 6-7-3 Minatojima-minamimachi, Chuo-ku, Kobe, Hyogo 650-0047, Japan.
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