Takayoshi Masuoka

Participation of the hippocampal theta rhythm in memory formation for an eight-arm radial maze task in rats

Participation of the hippocampal theta rhythm in memory formation was studied using an eight-arm radial maze task in rats. The numbers of reference memory and working memory errors were decreased gradually by daily training from session 10 and 6, respectively. On the other hand, the decrease in running time per choice was recognized from session 3. Theta power in the hippocampal CA1 area was gradually decreased from session 9, and there is a close relationship between the changes in theta power in the hippocampus and the number of reference memory errors. Based on those observations, it can be concluded that the hippocampal theta wave is intimately associated with the reference memory of the eight-arm radial maze in rats.

Role of hippocampal H1 receptors in radial maze performance and hippocampal theta activity in rats

Histamine H1 antagonists impaired the spatial memory performance. On the other hand, it is well recognized that the hippocampal theta rhythm plays a critical role in spatial memory. However, little work has been done the effect of H1 antagonists on the hippocampal theta rhythm which was associated with the memory performance. We investigated the effect of pyrilamine, a selective H1 receptor antagonist, on spatial memory performance as well as hippocampal theta rhythm during the memory task in rats. Effect of pyrilamine on spatial memory was measured using eight-arm radial maze with four arms baited. Hippocampal theta rhythm during the radial maze task was recorded with a polygraph system with a telemetric technique. Intraperitoneal injection of pyrilamine resulted in impairments of both reference and working memory on the radial maze task. The working memory deficit induced by pyrilamine was antagonized by the intrahippocampal injection of histamine and 6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptanecarboxamide (HTMT), a histamine H1 agonist. Intraperitoneal injection of pyrilamine decreased the hippocampal theta power at a dose that impaired reference and working memory. This effect was antagonized by the intrahippocampal injection of histamine and HTMT at a dose that ameliorated the working memory deficit. Intrahippocampal injection of pyrilamine impaired working memory and simultaneously decreased the hippocampal theta power. These results suggest that: (i) the hippocampal H1 receptors play an important role in the working memory processes on the radial maze performance and (ii) the decrease in the hippocampal theta power is associated with the working memory deficit induced by the blocking of H1 receptors.

The ameliorating effects of NMDA receptor agonists on histamine H1 antagonist-induced memory and hippocampal theta disruptions are prevented by the H3 receptor agonist in rats

In the present study, we investigated the effect of imetit, a selective histamine H(3) agonist, on the improvement of NMDA receptor agonists in H(1) antagonist-induced working memory deficit and the decrease of hippocampal theta activity in rats. Pyrilamine (35 mg/kg, i.p.) impaired spatial memory and decreased hippocampal theta activity during the radial maze task. In addition, intrahippocampal injection of D-cycloserine (1 microg/side) and spermidine (10 microg/side) improved the pyrilamine-induced working memory deficit and the decrease of hippocampal theta activity. The improvement effects of D-cycloserine and spermidine were antagonized by intrahippocampal injection of imetit (10 microg/side). These results indicate that, the facilitation of neurotransmitter release from the presynaptic terminals besides direct stimulation of postsynaptic NMDA receptors take part in the improvements of NMDA receptor agonists on pyrilamine-induced spatial memory deficit and the decrease of hippocampal theta activity.

Acknowledgement to Referees for Pharmacology 2009

www.karger.com/pha J. Ahamed, New York, N.Y., USA Jörg Ahrens, Hannover, Germany Reiko Akagi, Hiroshima, Japan Satoshi Akiba, Kyoto, Japan Y. Akiba, Los Angeles, Calif., USA Naohiko Anzai, Tochigi, Japan H. Aso, Sendai, Japan Jean Bastin, Paris, France Melvin L. Billingsley, Hershey, Pa., USA F. Boulle, Maastricht, Netherlands William Bowen, Rochester, N.Y., USA J. Breslin, Tampa, Fla., USA Keith K. Burkhart, Silver Spring, Md., USA Frederic Canini, La Tronche, France De-Liang Cao, Springfield, Ill., USA Kejiang Cao, Nanjing, China Rong Chu, Little Rock, Ark., USA George Crystal, Chicago, Ill., USA S.J. Czuczwar, Lublin, Poland Sergio De Marchi, Verona, Italy Carina Denny, Piracicaba, Brazil Le Ding, Kansas, Mo., USA Patrick D’Silva, Bangalore, India Michele Emdin, Pisa, Italy Qingfeng Fan, Philadelphia, Pa., USA J. Faridi, Stockton, Calif., USA Silvia Franchi, Milan, Italy Masanori Fujii, Kyoto, Japan M. Fujimuro, Kyoto, Japan Fenghua Fu, Yantai, China Stefano Fumagalli, Firenze, Italy Li Gan, Madison, Wis., USA Chantal Gauthier, Nantes, France Huiming Ge, Nanjing, China A. Gentilini, Firenze, Italy Lisa Giocomo, Palo Alto, Calif., USA Javier González-Maeso, New York, N.Y., USA Joseph Granchelli, Rochester, N.Y., USA Luis Granero, Valencia, Spain Xiu-Li Guo, Jinan, China E. Gussoni, Boston, Mass., USA Ki Baik Hahm, Seongnam, Korea R. Hardeland, Göttingen, Germany Noriyasu Hirasawa, Sendai, Japan Michael Holzer, Graz, Austria Martin Hönigl, Graz, Austria Lai S. Hooi, Johor Bahru, Malaysia Shigeo Horinaka, Tochigi, Japan Longshuang Huang, Chicago, Ill., USA Christian Humpel, Innsbruck, Austria Yoshimi Imura, Fujisawa, Japan N. Inagaki, Gifu, Japan Makoto Inui, Yamaguchi, Japan Keiichi Ishihara, Kyoto, Japan Yoichiro Isohama, Kumamoto, Japan Kazumi Iwata, Kyoto, Japan Yangfu Jiang, Sichuan, China Melanie S. Joy, Aurora, Colo., USA K. Kadoyama, Himeji, Japan Ira Kass, Brooklyn, N.Y., USA H. Katsuki, Kumamoto, Japan Atsufumi Kawabata, Higashiosaka, Japan Naoyuki Kawao, Osaka, Japan Zunji Ke, Shanghai, China Frieder Keller, Ulm, Germany H.R. Kim, Chungnam, Korea Yoshihisa Kitamura, Kyoto, Japan Yasuo Kizawa, Chiba, Japan T. Kobayashi, Tokyo, Japan J. Komano, Osaka, Japan Vasilios Kouloulias, Athens, Greece Toshiaki Kume, Kyoto, Japan Solene Le Douairon Lahaye, Rennes, France M-T. Lin, Tainan, Taiwan Yi-Wen Liu, Chiayi, Taiwan Zhen-Guo Liu, Columbus, Ohio, USA Pamela Lucchesi, Columbus, Ohio, USA Denisa Margina, Bucharest, Romania Xianfang Meng, Wuhan, China Francesca Menniti, Rome, Italy I. Mérida, Madrid, Spain Jing Miao, Philadelphia, Pa., USA S. Minagawa, Kyoto, Japan Keiji Miyata, Tsukuba, Japan Mizuo Miyazaki, Nagaokakyo, Japan Nobuaki Mizutani, Kobe, Japan M.J. Moshi, Dar es Salaam, Tanzania H. Motohashi, Kyoto, Japan Nariya Mukeshkumar, Jamnagar, India T. Murayama, Kanazawa, Japan H. Murota, Osaka, Japan

Within-Day Variation in Spatial Memory Deficit Induced by Scopolamine

We studied the effect of scopolamine on radial maze performance during both light and dark periods in sham and suprachiasmatic nucleus (SCN)-lesioned rats. Scopolamine dose-dependently caused a significant increase in the number of total, reference memory and working memory errors during both light and dark periods. The extent of memory deficit induced by scopolamine in the light period was significantly higher than in the dark period. The difference in the scopolamine effect between light and dark periods disappeared completely after SCN lesioning. These results clearly indicate that within-day variation in the effect of scopolamine was controlled by circadian rhythm.