title: Circadian rhythm modulates long-term potentiation induced at CA1 in rat hippocampal slices.
abstract: Circadian rhythm affects neuronal plasticity. Consistent with this, some forms of synaptic long-term potentiation (LTP) are modulated by the light/dark cycle (LD cycle). For example, this type of modulation is observed in hippocampal slices. In rodents, which are nocturnal, LTP is usually facilitated in the dark phase, but the rat hippocampal CA1 is an exception. The reason why LTP in the dark phase is suppressed in CA1 remains unknown. Previously, LTP was induced with high-frequency stimulation. In this study, we found that in the dark phase, theta-burst stimulation-induced LTP is indeed facilitated in CA1, similar to other regions in the rodent brain. Population excitatory postsynaptic potentials (pEPSP)-LTP and population spikes (PS)-LTP were recorded at CA1. The magnitude of PS-LTP in dark-phase slices was significantly larger than in light-phase slices, while that of pEPSP-LTP was unchanged. Using antidromic-orthodromic stimulation, we found that recurrent inhibition is suppressed in the dark phase. Local gabazine-application to stratum pyramidale in light-phase slices mimicked this disinhibition and facilitated LTP in dark-phase slices. These results suggest that the disinhibition of a GABAA recurrent inhibitory network can be induced in the dark phase, thereby facilitating LTP.
authors.affiliation: Department of Brain Science and Engineering, Graduate School of Life Science and Systems Engineering, Kyusyu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyusyu, Fukuoka 808-0196, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nakatsuka
authors.affiliation: Department of Brain Science and Engineering, Graduate School of Life Science and Systems Engineering, Kyusyu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyusyu, Fukuoka 808-0196, Japan; Research Center for Bio-microsensing Technology, Kyusyu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyusyu, Fukuoka 808-0196, Japan; Biomedical Informatics R&D Center, Kyusyu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyusyu, Fukuoka 808-0196, Japan. Electronic address: natume@brain.kyutech.ac.jp.
authors.forename: Kiyohisa
authors.initials: K
authors.lastname: Natsume
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001703:Biophysics; D056547:CA1 Region, Hippocampal / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D008027:Light; D008124:Locomotion / Q000502:physiology; D017774:Long-Term Potentiation / Q000502:physiology*; D008297:Male; D009434:Neural Pathways / Q000502:physiology; D011724:Pyridazines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D018756:GABA Antagonists; D011724:Pyridazines; C049853:gabazine
keywords: Disinhibition; GABA; Hippocampus; Learning and memory; Paired-pulse inhibition; Recurrent inhibitory neuron