Neurophysiology, basic and clinical 1209 Bidirectional control of spike timing by GABA A receptor-mediated inhibition during theta oscillation in CA1 pyramidal neurons Jeehyun Kwag and Ole Paulsen Precisely controlled spike times relative to h-frequency network oscillations play an important role in hippocampal memory processing. Here we study how inhibitory synaptic input during h oscillation contributes to the control of spike timing. Using whole-cell patch-clamp recordings from CA1 pyramidal cells in vitro with dynamic clamp to simulate h-frequency oscillation (5 Hz), we show that c-aminobutyric acid-A (GABA A ) receptor-mediated inhibitory postsynaptic potentials (IPSPs) can not only delay but also advance the postsynaptic spike depending on the timing of the inhibition relative to the oscillation. Spike time advancement with IPSP was abolished by the h-channel blocker ZD7288 (10 lM), suggesting that IPSPs can interact with intrinsic membrane conductances to yield bidirectional control of spike timing. NeuroReport 20:1209–1213  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins. NeuroReport 2009, 20:1209–1213 Keywords: CA1 pyramidal neuron, gamma-aminobutyric acid-A receptor, hippocampus, inhibition, rat, spike timing, theta oscillation Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK Correspondence to Dr Jeehyun Kwag, DPhil, Department of Physiology, Anatomy and Genetics, University of Oxford, Sherrington Building, Parks Road, Oxford, Oxfordshire OX1 3PT, UK Tel: + 44 1865 282492; fax: + 44 1865 272469; e-mail: jeehyun.kwag@dpag.ox.ac.uk Received 30 April 2009 accepted 11 June 2009 Introduction Increasing experimental and theoretical evidence sug- gests that the precise timing of neuronal spikes during network oscillations plays an important role in cortical information processing [1]. The best studied example is phase precession of hippocampal place cells during which the timing of place cell firing relative to y- frequency (4–12 Hz) network oscillations codes for the spatial location of the animal [2–5]. It has also been shown that the relative timing of individual presynaptic and postsynaptic spikes within approximately 20 ms time windows can control the direction of hippocampal synaptic plasticity, which is known as spike timing- dependent plasticity [6–8]. Thus, the precise timing of spikes seems to be important for hippocampal function, but how the hippocampal network and individual neuronal properties support the control of spike timing during oscillations is not yet fully understood. The control of spike timing by excitatory input during y oscillations has been studied in some detail [9–11], whereas the role of inhibitory synaptic inputs in the control of spike timing is less well investigated. Hippocampal CA1 pyramidal neurons are subject to rhythmic perisomatic inhibition during y activity [12–14]. Using dynamic clamp to simulate such in-vivo- like y oscillatory inhibitory conductance, we report here that, similar to excitatory inputs, phasic g-aminobutyric acid-A (GABA A ) receptor-mediated inhibitory synaptic inputs can also bidirectionally control spike timing of hippocampal CA1 pyramidal neurons depending on the timing of the inhibition relative to the y oscillation, and we show that h-channel activation is necessary for spike time advancement. Methods Slice preparation Wistar rats (postnatal day 14–40) of both sexes were deeply anesthetized with isoflurane and decapitated, in accordance with British Home Office regulations. The brain was removed and horizontal hippocampal slices (350 mm) were prepared in ice-cold artificial cerebrospinal fluid (ACSF) containing (mM): NaCl 126, KCl 3, NaH 2 PO 4 1.25, MgSO 4 2, CaCl 2 2, NaHCO 3 24, glucose 10, pH 7.2–7.4, bubbled with carbogen gas (95% O 2 –5% CO 2 ). Hippocampal slices were maintained in ACSF in a submerged-style holding chamber for 60 min until transferred one by one to the recording chamber. Electrophysiology Whole-cell patch-pipette recordings of hippocampal CA1 pyramidal neurons were made under visual guidance by infrared differential interference contrast video micro- scopy (Axioskop; Zeiss, Jena, Germany). Patch pipettes (5–8 MO) were pulled from standard-wall borosilicate glass (outer diameter: 1.2 mm, inner diameter: 0.69 mm) using a Sutter microelectrode puller (Sutter Instruments, Novato, California, USA) and were filled with a solution containing (mM): potassium gluconate 110; hepes 40; NaCl 4; ATP-Mg 4; GTP 0.3 (pH 7.2–7.3; osmolarity 270–290 mosmol/l). Whole-cell patch-clamp recordings were made with a Multiclamp 700B amplifier (Molecular 0959-4965  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/WNR.0b013e32832f5cc7 Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.