TY - JOUR T1 - Spike Resonance Properties in Hippocampal O-LM Cells Are Dependent on Refractory Dynamics JF - The Journal of Neuroscience JO - J. Neurosci. SP - 3637 LP - 3651 DO - 10.1523/JNEUROSCI.1361-11.2012 VL - 32 IS - 11 AU - Tilman J. Kispersky AU - Fernando R. Fernandez AU - Michael N. Economo AU - John A. White Y1 - 2012/03/14 UR - http://www.jneurosci.org/content/32/11/3637.abstract N2 - During a wide variety of behaviors, hippocampal field potentials show significant power in the theta (4–12 Hz) frequency range and individual neurons commonly phase-lock with the 4–12 Hz field potential. The underlying cellular and network mechanisms that generate the theta rhythm, however, are poorly understood. Oriens-lacunosum moleculare (O-LM) interneurons have been implicated as crucial contributors to generating theta in local hippocampal circuits because of their unique axonal projections, slow synaptic kinetics and the fact that spikes are phase-locked to theta field potentials in vivo. We performed experiments in brain slice preparations from Long–Evans rats to investigate the ability of O-LM cells to generate phase-locked spike output in response to artificial synaptic inputs. We find that O-LM cells do not respond with any preference in spike output at theta frequencies when injected with broadband artificial synaptic inputs. However, when presented with frequency-modulated inputs, O-LM spike output shows the ability to phase-lock well to theta-modulated inputs, despite their strong low-pass profiles of subthreshold membrane impedance. This result was dependent on spike refractory dynamics and could be controlled by real-time manipulation of the postspike afterhyperpolarization. Finally, we show that the ability of O-LM cells to phase-lock well to theta-rich inputs is independent of the h-current, a membrane mechanism often implicated in the generation of theta frequency activity. ER -