title: Spike resonance properties in hippocampal O-LM cells are dependent on refractory dynamics.
abstract: 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.
authors.affiliation: Program in Neuroscience and Department of Biomedical Engineering, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: Tilman J
authors.initials: TJ
authors.lastname: Kispersky
authors.forename: Fernando R
authors.initials: FR
authors.lastname: Fernandez
authors.forename: Michael N
authors.initials: MN
authors.lastname: Economo
authors.forename: John A
authors.initials: JA
authors.lastname: White
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D056547:CA1 Region, Hippocampal / Q000166:cytology / Q000502:physiology*; D005260:Female; D007395:Interneurons / Q000502:physiology*; D008297:Male; D009924:Organ Culture Techniques; D051381:Rats; D020318:Rats, Long-Evans; D012032:Refractory Period, Electrophysiological / Q000502:physiology*