Dataset Information

Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples.

ABSTRACT: Sharp wave-associated ?200-Hz ripple oscillations in the hippocampus have been implicated in the consolidation of memories. However, knowledge on mechanisms underlying ripples is still scarce, in particular with respect to synaptic involvement of specific cell types. Here, we used cell-attached and whole-cell recordings in vitro to study activity of pyramidal cells and oriens-lacunosum-moleculare (O-LM) interneurons during ripples. O-LM cells received ripple-associated synaptic input that arrived delayed (3.3 ± 0.3 ms) with respect to the maximum amplitude of field ripples and was locked to the ascending phase of field oscillations (mean phase: 209 ± 6°). In line, O-LM cells episodically discharged late during ripples (?6.5 ms after the ripple maximum), and firing was phase-locked to field oscillations (mean phase: 219 ± 9°). Our data unveil recruitment of O-LM neurons during ripples, suggesting a previously uncharacterized role of this cell type during sharp wave-associated activity.

SUBMITTER: Pangalos M

PROVIDER: S-EPMC3600450 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples.

Pangalos Maria M Donoso José R JR Winterer Jochen J Zivkovic Aleksandar R AR Kempter Richard R Maier Nikolaus N Schmitz Dietmar D

Proceedings of the National Academy of Sciences of the United States of America 20130225 11

Sharp wave-associated ∼200-Hz ripple oscillations in the hippocampus have been implicated in the consolidation of memories. However, knowledge on mechanisms underlying ripples is still scarce, in particular with respect to synaptic involvement of specific cell types. Here, we used cell-attached and whole-cell recordings in vitro to study activity of pyramidal cells and oriens-lacunosum-moleculare (O-LM) interneurons during ripples. O-LM cells received ripple-associated synaptic input that arrive ...[more]

PMID: 23440221

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Project description:The O-LM cell type mediates feedback inhibition onto hippocampal pyramidal cells and gates information flow in the CA1. Its functions depend on the presence of voltage-gated channels (VGCs), which affect its integrative properties and response to synaptic input. Given the challenges associated with determining densities and distributions of VGCs on interneuron dendrites, we take advantage of computational modeling to consider different possibilities. In this work, we focus on hyperpolarization-activated channels (h-channels) in O-LM cells. While h-channels are known to be present in O-LM cells, it is unknown whether they are present on their dendrites. In previous work, we used ensemble modeling techniques with experimental data to obtain insights into potentially important conductance balances. We found that the best O-LM models that included uniformly distributed h-channels in the dendrites could not fully capture the "sag" response. This led us to examine activation kinetics and non-uniform distributions of h-channels in the present work. In tuning our models, we found that different kinetics and non-uniform distributions could better reproduce experimental O-LM cell responses. In contrast to CA1 pyramidal cells where higher conductance densities of h-channels occur in more distal dendrites, decreasing conductance densities of h-channels away from the soma were observed in O-LM models. Via an illustrative scenario, we showed that having dendritic h-channels clearly speeds up back-propagating action potentials in O-LM cells, unlike when h-channels are present only in the soma. Although the present results were morphology-dependent, our work shows that it should be possible to determine the distributions and characteristics of O-LM cells with recordings and morphologies from the same cell. We hypothesize that h-channels are distributed in O-LM cell dendrites and endow them with particular synaptic integration properties that shape information flow in hippocampus.

Project description:Hippocampal theta is a 4-12 Hz rhythm associated with episodic memory, and although it has been studied extensively, the cellular mechanisms underlying its generation are unclear. The complex interactions between different interneuron types, such as those between oriens-lacunosum-moleculare (OLM) interneurons and bistratified cells (BiCs), make their contribution to network rhythms difficult to determine experimentally. We created network models that are tied to experimental work at both cellular and network levels to explore how these interneuron interactions affect the power of local oscillations. Our cellular models were constrained with properties from patch clamp recordings in the CA1 region of an intact hippocampus preparation in vitro. Our network models are composed of three different types of interneurons: parvalbumin-positive (PV+) basket and axo-axonic cells (BC/AACs), PV+ BiCs, and somatostatin-positive OLM cells. Also included is a spatially extended pyramidal cell model to allow for a simplified local field potential representation, as well as experimentally-constrained, theta frequency synaptic inputs to the interneurons. The network size, connectivity, and synaptic properties were constrained with experimental data. To determine how the interactions between OLM cells and BiCs could affect local theta power, we explored how the number of OLM-BiC connections and connection strength affected local theta power. We found that our models operate in regimes that could be distinguished by whether OLM cells minimally or strongly affected the power of network theta oscillations due to balances that, respectively, allow compensatory effects or not. Inactivation of OLM cells could result in no change or even an increase in theta power. We predict that the dis-inhibitory effect of OLM cells to BiCs to pyramidal cell interactions plays a critical role in the resulting power of network theta oscillations. Overall, our network models reveal a dynamic interplay between different classes of interneurons in influencing local theta power.

Project description:Multi-compartmental models of neurons provide insight into the complex, integrative properties of dendrites. Because it is not feasible to experimentally determine the exact density and kinetics of each channel type in every neuronal compartment, an essential goal in developing models is to help characterize these properties. To address biological variability inherent in a given neuronal type, there has been a shift away from using hand-tuned models towards using ensembles or populations of models. In collectively capturing a neuron's output, ensemble modeling approaches uncover important conductance balances that control neuronal dynamics. However, conductances are never entirely known for a given neuron class in terms of its types, densities, kinetics and distributions. Thus, any multi-compartment model will always be incomplete. In this work, our main goal is to use ensemble modeling as an investigative tool of a neuron's biophysical balances, where the cycling between experiment and model is a design criterion from the start. We consider oriens-lacunosum/moleculare (O-LM) interneurons, a prominent interneuron subtype that plays an essential gating role of information flow in hippocampus. O-LM cells express the hyperpolarization-activated current (Ih). Although dendritic Ih could have a major influence on the integrative properties of O-LM cells, the compartmental distribution of Ih on O-LM dendrites is not known. Using a high-performance computing cluster, we generated a database of models that included those with or without dendritic Ih. A range of conductance values for nine different conductance types were used, and different morphologies explored. Models were quantified and ranked based on minimal error compared to a dataset of O-LM cell electrophysiological properties. Co-regulatory balances between conductances were revealed, two of which were dependent on the presence of dendritic Ih. These findings inform future experiments that differentiate between somatic and dendritic Ih, thereby continuing a cycle between model and experiment.

Dataset Information

Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples.

Publications

Recruitment of oriens-lacunosum-moleculare interneurons during hippocampal ripples.

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