Abstracts

Rationale: Neuronal information processing relies on the interplay between synaptic properties, dendritic intrinsic properties that amplify or suppress synaptic signals, and firing properties that produce neuronal output in the form of action potentials. Disrupting this interplay can change the input/output properties of neurons, resulting in epilepsy and other neurological deficits. Mutations in the SCN1B gene have been linked to severe epileptic encephalopathies including Dravet syndrome (DS). Scn1b knockout (KO) mice model many symptoms of DS, including spontaneous and febrile seizures, ataxia, and SUDEP. SCN1B encodes the protein β1, which regulates several ion channels, and has roles in cell adhesion, neurite outgrowth, and gene expression. The goal of this project is to quantify how the loss of β1 affects synaptic, dendritic, and somatic physiologies to gain a better understanding of how disruptions in these properties and their interactions alter cellular information processing.

Methods: We used whole-cell electrophysiology and 2-photon imaging of CA1 pyramidal cells (PCs) filled with the calcium indicator OGB-1 in acute hippocampal slices from Scn1b KO and wild-type (WT) littermates, age p15-20. We measured synaptic properties via stimulation of Schaffer collateral (SC) axons, dendritic active properties via calcium imaging of backpropagating action potential generated by somatic current injections, and somatic intrinsic properties with current steps.

Results: We found that Scn1b KO CA1 PCs exhibit larger, prolonged depolarization, and an increased occurrence of simple and complex spikes during synaptic stimulation of SC inputs. This indicates that KO PCs have enhanced synaptic input, dendritic hyperexcitability, and/or changes in intrinsic excitability that promotes firing. At the synaptic level, KO PCs exhibited smaller, more facilitating excitatory and inhibitory postsynaptic currents compared to WT, without differences in E:I ratio. We used calcium imaging to measure dendritic active properties and found that single backpropagating action potentials showed similar propagation dynamics in WT and KO PCs. However, bursts of action potentials produced larger, prolonged calcium signals in distal apical dendrites in KO neurons compared to WT. Somatic current clamp recordings revealed that KO PCs fire more action potentials in response to current injection and exhibit a subtle increase in membrane resistance, decreased capacitance, and altered sag currents.

Conclusions: We found changes in synaptic, dendritic, and somatic physiology in Scn1b KO pyramidal cells. While synaptic responses were smaller in KO PCs, hyper-responsive dendrites and soma amplified patterned synaptic input, resulting in an inflated input/output relationship and a fundamental change in cellular information processing in the hippocampus with loss of β1. Thus, understanding the mechanisms of neural dysfunction in DS requires examination not only of individual aspects of cell physiology but their interactions.

Funding: Please list any funding that was received in support of this abstract.: Current: AES Postdoctoral Fellowship to J.H.C; R01 NS112500. Previous: Dravet Syndrome Foundation Postdoctoral Fellowship to J.H.C; AES Young Investigator Award to M.A.H.