Abstracts

Rationale: Many neurological diseases present with comorbid gastrointestinal (GI) abnormalities, suggesting parallel altered functionality of the central nervous system (CNS) and enteric nervous system (ENS). A potential mechanistic link between CNS and GI disorders is aberrant function of voltage-gated sodium channel (VGSC) a and β subunits, which are expressed in the CNS and ENS. VGSCs control the generation and propagation of action potentials in neurons and therefore play a critical role in determining neuronal signaling. VGSC β1/β1B subunits, encoded by SCN1B, modulate ion channel expression, trafficking, gating, and voltage-dependence. VGSC gene variants are linked to developmental and epileptic encephalopathies (DEEs) and GI motility disorders. Additionally, DEE patients with VGSC gene variants often exhibit chronic constipation – suggesting a connection between VGSCs and colonic motility. A subset of these DEE patients has homozygous loss-of-function variants in SCN1B. In addition to aberrations in neuronal firing within the CNS, multiple physicians report SCN1B-linked DEE patients presenting with GI symptomology such as constipation. The objective of this work is to understand how β1/β1B subunits contribute to GI function using a Scn1b-null mouse model (Scn1b^-/-). We hypothesize that β1/β1B subunits regulate excitability in colonic myenteric neurons via transcriptional regulation of voltage-gated ion channel expression. Successful completion of this work will provide novel insights that may lead to new therapeutics for the treatment of DEE patients with co-morbid neurological and GI symptomology.

Methods: Male and female postnatal-day (P) 13-17 Scn1b^-/- mice and age-matched wild-type (WT) mice were used for all observations and experiments. Distal colon was dissected and prepared for immunostaining, qPCR, electrophysiological recordings, or motility experiments.

Results: Our data show Scn1b^-/- mice exhibit a reduction in ad libitum defecation events in spite of increased feeding behavior (N= 3-6, P< 0.05. We also observe reduced colonic motility in the Scn1b^-/- mice, as measured by as measured by the time to expel a bead inserted into distal colon (N= 3, P< 0.01). Scn1b^-/- mice have no difference in total myenteric neuron counts, proportions of excitatory or inhibitory neurons, or average neuron size compared to WTs (N= 9-10). Preliminary electrophysiological data suggest altered inhibitory neuronal signaling in Scn1b^-/- colon (N= 4-8, P= 0.07), and preliminary qPCR data suggest differential expression of a gene encoding a voltage-gated calcium channel that controls inhibitory neurotransmitter release as well as multiple VGSC-encoding genes. Functional experiments to compare ex vivo motility patterns in Scn1b^-/- versus WT colons are ongoing.

Conclusions: Our data suggest Scn1b^-/- mice manifest with colonic dysmotility, which is not due to a developmental defect in enteric neuronal migration or development but rather due to potential changes in neuronal function driven by changes in voltage-gated ion channel expression.

Funding: Please list any funding that was received in support of this abstract.: NIH T32-GM008322 and F31-NS120942 to VCB; T32-DA7268 to APM; P30-AR069620; R37-NS076752 to LLI.