Blockade of TRPC Channels Limits Cholinergic-Driven Hyperexcitability and Seizure Susceptibility After Traumatic Brain Injury.

Chase M Carver,Aiola P Stoja,Mark S Shapiro,Haley R Dewitt

doi:10.3389/fnins.2021.681144

Abstract

We investigated the contribution of excitatory transient receptor potential canonical (TRPC) cation channels to posttraumatic hyperexcitability in the brain 7 days following controlled cortical impact model of traumatic brain injury (TBI) to the parietal cortex in male adult mice. We investigated if TRPC1/TRPC4/TRPC5 channel expression is upregulated in excitatory neurons after TBI in contribution to epileptogenic hyperexcitability in key hippocampal and cortical circuits that have substantial cholinergic innervation. This was tested by measuring TRPC1/TRPC4/TRPC5 protein and messenger RNA (mRNA) expression, assays of cholinergic function, neuronal Ca2+ imaging in brain slices, and seizure susceptibility after TBI. We found region-specific increases in expression of TRPC1, TRPC4, and TRPC5 subunits in the hippocampus and cortex following TBI. The dentate gyrus, CA3 region, and cortex all exhibited robust upregulation of TRPC4 mRNA and protein. TBI increased cFos activity in dentate gyrus granule cells (DGGCs) and layer 5 pyramidal neurons both at the time of TBI and 7 days post-TBI. DGGCs displayed greater magnitude and duration of acetylcholine-induced rises in intracellular Ca2+ in brain slices from mice subjected to TBI. The TBI mice also exhibited greater seizure susceptibility in response to pentylenetetrazol-induced kindling. Blockade of TRPC4/TRPC5 channels with M084 reduced neuronal hyperexcitation and impeded epileptogenic progression of kindling. We observed that the time-dependent upregulation of TRPC4/TRPC5-containing channels alters cholinergic responses and activity of principal neurons acting to increase proexcitatory sensitivity. The underlying mechanism includes acutely decreased acetylcholinesterase function, resulting in greater Gq/11-coupled muscarinic receptor activation of TRPC channels. Overall, our evidence suggests that TBI-induced plasticity of TRPC channels strongly contributes to overt hyperexcitability and primes the hippocampus and cortex for seizures.

Highlights

Traumatic brain injury (TBI) accounts for 20% of symptomatic epilepsies and 5–6% of all epilepsy (Garga and Lowenstein, 2006)
cortical impact (CCI)-traumatic brain injury (TBI) induces acute cortical and hippocampal damage and deficits that accrue across the first week after TBI (Saatman et al, 2006), and we hypothesized that TBI induces upregulation of TRPC1/TRPC4/TRPC5 channel expression in the brain
We investigate the mechanism of hyperexcitatory activity in the cortex and hippocampus that contributes to posttraumatic seizure susceptibility in a mouse model of TBIinduced epileptogenesis

Summary

Introduction

Traumatic brain injury (TBI) accounts for 20% of symptomatic epilepsies and 5–6% of all epilepsy (Garga and Lowenstein, 2006). Even though the site of physical injury may be localized to the cerebral cortex, the hippocampus experiences selective neuronal loss and shows robust plasticity in neuronal properties within the first week after TBI, and this can lead to pathophysiological and chronic hyperexcitability (Golarai et al, 1992; Lowenstein et al, 1992; Smith et al, 1995; Witgen et al, 2005; Neuberger et al, 2017, 2019) Due to this important role in seizure susceptibility, the hippocampus serves as a critical structure in preventing posttraumatic seizures (PTS) from spreading throughout the brain

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