Adaptive Mechanisms of Somatostatin-Positive Interneurons after Traumatic Brain Injury through a Switch of α Subunits in L-Type Voltage-Gated Calcium Channels

Abstract

Unilateral traumatic brain injury (TBI) causes cortical dysfunctions spreading to the primarily undamaged hemisphere. This phenomenon, called transhemispheric diaschisis, is mediated by an imbalance of glutamatergic versus GABAergic neurotransmission. This study investigated the role of GABAergic, somatostatin-positive (SST) interneurons in the contralateral hemisphere 72 h after unilateral TBI. The brain injury was induced to the primary motor/somatosensory cortex of glutamate decarboxylase 67–green fluorescent protein (GAD67-GFP) knock-in mice at postnatal days 19–21 under anesthesia in vivo. Single GFP+ interneurons of the undamaged, contralateral cortex were isolated by fluorescence-activated cell sorting and analyzed by mass spectrometry. TBI caused a switch of 2 α subunits of pore-forming L-type voltage-gated calcium channels (VGCC) in GABAergic interneurons, an increased expression of CaV1.3, and simultaneous ablation of CaV1.2. This switch was associated with 1) increased excitability of single SST interneurons in patch-clamp recordings and (2) a recovery from early network hyperactivity in the contralateral hemisphere in microelectrode array recordings of acute slices. The electrophysiological changes were sensitive to pharmacological blockade of CaV1.3 (isradipine, 100 nM). These data identify a switch of 2 α subunits of VGCCs in SST interneurons early after TBI as a mechanism to counterbalance post-traumatic hyperexcitability.

GABAA Receptor-Stabilizing Protein Ubqln1 Affects Hyperexcitability and Epileptogenesis after Traumatic Brain Injury and in a Model of In Vitro Epilepsy in Mice

“…Cortices from the contralateral hemisphere of TBI-treated ( n = 6) and sham-treated ( n = 6) GAD67-GFP mice were isolated 24 h post-TBI ( Figure 1 A) to generate a single-cell suspension. GAD67-GFP positive interneurons and a GFP population of cells were isolated from the single-cell suspension using FACS, as described in [ 30 ]. We isolated a total of 56681 +/− 7278 GFP+ interneurons from the contralateral cortices of sham-treated animals and 46388 +/− 8901 GFP+ interneurons from TBI-treated animals ( Figure 1 B.i.).…”

“…Proteins of sorted cells were extracted and digested as described before in [ 30 ]. Here, the optimized single-pot solid-phase-enhanced sample preparation (SP3) protocol was used [ 64 ].…”

Modified mouse model of repeated mild traumatic brain injury through a thinned‐skull window and fluid percussion

“…Post‐traumatic cell loss is the major cause of TBI‐associated neurological deficits and mortality (Guo & Ma, 2021). More recently, it was found that targeting 2α subunits of pore‐forming L‐type voltage‐gated Ca 2+ channels (VGCCs) of interneurons may help to counterbalance hyperexcitability post‐mTBI (Ihbe et al, 2021). Meanwhile, blockade of Ca 2+ ‐permeable AMPA receptors (AMPARs) function was also found critical to reduce the secondary damage following mild in vitro mechanical injury in cortical neurons by maintaining the neural circuit dynamics (Goforth et al, 2011; Spaethling et al, 2012).…”

Tonic activation of GABAB receptors via GAT-3 mediated GABA release reduces network activity in the developing somatosensory cortex in GAD67-GFP mice

“…However, we have previously observed an impaired GABAergic signaling in the contralateral cortical hemisphere in adolescent mice early after traumatic brain injury (TBI), resulting in a shift of the cortical E/I ratio toward excitation ( Le Prieult et al, 2017 ). Such a trauma-induced E/I- imbalance was linked to the development of post traumatic epilepsy ( Pavlov et al, 2011 ; Le Prieult et al, 2017 ; Dulla and Pitkanen, 2021 ; Ihbe et al, 2022 ). However, we found that expression of a presynaptic voltage-gated calcium channel (CaV1.3) in somatostatin-positive interneurons counterbalances the early impaired GABAergic inhibition and hyperactivity on the cortical network after TBI ( Ihbe et al, 2022 ).…”

“…Such a trauma-induced E/I- imbalance was linked to the development of post traumatic epilepsy ( Pavlov et al, 2011 ; Le Prieult et al, 2017 ; Dulla and Pitkanen, 2021 ; Ihbe et al, 2022 ). However, we found that expression of a presynaptic voltage-gated calcium channel (CaV1.3) in somatostatin-positive interneurons counterbalances the early impaired GABAergic inhibition and hyperactivity on the cortical network after TBI ( Ihbe et al, 2022 ). In search for compensatory mechanisms, which can rebalance the E/I ratio in the cortex, the present study made use of the GAD67-GFP knock-in mouse line (KI), a well-established mouse model to study GABAergic interneurons in living tissues ( Tamamaki et al, 2003 ).…”