Functional and Molecular Analysis of Proprioceptive Sensory Neuron Excitability in Mice

Biophysical essentials - A full stack open-source software framework for conserved and advanced analysis of patch-clamp recordings

BACKGROUND AND OBJECTIVES

Patch-Clamp recordings allow for in depth electrophysiological characterization of single cells, their general biophysical properties as well as characteristics of voltage- and ligand-gated ionic currents. Different acquisition modes, such as whole-cell patch-clamp recordings in the current or voltage clamp configuration, capacitance measurements or single channel recordings from cultured cells as well as acute brain slices are routinely performed for these purposes. Nevertheless, multipurpose transparent and adaptable software tools to perform reproducible state-of-the-art analysis of multiple experiment types and to manage larger sets of experimental data are currently unavailable.

METHODS

Biophysical Essentials (BPE) was developed as an open-source full stack python software for transparent and reproducible analysis of electrophysiological recordings. For validation, BPE results were compared with manually analyzed single-cell patch-clamp data acquired from a human in vitro nociceptor-model and mouse dorsal root ganglia neurons.

RESULTS

While initially designed to improve time consuming and repetitive analysis steps, BPE was further optimized as a technical software solution for entire workflow processing including data acquisition, data preprocessing, normalization and visualization and of single recordings up to stacked calculations and statistics of multiple experiments. BPE can operate with different file formats from different amplifier systems and producers. An in-process database logs all analysis steps reproducible review and serves as a central storage point for recordings. Statistical testing as well as advanced analysis functions like Boltzmann-fitting and dimensional reduction methods further support the researchers' needs in projects involving electrophysiology techniques.

CONCLUSIONS

BPE extends beyond available patch-clamp specific, open source - and commercial analysis tools in particular because of reproducible and sharable analysis workflows. BPE enables full analysis from raw data acquisition to publication ready result visualizations - all within one single program. Thereby, BPE significantly enhances transparency in the analytical process of patch-clamp data analysis. BPEs function scope is completely accessible through an easy-to-use graphical user interface eliminating the need for programing language proficiency as required by many community patch-clamp analysis frameworks and algorithms.

Whole body vibration training promotes proprioceptive pathway for the treatment of stress urinary incontinence in rats

Background

Stress urinary incontinence (SUI) is the most ubiquitous form of urinary incontinence in women. The therapeutic management of patients with SUI is challenging. The aim of this study is to evaluate the efficacy of whole body vibration training (WBVT) for SUI.

Methods

Thirty-five female rats were randomly divided into a sham group (Sham group, n=5), SUI + WBVT group (n=15) and SUI + whole body rest group (SUI + WBR group, n=15). The SUI + WBVT group was trained as follows: frequency 30 Hz, amplitude four mm, one min/repeat, four min rest, repeated 10 times, five days/week. After the intervention, five rats were taken on the 7th, 14th and 21st day to observe the urodynamic changes, levator ani muscle and dorsal root ganglia (DRG) morphology, and to observe the expression of neurotrophic factor-3/tyrosine protein kinase C (NT-3/TrkC) by Western blot.

Results

The urodynamic results showed that the difference in bladder leak point pressure/abdominal leak point pressure (BLPP/ALPP) between the Sham group and the SUI + WBR group was statistically significant (P<0.001) on 7th day, indicating successful modeling. The BLPP/ALPP of the SUI + WBVT group and the SUI + WBR group improved on 7th, 14th, and 21st day, and the BLPP/ALPP of SUI + WBVT group was higher than the SUI + WBR group. Compared with the Sham group, pathological changes appeared in the muscle shuttles in the SUI + WBVT group and SUI + WBR group. Western blot showed a gradual up-regulation of NT-3/TrkC.

Conclusions

WBVT can be used to treat SUI by affecting the expression of NT-3/TrkC, improving the structural morphology of the proprioceptors, and restoring the urinary control function. This study provides evidence for the clinical practice of WBVT. Future studies could further refine the behavioral and electrophysiological aspects of the assessment.

YTHDF1-mediated sphingosine kinase 2 upregulation alleviates bupivacaine-induced neurotoxicity via the PI3K/AKT axis

BACKGROUND

Bupivacaine (BUP), a long-acting local anesthetic, has been widely used in analgesia and anesthesia. However, evidence strongly suggests that excessive application of BUP may lead to neurotoxicity in neurons. Sphingosine kinase 2 (SPHK2) has been reported to exert neuroprotective effects. In this study, we intended to investigate the potential role and mechanism of SPHK2 in BUP-induced neurotoxicity in dorsal root ganglion (DRG) neurons.

METHODS

DRG neurons were cultured with BUP to simulate BUP-induced neurotoxicity in vitro. CCK-8, LDH, and flow cytometry assays were performed to detect the viability, LDH activity, and apoptosis of DRG neurons. RT-qPCR and western blotting was applied to measure gene and protein expression. Levels. MeRIP-qPCR was applied for quantification of m6A modification. RIP-qPCR was used to analyze the interaction between SPHK2 and YTHDF1.

RESULTS

SPHK2 expression significantly declined in DRG neurons upon exposure to BUP. BUP challenge substantially reduced the cell viability and increased the apoptosis rate in DRG neurons, which was partly abolished by SPHK2 upregulation. YTHDF1, an N6-methyladenosine (m6A) reader, promoted SPHK2 expression in BUP-treated DRG neurons in an m6A-dependent manner. YTHDF1 knockdown partly eliminated the increase in SPHK2 protein level and the protection against BUP-triggered neurotoxicity in DRG neurons mediated by SPHK2 overexpression. Moreover, SPHK2 activated the PI3K/AKT signaling to protect against BUP-induced cytotoxic effects on DRG neurons.

CONCLUSIONS

In sum, YTHDF1-mediated SPHK2 upregulation ameliorated BUP-induced neurotoxicity in DRG neurons via promoting activation of the PI3K/AKT signaling pathway.

T12-L3 Nerve Transfer-Induced Locomotor Recovery in Rats with Thoracolumbar Contusion: Essential Roles of Sensory Input Rerouting and Central Neuroplasticity

Locomotor recovery after spinal cord injury (SCI) remains an unmet challenge. Nerve transfer (NT), the connection of a functional/expendable peripheral nerve to a paralyzed nerve root, has long been clinically applied, aiming to restore motor control. However, outcomes have been inconsistent, suggesting that NT-induced neurological reinstatement may require activation of mechanisms beyond motor axon reinnervation (our hypothesis). We previously reported that to enhance rat locomotion following T13-L1 hemisection, T12-L3 NT must be performed within timeframes optimal for sensory nerve regrowth. Here, T12-L3 NT was performed for adult female rats with subacute (7-9 days) or chronic (8 weeks) mild (SCImi: 10 g × 12.5 mm) or moderate (SCImo: 10 g × 25 mm) T13-L1 thoracolumbar contusion. For chronic injuries, T11-12 implantation of adult hMSCs (1-week before NT), post-NT intramuscular delivery of FGF2, and environmentally enriched/enlarged (EEE) housing were provided. NT, not control procedures, qualitatively improved locomotion in both SCImi groups and animals with subacute SCImo. However, delayed NT did not produce neurological scale upgrading conversion for SCImo rats. Ablation of the T12 ventral/motor or dorsal/sensory root determined that the T12-L3 sensory input played a key role in hindlimb reanimation. Pharmacological, electrophysiological, and trans-synaptic tracing assays revealed that NT strengthened integrity of the propriospinal network, serotonergic neuromodulation, and the neuromuscular junction. Besides key outcomes of thoracolumbar contusion modeling, the data provides the first evidence that mixed NT-induced locomotor efficacy may rely pivotally on sensory rerouting and pro-repair neuroplasticity to reactivate neurocircuits/central pattern generators. The finding describes a novel neurobiology mechanism underlying NT, which can be targeted for development of innovative neurotization therapies.

Sensory innervation of the lumbar 5/6 intervertebral disk in mice

Introduction

Over the years, most back pain-related biological studies focused on the pathogenesis of disk degeneration. It is known that nerve distributions at the outer layer of the annulus fibrosus (AF) may be an important contributor to back pain symptoms. However, the types and origins of sensory nerve terminals in the mouse lumbar disks have not been widely studied. Using disk microinjection and nerve retrograde tracing methods, the current study aimed to characterize the nerve types and neuropathway of the lumbar 5/6 (L5/6) disk in mice.

Methods

Using an anterior peritoneal approach, the L5/6 disk of adult C57BL/6 mice (males, 8–12 weeks) disk microinjection was performed. Fluorogold (FG) was injected into the L5/6 disk using the Hamilton syringe with a homemade glass needle driven by a pressure microinjector. The lumbar spine and bilateral thoracic 13 (Th13) to L6 DRGs were harvested at 10 days after injection. The number of FG+ neurons among different levels was counted and analyzed. Different nerve markers, including anti-neurofilament 160/200 (NF160/200), anti-calcitonin gene-related peptide (CGRP), anti-parvalbumin (PV), and anti-tyrosine hydroxylase (TH), were used to identify different types of nerve terminals in AF and their origins in DRG neurons.

Results

There were at least three types of nerve terminals at the outer layer of L5/6 AF in mice, including NF160/200+ (indicating Aβ fibers), CGRP+ (Aδ and C fibers), and PV+ (proprioceptive fibers). No TH+ fibers (sympathetic nerve fibers and some C-low threshold mechanoreceptors) were noticed in either. Using retrograde tracing methods, we found that nerve terminals in the L5/6 disk were multi-segmentally from Th13-L6 DRGs, with L1 and L5 predominately. An immunofluorescence analysis revealed that FG+ neurons in DRGs were co-localized with NF160/200, CGRP, and PV, but not TH.

Conclusion

Intervertebral disks were innervated by multiple types of nerve fibers in mice, including Aβ, Aδ, C, and proprioceptive fibers. No sympathetic nerve fibers were found in AF. The nerve network of the L5/6 disk in mice was multi-segmentally innervated by the Th13-L6 DRGs (mainly L1 and L5 DRGs). Our results may serve as a reference for preclinical studies of discogenic pain in mice.

Transcriptional Alterations of Mouse Trigeminal Ganglion Neurons Following Orofacial Inflammation Revealed by Single-Cell Analysis

Orofacial inflammation leads to transcriptional alterations in trigeminal ganglion (TG) neurons. However, diverse alterations and regulatory mechanisms following orofacial inflammatory pain in different types of TG neurons remain unclear. Here, orofacial inflammation was induced by injection of complete Freund’s adjuvant (CFA) in mice. After 7 days, we performed single-cell RNA-sequencing on TG cells of mice from control and treatment groups. We identified primary sensory neurons, Schwann cells, satellite glial cells, oligodendrocyte-like cells, immune cells, fibroblasts, and endothelial cells in TG tissue. After principal component analysis and hierarchical clustering, we identified six TG neuronal subpopulations: peptidergic nociceptors (PEP1 and PEP2), non-peptidergic nociceptors (NP1 and NP2), C-fiber low-threshold mechanoreceptors (cLTMR) and myelinated neurons (Nefh-positive neurons, NF) based on annotated marker gene expression. We also performed differential gene expression analysis among TG neuronal subtypes, identifying several differential genes involved in the inflammatory response, neuronal excitability, neuroprotection, and metabolic processes. Notably, we identified several potential novel targets associated with pain modulation, including Arl6ip1, Gsk3b, Scn7a, and Zbtb20 in PEP1, Rgs7bp in PEP2, and Bhlha9 in cLTMR. The established protein–protein interaction network identified some hub genes, implying their critical involvement in regulating orofacial inflammatory pain. Our study revealed the heterogeneity of TG neurons and their diverse neuronal transcriptomic responses to orofacial inflammation, providing a basis for the development of therapeutic strategies for orofacial inflammatory pain.

Calcium homeostasis in parvalbumin DRG neurons is altered after sciatic nerve crush and sciatic nerve transection injuries

Reflex abnormalities mediated by proprioceptive sensory neurons after peripheral nerve injury (PNI) can limit functional improvement, leaving patients with disability that affects their quality of life. We examined postinjury calcium transients in a subpopulation of dorsal root ganglion (DRG) neurons consisting primarily of proprioceptors to determine whether alterations in calcium homeostasis are present in proprioceptors, as has been documented in other DRG neurons after PNI. Using transgenic mice, we restricted expression of the calcium indicator GCaMP6s to DRG neurons containing parvalbumin (PV). Mice of both sexes were randomly assigned to sham, sciatic nerve crush, or sciatic nerve transection and resuture conditions. Calcium transients were recorded from ex vivo preparations of animals at one of three postsurgery time points: 1-3 days, 7-11 days, and after 60 days of recovery. Results demonstrated that the post-PNI calcium transients of PV DRG neurons are significantly different than sham. Abnormalities were not present during the acute response to injury (1-3 days), but transients were significantly different than sham at the recovery stage where axon regeneration is thought to be underway (7-11 days). During late-stage recovery (60 days postinjury), disturbances in the decay time course of calcium transients in transection animals persisted, whereas parameters of transients from crush animals returned to normal. These findings identify a deficit in calcium homeostasis in proprioceptive neurons, which may contribute to the failure to fully recover proprioceptive reflexes after PNI. Significant differences in the calcium transients of crush versus transection animals after reinnervation illustrate calcium homeostasis alterations are distinctive to injury type.NEW & NOTEWORTHY This study examines calcium homeostasis after peripheral nerve injury in dorsal root ganglion (DRG) neurons expressing parvalbumin, a group of large-diameter afferents primarily consisting of proprioceptors, using two-photon calcium imaging in the intact DRG. Our findings identify aberrant calcium homeostasis as an additional source of sensory neuron dysfunction following peripheral nerve injury, uncover differences between two injury models, and track how these changes develop and resolve over the course of recovery.

Improving NKCC1 Function Increases the Excitability of DRG Neurons Exacerbating Pain Induced After TRPV1 Activation of Primary Sensory Neurons

Background Our aim was to investigate the effects of the protein expression and the function of sodium, potassium, and chloride co-transporter (NKCC1) in the dorsal root ganglion (DRG) after activation of transient receptor potential vanilloid 1 receptor (TRPV1) in capsaicin-induced acute inflammatory pain and the possible mechanism of action.

Methods Male Sprague–Dawley rats were randomly divided into control, capsaicin, and inhibitor groups. The expression and distribution of TRPV1 and NKCC1 in rat DRG were observed by immunofluorescence. Thermal radiation and acetone test were used to detect the pain threshold of heat and cold noxious stimulation in each group. The expressions of NKCC1 mRNA, NKCC1 protein, and p-NKCC1 in the DRG were detected by PCR and western blotting (WB). Patch clamp and chloride fluorescent probe were used to observe the changes of GABA activation current and intracellular chloride concentration. After intrathecal injection of protein kinase C (PKC) inhibitor (GF109203X) or MEK/extracellular signal-regulated kinase (ERK) inhibitor (U0126), the behavioral changes and the expression of NKCC1 and p-ERK protein in L_4–6 DRG were observed.

Result: TRPV1 and NKCC1 were co-expressed in the DRG. Compared with the control group, the immunofluorescence intensity of NKCC1 and p-NKCC1 in the capsaicin group was significantly higher, and the expression of NKCC1 in the nuclear membrane was significantly higher than that in the control group. The expression of NKCC1 mRNA and protein of NKCC1 and p-NKCC1 in the capsaicin group were higher than those in the control group. After capsaicin injection, GF109203X inhibited the protein expression of NKCC1 and p-ERK, while U0126 inhibited the protein expression of NKCC1. In the capsaicin group, paw withdrawal thermal latency (WTL) was decreased, while cold withdrawal latency (CWL) was prolonged. Bumetanide, GF109203X, or U0126 could reverse the effect. GABA activation current significantly increased in the DRG cells of the capsaicin group, which could be reversed by bumetanide. The concentration of chloride in the DRG cells of the capsaicin group increased, but decreased after bumetanide, GF109203X, and U0126 were administered.

Conclusion Activation of TRPV1 by exogenous agonists can increase the expression and function of NKCC1 protein in DRG, which is mediated by activation of PKC/p-ERK signaling pathway. These results suggest that DRG NKCC1 may participate in the inflammatory pain induced by TRPV1.