Differential Regulation of the Glucocorticoid Receptor in a Rat Model of Inflammatory Pain

mRNA Expression of Mineralocorticoid and Glucocorticoid Receptors in Human and Mouse Sensory Neurons of the Dorsal Root Ganglia

BACKGROUND

Corticosteroid receptors, including mineralocorticoid receptor (MR) and glucocorticoid receptor (GR), play important roles in inflammatory pain in the dorsal root ganglion (DRG). Although it is widely known that activating the GR reduces inflammatory pain, it has recently been shown that MR activation contributes to pain and neuronal excitability in rodent studies. Moreover, little is known about the translation of this work to humans, or the mechanisms through which corticosteroid receptors regulate inflammatory pain.

METHODS

Corticosteroid receptor expression in human and mouse DRGs was characterized. RNAscope was used to perform high-resolution in situ hybridization for GR and MR mRNAs and to examine their colocalization with markers for nociceptors ( SCN10A , Na V 1.8 mRNA) and Aβ mechanoreceptors ( KCNS1 , Kv9.1 mRNA) in human DRG and C57BL/6J mouse DRG samples.

RESULTS

GR and MR mRNAs are expressed in almost all DRG neurons across species. The 2 receptors colocalize in 99.2% of human DRG neurons and 95.9% of mouse DRG neurons ( P = .0004, Fisher exact test). In both human and mouse DRGs, the large-diameter KCNS1+ Aβ mechanoreceptors showed a significantly higher MR/GR ratio (MR-leaning) compared to KCNS1- neurons (human: 0.23 vs 0.04, P = .0002; mouse: 0.35 vs -0.24, P < .0001; log ratios, unpaired t test), whereas small-diameter SCN10A+ nociceptive neurons showed a significantly lower MR/GR ratio (GR-leaning) compared to SCN10A- neurons (human: -0.02 vs 0.18, P = .0001; mouse: -0.16 vs 0.08, P < .0001; log ratios, unpaired t test).

CONCLUSIONS

These findings indicate that mouse corticosteroid receptor mRNA expression reflects human expression in the DRG, and that mice could be a suitable model for studying corticosteroid receptor involvement in pain. Additionally, this study supports the translatability of rodent data to humans for the use of more selective corticosteroids at the DRG in pain treatments.

Early life stress modulates neonatal somatosensation and the transcriptional profile of immature sensory neurons

ABSTRACT

Early life stress (ELS) is associated with an increased risk of experiencing chronic pain during adulthood, but surprisingly little is known about the short-term influence of ELS on nociceptive processing in the immature nervous system and the concomitant effects on somatosensation in the neonate. Here, we investigate how ELS modulates pain in neonatal mice and the transcriptional and electrophysiological signatures of immature dorsal root ganglia (DRG). Shortly after the administration of a neonatal limiting bedding (NLB) paradigm from postnatal days (P)2 to P9, both male and female pups exhibited robust hypersensitivity in response to tactile, pressure, and noxious cold stimuli compared with a control group housed under standard conditions, with no change in their sensitivity to noxious heat. Bulk RNA-seq analysis of L3-L5 DRGs at P9 revealed significant alterations in the transcription of pain- and itch-related genes following ELS, highlighted by a marked downregulation in Sst , Nppb , Chrna6 , Trpa1 , and Il31ra . Nonetheless, ex vivo whole-cell patch-clamp recordings from putative A- and C-fiber sensory neurons in the neonatal DRG found no significant changes in their intrinsic membrane excitability following NLB. Overall, these findings suggest that ELS triggers hyperalgesia in neonates across multiple pain modalities that is accompanied by transcriptional plasticity within developing sensory neurons. A better understanding of the mechanisms governing the interactions between chronic stress and pain during the neonatal period could inform the future development of novel interventional strategies to relieve pain in infants and children who have experienced trauma.

Glucose attenuates the long-term adverse neurodevelopment effect of neonate pain stimulus via CRF/GR in rats

BACKGROUND

Neonates undergo numerous painful procedures throughout their hospitalization. Repeated procedural pain may cause adverse long-term effects. Glucose as a non-pharmacological analgesia, is used for neonate pain management. In this study, potential mechanism of attenuate pain induced by glucose in neurodevelopment effect of neonate pain stimulus was investigated.

METHODS

Neonatal rats to perform a repetitive injury model and glucose intervention model in the postnatal day 0-7(P0-7). Pain thresholds were measured by von Frey test weekly. The puberty behavioral outcome, tissue loss and protein expression in hippocampus were analyzed.

RESULTS

Oral administration of glucose after repeated pain stimulation can maintain the hippocampal structure in, and reduce the expressions of corticotropin releasing factor (CFR) and glucocorticoid receptor (GR), therefore, resulted in long-term threshold of pain and cognitive improvement.

CONCLUSION

Exposure to neonatal repeated procedural pain causes persistent mechanical hypersensitivity and the dysfunction of spatial memory retention at puberty. In addition, glucose can relieve these adverse effects, possibly via decreasing CRF/GR levels to change the hypothalamus-pituitary-adrenal (HPA) axis.

TRPV1 and mast cell involvement in repeated variate stress-induced urinary bladder dysfunction in adult female mice

The etiology of interstitial cystitis/bladder pain syndrome (IC/BPS) is unknown but likely multifactorial. IC/BPS symptoms can be exacerbated by psychological stress, but underlying mechanisms remain to be defined. Transient receptor potential vanilloid 1 (TRPV1) channels, expressed on nerve fibers, have been implicated in bladder dysfunction and colonic hypersensitivity with stress in rodents. Histamine/H1R activation of TRPV1+ nerves increases bladder afferent fiber sensitivity to distension. TRPV1 channels are also expressed on mast cells, previously implicated in contributing to IC/BPS etiology and symptoms. We have examined the contribution of TRPV1 and mast cells to bladder dysfunction after repeated variate stress (RVS). RVS increased (P ≤ 0.05) serum and fecal corticosterone expression and induced anxiety-like behavior in wild-type (WT) mice. Intravesical instillation of the selective TRPV1 antagonist capsazepine (CPZ) rescued RVS-induced bladder dysfunction in WT mice. Trpv1 knockout (KO) mice did not increase voiding frequency with RVS and did not exhibit increased serum corticosterone expression despite exhibiting anxiety-like behavior. Mast cell-deficient mice (B6.Cg-Kitw-sh) failed to demonstrate RVS-induced increased voiding frequency or serum corticosterone expression, whereas control (no stress) mast cell-deficient mice had similar functional bladder capacity to WT mice. TRPV1 protein expression was significantly increased in the rostral lumbar (L1-L2) spinal cord and dorsal root ganglia (DRG) in WT mice exposed to RVS, but no changes were observed in lumbosacral (L6-S1) spinal segments or DRG. These studies demonstrated TRPV1 and mast cell involvement in RVS-induced increased voiding frequency and suggest that TRPV1 and mast cells may be useful targets to mitigate stress-induced urinary bladder dysfunction.NEW & NOTEWORTHY Using pharmacological tools and transgenic mice in a repeated variate stress (RVS) model in female mice, we demonstrate that transient receptor potential vanilloid 1 (TRPV1) and mast cells contribute to the increased voiding frequency observed following RVS. TRPV1 and mast cells should continue to be considered as targets to improve bladder function in stress-induced bladder dysfunction.

Models of Inflammation: Carrageenan- or Complete Freund's Adjuvant (CFA)-Induced Edema and Hypersensitivity in the Rat

Animal models of inflammation are used to assess the production of inflammatory mediators at sites of inflammation, the processing of pain sensation at CNS sites, the anti-inflammatory properties of agents such as nonsteroidal anti-inflammatory drugs (NSAIDs), and the efficacy of putative analgesic compounds in reversing cutaneous hypersensitivity. Detailed in this article are methods to elicit and measure carrageenan- and complete Freund's adjuvant (CFA)-induced cutaneous inflammation. Due to possible differences between the dorsal root sensory system and the trigeminal sensory system, injections into either the footpad or vibrissal pad are described. In this manner, cutaneous inflammation can be assessed in tissue innervated by the lumbar dorsal root ganglion neurons (footpad) or by the trigeminal ganglion neurons (vibrissal pad). © 2021 Wiley Periodicals LLC.