Animal Studies

Pain is one of the first presenting symptoms in patients with head and neck cancer, who often develop chronic and debilitating pain as the disease progresses. Pain is also an important prognostic marker for survival. Unfortunately, patients rarely receive effective pain treatment due to our limited knowledge of the mechanisms underlying head and neck cancer pain (HNCP). Pain is often associated with neuroinflammation and particularly interleukin (IL)-1 signaling. The purpose of this study is to develop a novel syngeneic model of HNCP in immunocompetent mice to examine the contribution of IL-1 signaling.

Neuropathic pain is a type of spontaneous pain that causes damage to the central nervous system. Long noncoding RNAs (lncRNAs) participate in the progression of various nervous system diseases, including neuropathic pain. However, the biological function of GAS5 in neuropathic pain remains unclear. Our findings revealed that GAS5 was downregulated in chronic constriction injury (CCI) rats. Besides, ELISA showed that the concentration of IL-6, TNF-α, and IL-1β were reduced by overexpressed GAS5 in spinal cord homogenates of CCI rats. Moreover, mechanical allodynia and thermal hyperalgesia in CCI rats were inhibited by GAS5 overexpression, suggesting that GAS5 overexpression attenuated neuropathic pain. Subsequently, we found that GAS5 served as a sponge for miR-452-5p in CCI rats and CELF2 was the downstream target of miR-452-5p. Finally, through a rescue assay, we found that GAS5 ameliorated neuropathic pain in CCI rats by sponging miR-452-5p to regulate CELF2 expression. Our study confirmed that GAS5 ameliorated neuropathic pain in rats by modulation of the miR-452-5p/CELF2 axis, which may provide some clues for neuropathic pain treatment.

Aging is a major risk factor for numerous painful, inflammatory, and degenerative diseases including disc degeneration. A better understanding of how the somatosensory nervous system adapts to the changing physiology of the aging body will be of great significance for our expanding aging population. Previously, we reported that chronological aging of mouse lumbar discs is pathological and associated with behavioral changes related to pain. It is established that with age and degeneration the lumbar discs become inflammatory and innervated. Here we analyze the aging lumbar dorsal root ganglia (DRGs) and spinal cord dorsal horn (SCDH) in mice between 3 and 24 months of age for age-related somatosensory adaptations. We observe that as mice age there are signs of peripheral sensitization, and response to inflammation at the molecular and cellular level in the DRGs. From 12 months onwards the mRNA expression of vasodilator and neurotransmitter, (CGRP); stress (and survival) marker, ; and neurotrophic factor, , increases linearly with age in the DRGs. Further, while the mRNA expression of neuropeptide, precursor of Substance P, did not change at the transcriptional level, TAC1 protein expression increased in 24-month-old DRGs. Additionally, elevated expression of NFκB subunits, and , but not inflammatory mediators, , in the DRGs suggest peripheral nerves are responding to inflammation, but do not increase the expression of inflammatory mediators at the transcriptional level. These results identify a progressive, age-related shift in the molecular profile of the mouse somatosensory nervous system and implicates nociceptive sensitization and inflammatory response.

Diabetic neuropathy (DN) is an early, common complication of diabetes mellitus (DM) leading to chronic pain, sensory loss and muscle atrophy. Due to its multifactorial etiology, neuron cultures have been proposed as simplified systems for DN studies. However, the most used models currently available do not recreate the chronic and systemic damage suffered by peripheral neurons of type-2 DM (T2DM) individuals. Here, we cultured neurons derived from dorsal root ganglia from 6-month-old diabetic db/db-mice, and evaluated their morphology by the Sholl method as an easy-to-analyze readout of neuronal function. We showed that neurons obtained from diabetic mice exhibited neuritic regeneration defects in basal culture conditions, compared to neurons from non-diabetic mice. Next, we evaluated the morphological response to common neuritogenic factors including NGF and laminin. Neurons derived from diabetic mice exhibited reduced regenerative responses to these factors compared to neurons from non-diabetic mice. Finally, we analyzed the neuronal response to a putative DN therapy based on the secretome of mesenchymal stem cells (MSC). Neurons from diabetic mice treated with MSC-secretome displayed a significant improvement in neuritic regeneration, but still reduced when compared to neurons derived from non-diabetic mice. This model recapitulates many alterations observed in sensory neurons of T2DM individuals, suggesting the possibility of studying neuronal functions without the need of adding additional toxic factors to culture plates. This model may be useful for evaluating intrinsic neuronal responses in a cell-autonomous manner, and as a throughput screening for the pre-evaluation of new therapies for DN.

The skin covering the human palm and other specialized tactile organs contains a high density of mechanosensory corpuscles tuned to detect transient pressure and vibration. These corpuscles comprise a sensory afferent neuron surrounded by lamellar cells. The neuronal afferent is thought to be the mechanical sensor, whereas the function of lamellar cells is unknown. We show that lamellar cells within Meissner and Pacinian corpuscles detect tactile stimuli. We develop a preparation of bill skin from tactile-specialist ducks that permits electrophysiological recordings from lamellar cells and demonstrate that they contain mechanically gated ion channels. We show that lamellar cells from Meissner corpuscles generate mechanically evoked action potentials using R-type voltage-gated calcium channels. These findings provide the first evidence for R-type channel-dependent action potentials in non-neuronal cells and demonstrate that lamellar cells actively detect touch. We propose that Meissner and Pacinian corpuscles use neuronal and non-neuronal mechanoreception to detect mechanical signals.

Osteo-arthritis (OA) involves joint degradation and usually pain; with mechanisms poorly understood and few treatment options. There is evidence that the transient receptor potential canonical 5 (TRPC5) mRNA expression is reduced in OA patients' synovia. Here we examine the profile of TRPC5 in DRG and involvement in murine models of OA.

We evaluated the mechanisms underlying the oxytocin (OXT)-induced analgesic effect on orofacial neuropathic pain following infraorbital nerve injury (IONI). IONI was established through tight ligation of one-third of the infraorbital nerve thickness. Subsequently, the head withdrawal threshold for mechanical stimulation (MHWT) of the whisker pad skin was measured using a von Frey filament. Trigeminal ganglion (TG) neurons innervating the whisker pad skin were identified using a retrograde labeling technique. OXT receptor-immunoreactive (IR), transient receptor potential vanilloid 1 (TRPV1)-IR, and TRPV4-IR TG neurons innervating the whisker pad skin were examined on post-IONI day 5. The MHWT remarkably decreased from post-IONI day 1 onward. OXT application to the nerve-injured site attenuated the decrease in MHWT from day 5 onward. TRPV1 or TRPV4 antagonism significantly suppressed the decrement of MHWT following IONI. OXT receptors were expressed in the uninjured and Fluoro-Gold (FG)-labeled TG neurons. Furthermore, there was an increase in the number of FG-labeled TRPV1-IR and TRPV4-IR TG neurons, which was inhibited by administering OXT. This inhibition was suppressed by co-administration with an OXT receptor antagonist. These findings suggest that OXT application inhibits the increase in TRPV1-IR and TRPV4-IR TG neurons innervating the whisker pad skin, which attenuates post-IONI orofacial mechanical allodynia.