Preclinical models of deep craniofacial nociception and temporomandibular disorder pain

Involvement of the Transient Receptor Channels in Preclinical Models of Musculoskeletal Pain

BACKGROUND

Musculoskeletal pain is a condition that affects bones, muscles, and tendons and is present in various diseases and/or clinical conditions. This type of pain represents a growing problem with enormous socioeconomic impacts, highlighting the importance of developing treatments tailored to the patient's needs. TRP is a large family of non-selective cation channels involved in pain perception. Vanilloid (TRPV1 and TRPV4), ankyrin (TRPA1), and melastatin (TRPM8) are involved in physiological functions, including nociception, mediation of neuropeptide release, heat/cold sensing, and mechanical sensation.

OBJECTIVE

In this context, we provide an updated view of the most studied preclinical models of muscle hyperalgesia and the role of transient receptor potential (TRP) in these models.

METHODS

This review describes preclinical models of muscle hyperalgesia induced by intramuscular administration of algogenic substances and/or induction of muscle damage by physical exercise in the masseter, gastrocnemius, and tibial muscles.

RESULTS

The participation of TRPV1, TRPA1, and TRPV4 in different models of musculoskeletal pain was evaluated using pharmacological and genetic tools. All the studies detected the antinociceptive effect of respective antagonists or reduced nociception in knockout mice.

CONCLUSION

Hence, TRPV1, TRPV4, and TRPA1 blockers could potentially be utilized in the future for inducing analgesia in muscle hypersensitivity pathologies.

Preventive Roles of Rice-koji Extracts and Ergothioneine on Anxiety- and Pain-like Responses under Psychophysical Stress Conditions in Male Mice

This study determined the effect of daily administration of Rice-koji on anxiety and nociception in mice subjected to repeated forced swim stress (FST). In a parallel experiment, it was determined whether ergothioneine (EGT) contained in Rice-koji displayed similar effects. Anxiety and nociception were assessed behaviorally using multiple procedures. c-Fos and FosB immunoreactivities were quantified to assess the effect of both treatments on neural responses in the paraventricular nucleus of the hypothalamus (PVN), nucleus raphe magnus (NRM), and lumbar spinal dorsal horn (DH). FST increased anxiety- and pain-like behaviors in the hindpaw. Rice-koji or EGT significantly prevented these behaviors after FST. In the absence of formalin, both treatments prevented decreased FosB expressions in the PVN after FST, while no effect was seen in the NRM and DH. In the presence of formalin, both treatments prevented changes in c-Fos and FosB expressions in all areas in FST mice. Further, in vitro experiments using SH-SY5Y cells were conducted. Rice-koji and EGT did not affect cell viability but changed the level of brain-derived neurotrophic factor. In conclusion, Rice-koji could reduce anxiety and pain associated with psychophysical stress, possibly mediated by the modulatory effects of EGT on neural functions in the brain.

Effects of stress contagion on anxiogenic- and orofacial inflammatory pain-like behaviors with brain activation in mice

The conditions of stress contagion are induced in bystanders without direct experiences of stressful events. This study determined the effects of stress contagion on masseter muscle nociception in mice. Stress contagion was developed in the bystanders after cohabitating with a conspecific mouse subjected to social defeat stress for 10 days. On Day 11, stress contagion increased anxiety- and orofacial inflammatory pain-like behaviors. The c-Fos and FosB immunoreactivities evoked by masseter muscle stimulation were increased in the upper cervical spinal cord, while c-Fos expressions were increased in the rostral ventromedial medulla, including the lateral paragigantocellular reticular nucleus and nucleus raphe magnus in stress contagion mice. The level of serotonin in the rostral ventromedial medulla was increased under stress contagion, while the number of serotonin positive cells was increased in the lateral paragigantocellular reticular nucleus. Stress contagion increased c-Fos and FosB expressions in the anterior cingulate cortex and insular cortex, both of which were positively correlated with orofacial inflammatory pain-like behaviors. The level of brain-derived neurotrophic factor was increased in the insular cortex under stress contagion. These results indicate that stress contagion can cause neural changes in the brain, resulting in increased masseter muscle nociception, as seen in social defeat stress mice.

Human Brain Organoids in Migraine Research: Pathogenesis and Drug Development

Human organoids are small, self-organized, three-dimensional (3D) tissue cultures that have started to revolutionize medical science in terms of understanding disease, testing pharmacologically active compounds, and offering novel ways to treat disease. Organoids of the liver, kidney, intestine, lung, and brain have been developed in recent years. Human brain organoids are used for understanding pathogenesis and investigating therapeutic options for neurodevelopmental, neuropsychiatric, neurodegenerative, and neurological disorders. Theoretically, several brain disorders can be modeled with the aid of human brain organoids, and hence the potential exists for understanding migraine pathogenesis and its treatment with the aid of brain organoids. Migraine is considered a brain disorder with neurological and non-neurological abnormalities and symptoms. Both genetic and environmental factors play essential roles in migraine pathogenesis and its clinical manifestations. Several types of migraines are classified, for example, migraines with and without aura, and human brain organoids can be developed from patients with these types of migraines to study genetic factors (e.g., channelopathy in calcium channels) and environmental stressors (e.g., chemical and mechanical). In these models, drug candidates for therapeutic purposes can also be tested. Here, the potential and limitations of human brain organoids for studying migraine pathogenesis and its treatment are communicated to generate motivation and stimulate curiosity for further research. This must, however, be considered alongside the complexity of the concept of brain organoids and the neuroethical aspects of the topic. Interested researchers are invited to join the network for protocol development and testing the hypothesis presented here.

Development of a model to investigate the effects of prolonged ischaemia on the muscles of mastication of male Sprague Dawley rats

OBJECTIVE

The aims of this study were to develop a novel rodent model of masticatory muscle ischaemia via unilateral ligation of the external carotid artery (ECA), and to undertake a preliminary investigation to characterize its downstream effects on mechanosensitivity and cellular features of the masseter and temporalis muscles.

DESIGN

The right ECA of 18 male Sprague-Dawley rats was ligated under general anaesthesia. Mechanical detection thresholds (MDTs) at the masseter and temporalis bilaterally were measured immediately before ECA ligation and after euthanasia at 10-, 20-, and 35-days (n = 6 rats/timepoint). Tissue samples from both muscles and sides were harvested for histological analyses and for assessing changes in the expression of markers of hypoxia and muscle degeneration (Hif-1α, VegfA, and Fbxo32) via real time PCR. Data were analyzed using mixed effect models and non-parametric tests. Statistical significance was set at p < 0.05.

RESULTS

MDTs were higher in the right than left hemiface (p = 0.009) after 20 days. Histological changes indicative of muscle degeneration and fibrosis were observed in the right muscles. Hif-1α, VegfA, and Fbxo32 were more highly expressed in the masseter than temporalis muscles (all p < 0.05). Hif-1α and, VegfA did not change significantly with time in all muscles (all p > 0.05). Fbxo32 expression gradually increased in the right masseter (p = 0.024) and left temporalis (p = 0.05).

CONCLUSIONS

ECA ligation in rats induced hyposensitivity in the homolateral hemiface after 20 days accompanied by tissue degenerative changes. Our findings support the use of this model to study pathophysiologic mechanisms of masticatory muscle ischaemia in larger investigations.

Annual review of selected scientific literature: A report of the Committee on Scientific Investigation of the American Academy of Restorative Dentistry

The Scientific Investigation Committee of the American Academy of Restorative Dentistry offers this review of the 2021 dental literature in restorative dentistry to inform busy dentists regarding noteworthy scientific and clinical progress over the past year. Each member of the committee brings discipline-specific expertise to coverage of this broad topical area. Specific subject areas addressed, in order of the appearance in this report, include COVID-19 and the dental profession (new); prosthodontics; periodontics, alveolar bone, and peri-implant tissues; implant dentistry; dental materials and therapeutics; occlusion and temporomandibular disorders; sleep-related breathing disorders; oral medicine and oral and maxillofacial surgery; and dental caries and cariology. The authors focused their efforts on reporting information likely to influence daily dental treatment decisions with an emphasis on future trends in dentistry. With the tremendous volume of dentistry and related literature being published daily, this review cannot possibly be comprehensive. Rather, its purpose is to update interested readers and provide important resource material for those interested in pursuing greater details on their own. It remains our intent to assist colleagues in negotiating the extensive volume of important information being published annually. It is our hope that readers find this work useful in successfully managing the patients and dental problems they encounter.