The Effect of Sensory Innervation on the Inorganic Component of Bones and Teeth; Experimental Denervation - Review.

The effect of the nervous system on bone remodelling has been described by many studies. Sensory and autonomic nerves are present in the bone. Immunohistochemical analysis of the bone have indicated the presence of neuropeptides and neurotransmitters that act on bone cells through receptors. Besides carrying sensory information, sensory neurons produce various neuropeptides playing an important role in maintaining bone and tooth pulp homeostasis, and dentin formation. Bone tissue and teeth contain organic and inorganic components. Bone cells enable bone mineralization and ensure its formation and resorption. Studies focused on the effects of the nervous system on the bone are proceeded using various ways. Sensory denervation itself can be achieved using capsaicin causing chemical lesion to the nerve. Surgical ways of causing only sensory lesion to nerves are substantially limited because many peripheral nerves are mixed and contain a motor component as well. From this point of view, the experimental model with transection of inferior alveolar nerve is appropriate. This nerve provides sensory innervation of the bone and teeth of the mandible. The purpose of our paper is to provide an overview of the effects exerted by the nervous system on the inorganic component of the bone and teeth, and also to present an overview of the used experimental models. As we assume, the transection of inferior alveolar nerve could be reflected in changed contents and distribution of chemical elements in the bone and teeth of rat mandible. This issue has not been studied so far.

Pathogenesis and clinical aspects of pain in patients with osteoporosis.

Bone pain is one of the most frequent kinds of chronic pain, mainly in elderly patients. It causes a significant worsening of functional capacity and deterioration in the quality of life in people affected. Mechanisms of pain in osteoporosis are poorly known and often extrapolated by other pathologies or other experimental model. One of principal causes would be a "hyper-remodeling" of bone, that involves osteoclasts activity and pathological modifications of bone innervation. Several studies show that osteoclasts play a significant role in bone pain etiology. Pain in osteoporosis is mainly nociceptive, if it become persistent a sensitization of peripheral and central nervous system can occur, so underlining the transition to a chronic pain syndrome. Central sensitization mechanisms are complex and involve several neuromediators and receptors (Substance P, NMDA, etc.). Most common manifestations of osteoporosis are vertebral compression fractures that cause persistent pain, though to differentiate from pain originating in structures as joint or muscle. First manifestation can be an acute pain due to pathological fracture, those of hip often causes disability. Pain in osteoporosis is an important clinical challenge. Often its complications and consequences on patient quality of life are underestimated with not negligible social implications. A balanced and early multimodal pain therapy including opioids as necessary, even in cases of acute pain, improve the functional capacity of patients and helps to prevent neurological alterations that seems to contribute in significant way in causing irreversible pain chronic syndromes.

Bone Pain in Multiple Myeloma (BPMM)-A Protocol for a Prospective, Longitudinal, Observational Study.

Multiple myeloma (MM) is a bone marrow neoplasia that causes bone pain in 70% patients. While preclinical models of MM have suggested that both nerve sprouting and nerve injury may be causative for the pain, there is a lack of clinical data. Thus, the primary aims of this clinical study are: (1) to provide a deep characterization of the subjective experience of pain and quality of life in MM patients; (2) to investigate disturbances in the bone innervation of MM patients. Secondary aims include exploring correlations between pain and serum inflammatory and bone turnover biomarkers. In a prospective, observational study (clinicaltrials.gov: NCT04273425), patients with suspected MM requiring a diagnostic iliac crest biopsy at Sheffield Teaching Hospital (UK) are invited to participate. Consenting patients answer seven standardized questionnaires assessing pain, quality of life and catastrophizing. Bone turnover biomarkers and inflammatory cytokines are measured in fasting serum samples, and bone innervation is evaluated in diagnostic biopsies. MM patients are invited to a follow-up upon completion of first line treatment. This will be the first deep characterization of pain in MM patients and its correlation with disturbances in bone innervation. Understanding how bone turnover and inflammation correlate to pain in MM is crucial to identify novel analgesic targets for this condition.

Fracture pain-Traveling unknown pathways.

An increase of fracture incidence is expected for the next decades, mostly due to the undeniable increase of osteoporotic fractures, associated with the rapid population ageing. The rise in sports-related fractures affecting the young and active population also contributes to this increased fracture incidence, and further amplifies the economical burden of fractures. Fracture often results in severe pain, which is a primary symptom to be treated, not only to guarantee individual's wellbeing, but also because an efficient management of fracture pain is mandatory to ensure proper bone healing. Here, we review the available data on bone innervation and its response to fracture, and discuss putative mechanisms of fracture pain signaling. In addition, the common therapeutic approaches to treat fracture pain are discussed. Although there is still much to learn, research in fracture pain has allowed an initial insight into the mechanisms involved. During the inflammatory response to fracture, several mediators are released and will putatively activate and sensitize primary sensory neurons, in parallel, intense nerve sprouting that occurs in the fracture callus area is also suggested to be involved in pain signaling. The establishment of hyperalgesia and allodynia after fracture indicates the development of peripheral and central sensitization, still, the underlying mechanisms are largely unknown. A major concern during the treatment of fracture pain needs to be the preservation of proper bone healing. However, the most common therapeutic agents, NSAIDS and opiates, can cause significant side effects that include fracture repair impairment. The understanding of the mechanisms of fracture pain signaling will allow the development of mechanisms-based therapies to effectively and safely manage fracture pain.

Methotrexate chemotherapy triggers touch-evoked pain and increased CGRP-positive sensory fibres in the tibial periosteum of young rats.

Although bone pain caused by cancer chemotherapy is a well-recognized and significant problem, with approximately 1 in 10 childhood cancer patients being reported to experience isolated bone pain along with other skeletal complications, the underlying mechanisms are poorly understood and there is no specific treatment. In this study, effects of methotrexate (MTX) treatment on pain in the hind legs and the extent of sensory innervation of the tibial bone were examined through a 20-day time course in young rats after 5 daily 0.75 mg/kg MTX injections. MTX treatment increased von-Frey filament stimulation-induced mechanical allodynia and palpation nocifensive score in the tibia. MTX-treated rats showed trends in reduced loading (numbers of stands) on hind limbs after palpation, commencing early during treatment and 2 weeks after the end of treatment despite no signs of ongoing pain during normal locomotion. Immunohistochemical analyses showed an increase in innervation of calcitonin gene-related peptide (CGRP)-positive sensory nerve fibres in tibial periosteum on days preceding and overlapping with those rats with touch-evoked pain responses and the bone repair phase. These data suggest that methotrexate chemotherapy triggers touch-evoked pain involving enhanced sensory nerve innervation of the bone.

Ontogeny of sensory and autonomic nerves in the developing mouse skeleton.

BACKGROUND: Bone innervation is implicated in bone modeling and remodeling. This study investigates skeletal nerve development in embryonic and newborn mice, focusing on sensory and autonomic nerves and their temporal occurrence. MATERIALS AND METHODS: The ontogeny of innervation and angiogenesis in the hindlimb skeleton of mice was studied from embryonic day (E) 15 to postnatal day (P) 20. Neuronal tissue was immunohistochemically labeled for detection of growth associated protein 43 (GAP-43), protein gene product 9.5 (PGP 9.5), calcitonin gene-related peptide (CGRP), tyrosine hydroxylase (TH), and neuropeptide Y (NPY). Vascular endothelium was labeled for platelet endothelium cell adhesion molecule-1 (PECAM-1). Morphology was evaluated with hematoxylin and eosin staining. RESULTS: GAP-43, PGP 9.5, CGRP, and PECAM-1 were all present at E 15, adjacent to areas with high osteogenic and chondrogenic activity. In the primary ossification centers, GAP-43 was found at E 15, PGP 9.5 at E 17, CGRP at E 19, and NPY at P 4. The same time lag in appearance was observed in the secondary ossification centers. The covering capillary network was initially dense, but became mature and sparse from P 12 onwards. CONCLUSION: A functional nerve supply co-localized with a rich capillary network is seen early in the developing mouse skeleton, especially in areas with high osteogenic activity. Sensory innervation occurs prior to partus, while autonomic innervation (revealed by the presence of NPY and TH) is established post partum. The findings indicate a time-related development of nerves with different qualities, according to skeletal development.