Bone cancer induces a unique central sensitization through synaptic changes in a wide area of the spinal cord

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Abstract

Background

Chronic bone cancer pain is thought to be partly due to central sensitization. Although murine models of bone cancer pain revealed significant neurochemical changes in the spinal cord, it is not known whether this produces functional alterations in spinal sensory synaptic transmission. In this study, we examined excitatory synaptic responses evoked in substantia gelatinosa (SG, lamina II) neurons in spinal cord slices of adult mice bearing bone cancer, using whole-cell voltage-clamp recording techniques.

Results

Mice at 14 to 21 days after sarcoma implantation into the femur exhibited hyperalgesia to mechanical stimuli applied to the skin of the ipsilateral hind paw, as well as showing spontaneous and movement evoked pain-related behaviors. SG neurons exhibited spontaneous excitatory postsynaptic currents (EPSCs). The amplitudes of spontaneous EPSCs were significantly larger in cancer-bearing than control mice without any changes in passive membrane properties of SG neurons. In the presence of TTX, the amplitude of miniature EPSCs in SG neurons was increased in cancer-bearing mice and this was observed for cells sampled across a wide range of lumbar segmental levels. Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor- and N-methyl- D-aspartate (NMDA) receptor-mediated EPSCs evoked by focal stimulation were also enhanced in cancer-bearing mice. Dorsal root stimulation elicited mono- and/or polysynaptic EPSCs that were caused by the activation of Aδ and/or C afferent fibers in SG neurons from both groups of animals. The number of cells receiving monosynaptic inputs from Aδ and C fibers was not different between the two groups. However, the amplitude of the monosynaptic C fiber-evoked EPSCs and the number of SG neurons receiving polysynaptic inputs from Aδ and C fibers were increased in cancer-bearing mice.

Conclusions

These results show that spinal synaptic transmission mediated through Aδ and C fibers is enhanced in the SG across a wide area of lumbar levels following sarcoma implantation in the femur. This widespread spinal sensitization may be one of the underlying mechanisms for the development of chronic bone cancer pain.

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Most cited references 42

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Ca2+-permeable AMPA receptors in synaptic plasticity and neuronal death.

Stephanie S. Liu, R. Zukin (2007)

AMPA receptors mediate fast synaptic transmission at excitatory synapses in the CNS and are crucial during neuronal development, synaptic plasticity and structural remodeling. AMPA receptors lacking GluR2 subunits are permeable to Ca(2+) and Zn(2+). Ca(2+) permeation through AMPA receptors is crucial in several forms of synaptic plasticity and cell death associated with neurological diseases and disorders. The subunit composition and Ca(2+) permeability of AMPA receptors are not static, but they are dynamically remodeled in a cell- and synapse-specific manner during development and in response to neuronal activity, sensory experience and neuronal insults. Exciting new research shows that these changes arise not only because of regulated expression of the AMPA receptor subunit GluR2, but also as a consequence of RNA editing, receptor trafficking and dendritic protein synthesis. This article reviews new insights into the role of Ca(2+)-permeable AMPA receptors in neuronal function and survival.

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Breakthrough pain: characteristics and impact in patients with cancer pain.

Jessica Payne, R Portenoy, P. Jacobsen (1999)

Few surveys have been performed to define the characteristics and impact of breakthrough pain in the cancer population. In this cross-sectional survey of inpatients with cancer, patients responded to a structured interview (the Breakthrough Pain Questionnaire) designed to characterize breakthrough pain, and also completed measures of pain and mood (Memorial Pain Assessment Card (MPAC)), pain-related interference in function (Brief Pain Inventory (BPI)), depressed mood (Beck Depression Inventory (BDI)), and anxiety (Beck Anxiety Inventory (BAI)). Of 178 eligible patients, 164 (92.2%) met the criteria for controlled background pain. The median age was 50.6 years (range 26 to 77 years), 52% were men, and 80.6% were Caucasian. Tumor diagnoses were mixed, 75% had metastatic disease, 65% had pain caused directly by the neoplasm, and a majority had mixed nociceptive-neuropathic pain. The median Karnofsky Performance Status score was 60 (range 40 to 90). Eighty-four (51.2%) patients had experienced breakthrough pain during the previous day. The median number of episodes was six (range 1 to 60) and the median interval from onset to peak was 3 min (range 1 s to 30 min). Although almost two-thirds (61.7%) could identify precipitants (movement 20.4%; end-of-dose failure 13.2%), pain was unpredictable in a large majority (78.2%). Patients with breakthrough pain had more intense (P < 0.001) and more frequent (P < 0.01) background pain than patients without breakthrough pain. Breakthrough pain was also associated with greater pain-related functional impairment (difference in mean BPI. P < 0.001), worse mood (mood VAS, P < 0.05; BDI, P < 0.001), and more anxiety (BAI, P < 0.001). Multivariate analysis confirmed that breakthrough pain independently contributed to impaired functioning and psychological distress. These data confirm that cancer-related breakthrough pain is a prevalent and heterogeneous phenomenon. The presence of breakthrough pain is a marker of a generally more severe pain syndrome, and is associated with both pain-related functional impairment and psychological distress. The findings suggest the need for further studies of breakthrough pain and more effective therapeutic strategies.

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Malignant bone pain: pathophysiology and treatment.

S Mercadante (1996)

The presence of bone metastases predicts the presence of pain and is the most common cause of cancer-related pain. Although bone metastases do not involve vital organs, they may determine deleterious effects in patients with prolonged survival. Bone fractures, hypercalcaemia, neurologic deficits and reduced activity associated with bone metastases result in an overall compromise in the patient's quality of life. A metastasis is a consequence of a cascade of events including a progressive growth at the primary site, vascularization phase, invasion, detachment, embolization, survival in the circulation, arrest at the site of a metastasis, extravasion, evasion of host defense and progressive growth. Once cancer cells establish in the bone, the normal process of bone turnover is disturbed. The different mechanisms responsible for osteoclast activation correspond to typical radiologic features showing lytic, sclerotic or mixed metastases, according to the primary tumor. The release of chemical mediators, the increased pressure within the bone, microfractures, the stretching of periosteum, reactive muscle spasm, nerve root infiltration and compression of nerves by the collapse of vertebrae are the possible mechanisms of malignant bone pain. Pain is often disproportionate to the size or degree of bone involvement. A comprehensive assessment including a trusting relationship with the patient, taking a careful history of the pain complaint, the characteristics of the pain, the evaluation of the psychological status of the patient, neurological examination, the reviewing of diagnostic studies and laboratory findings, and individualization of the therapeutic approach, should precede any treatment. Radiotherapy is the cornerstone of the treatment. Low doses given in a single session are safe and effective, and reduce distress and inconvenience associated with repeated session. Radioisotopes are more imprecise in delivering specific doses of radiation, but have less toxicity and easy administration as well as effectiveness in subclinical sites of metastases, although storage, dispensing and administration should be under strict control. Chemotherapy and endocrine therapy are difficult to measure in terms of pain relief. Prophylactic fixation surgery can lead to improved survival and quality of life of patients with bone metastases. Surgical treatment should be undertaken when fracture occurs. Careful selection of patients for surgical spinal decompression is required. The potential benefits of surgical interventions have to be tempered with patient survival. The use of analgesics according to the WHO ladder is recommended. There is no clear evidence that non-steroidal anti-inflammatory drugs (NSAIDs) have a specific efficacy in malignant bone pain. The difficulty with incident pain is not a lack of response to systemic opioids, but rather that the doses required to control the incidental pain produce unacceptable side-effects at rest. Alternative measures are often required. The inhibition of bone resorption and hypercalcaemia can be reduced by the use of bisphosphonates. This class of drugs potentiate the effects of analgesics in improving metastatic bone pain. Invasive techniques are rarely indicated, but may provide analgesia in the treatment of pain resistant to the other modalities. Neural blockade should never be used as the sole modality for malignant bone pain, but should be considered as a helpful in specific pain situations. Careful appraisal and the application of a correct approach should enable the patient with bone metastases to obtain an acceptable pain relief despite the advanced nature of their malignant disease.

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Author and article information

Journal

Journal ID (nlm-ta): Mol Pain

Title: Molecular Pain

Publisher: BioMed Central

ISSN (Electronic): 1744-8069

Publication date Collection: 2010

Publication date (Electronic): 5 July 2010

Volume: 6

Page: 38

Affiliations

[1 ]Department of Integrative Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan

[2 ]Department of Orthopedic Surgery, Kyushu University, Fukuoka, Japan

[3 ]Department of Information Physiology, National Institute for Physiological Sciences, Okazaki, Japan

[4 ]Department of Anesthesiology, Sapporo Medical University, Sapporo, Japan

[5 ]Department of Anesthesiology and Resuscitology, Shinshu University School of Medicine, Matsumoto, Japan

[6 ]Graduate School of Health Sciences, Kumamoto Health Science University, Kumamoto, Japan

Article

Publisher ID: 1744-8069-6-38

DOI: 10.1186/1744-8069-6-38

PMC ID: 3020802

PubMed ID: 20602757

SO-VID: dc7d8f8c-a762-4708-b191-1673c4a0962c

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Bone cancer induces a unique central sensitization through synaptic changes in a wide area of the spinal cord

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Abstract

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Cancer Immunotherapy

Most cited references 42

Ca2+-permeable AMPA receptors in synaptic plasticity and neuronal death.

Breakthrough pain: characteristics and impact in patients with cancer pain.

Malignant bone pain: pathophysiology and treatment.

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