Functional Interactions between Tumor and Peripheral Nerve: Changes in Excitability and Morphology of Primary Afferent Fibers in a Murine Model of Cancer Pain

Abstract

We used a murine model to investigate functional interactions between tumors and peripheral nerves that may contribute to pain associated with cancer. Implantation of fibrosarcoma cells in and around the calcaneus bone produced mechanical hyperalgesia of the ipsilateral paw. Electrophysiological recordings from primary afferent fibers in control and hyperalgesic mice with tumor revealed the development of spontaneous activity (0.2-3.4 Hz) in 34% of cutaneous C-fibers adjacent to the tumor (9-17 d after implantation). C-fibers in tumor-bearing mice exhibited a mean decrease in heat threshold of 3.5 +/- 0.10 degrees C. We also examined innervation of the skin overlying the tumor. Epidermal nerve fibers (ENFs) were immunostained for protein gene product 9.5, imaged using confocal microscopy, and analyzed in terms of number of fibers per millimeter of epidermal length and branching (number of nodes per fiber). Divergent morphological changes were linked to tumor progression. Although branching of ENFs increased significantly relative to control values, in later stages (16-24 d after implantation) of tumor growth a sharp decrease in the number of ENFs was observed. This decay of epidermal innervation of skin over the tumor coincided temporally with gradual loss of electrophysiological activity in tumor-bearing mice. The development of spontaneous activity and sensitization to heat in C-fibers and increased innervation of cutaneous structures within the first 2 weeks of tumor growth suggest activation and sensitization of a proportion of C-fibers. The decrease in the number of ENFs observed in later stages of tumor development implicates neuropathic involvement in this model of cancer pain.

Acute and chronic administration of the cannabinoid receptor agonist CP 55,940 attenuates tumor-evoked hyperalgesia

“…Second, this model allows examination of the electrophysiological responses of primary afferent fibers in mice with tumor-evoked hyperalgesia. We have determined that implantation of fibrosarcoma cells results in the sensitization of a subpopulation of C-nociceptors that innervate the plantar surface of the hind paw (Cain et al, 2001). Furthermore, the peripheral terminals of primary afferent fibers innervating the skin overlying the tumor show morphological changes such as an increase in epidermal nerve fibers during the early development of tumor-evoked hyperalgesia, upregulation of purinergic P2X 3 receptors on these fibers, and subsequent decrease in epidermal innervation (Gilchrist et al, 2005).…”

“…The aim of this study was to determine if a more potent cannabinoid, CP 55,940, attenuates tumor-evoked cutaneous mechanical hyperalgesia in a well-characterized murine model of cancer pain. In this model, implantation of osteolytic fibrosarcoma cells into and around the calcaneous bone produces robust mechanical hyperalgesia and sensitization of C nociceptors (Cain et al, 2001;Wacnik et al, 2001). This model will allow us to correlate the antihyperalgesic effects of cannabinoids to its effects on tumor-evoked sensitization of nociceptors.…”

Protective Effects of Cyclooxygenase-2 Gene Inactivation Against Peripheral Nerve Dysfunction and Intraepidermal Nerve Fiber Loss in Experimental Diabetes

“…Intraepidermal nerve fiber density. Intraepidermal nerve fiber (IENF) density was examined in hindpaw footpads using previously reported techniques (18). Briefly, footpads were collected from the plantar surface of the hindpaws before animal perfusion, fixed in Zamboni's fixative (2% paraformaldehyde, 0.2% picric acid, and 0.1 mol/l sodium phosphate buffer) for 14 h, and cryoprotected through a series of sucrose gradients and embedded in OCT. Free-floating 30-m footpad sections were stained with anti-PGP 9.5 antibody (a panaxonal marker) (19).…”

Advances in the therapy of cancer pain: from novel experimental models to evidence-based treatments

“…The subsequent development of thermal hyperalgesia may be secondary to release of pro-nociceptive substances by the tumor cells, such as endothelin-1, a mediator able to induce thermal hyperalgesia (34). Furthermore tumor development has been shown to induce development of spontaneous electrical activity and sensitization of C-fibers which provide innervation in and around the affected bone (35). The role of endogenous opioid-ergic analgesia systems has been also demonstrated by Mantyh's group, in another animal cancer pain model, wherein genetically modified transgenic mice under control of a promoter, spontaneously develop pancreatic cancer.…”

“…Release of endothelin-1 from tumor cells (34) has been implicated in the induction of thermal hyperalgesia. Furthermore, in the same model of bone cancer pain in mice, tumor growth has been reported to induce development of spontaneous electrical activity and sensitization of Cfibers, which provide innervation in and around the affected bone (35). It has been shown that some small unmyelinated primary afferent fibers express endothelin receptors, the activation of which may result in sensitization or excitation (61).…”