Bone cancer induces a unique central sensitization through synaptic changes in a wide area of the spinal cord.
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 Adelta and/or C afferent fibers in SG neurons from both groups of animals. The number of cells receiving monosynaptic inputs from Adelta 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 Adelta and C fibers were increased in cancer-bearing mice.


CONCLUSIONS
These results show that spinal synaptic transmission mediated through Adelta 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.
Yanagisawa
Yoshikazu
Y
Department of Integrative Physiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Furue
Hidemasa
H
Kawamata
Tomoyuki
T
Uta
Daisuke
D
Yamamoto
Jun
J
Furuse
Shingo
S
Katafuchi
Toshihiko
T
Imoto
Keiji
K
Iwamoto
Yukihide
Y
Yoshimura
Megumu
M
D000818:Animals; D001859:Bone Neoplasms / Q000150:complications / Q000503:physiopathology*; D045744:Cell Line, Tumor; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D013116:Spinal Cord / Q000503:physiopathology*; D009435:Synaptic Transmission