Monocyte chemoattractant protein-1 contributes to morphine tolerance in rats with cancer-induced bone pain.

Cancer-induced bone pain can severely compromise the life quality of patients, while tolerance limits the use of opioids in the treatment of cancer pain. Monocyte chemoattractant protein-1 (MCP-1) is known to contribute to neuropathic pain. However, the role of spinal MCP-1 in the development of morphine tolerance in patients with cancer-induced bone pain remains unclear. The aim of the present study was to investigate the role of spinal MCP-1 in morphine tolerance in bone cancer pain rats (MTBP rats). Bone cancer pain was induced by intramedullary injection of Walker 256 cells into the tibia of the rats, while morphine tolerance was induced by continuous intrathecal injection of morphine over a period of 9 days. In addition, anti-MCP-1 antibodies were intrathecally injected to rats in various groups in order to investigate the association of MCP-1 with mechanical and heat hyperalgesia using the paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL) tests, respectively. Furthermore, MCP-1 and CCR2 expression levels were measured using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blot analysis, and CCR2 expression levels were measured using RT-qPCR. The results indicated that MCP-1 and CCR2 expression levels were significantly increased in the spinal cord of MTBP rats. Intrathecal administration of anti-MCP-1 neutralizing antibodies was observed to attenuate the mechanical and thermal allodynia in MTBP rats. Therefore, the upregulation of spinal MCP-1 and CCR2 expression levels may contribute to the development of mechanical allodynia in MTBP rats. In conclusion, MCP-1/CCR2 signaling may serve a crucial role in morphine tolerance development in rats suffering from cancer-induced bone pain.

MCP-1 stimulates spinal microglia via PI3K/Akt pathway in bone cancer pain.

Accumulating evidence suggests that chemokine monocyte chemoattractant protein-1 (MCP-1) is significantly involved in the activation of spinal microglia associated with pathological pain, at the same time that the phosphatidylinositol 3-kinase/Protein Kinase B (PI3K/Akt) pathway localized in spinal microglia is involved in both neuropathic and inflammatory pain. However, whether there is a connection between MCP-1 and the PI3K/Akt pathway and in their underlying mechanisms in bone cancer pain (BCP) has not yet been elucidated. In the current study, we investigated the expression changes of p-Akt in microglia and OX-42 (microglia marker) after being stimulated with MCP-1 in vitro, as well as in a BCP model that was established by an intramedullary injection of mammary gland carcinoma cells(Walker 256 cells) into the tibia of rats. We observed a significant increase in expression levels of p-Akt and OX-42 in microglia as well as in spinal dorsal horns of BCP rats. Furthermore, the intrathecal administration of an anti-MCP-1 neutralizing antibody or PI3K inhibitor LY294002 reduced the expression of p-Akt or OX-42, and LY294002 attenuated the mechanical allodynia of BCP rats. These results suggest that MCP-1 may stimulate spinal microglia via the PI3K/Akt pathway in BCP.

Changes in protein expression and distribution of spinal CCR2 in a rat model of bone cancer pain.

Accumulating evidence suggests that chemokine C-C motif receptor 2 (CCR2) plays an important role in neuropathic pain. It has been shown that spinal CCR2 is upregulated in several neuropathic pain models and expressed by neuronal and glial cells in the spinal cord. In this study, we investigated the expression changes and cellular localization of spinal CCR2 in a rat model of bone cancer induced by Walker 256 cell inoculation. The present results indicated that mechanical allodynia progressively increased in bone cancer pain (BCP) rats. Western blot and immunohistochemical analysis demonstrated that the expression of CCR2 in the spinal cord was significantly increased on day 6, 12, and 18 in BCP rats, with a peak on day 6. Furthermore, double immunofluorescence labeling indicated that CCR2 was expressed by both microglia and neurons in the spinal cord. These results suggest that CCR2 may be involved in the development of BCP, and that targeting CCR2 may be a new strategy for the treatment of BCP.

Involvement of CX3CR1 in bone cancer pain through the activation of microglia p38 MAPK pathway in the spinal cord.

Previous studies have demonstrated that fractalkine, a newly discovered chemokine, is implicated in spinal cord neuron-to-microglia activation signaling as well as mediation of neuropathic and inflammatory pain via its sole receptor CX3CR1, which is specifically expressed on microglia. However, whether it is involved in bone cancer pain (BCP) and the underlying mechanisms have not been elucidated. In this study we utilized a Sprague-Dawley rat animal model, and our findings indicated that on day 6, 12, and 18 following bone cancer pain induced by Walker 256 cell inoculation, the expression level of CX3CR1 in the spinal cord gradually increased. Intrathecal injection of a neutralizing antibody against CX3CR1 not only delayed the initiation of mechanical allodynia, but also attenuated established pain sensitization of BCP rats. Furthermore, we demonstrated that blockade of CX3CR1 suppressed the activation of microglia and the expression of p38 mitogen-activated protein kinase (MAPK) in the spinal cord in BCP rats. These results suggest a new mechanism of BCP, in which the microglia CX3CR1/p38 signaling cascade potentially plays an important role in facilitating pain processing in BCP rats.

Involvement of spinal monocyte chemoattractant protein-1 (MCP-1) in cancer-induced bone pain in rats.

In this study, we examined the involvement of chemokine monocyte chemoattractant protein-1 (MCP-1) in the spinal cord of a rat model of cancer-induced bone pain (CIBP). In this model, CIBP was established by an intramedullary injection of Walker 256 cells into the tibia of rats. We observed a significant increase in expression levels of MCP-1 and its receptor CCR2 in the spinal cord of CIBP rats. Furthermore, the intrathecal administration of an anti-MCP-1 neutralizing antibody attenuated the mechanical allodynia established in CIBP rats. Likewise, an intrathecal injection of exogenous recombinant MCP-1 induced a striking mechanical allodynia in naïve rats. These results suggest that increases in spinal MCP-1 and CCR2 expression are involved in the development of mechanical allodynia associated with bone cancer rats.

Anatomical organization of antennal-lobe glomeruli in males and females of the scarab beetle Holotrichia diomphalia (Coleoptera: Melolonthidae).

The glomerular organization of the primary olfactory brain center, the antennal lobe, was studied in males and females of Holotrichia diomphalia adults using serial histological sections labeled by the reduced silver-stain technique. The results revealed an apparent sexual dimorphism. Whereas an enlarged cap-shaped glomerulus was found at the antennal nerve entrance into the antennal lobe in males, no such unit was present in females. Also the size of the antennal lobe differed between the sexes, the antennal lobe of males being larger than that of females. We estimated the total number of glomeruli at approximately 60 units in the female antennal lobe. In males, we could discriminate only those glomeruli that were located in the anterior area of the antennal lobe.