Xue-Hai Guan

Activation of spinal chemokine receptor CXCR3 mediates bone cancer pain through an Akt-ERK crosstalk pathway in rats

Previously, we showed that activation of the spinal CXCL9, 10/CXCR3 pathway mediated bone cancer pain (BCP) in rats. However, the cellular mechanism involved is poorly understood. Here, we found that the activated CXCR3 was co-localized with either neurons, microglia, and astrocytes in the spinal cord, or non-peptidergic-, peptidergic-, and A-type neurons in the dorsal root ganglion. The inoculation of Walker-256 mammary gland carcinoma cells into the rats tibia induced a time-dependent phosphorylation of Akt and extracellular signal-regulated kinase (ERK1/2) in the spinal cord, and CXCR3 was necessary for the phosphorylation of Akt and ERK 1/2. Meanwhile, CXCR3 was co-localized with either pAkt or pERK1/2. Blockage of either Akt or ERK1/2 prevented or reversed the mechanical allodynia in BCP rats. Furthermore, there was cross-activation between PI3K/Akt and Raf/MEK/ERK pathway under the BCP condition. Our results demonstrated that the activation of spinal chemokine receptor CXCR3 mediated BCP through Akt and ERK 1/2 kinase, and also indicated a crosstalk between PI3K/Akt and Raf/MEK/ERK signaling pathways under the BCP condition.

The cuneiform nucleus may be involved in the regulation of skeletal muscle tone by motor pathway: a virally mediated trans-synaptic tracing study in surgically sympathectomized mice

ARTICLE Sir, The review article entitled ‘The pedunculopontine nucleus area: critical evaluation of interspecies differences relevant for its use as a target for deep brain stimulation’ by Alam et al. (2011), addressed that the cuneiform nucleus, an adjacent region of the pedunculopontine nucleus, was the important area of the mesencephalic locomotor region and played a major role in the initiation of gait. It has been suggested by many studies that neurons in the cuneiform nucleus are involved in the generation of locomotion, and signals from the cuneiform nucleus activate central pattern generators in the spinal cord, mainly through the medullary reticulospinal tract (Takakusaki et al. , 2003). The understanding of neuroanatomical motor circuitry and neuronal connections from cuneiform nucleus to skeletal muscle is important for studying the possible mechanism of cuneiform nucleus involved in the regulation of skeletal muscle tone by motor pathway. We would like to further complete the discussion of Alam et al. (2011) by introducing a virally-mediated trans-synaptic tracing study. Deep brain stimulation has become a remarkable treatment option for several different movement disorders, such as neuropsychiatric disorders, intractable pain, epilepsy, restless legs syndrome, Parkinson’s disease, and Alzheimer’s disease (Wichmann and Delong, 2006; Halpern et al. , 2007; Lyons, 2011; Thevathasan et al. , 2011). The mesencephalic pedunculopontine tegmental nucleus has been suggested as a target for deep brain stimulation, but the exact mechanism of deep brain stimulation in the pedunculopontine tegmental nucleus area is not fully understood. Because clinical data have demonstrated that the outcome of deep brain stimulation in the pedunculopontine nucleus area can be quite variable, there is great controversy about the …

Activation of CXCL10/CXCR3 Signaling Attenuates Morphine Analgesia: Involvement of Gi Protein

Morphine is a potent agonist of μ-opioid receptor and is widely used to relieve severe pain, including cancer pain. Some chemokines, for example, CX3CL1 and CCL2, participate in the regulation of opioid santinociception. In our previous study, we found overexpression of chemokine CXCL10/CXCR3 in spinal cord participated in the development of cancer-induced bone pain, so we supposed that CXCL10 may have influence in morphine analgesia in cancer pain relief. In this study, we found that a single dose of morphine could transiently increase the expression of CXCL10 in spinal cord. Blocking the function of CXCL10 enhanced morphine antinociception in cancer-induced bone pain rats. However, overexpression of CXCL10 induced acute algesia and decreased the analgesic effect of morphine in normal mice. The algesic effect of CXCL10 was blocked by inhibition of CXCR3 and Gi protein. These results suggested that CXCL10 in spinal cord serves as a novel negative regulator of morphine analgesia and provided evidence that activation of CXCL10/CXCR3 in spinal cord may attenuate antinociceptive potency of morphine in cancer pain relief.

Minocycline attenuates bone cancer pain in rats by inhibiting NF-κB in spinal astrocytes

AIM To investigate the mechanisms underlying the anti-nociceptive effect of minocycline on bone cancer pain (BCP) in rats. METHODS A rat model of BCP was established by inoculating Walker 256 mammary carcinoma cells into tibial medullary canal. Two weeks later, the rats were injected with minocycline (50, 100 μg, intrathecally; or 40, 80 mg/kg, ip) twice daily for 3 consecutive days. Mechanical paw withdrawal threshold (PWT) was used to assess pain behavior. After the rats were euthanized, spinal cords were harvested for immunoblotting analyses. The effects of minocycline on NF-κB activation were also examined in primary rat astrocytes stimulated with IL-1β in vitro. RESULTS BCP rats had marked bone destruction, and showed mechanical tactile allodynia on d 7 and d 14 after the operation. Intrathecal injection of minocycline (100 μg) or intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced mechanical tactile allodynia. Furthermore, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of GFAP (astrocyte marker) and PSD95 in spinal cord. Moreover, intraperitoneal injection of minocycline (80 mg/kg) reversed BCP-induced upregulation of NF-κB, p-IKKα and IκBα in spinal cord. In IL-1β-stimulated primary rat astrocytes, pretreatment with minocycline (75, 100 μmol/L) significantly inhibited the translocation of NF-κB to nucleus. CONCLUSION Minocycline effectively alleviates BCP by inhibiting the NF-κB signaling pathway in spinal astrocytes.

Activation of spinal phosphatidylinositol 3-kinase/protein kinase B mediates pain behavior induced by plantar incision in mice.

The etiology of postoperative pain may be different from antigen-induced inflammatory pain and neuropathic pain. However, central neural plasticity plays a key role in incision pain. It is also known that phosphatidylinositol 3-kinase (PI3K) and protein kinase B/Akt (PKB/Akt) are widely expressed in laminae I-IV of the spinal horn and play a critical role in spinal central sensitization. In the present study, we explored the role of PI3K and Akt in incision pain behaviors. Plantar incision induced a time-dependent activation of spinal PI3K-p110γ and Akt, while activated Akt and PI3K-p110γ were localized in spinal neurons or microglias, but not in astrocytes. Pre-treatment with PI3K inhibitors, wortmannin or LY294002 prevented the activation of Akt brought on by plantar incision in a dose-dependent manner. In addition, inhibition of spinal PI3K signaling pathway prevented pain behaviors (dose-dependent) and spinal Fos protein expression caused by plantar incision. These data demonstrated that PI3K signaling mediated pain behaviors caused by plantar incision in mice.

Activation of PI3Kγ/Akt pathway mediates bone cancer pain in rats

Bone cancer pain (BCP) is one of the most common and severe complications in patients suffering from primary bone cancer or metastatic bone cancer such as breast, prostate, or lung, which profoundly compromises their quality of life. Emerging lines of evidence indicate that central sensitization is required for the development and maintenance of BCP. However, the underlying mechanisms are largely unknown. In this study, we investigated the role of PI3Kγ/Akt in the central sensitization in rats with tumor cell implantation in the tibia, a widely used model of BCP. Our results showed that PI3Kγ and its downstream target pAkt were up‐regulated in a time‐dependent manner and distributed predominately in the superficial layers of the spinal dorsal horn neurons, astrocytes and a minority of microglia, and were colocalized with non‐peptidergic, calcitonin gene‐related peptide‐peptidergic, and A‐type neurons in dorsal root ganglion ipsilateral to tumor cell inoculation in rats. Inhibition of spinal PI3Kγ suppressed BCP‐associated behaviors and the up‐regulation of pAkt in the spinal cord and dorsal root ganglion. This study suggests that PI3Kγ/Akt signal pathway mediates BCP in rats.

Stimulation of the pedunculopontine tegmental nucleus may affect renal function by melanocortinergic signaling

Deep brain stimulation of the pedunculopontine tegmental nucleus (PPTg) has been reported to improve gait disturbance in animal models of Parkinsonism and among patients with Parkinsons disease. Evidence suggests that neurons in the PPTg are involved in the control of the sympathetic outflow to the kidneys, and sympathetic regulation is a major component of central melanocortin action. Our recent studies using transneuronal labeling pseudorabies virus (PRV)-614 and melanocortin-4 receptor (MC4R)-green fluorescent protein (GFP) transgenic mice supported the melanocortinergic nature of the middle and caudal PPTg (mPPTg and cPPTg). Because PRV-614/MC4R-GFP double-labeled neurons in the mPPTg and cPPTg were detected, we propose a hypothesis that deep brain stimulation of the PPTg may influence renal function by the melanocortinergic pathway.

Possible mechanism of deep brain stimulation for pedunculopontine nucleus-induced urinary incontinence: a virally mediated transsynaptic tracing study in a transgenic mouse model

To the editor: The case report titled ‘Urinary incontinence following deep brain stimulation of the pedunculopontine nucleus’ by Aviles-Olmos et al. [1] stated that a possible explanation for the detrusor overactivity that developed immediately after right pedunculopontine tegmental nucleus (PPTg) deep brain stimulation (DBS) is the proximity between the caudal PPTg and brainstem structures, which is implicated in the control of micturition. The pontine micturition center (also known as “Barrington’s nucleus”) is widely acknowledged to be involved in the maintenance of high bladder pressure and modulation of urinary tract functions [7, 12, 17]. Understanding of the neuroanatomical sympathetic circuitry and neuronal connections from the pontine micturition center to the kidney is important for studying the possible mechanism of PPTg DBS-induced urinary incontinence. We would like to further complete the discussion of Aviles-Olmos and colleagues by introducing a virally mediated transsynaptic tracing study in a transgenic mouse model. Barrington’s nucleus (BN) has been considered a pontine center related exclusively to the control of micturition and is located in the dorsolateral tegmentum of the pons [2, 9, 14]. Neurourological studies show that neurons within BN are non-noradrenergic and that the nucleus is clearly separated from the noradrenergic (dopamine-β-hydroxylase–immunoreactive) locus coeruleus and subcoeruleus [3]. To clarify the functional role of BN, we characterized projections from the kidney to BN in adult male MC4R-green fluorescent protein (GFP) transgenic mice using retrograde tracing techniques of pseudorabies virus (PRV)-614, expressing a novel monomeric red fluorescent protein (mRFP1) under control of the cytomegalovirus immediate early promoter for direct visualization under a fluorescence microscope [20–23]. We found that injections of PRV-614 into the kidney resulted in retrograde infection of neurons in BN of the pontine, and PRV-614-infecting cells were most heavily concentrated in BN (Fig. 1-A1, B1 and C1), indicating that a direct neuroanatomical pathway between the kidney and BN exists. Otherwise, fluorescence immunohistochemistry revealed that PRV-614/MC4R-GFP, PRV614/tyrosine hydroxylase (TH), PRV-614/tryptophan hydroxylase (TPH) dual-labeled neurons were detected in BN (Fig. 1), indicating that BN is melanocortinergic, catecholaminergic and serotonergic. Based on all these findings, we speculate that BN may be primarily involved in sympathetic regulation of renal functions, except the control of pelvic parasympathetic activity. Animal studies have showed that BN is critically involved in the micturition reflex [16, 18], but little is known about the neuronal mechanisms involved. A considerable amount of literature demonstrated that there is a close interaction between the kidney and the central nervous system [6, 13], and sympathetic influence in kidney functions is under H.

STAT1 as a downstream mediator of ERK signaling contributes to bone cancer pain by regulating MHC II expression in spinal microglia

Major histocompatibility class II (MHC II)-specific activation of CD4+ T helper cells generates specific and persistent adaptive immunity against tumors. Emerging evidence demonstrates that MHC II is also involved in basic pain perception; however, little is known regarding its role in the development of cancer-induced bone pain (CIBP). In this study, we demonstrate that MHC II expression was markedly induced on the spinal microglia of CIBP rats in response to STAT1 phosphorylation. Mechanical allodynia was ameliorated by either pharmacological or genetic inhibition of MHC II upregulation, which was also attenuated by the inhibition of pSTAT1 and pERK but was deteriorated by intrathecal injection of IFNγ. Furthermore, inhibition of ERK signaling decreased the phosphorylation of STAT1, as well as the production of MHC II in vivo and in vitro. These findings suggest that STAT1 contributes to bone cancer pain as a downstream mediator of ERK signaling by regulating MHC II expression in spinal microglia.