Nerve Growth Factor/Tyrosine Kinase A Receptor Pathway Enhances Analgesia in an Experimental Mouse Model of Bone Cancer Pain by Increasing Membrane Levels of δ-Opioid Receptors.

BACKGROUND: The role of nerve growth factor (NGF)/tyrosine kinase A receptor (TrKA) signaling, which is activated in a variety of pain states, in regulating membrane-associated δ-opioid receptor (mDOR) expression is poorly understood. The hypothesis was that elevated NGF in bone cancer tumors could upregulate mDOR expression in spinal cord neurons and that mDOR agonism might alleviate bone cancer pain. METHODS: Bone cancer pain (BCP) was induced by inoculating Lewis lung carcinoma cells into the femoral marrow cavity of adult C57BL/6J mice of both sexes. Nociceptive behaviors were evaluated by the von Frey and Hargreaves tests. Protein expression in the spinal dorsal horn of animals was measured by biochemical analyses, and excitatory synaptic transmission was recorded in miniature excitatory synaptic currents. RESULTS: The authors found that mDOR expression was increased in BCP mice (BCP vs. sham, mean ± SD: 0.18 ± 0.01 g vs. mean ± SD: 0.13 ± 0.01 g, n = 4, P < 0.001) and that administration of the DOR agonist deltorphin 2 (Del2) increased nociceptive thresholds (Del2 vs. vehicle, median [25th, 75th percentiles]: 1.00 [0.60, 1.40] g vs. median [25th, 75th percentiles]: 0.40 [0.16, 0.45] g, n = 10, P = 0.001) and reduced miniature excitatory synaptic current frequency in lamina II outer neurons (Del2 vs. baseline, mean ± SD: 2.21 ± 0.81 Hz vs. mean ± SD: 2.43 ± 0.90 Hz, n = 12, P < 0.001). Additionally, NGF expression was increased in BCP mice (BCP vs. sham, mean ± SD: 0.36 ± 0.03 vs. mean ± SD: 0.16 ± 0.02, n = 4, P < 0.001), and elevated NGF was associated with enhanced mDOR expression via TrKA signaling. CONCLUSIONS: Activation of mDOR produces analgesia that is dependent on the upregulation of the NGF/TrKA pathway by increasing mDOR levels under conditions of BCP in mice.

Chronic nicotine exposure elicits pain hypersensitivity through activation of dopaminergic projections to anterior cingulate cortex.

BACKGROUND: Cigarette smoking is commonly reported among chronic pain patients in the clinic. Although chronic nicotine exposure is directly linked to nociceptive hypersensitivity in rodents, underlying neurobiological mechanisms remain unknown. METHODS: Multi-tetrode recordings in freely moving mice were used to test the activity of dopaminergic projections from the ventral tegmental area (VTA) to pyramidal neurones in the anterior cingulate cortex (ACC) in chronic nicotine-treated mice. The VTA→ACC dopaminergic pathway was inhibited by optogenetic manipulation to detect chronic nicotine-induced allodynia (pain attributable to a stimulus that does not normally provoke pain) assessed by von Frey monofilaments (force units in g). RESULTS: Allodynia developed concurrently with chronic (28-day) nicotine exposure in mice (0.36 g [0.0141] vs 0.05 g [0.0018], P<0.0001). Chronic nicotine activated dopaminergic projections from the VTA to pyramidal neurones in the ACC, and optogenetic inhibition of VTA dopaminergic terminals in the ACC alleviated chronic nicotine-induced allodynia in mice (0.06 g [0.0064] vs 0.28 g [0.0428], P<0.0001). Moreover, optogenetic inhibition of Drd2 dopamine receptor signalling in the ACC attenuated nicotine-induced allodynia (0.07 g [0.0082] vs 0.27 g [0.0211], P<0.0001). CONCLUSIONS: These findings implicate a role of Drd2-mediated dopaminergic VTA→ACC pathway signalling in chronic nicotine-elicited allodynia.

Intraoperative transcutaneous electroacupoint stimulation on early postoperative fatigue in patients with Parkinson's disease undergoing deep brain stimulation surgery.

Background: In this clinical trial, we evaluated the effects of transcutaneous electroacupoint stimulation (TEAS) on postoperative fatigue (POF) in Parkinson disease (PD) patients undergoing deep brain stimulation (DBS) surgery. Methods: A total 60 PD patients undergoing DBS surgery were enrolled. They were randomized to receive either electrical stimulation [alternative frequency 2/10 Hz, dense and disperse, intensity adjusted to the maximum tolerated by the participants (6-15 mAmp)] via surface electrodes (TEAS group) or surface electrodes only without electrical stimulation (Con group) at bilateral Zusanli and Sanyinjiao acupuncture points. All participants received their assigned intervention (TEAS or Con) during the 1st stage of surgery [(except during microelectrode recording (MER)] and the entire 2nd stage of surgery. Intraoperative anesthetic requirements were adjusted based on bispectral index (BIS) monitor. POF was assessed by Christensen fatigue scales (ChrFS), along with Quality of Recovery-15 (QoR-15) and mini-mental state examination (MMSE) postoperatively over a 7-day-period. We recorded the usage of rescue analgesics and anti-emetics. Results: Fifty-nine patients' datasets were included for final analyses. Fewer patients in TEAS experienced severe POF (defined as ChrFS ≥6) at T3 than those in the Con group (TEAS vs. Con: 7 vs. 22, p < 0.001). During the 1st stage of surgery, more patients in Con group required dexmedetomidine infusion (TEAS vs. Con: 2 vs. 6; P < 0.01). Total dosages of propofol and remifanil during the 2nd stage of surgery were TEAS vs. Con: 374.7 ± 61.2 vs 421.5 ± 81.9; p < 0.001 and 572.3 ± 82.0 vs. 662 ± 148.2; P < 0.001, respectively. Postoperative rescue analgesics (TEAS vs. Con: 2 vs. 6; P < 0.001) were used less in the TEAS group. TEAS patients reported better POF, MMSE and QoR15 scores than those in the Con group during most of the assessment period. Conclusions: Intraoperative TEAS decreased the severity of POF, reduced intraoperative anesthetic requirements and facilitated post-DBS recovery in this group of PD patients.