mechanism of analgesic effect on prolonged continuous theta burst stimulation

Conditions: Chronic Pain; rTMS

Summary: it has been shown that prolonged continuous theta burst stimulation (pctbs) , a relatively new repetitive transcranial magnetic simulation (rtms) protocol, of the primary motor cortex (m1) or dorsolateral prefrontal cortex (dlpfc) decreases pain in healthy volunteers, in various experimental models. in addition, rtms of m1 has also been shown to have analgesic effects in various chronic pain conditions, including neuropathic pain.the mechanisms underlying rtms-induced analgesia remain unclear. functional neuroimaging studies have shown that rtms of m1 and dlpfc induces changes in the activity of cortical and subcortical structures involved in pain processing and modulation. endogenous opioids and e n-methyl-d-aspartate (nmda) receptor are known to play a major role in these processes. the investigator hypothesized that the endogenous opioids systems (eos) and nmda receptor might be involved in the analgesic action of pctbs. in the first part,the investigator compares the analgesic effects of motor cortex (m1) or dorsolateral prefrontal cortex (dlpfc) stimulation before and after naloxone or placebo treatment, the intensity of pain induced by capsaicin were used to evaluate the analgesic effects of pctbs. if naloxone does not reverse the analgesic effect of pctbs,the volunteers will be invited to participant the second part of the study, which the investigator compares the analgesic effects of motor cortex (m1) or dorsolateral prefrontal cortex (dlpfc) stimulation before and after ketamine treatment.

this study comprised 3 parallel arms corresponding to 3 types of stimulation: active stimulation of m1, active stimulation of dlpfc-pctbs, and sham stimulation (of m1 or dlpfc). volunteers were randomly assigned to the 3 arms. in the first part, these volunteers participated in 2 experimental sessions 1 weeks apart, in which we compared the effects of naloxone and placebo (saline), administered according to a randomized, double-blind crossover design, on pctbs-induced analgesia. each experimental session started with the determination of baseline pain intensity and cortical excitability as well as plasma opioid peptide concentrations. ten minutes before pctbs (of m1, dlpfc, or sham), the volunteer received an intravenous bolus followed by a continuous infusion of either placebo (ie, saline) or naloxone, which was continued throughout the rtms session (2 minutes). the participant was then allowed to rest for 60 minutes. posttreatment pain intensity, cortical excitability and plasma opioid peptide concentrations will be determined by the same procedure used at baseline.in the second part, ketamine will be delivered the same as the first part.

Eligibility criteria:
inclusion criteria: 1）woman or man over 18 and under 85 years old; 2）clinical diagnosis of physical and mental health people; 3) able to cooperate in completing questionnaire. exclusion criteria: 1)clinical diagnosis of psychiatric disorder including major depression; 2) history of substance abuse (alcohol, drugs); 3) past treatment with repetitive transcranial magnetic stimulation (rtms); 4) contraindications to rtms (previous severe head trauma or neurosurgical intervention, past or current epilepsy, active brain tumor, intracranial hypertension, implanted ferromagnetic devices, e.g., cardiac pacemaker, neurostimulator, or cochlear implants); 5) any difficulty to fill out questionnaires (due to language or cognitive problems);