Pain
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Amitriptyline, nortriptyline, imipramine, doxepin, desipramine, protriptyline, trimipramine, and maprotiline are tricyclic antidepressants (TCAs) used orally in treating major depressive disorders. Recent studies showed that amitriptyline is more potent in blocking the sciatic nerve functions in vivo by local injection than bupivacaine, a long-acting local anesthetic. We therefore tested whether various TCAs could likewise act as local anesthetics in vivo after single injection via the rat sciatic notch. ⋯ With this in vitro expression system, TCAs appear more potent than bupivacaine as Na(+) channel blockers in Nav1.5 Na(+) channels. We suggest that the ability of TCAs to pass through various membrane barriers within peripheral nerve trunks is crucial to their local anesthetic efficacy in vivo. TCAs with a tertiary amine appear more effective in penetrating these membrane barriers than TCAs with a secondary amine.
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Randomized Controlled Trial Comparative Study Clinical Trial
Intravenous adenosine alleviates neuropathic pain: a double blind placebo controlled crossover trial using an enriched enrolment design.
Adenosine analogs produce analgesic actions in nociceptive paradigms and alleviate manifestations of neuropathic pain in nerve injury models in rodents. In humans, previous work indicates an analgesic effect for adenosine administered intravenously in postoperative and neuropathic pain. In this double blind placebo controlled crossover trial, we used an enriched enrolment design to determine the effects of intravenous adenosine (50 microg/kg/min over 60min) on neuropathic pain. ⋯ Adenosine also led to a significant reduction in pinprick hyperalgesia, but not in allodynia. Three patients from Phase 1 of the trial experienced long term resolution of their pain following intravenous adenosine (5,16,25 months). The results of this study support previous reports that indicate intravenous adenosine alleviates neuropathic pain and hyperalgesia.
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Comparative Study
Complex regional pain syndrome type I: incidence and prevalence in Olmsted county, a population-based study.
The objective of this study is to undertake a population based study on the incidence, prevalence, natural history, and response to treatment of complex regional pain syndrome (CRPS). All Mayo Clinic and Olmsted Medical Group medical records with codes for reflex sympathetic dystrophy (RSD), CRPS, and compatible diagnoses in the period 1989-1999 were reviewed as part of the Rochester Epidemiology Project. We used IASP criteria for CRPS. ⋯ Seventy-four percent of patients underwent resolution, often spontaneously. CRPS I is of low prevalence, more commonly affects women than men, the upper more than the lower extremity, and three out of four cases undergo resolution. These results suggest that invasive treatment of CRPS may not be warranted in the majority of cases.
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Comparative Study
Assessment of nociceptive trigeminal pathways by laser-evoked potentials and laser silent periods in patients with painful temporomandibular disorders.
We assessed the trigeminal nociceptive pathways in patients with painful temporomandibular disorders (TMD) and control subjects using a CO(2)-laser stimulator which provides a predominant activation of the nociceptive system. Fifteen patients with unilateral pain were examined in accordance with the Research Diagnostic Criteria for TMD and 30 gender- and age-matched individuals were included as a control group. Laser-evoked potentials (LEPs) and laser silent periods (LSPs) after stimulation of the perioral region (V2/V3) on the painful and non-painful sides were recorded in all subjects. ⋯ TMD patients perceived the laser stimulus less intense on the painful than the non-painful side (P<0.05). We found suppression of cortical responses and brainstem reflexes elicited by a predominantly nociceptive input in TMD patients. These findings are consistent with recent experimental pain studies and suggest that chronic craniofacial pain in TMD patients may be associated with a dysfunction of the trigeminal nociceptive system.
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Comparative Study
Central representation of visceral and cutaneous hypersensitivity in the irritable bowel syndrome.
We have previously shown that irritable bowel syndrome (IBS) patients have both visceral and cutaneous hyperalgesia. The neural mechanisms of these forms of hyperalgesia were further characterized by comparing cortical processing of both rectal distension (35, 55mmHg) and cutaneous heat nociceptive stimuli (foot immersion in 45 and 47 degrees C water bath) in IBS patients and in a group of healthy age/sex-matched controls. Our approach relied on functional magnetic resonance imaging neuroimaging analyses in which brain activation in age/sex-matched control subjects was subtracted from that found in IBS patients. ⋯ This was found to be the case not only for visceral hyperalgesia but also for cutaneous heat hyperalgesia, a likely form of secondary hyperalgesia. Furthermore, visceral and heat hyperalgesia were accompanied by increased neural activity within the same brain structures. These results support the hypothesis that visceral and cutaneous hyperalgesia in IBS patients is related to increased afferent processing in pathways ascending to the brain rather than to selectively increased activity at higher cortical levels (e.g. limbic and frontal cortical areas).