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How is the sensory (or other) experience of pain related to the words used to describe such experiences? Answering this question would not only improve our general understanding of the relationship between the experience of pain and the report of pain, but also would allow one to quantify inaccuracies or idiosyncracies in this regard. A continuous multidimensional scaling model was used to examine...
The non-competitive NMDA-antagonist, Ketamine, was infused (i.v.) in healthy volunteers to study the effect on central excitability with the presence of cutaneous hyperalgesia. Hyperalgesia was established experimentally on the dorsum of the foot by topical application of capsaicin (1%). Different thermal and mechanical conditioning stimuli were applied to the primary and secondary hyperalgesic areas...
To test the hypothesis that nociception from veins plays a role in the formation of perivenous edema, we looked at edema along hand veins of humans during painful noxious stimulation in the presence and absence of nerve conduction block. Pain from vascularly isolated hand vein segments was evoked by perfusion with hyperosmolar saline and rated with the help of an electronically controlled visual analogue...
Topical desensitization of the tongue was assessed during multiple bouts of exposure to capsaicin. In the first experiment subjects rated perceived irritation as 30 capsaicin stimuli (33 μM) were applied to the tongue tip in three blocks of 10, with 15 min breaks between blocks. Significant desensitization was measured at the beginning of the second and third blocks within each session. However, as...
Cyclic GMP is probably a second messenger in vascular nociceptors that are excited by nitric oxide (NO), because NO is known to activate the guanylate cyclase. If so, inhibition of this enzyme should render nociceptors insensitive to algesics that act via NO. To test this hypothesis, the effect of the specific guanylate cyclase inhibitor methylene blue was studied on bradykinin-evoked, i.e. NO-mediated...
Dorsal horn neurons that respond to noxious cold also respond to noxious heat, suggesting the hypothesis that pain evoked by temperature extremes, whether hot or cold, may be processed similarly in the CNS. In this study, we tested perceptual consequences of this hypothesis by comparing characteristics of heat and cold pain, as well as of innocuous warm and cool. Eight healthy subjects performed psychophysical...
Psychophysical studies were performed in 10 healthy, female volunteers using urinary bladder distension (UBD) as a visceral stimulus. Stimulus methodology was similar to that used clinically for obtaining cystometrograms with a fixed-rate (100 cc/min normal saline) filling of the urinary bladder, occasional pauses and simultaneous measure of bladder pressure using a catheter-transducer assembly. During...
Post-injury inflammation activates nociceptive systems and recruits normally non-nociceptive afferents into a pain processing role. During inflammation, Aβ low threshold mechanoreceptor afferents that usually mediate tactile sensation acquire properties of nociceptors, allowing them to participate in post-injury spontaneous pain and evoked abnormalities such as tenderness and pain to light touch....
Neuropathic pain may be produced, at least in part, by the increased activity of primary afferent neurons. Studies have suggested that an accumulation of voltage-gated sodium channels at the site of peripheral nerve injury is a primary precursory event for subsequent afferent hyperexcitability. In this study, a human sodium channel (hPN3, SCN10A) has been cloned from the lumbar 4/5 dorsal root ganglia...
Thalamic neurons are known to switch their firing from a tonic pattern during wakefulness to a bursting pattern during sleep. Several studies have described the existence of bursting activity in awake chronic pain patients and have suggested that this activity is abnormal and may be related to their pain. However, we have frequently observed bursting activity in awake non-pain patients suggesting...
Background: Complex regional pain syndromes (causalgia and RSD) can be relieved by blockade of the sympathetic efferent activity. The mechanisms of sympathetically maintained pain (SMP) are unclear. So far an adrenergic interaction between sympathetic vasoconstrictor neurons and nociceptors has been proposed. Alternatively, a cholinergic coupling of sympathetic sudomotor neurons and nociceptors is...
The present study compared capsaicin-induced muscle and skin pain in humans. Twelve healthy subjects received, in a randomised, balanced order, 3 intramuscular (i.m.) injections into the brachioradial muscle: capsaicin 100 μg/1 ml, capsaicin 100 μg/20 μl or 1 ml solvent (Tween 80), and one intradermal injection (i.d.): capsaicin 100 μg/20 μl. Local and referred pain intensities and areas were assessed...
Successive inhibitory, excitatory, inhibitory and excitatory reflexes (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by applying non-painful taps to an incisor tooth, were recorded from the jaw-closing muscles of 15 subjects. The effects on these reflexes of the subjects undertaking mental exercises (MEx) in the form of arithmetic calculations were compared...
The effect of age on hyperalgesia, one of the most common signs of injury, has not been previously examined in humans. A psychophysical study was conducted in 10 young (26.9+/-4.6 years) and 10 older (79.0+/-5.7 years) healthy volunteers to investigate the effect of age on the development of hyperalgesia induced by topical application of capsaicin (0.1 ml, 5 mg/ml). The capsaicin patch (diameter 2...
The tetrodotoxin-resistant (TTX-R) voltage-gated sodium channel SNS/PN3 and the newly discovered NaN/SNS2 are expressed in sensory neurones, particularly in nociceptors. Using specific antibodies, we have studied, for the first time in humans, the presence of SNS/PN3 and NaN/SNS2 in peripheral nerves, including tissues from patients with chronic neurogenic pain. In brachial plexus injury patients,...
Variations in baseline skin temperature can be encountered in experimental and clinical pain states. Such variations have been shown to greatly alter the response to radiant heat stimuli when the temperature of the stimulus is not controlled. We carried out a psychophysical investigation to examine the influence of baseline skin temperature on pain ratings to temperature-controlled heat stimuli. A...
Recent theories of pathogenesis of pain in chronic pancreatitis (CP) are neuroimmune interactions of intrapancreatic nerves and inflammatory cells and increase in levels of pain neurotransmitters such as substance P (SP). This study analyzed the expression and localization of neurokinin 1 receptor (NK-1R), which binds SP, and its association with pain and inflammation in CP. Pancreatic tissues from...
Hypertonic saline effectively excites muscle nociceptors. Muscle hyperalgesia was assessed in osteoarthritis (OA) by intramuscular infusion of 0.5 ml hypertonic saline (6%) into the tibialis anterior muscle in humans. Patients (n=14) with OA in the lower extremities were compared with an equal number of age- and sex-matched healthy controls. Ten of the 14 OA patients had pain in the knee joint as...
Pain intensity is frequently measured on an 11-point pain intensity numerical rating scale (PI-NRS), where 0=no pain and 10=worst possible pain. However, it is difficult to interpret the clinical importance of changes from baseline on this scale (such as a 1- or 2-point change). To date, there are no data driven estimates for clinically important differences in pain intensity scales used for chronic...
The aim of this study was to determine the analgesic efficacy of a single dose intra-articular injection (i.a.) of morphine in 53 patients with unilateral arthralgia/osteoarthritis of the temporomandibular joint (TMJ). This randomized, double-blind, parallel group, multicenter study included a screening visit, a treatment visit, and a follow-up visit 1 week after treatment. Recordings of visual analog...
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