Alternative approach: a systematic review of non-pharmacological non-spastic and non-trigeminal pain management in multiple sclerosis

The aim of this paper was to evaluate non-pharmacological strategies for the reduction of non-spastic and non-trigeminal pain in patients with multiple sclerosis (MS) by conducting a systematic review. Experimental studies published after 1965 were chosen for review by searching electronic databases (e.g. PubMed, Cumulative Index to Nursing and Allied Health Literature, Science Citation Index Expanded, Conference Proceedings Citation Index- Science, and clinicaltrials.gov) and bibliographies/citations of previously published reviews. Studies were included if all participants were adults clinically diagnosed with MS, study sample was not restricted to participants with spasticity or trigeminal neuralgia, and participant-reported pain was a primary or secondary outcome measured with a previously validated tool. Records were screened and methodological qualities of included studies were assessed independently by two reviewers under the supervision of another reviewer. Pain scores were recorded as mean differences between or within groups weighted by the inverse of the pooled standard deviation (Cohen's d). A total of 13 studies which met the inclusion and exclusion criteria were identified for review; interventions included education, electrical stimulation, and physical therapies. Meta-analyses were not performed due to few trials identified per treatment within these classes. Pain relief was reported compared to placebo for two trials in transcutaneous electrical nerve stimulation (TENS) with effect sizes of -3.37 and -3.32, respectively. Inconclusive pain relief was reported for other education and physical therapies. TENS may be effective in reducing central neuropathic pain in MS. More trials with rigorous design and reporting are needed to determine effective treatments for specific pain types presenting in people living with MS.

Impaired long-term memory and long-term potentiation in N-type Ca2+ channel-deficient mice

Voltage-dependent N-type Ca(2+) channels, along with the P/Q-type, have a crucial role in controlling the release of neurotransmitters or neuromodulators at presynaptic terminals. However, their role in hippocampus-dependent learning and memory has never been examined. Here, we investigated hippocampus-dependent learning and memory and synaptic plasticity at hippocampal CA3-CA1 synapses in mice deficient for the alpha(1B) subunit of N-type Ca(2+) channels. The mutant mice exhibited impaired learning and memory in the Morris water maze and the social transmission of food preference tasks. In particular, long-term memory was impaired in the mutant mice. Interestingly, among activity-dependent long-lasting synaptic changes, theta burst- or 200-Hz-stimulation-induced long-term potentiation (LTP) was decreased in the mutant, compared with the wild-type mice. This type of LTP is known to require brain-derived neurotrophic factor (BDNF). It was found that both BDNF-induced potentiation of field excitatory postsynaptic potentials and facilitation of the frequency of miniature excitatory postsynaptic currents (mEPSCs) were reduced in the mutant. Taken together, these results demonstrate that N-type Ca(2+) channels are required for hippocampus-dependent learning and memory, and certain forms of LTP.

Brain volume measurements in patients with human T-cell lymphotropic virus-1–associated tropical spastic paraparesis

Human T-cell lymphotropic virus (HTLV)-1 is associated with a chronic progressive neurologic disease known as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) that affects 0.2% to 3% of HTLV-1-infected people. The authors aimed at exploring, in vivo, whether brain volume reduction occurs in patients with HAM/TSP through the use of magnetic resonance imaging (MRI). T1 pre/postcontrast spin echo-weighted images (WIs) and T2WIs of the brain were obtained in 19 HAM/TSP patients and 14 age-and sex-matched healthy volunteers. Both patients and healthy individuals were imaged at a 1.5-Tesla magnet by employing a conventional head coil. Focal T1 and T2 abnormalities were calculated and two measurements of brain parenchyma fraction (BPF) were obtained by using SIENAx (Structural Image Evaluation,using Normalisation, of Atrophy; University of Oxford, Oxford, UK) and MIPAV (Medical Image Processing, Analysis, and Visualization; National Institutes of Health, Bethesda, USA) from T1WIs. No significant differences in BPF were found between patients and healthy subjects when using either SIENAx or MIPAV. Analysis of individual patients detected that BPF was lower by 1 standard deviation (SD) relative to patients' average BPF in one patient. The authors conclude that reductions in BPF do not occur frequently in patients with HAM/TSP. However, the authors believe that one individual case of significant brain atrophy raises the question as to whether atrophy selectively targets the spinal cord of HAM/TSP patients or may involve the brain as well. A larger patient population analyzing regional brain volume changes could be helpful in determining whether brain atrophy is a marker of disease in patients with HAM/TSP.

Reversible leukoencephalopathy associated with cerebral amyloid angiopathy

The authors describe three patients with reversible leukoencephalopathy associated with cerebral amyloid angiopathy (CAA). Rapid progression of neurologic symptoms was followed by dramatic clinical and radiographic improvement. Pathologically, CAA was associated with varying degrees of inflammation ranging from none to transmural granulomatous infiltration. In the appropriate clinical context, the MRI finding of lobar white matter edema with evidence of prior hemosiderin deposition may indicate the presence of a reversible CAA leukoencephalopathy.

Effects of ginsenosides on vanilloid receptor (VR1) channels expressed in Xenopus oocytes

Ginsenosides, or ginseng saponins, are biologically active ingredients of Panax ginseng. Accumulating evidence suggests that ginsenosides can alleviate pain from injections of noxious chemicals, such as capsaicin [Nah et al. (2000)]. In this study we examined the effects of ginsenoside Rc on the capsaicin-induced inward current in Xenopus oocytes that expresses the vanilloid receptor 1 (VR1). Ginsenoside Rc enhanced the capsaicin-induced inward current in a concentration-dependent and reversible manner, but ginsenoside Rc itself elicited no membrane currents. The VR1 antagonist capsazepine almost completely blocked the inward current that was elicited by capsaicin plus ginsenoside Rc. We also tested the effect of seven other fractionated ginsenosides (i.e., Rb1, Rb2, Rd, Re, Rf, Rg1, and Rg2) in addition to ginsenoside Rc. We found that six of them significantly enhanced the inward current that is induced by capsaicin with the following order of potency: Rc > Rf > Rg1 approximately Rd > Rb2 > Rb1. These results show the possibility that the in vivo effect of ginsenosides against capsaicin-induced pain is derived from their modulation of the VR1 channel function.

Differences in sensitivity of vanilloid receptor 1 transfected to human embryonic kidney cells and capsaicin-activated channels in cultured rat dorsal root ganglion neurons to capsaicin receptor agonists

Heterologously expressed vanilloid receptor 1 (VR1), a cloned cDNA encoding for capsaicin (CAP)-sensitive currents, resembles the native CAP channels in cultured sensory neurons in channel property. But, the pharmacological profile of VR1 to various CAP analogs is not known. The stable expression of VR1 in human embryonic kidney (HEK) cells was generated and confirmed by reverse transcription-polymerase chain reaction and Western blots. VR1 expressed in HEK cells retained single-channel properties similar to those of the native channels. When concentration-response relationships were compared, CAP and DA-5018.HCl, a synthetic analog of CAP, exhibited a greater potency in activating VR1 than the native channels in sensory neurons. In contrast, resiniferatoxin and its analog, phorbol 12-phenylacetate 13-acetate 20-homovanillate, was more potent in activating the CAP-activated channels in cultured sensory neurons than VR1. Thus, the difference in pharmacological profiles of VR1 and the native channels suggests the possible presence of subtypes of the CAP receptor or regulatory mechanisms associated with VR1.

N-(3-Acyloxy-2-benzylpropyl)-N'-(4-hydroxy-3-methoxybenzyl) thiourea derivatives as potent vanilloid receptor agonists and analgesics

A series of N-(3-acyloxy-2-benzylpropyl)-N'-(4-hydroxy-3-methoxybenzyl) thiourea derivatives were investigated as vanilloid receptor ligands in an effort to discover a novel class of analgesics. The proposed pharmacophore model of resiniferatoxin. which includes the C20 homovanillic moiety, the C3-carbonyl and the orthoester phenyl ring as key pharmacophoric groups, was utilized as a guide for drug design. The compounds were synthesized after several steps from diethylmalonate and evaluated in vitro in a receptor binding assay and in a capsaicin-activated channel assay. Additional evaluation of analgesic activity, anti-inflammatory activity and pungency was conducted in animal models by the writhing test, the ear edema assay, and the eye-wiping test, respectively. Among the new compounds, 23 and 28 were found to be the most potent receptor agonists of the series with Ki values of 19 nM and 11 nM, respectively. Their strong in vitro potencies were also reflected by an excellent analgesic profile in animal tests with ED50 values of 0.5 microg kg for 23 and 1.0 microg/kg for 28. Relative to capsaicin these compounds appear to be ca. 600 and 300 times more potent. Both 23 and 28 were found to be less pungent than capsaicin based on the eye-wiping test. However, the compounds did not show significant anti-inflammatory activity. A molecular modeling study comparing the energy-minimized structures of resiniferatoxin and 35 demonstrated a good correlation in the spatial disposition of the corresponding key pharmacophores. The thioureas described in this investigation, which were designed as simplified resiniferatoxin surrogates, represent a novel class of potent vanilloid receptor agonists endowed with potent analgesic activity and reduced pungency.

Intracellular ATP increases capsaicin-activated channel activity by interacting with nucleotide-binding domains

Capsaicin (CAP)-activated ion channel plays a key role in generating nociceptive neural signals in sensory neurons. Here we present evidence that intracellular ATP upregulates the activity of capsaicin receptor channel. In inside-out membrane patches isolated from sensory neurons, application of CAP activated a nonselective cation channel (i(cap)). Further addition of ATP to the bath caused a significant increase in i(cap), with a K(1/2) of 3.3 mm. Nonhydrolyzable analogs of ATP, adenylimidodiphosphate and adenosine 5'-O-(3-thio)-triphosphate, also increased i(cap). Neither Mg(2+)-free medium nor inhibitors of various kinases blocked the increase in i(cap) induced by ATP. The enhancing effect of ATP was also observed in inside-out patches of oocytes expressing vanilloid receptor 1, a cloned capsaicin receptor. Single point mutations (D178N, K735R) within the putative Walker type nucleotide-binding domains abolished the effect of ATP. These results show that ATP increases i(cap) in sensory neurons by direct interaction with the CAP channel without involvement of phosphorylation.

Amino acid substitution within the S2 and S4 transmembrane segments in Shaker potassium channel modulates channel gating

To investigate of the gating properties in the voltage-activated potassium channel, we have mutated a variety of S2 and S4 residues in the Shaker potassium protein. Results showed that the R365C and R368C, but not the E283C, R362C, R365S, R368S or the ShB-IR, were sensitive to micromolar concentrations of Cd(2+) ions. This indicates that R365 and R368 play a crucial role in the channel gating due to a conformational modulation of the channel structure. Doubly mutated channels of the E283C/R365E and E283C/R368E caused a transient increase in current amplitude, which reached a peak within a few seconds and then decreased toward initial levels, despite the continual presence of Cd(2+). Taken together, our results suggest that E283, R365, and R368 form a network of strong, local, and electrostatic interactions that relate closely to the mechanism of the channel gating.

The cAMP-dependent kinase pathway does not sensitize the cloned vanilloid receptor type 1 expressed in xenopus oocytes or Aplysia neurons

Capsaicin-activated channels present in sensory neurons are ligand-gated cation channels that largely account for mediating some types of pain. The cAMP-dependent protein kinase (PKA) signal pathway was suggested to mediate the prostaglandin-induced enhancement of capsaicin-evoked inward current (I(CAP)) in rat sensory neurons. It is not clear, however, whether PKA acts directly on the capsaicin-sensitive channel that is responsible for I(CAP). To address this issue, we overexpressed the cloned capsaicin receptor, VR1, in heterologous expression systems such as Xenopus oocytes or Aplysia R2 neuron and stimulated PKA pathways. As a result, activation of PKA by applying either 8-bromo-cAMP or forskolin with 3-isobutyl-1-methylxanthine or through activation of beta(2) adrenergic receptors failed to enhance I(CAP) in oocytes or R2 neurons expressing VR1. Our results raise two possibilities. (1) Direct phosphorylation of VR1 by PKA may not be responsible for the sensitization; instead, phosphorylation of regulatory proteins associated with VR1 would account for the sensitization of I(CAP) evoked by prostaglandin E(2) in dorsal root ganglion (DRG) neurons. (2) DRG neurons may have a different PKA signaling mechanism that is not replicable in Xenopus oocytes or Aplysia R2 neurons.

Direct activation of capsaicin receptors by products of lipoxygenases: endogenous capsaicin-like substances

Capsaicin, a pungent ingredient of hot peppers, causes excitation of small sensory neurons, and thereby produces severe pain. A nonselective cation channel activated by capsaicin has been identified in sensory neurons and a cDNA encoding the channel has been cloned recently. However, an endogenous activator of the receptor has not yet been found. In this study, we show that several products of lipoxygenases directly activate the capsaicin-activated channel in isolated membrane patches of sensory neurons. Among them, 12- and 15-(S)-hydroperoxyeicosatetraenoic acids, 5- and 15-(S)-hydroxyeicosatetraenoic acids, and leukotriene B(4) possessed the highest potency. The eicosanoids also activated the cloned capsaicin receptor (VR1) expressed in HEK cells. Prostaglandins and unsaturated fatty acids failed to activate the channel. These results suggest a novel signaling mechanism underlying the pain sensory transduction.

Ligand binding inhibitors of A1 adenosine receptor from Rana rugosa are phospholipase A2s

Inhibitors of the A1 adenosine receptor were isolated from the skin extract of Korean frog, Rana rugosa. The frog-skin extract was prepared by an electrical shock and fractionated with C4 followed by C18 reverse-phase HPLC. Two A1 receptor inhibitors were isolated using a filter binding assay and the molecular masses of the proteins were estimated by matrix-assisted laser desorption ionization time-of-flight mass spectrometry to be 15 347 and 15 404 Da, respectively. The inhibitory activity was also measured against other membrane receptors, such as the A2 adenosine receptor, muscarinic acetylcholine receptor and capsaicin receptor. Ligand binding to the A2 and muscarinic receptors was also severely inhibited by these proteins. However, they did not inhibit the functional activation of the capsaicin receptor by its ligand, capsaicin, suggesting that inhibition of ligand-receptor binding occurs specifically. Their N-terminal sequences were determined by Edman degradation. Surprisingly, they showed sequence similarity to the secretory protein, phospholipase A2 from various organisms. The phospholipase A2 activity of both proteins was tested using Dole's assay technique. Both proteins showed phospholipase A2 activity, and therefore, they were designated as PLA2-R1 and PLA2-R2, respectively. In addition, their ligand-binding inhibitory activity depended on their phospholipase A2 activity. This is the first finding that the frog secretes a phospholipase A2 similar to that of snake venoms, which posess inhibitory activity against the adenosine A1, adenosine A2 and muscarinic receptors.

Dynamic chromatin remodeling in the vicinity of J chain gene for the regulation of two stage-specific genes during B cell differentiation

Dynamic chromatin remodeling during B cell differentiation was identified in the vicinity of J chain gene. In pre-B cells, the enhancer-containing DNase I hypersensitive sites (HSSs) 3-4 were open. However, these HSSs 3-4 turned out to be unassociated with J chain gene expression, as the J chain promoter-containing HSS1 remained in a closed state. The open enhancer HSSs 3-4 in the pre-B cells might be related to the expression of a pre-B cell-specific gene upstream of the HSSs 3-4, which was identified in our Northern blot analyses. The HSSs 3-4 are then closed in the next immature and mature B cell stages until the IL-2 opens the HSSs 3-4 again as well as HSS1 to express J chain gene in the primary immune responses. The dynamic regulation of chromatin structure during B cell differentiation for the expression of two stage-specific genes will provide a good model system for the study of B cell differentiation and gene expression.

3-Acyloxy-2-phenalkylpropyl amides and esters of homovanillic acid as novel vanilloid receptor agonists

A series of 3-acyloxy-2-phenalkylpropyl amides and esters of homovanillic acid were designed and synthesized as vanilloid receptor agonists containing the three principal pharmacophores of resiniferatoxin. Amide analogues 23, 5 and 11 were found to be potent agonists in vanilloid receptor assay both for ligand binding and for activation.

Capsaicin binds to the intracellular domain of the capsaicin-activated ion channel

Capsaicin (CAP) excites small sensory neurons, causing pain, neurogenic inflammation, and other visceral reflexes. These effects have been proposed to be the result of CAP activation of a nonselective cation current. It is generally assumed that CAP binds to an extracellular domain of the membrane receptor. However, the exact binding site is not known because of the lipophilic nature of CAP. To determine whether the binding domain is extracellular or intracellular, we tested the effect of a synthetic water-soluble CAP analog, DA-5018.HCl, on current activation. CAP activated the 45 pS (at -60 mV) nonselective cation channel from either side of the membrane. However, DA-5018.HCl, which had a greater potency and efficacy than CAP, activated the channels only from the cytosolic side of the patch membrane in a capsazepine, a CAP receptor antagonist, reversible manner. When applied extracellularly, DA-5018. HCl did not, but CAP did, activate whole-cell currents in sensory neurons, as well as in oocytes expressing vanilloid receptor 1, a recently cloned CAP receptor. Hydrogen ions, reported as a possible endogenous activator of cation current, failed to elicit any current when acidic medium (pH 5.0-6.0) was applied intracellularly, indicating that H+ does not mediate the CAP effect. These results indicate that CAP and its analog bind to the cytosolic domain of the CAP receptor and suggest that an endogenous CAP-like substance other than H+ may be present in the cell.

A capsaicin-receptor antagonist, capsazepine, reduces inflammation-induced hyperalgesic responses in the rat: evidence for an endogenous capsaicin-like substance

In the present study, the presence of an endogenous capsaicin-like substance and the role of capsaicin receptors in nociception during inflammation were assessed using Fos immunohistochemistry and the paw-withdrawal test in rats. Intradermal injection of carrageenan in the hind-paw produced inflammation in the foot pad, increased the number of cells exhibiting Fos-like immunoreactivity in the dorsal horn of the spinal cord, and decreased the paw-withdrawal latency. Intradermal injection of capsazepine, a capsaicin-receptor antagonist, significantly reduced the number of cells exhibiting Fos-like immunoreactivity, significantly increased the paw-withdrawal latency, but did not decrease inflammation induced by carrageenan injection. Intradermal injection of capsaicin or formalin also increased Fos-positive neurons. Capsaicin- or formalin-induced Fos expression was reduced in both cases by pretreatment of capsazepine, but to a much lesser extent for formalin. The capsazepine inhibition of carrageenan inflammation-induced hyperalgesic responses strongly suggests that an endogenous capsaicin-like substance is released in inflamed tissues and produces nociceptive neural impulses by acting on capsaicin receptors present on sensory neurons. Furthermore, our results indicate that capsaicin receptors take part only in generating nociceptive signals in sensory neurons, but not in activating the inflammation-promoting cells.

Capsaicin activates a nonselective cation channel in cultured neonatal rat dorsal root ganglion neurons

Capsaicin (CAP), a neurotoxin, has been reported to activate a nonselective cation current in dorsal root ganglion (DRG) neurons. In this paper, we identify and describe the properties of CAP-activated single channels in cultured neonatal rat DRG neurons. We first identified CAP-sensitive whole-cell currents that reversed near 0 mV in physiological solution. In solution containing 140 mM Na+, extracellular application of CAP to outside-out patches caused activation of an ion channel in a concentration-dependent manner (EC50 = 1.1 microM). The channel was blocked by the CAP antagonist capsazepine (10 microM). The channel was also activated by 2-10 nM resiniferatoxin, a potent analog of CAP. In symmetrical 140 mM Na+, the single-channel slope conductances were 45.3 +/- 1.0 and 80.0 +/- 4.2 pS at -60 and +60 mV, respectively, showing outward rectification (n = 9). The reversal potential did not shift significantly when Na+ was replaced by K+, Cs+, Rb+, or Li+, showing that the channel discriminated poorly among cations. The channel was also permeable to Ca2+. Although acid (pH < 6.2) was suggested to be an endogenous activator of the CAP receptor, an acid solution (pH 5.9-6.0) failed to activate the channels in outside-out patches. This is the first clear demonstration of the presence of the CAP-activated ion channel in DRG neuron. Opening of these ligand-gated, cation-selective channels gives rise to the whole-cell CAP-activated current in DRG neurons and may underlie the neurotoxic effects of CAP.

Modulation of the serotonin-activated K+ channel by G protein subunits and nucleotides in rat hippocampal neurons

In hippocampal neurons, 5-hydroxytryptamine (5-HT) activates an inwardly rectifying K+ current via G protein. We identified the K+ channel activated by 5-HT (K5-HT channel) and studied the effects of G protein subunits and nucleotides on the K+ channel kinetics in adult rat hippocampal neurons. In inside-out patches with 10 microM 5-HT in the pipette, application of GTP (100 microM) to the cytoplasmic side of the membrane activated an inwardly rectifying K+ channel with a slope conductance of 36 +/- 1 pS (symmetrical 140 mM K+) at -60 mV and a mean open time of 1.1 +/- 0.1 msec (n = 5). Transducin beta gamma activated the K5-HT channels and this was reversed by alpha-GDP. Whether the K5-HT channel was activated endogenously (GTP, GTP gamma S) or exogenously (beta gamma), the presence of 1 mM ATP resulted in a approximately 4-fold increase in channel activity due in large part to the prolongation of the open time duration. These effects of ATP were irreversible and not mimicked by AMPPMP, suggesting that phosphorylation might be involved. However, inhibitors of protein kinases A and C (H-7, staurosporine) and tyrosine kinase (tyrphostin 25) failed to block the effect of ATP. These results show that G beta gamma activates the G protein-gated K+ channel in hippocampal neurons, and that ATP modifies the gating kinetics of the channel, resulting in increased open probability via as yet unknown pathways.

Different properties of the atrial G protein-gated K+ channels activated by extracellular ATP and adenosine

Extracellular ATP (ATPo) and adenosine activate G protein-gated inwardly rectifying K+ currents in atrial cells. Earlier studies have suggested that the two agonists may use separate pathways to activate the K+ current. Therefore, we examined whether the K+ channels activated by the two agonists have different properties under identical ionic conditions. In cell-attached patches, K+ channels activated by 100 microM ATP in the pipette had a single-channel conductance and mean open time of 32.0 +/- 0.2 pS and 0.5 +/- 0.1 ms, respectively, compared with 31.3 +/- 0.3 pS and 0.9 +/- 0.1 ms for the K+ channels activated by adenosine (140 mM KCl). With ATPo as the agonist, the K+ channel activity in cell-attached patches was approximately threefold lower than that in inside-out patches with 100 microM GTP in the bath. Applying ATP to the cytoplasmic side of the membrane (ATPi) produced a biphasic concentration-dependent effect on channel activity: an increase at low [mean affinity constant (K0.5) = 190 microM] and a decrease at high (K0.5 = 1.3 mM) concentrations. In contrast, with adenosine as the agonist, K+ channel activity in cell-attached patches was approximately fourfold greater than that in inside-out patches with 100 microM GTP in the bath. In inside-out patches, ATPi only augmented the K+ channel activity (K0.5 = 32 microM). These results show that although both ATPo and adenosine activate kinetically similar K+ channels in atrial cells, the channels are regulated differently by intracellular nucleotides.

Neurogenic hyperalgesia: central neural correlates in responses of spinothalamic tract neurons

1. The contribution of activity in spinothalamic tract (STT) neurons to the pain and neurogenic hyperalgesia produced by an intradermal injection of 100 micrograms of capsaicin was investigated. Electrophysiological responses of identified STT neurons recorded in anesthetized monkeys were compared with psychophysical measurements of pain and hyperalgesia obtained in humans using identical stimuli. 2. Magnitude estimates of pain in humans were obtained after an injection of capsaicin or the vehicle. Capsaicin produced immediate burning pain that was most intense within 15 s after injection and then declined over the next 10-30 min. The vehicle produced no pain. 3. Cutaneous hyperalgesia to gentle stroking (allodynia) and also hyperalgesia to punctate stimulation developed in a wide area surrounding the capsaicin injection. Within this area, magnitude estimates of pain produced by a punctate stimulus (von Frey type with force of 225 mN) increased over preinjection values by an average of sixfold at test sites, 1, 2, and 3 cm away from the injection site. At the capsaicin injection site, magnitude estimates of pain in response to punctate simulation typically remained the same or were decreased. 4. After capsaicin, but not vehicle, the mean heat pain thresholds were lowered from approximately 45 degrees C before injection to 34 degrees C after, but only in the immediate vicinity of the injection site. At a site located 2 cm away, the thresholds were not significantly altered. Similarly, magnitude estimates of pain produced by suprathreshold heat stimuli were increased after capsaicin only at the injection site. 5. STT neurons were classified as high-threshold (HT) or wide-dynamic-range (WDR) cells according to responses evoked by graded cutaneous mechanical stimulation. An intradermal injection of capsaicin excited 4 of 7 HT cells and 10 of 12 WDR cells. The discharge rates of STT neurons correlated in time course with the magnitude estimates of pain in humans. The correlation was considerably better for WDR than for HT neurons, suggesting a predominant contribution of WDR neurons to the pain from capsaicin. 6. Capsaicin significantly increased the responses of HT neurons (9-fold) and the responses of WDR neurons (2-fold) to stroking the skin within the receptive field. Similar increases in responses to a standard punctate stimulus were observed at test sites, 1, 2, and 3 cm away from the injection site. After injection of vehicle, the responses to punctate stimulation increased by a mean of only 1.2- and 1.4-fold for HT and WDR neurons, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)