Effect of red peppers (Capsicum frutescens) intake during gestation on thermonociceptive response of rat offspring

Oral administration of aqueous red pepper (Capsicum frutescens, Cf) solution and low capsaicin (8-methyl-N-vanillyl-6-nonenamide) doses during gestation produces an increase in the latency of the thermonociceptive escape response of rat offspring. The present work shows that different amounts of Cf (10%, 25% and 50%) incorporated to normal food of gestating rats modify in a dose-dependent manner the flexion reflex latency (R), as well as the latency of appearance of antialgesic behaviours expressed as paw lick (P) and escape response (E) using the hot plate test (53 degrees C+/-0.5 degrees C). The latency of the same parameters was tested in the same subjects 55 days later to determine the persistence of this effect. Results show an increase in latency of the three parameters R, P and E in all experimental groups with respect to controls. Animals (Cf, 25% group) tested 55 days after the first test exhibited latencies similar to controls, which suggests that the process is reversible.

Antipruritic and thermal sensation effects of hydrocortisone creams in human skin

Few studies evaluate the effect of topical corticosteroids on thermal sensation and in alleviation of itch produced by intradermal injection of histamine. We evaluated the antipruritic effect of hydrocortisone (1% and 2.5%) on histamine-induced itch and sensory effects by measuring itch magnitude, itch duration and thermal thresholds using a computerized thermal sensory analyzer (TSA). This was a double-blind, random, comparative, controlled, single-dose and single-center study. Itch was experimentally induced in both forearms by intracutaneous injection of histamine in 18 subjects. Hydrocortisone 1%, 2.5% and placebo were applied to test sites on both forearms. The thermal threshold for warmth sensation, cold sensation, cold and heat pain was measured with the TSA. Itch magnitude was measured each minute after histamine injection for 10 min with a visual analogue scale (VAS). Itch duration was also recorded. In comparison to placebo, 2.5% hydrocortisone significantly (p = 0.03) reduced itch duration from 12.6 +/- 11.0 min (mean +/- SD) to 8.6 +/- 8.2 min (the reducing rate was 32%) as well as itch magnitude (at minutes 3, 6, 7 and overall). Placebo, 1% and 2.5% hydrocortisone significantly altered (p <0.05) the cold sensation threshold. No treatment altered cold or heat pain thresholds. These data suggest that topical application of 2.5% hydrocortisone may be significantly beneficial for the treatment of histamine-induced itch. The correlation between thermal measurements and antipruritic effects warrants further study.

Prostaglandin I(2), a possible thermo-sensory mediator in Paramecium

Thermo-sensory mechanisms are little understood. The protozoan, Paramecium multimicronucleatum, is sensitive and responsive to a cooling stimulus. We found that inhibitors of prostaglandin (PG) biosynthesis reduced the response to the cooling stimulus. Inversely, the response suppressed by the inhibitors was recovered by application of stable PGI(2) analogs, including iloprost. Paramecium cells showed binding activity specific for [(3)H]iloprost. Moreover, an arachidonic acid metabolite, possibly PGI(2), was rapidly increased in response to the cooling stimulus, suggesting that prostaglandin biosynthesis plays a crucial role in the cooling-sensory transduction. Paramecium may be a useful model for the investigation of the molecular basis of thermo-sensory mechanisms.

Antiretroviral therapy may improve sensory function in HIV-infected patients: a pilot study

OBJECTIVE

To evaluate thermal and nociceptive function in a prospective, longitudinal study of 49 consecutive HIV-1-infected patients before and at 1, 4, and 8 months after initiation of highly active antiretroviral therapy.

METHODS

Quantitative assessments of thermal perception thresholds for warmth (dWT), cold (dCT), and heat pain (HPT) were performed. CD4+ cell levels in blood and HIV-1 RNA levels in plasma were determined. Depending on the virologic response to treatment, the patients were divided into two groups: responders (37 of 49, 76%) and nonresponders (12 of 49, 24%).

RESULTS

Before treatment, impairment of dWT was found in 26 of 49 patients, of dCT in 33 of 49 patients, and of HPT in 19 of 49 patients. Improvements of perception thresholds for dWT (p < 0.0001), dCT (p < 0.001), and HPT (p < 0.01) were observed after 8 months of treatment in the responder group but not in the nonresponders. Within the responder group, improved thermal perception thresholds was associated with higher pretreatment CD4+ levels than in patients without improvement.

CONCLUSIONS

Virologically successful antiretroviral combination therapy of HIV-1-infected patients has a capacity to improve function of the thermal and nociceptive systems, especially in patients with less advanced immunodeficiency.

Preinjury treatment with morphine or ketamine inhibits the development of experimentally induced secondary hyperalgesia in man

We examine the effect of morphine or ketamine (N-methyl-D-aspartate receptor antagonist; NMDA) treatment on secondary hyperalgesia. Drug treatment started preinjury and continued into the early postinjury period. Hyperalgesia was induced by a local 1 degrees burn injury covering 12.5 cm(2) on the medial side of the calf. In this double-blind, cross-over study, 12 healthy volunteers received, on 3 separate days and in randomized order: (1) placebo; (2) morphine, bolus 150 microg/kg + infusion 1 microg/kg per min and 0.5 microg/kg per min; and (3) ketamine, bolus 60 microg/kg + infusion 6 microg/kg per min and 3 microg/kg per min. Bolus + infusion started 30 min before injury and ended 50 min after it. The area of secondary hyperalgesia was quantitated using punctate (von Frey filaments) and brush stimuli (electric brush). On the day of placebo, all subjects developed an area of hyperalgesia to punctate and brush stimuli outside the thermal injury (secondary hyperalgesia). We show that ketamine or morphine treatment starting preinjury significantly reduces this development (P<0.01, both). In a previous study, we found that postinjury treatment alone with morphine did not affect secondary hyperalgesia, whereas ketamine did so significantly. The differential response to morphine administered pre- or postinjury may be relevant to the recently shown NMDA receptor mediated interaction of central hyperexcitability and morphine antinociception. The effect of ketamine supports the hypothesis of the role of NMDA receptor mediation in central hyperexcitability.

Genetic differences in morphine sensitivity, tolerance and withdrawal in rats

Significant genetic differences in the endogenous opioid system and in response to a variety of noxious stimuli are present in rodents. We now compared the response to noxious heat with the hot plate test, morphine sensitivity and the development of tolerance and dependence to morphine in spontaneously hypertensive (SHR), Wistar-Kyoto (WK) and Sprague-Dawley (SD) rats. Significant differences were observed in basal nociception among the three strains, where SHRs were hypoalgesic compared to WK and SD. The antinociceptive effect of morphine varied among strains (SD>SHR>WK) as did the rate of tolerance development (10 mg/kg morphine 2/day for 4 days) where WK>SD=SHR. SHR rats developed hyperalgesia following morphine administration during the course of tolerance development. Furthermore, although naloxone (2 mg/kg) precipitated withdrawal symptoms in all tolerant rats, the panorama of symptoms varied among the three strains. Thus, there are significant genetic differences in a variety of effect of opiates.

Effects of systemic, intracerebral, or intrathecal administration of an N-methyl-D-aspartate receptor antagonist on associative morphine analgesic tolerance and hyperalgesia in rats

A flavor paired with morphine shifted to the right the function relating morphine dose to tail-flick latencies and provoked hyperalgesic responses when rats were tested in the absence of morphine. These learned increases in nociceptive sensitivity were not mediated by alterations in tail-skin temperature. Microinjection of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist D,L-2-amino-5-phosphonopentanoic acid (AP-5) into the lateral ventricle reversed the hyperalgesic responses but spared the tolerance to morphine analgesia. By contrast, systemic administration of the noncompetitive NMDA receptor antagonist MK-801 or intrathecal infusion of AP-5 reversed the hyperalgesic responses as well as the tolerance to morphine analgesia. The results demonstrate that associatively mediated tolerance to morphine analgesia can co-occur with hyperalgesic responses and are discussed relative to learned activation of endogenous pronociceptive mechanisms.

Effects of kappa and delta opioid agonists on activity and thermosensitivity of rat hypothalamic neurons

Extracellular recordings were made from 161 warm-sensitive, six cold-sensitive and 153 temperature-insensitive neurons in slices of the preoptic area/anterior hypothalamus (PO/AH) of rats, to investigate the effects of the kappa-receptor opioid agonist dynorphin A1-17 and the delta-receptor opioid agonist DPDPE on neuronal response characteristics. While 61% of the neurons exhibited kappa-receptors, delta-receptors were only present in 37% of the neurons. No co-localization was observed between kappa- and delta-receptors, whereas mu-receptors could be co-localized with kappa- as well as delta-receptors. Antagonistic effects on tonic activity were induced by different concentrations of the kappa-agonist dynorphin A1-17. At 0.5 nM, the excitatory effect was predominant, while 50% of the neurons were already inhibited at 5 nM and inhibition was the major effect at 100 nM. A significant increase in temperature sensitivity was observed in warm-sensitive neurons during administration of 0.5 nM dynorphin A1-17; in contrast, the temperature sensitivity was significantly decreased at the high dose of 100 nM. In most of the neurons responding to the delta-receptor agonist DPDPE (0.5-100 nM) the firing rate was decreased. The temperature sensitivity was only affected in warm-sensitive neurons, and was increased in the majority of neurons at 0.5 and 5 nM, but predominantly decreased at higher concentrations. The effects of low concentrations of dynorphin A1-17 and DPDPE were prevented by pre- and co-perfusion of the appropriate antagonists. The present results suggest that changes of the temperature sensitivity of warm-sensitive PO/AH neurons are an important mechanism for the effect of low doses of opioids on body temperature.

Inescapable shock-induced potentiation of morphine analgesia

Exposure to various stressors potentiates nociceptive and nonnociceptive responses to morphine. These phenomena have received little study despite their seeming generality and importance for understanding analgesia and opiate action. The present experiments characterize inescapable shock (IS)-induced potentiation of morphine analgesia. Rats were exposed to IS, equal escapable shocks (ESs), or restraint (control). Potentiation of analgesia (tail-flick [TF] test and hotplate test) was observed only in rats given IS 24 or 48 hr earlier, in agreement with previously reported learned-helplessness effects. Finally, no change in tail temperature or motor function was found that could be inaccurately interpreted as analgesia. The relevance of these findings to stressor-induced enhancement of morphine analgesia and potential substrates of IS effects are discussed.

Defect of cold-sensitive response in calmodulin mutants of Paramecium and the restoration by cyclic nucleotide

Wild type and calmodulin mutants (cam) of Paramecium tetraurelia were examined for cold-sensitive responses. Among mutants tested, cam12 and cam13 mutants, which have substitutions in N-terminal lobe of calmodulin molecule, reduced both responses in the swimming and the membrane potential. Under voltage clamp conditions, the cooling stimulus to the wild type cell induced a transient inward current whose amplitude increased with the rate of temperature drop. The cam12 cell did not induce inward currents in response to cooling with a rate slower than -0.4 degree C/s. The reduced current response of cam12 mutant was restored by an external application of a phosphodiesterase inhibitor, theophylline. Also, an intracellular injection of hydrolysis-resistant cyclic nucleotides, either 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP) or 8-bromoguanosine 3,5'-cyclic monophosphate (8-Br-cGMP), restored the current response. Such restoration was accompanied by shifts of the resting potential to hyperpolarized levels and by an increase in the membrane conductance. The results suggest the possibility that calmodulin and cyclic nucleotide regulate K+ channels responsive to the cooling stimulus.

Spinal anaesthesia for Caesarean section: effect of Sprotte needle orientation

We induced spinal anaesthesia in 100 women presenting for elective Caesarean section with the mother in the right lateral position. Patients were allocated randomly to have the side eye of the 24-gauge Sprotte spinal needle pointing in one of four directions: group A, cephalad; group B, right lateral; group C, left lateral; group D, caudad. Isobaric bupivacaine 0.5% (2.5 ml) was injected over 30 s before the mother was placed supine with a 15 degree left lateral tilt. Onset time and height of the subsequent analgesic and anaesthetic blocks were assessed by a blinded observer. Onset of sensory block to T4 was significantly faster in group A (P = 0.001). There were no differences in final block height, incidence of hypotension, nausea and vomiting or ephedrine requirements.

Effect of topically applied menthol on thermal, pain and itch sensations and biophysical properties of the skin

The effect of menthol and alcohol as its vehicle on thermal sensations, pain, experimental itch and irritation were studied in 18 subjects, using a computerized thermal sensory analyzer, laser Doppler flowmetry and an evaporimeter for transepidermal water loss (TEWL). Menthol had a subjective cooling effect lasting up to 70 min in 12/18 subjects; however, it did not affect cold and heat threshold, nor did it affect cold and heat pain threshold. Alcohol produced an immediate cold sensation lasting up to 5 min in 4/18 subjects and lowered the sensitivity of cold sensation threshold (P < 0.05). Histamine injection did not change thermal and pain thresholds. Menthol did not alleviate histamine-induced itch magnitude, nor its duration. Following histamine injection, cold sensation median threshold decreased by 1.2 degrees C from (29.9 degrees C to 28.7 degrees C) on the site treated with menthol (P < 0.01) with similar changes in thresholds at the alcohol-treated site (P < 0.05). Warm sensation and pain threshold in subjects receiving histamine injections, measured after menthol and alcohol application, did not differ from their baseline values with histamine alone. TEWL at the site treated with menthol was significantly higher (P < 0.05) than at the alcohol-treated and the control site (P < 0.01), suggesting that menthol has a higher skin irritating effect, or at least alters the stratum corneum water permeability. Our results suggest that menthol fulfills the definition of a counterirritant, but does not affect histamine-induced itch, nor does it affect pain sensation.

[Semiquantitative detection of pain and heat sensations in evaluation of contrast media in pelvic/leg angiography. Intraindividual double-blind study with iomeprol 350 and iopentol 350]

The effect on pain and heat sensation of monomere non-ionic contrast media with different osmolality was assessed in a randomized double-blind study. Peripheral angiography was performed in 29 patients who suffered from chronic occlusive vessel disease. The two non-ionic contrast media iomeprol and iopentol were applied intraindividually. The contrast media with an iodine concentration of 350 mg/ml had an osmolality of 618 or 810 mosm/kg. A contrast medium volume of 80 or 90 ml was injected in the abdominal aorta. The mean flow was 13.9 ml/s. The two contrast medium injections were separated by an interval of 10 min. No analgesic premedication was given. The pain and heat intensity was semiquantatively measured using a visual analogue scale ranging from 0 (no heat/pain) to 100 (intractable heat/pain). The median after the first injection was calculated as 40 for iomeprol and 70 for iopentol. The comparison of heat and pain sensations after the second injection showed a less distinct difference with a scale rating of 60 for iomeprol and of 65 for iopentol. The statistical variance was highly significant (p < 0.01) in favor of iomeprol.

A noninvasive method for studying quantitatively heat-evoked nocifensive hindlimb withdrawal reflexes in lightly anesthetized rats

We have developed a noninvasive method for studying quantitatively the magnitude of hindlimb withdrawal reflexes induced by noxious heat in lightly anesthetized rats. The amplitude, latency, and duration of the hindlimb withdrawal was determined by a very small piezoceramic device placed on the hamstring muscle while the glabrous skin of the hindpaw was stimulated using a feedback-controlled contact thermostimulator. An increase in the amplitude and duration of the withdrawal response, concomitant with a decrease in the response latency, was found with increasing stimulus temperature. The sensitivity of the method was verified using morphine, which produced a dose-related (3.5-7.0 mg/kg) attenuation of all these response components. The use of a piezoceramic device for measuring the withdrawal response provides a quantitative, noninvasive method for evaluating the magnitude of various components of the nocifensive withdrawal reflexes induced by noxious stimuli in lightly anesthetized rats.

A comparison of iodixanol with iopamidol in aorto-femoral angiography

This double-blind, randomized, parallel group clinical investigation in 140 consecutive patients undergoing aorto-femoral arteriography was carried out to compare iodixanol (Visipaque) 270 mgI ml-1 with iopamidol (Iopamiro) 300 mgI ml-1. The aims of the study were to compare adverse events and discomfort, clinical chemistry parameters in blood, haemodynamics and diagnostic information of the angiograms in the two groups. The main parameter for statistical analysis was the visual analogue scale (VAS) score for overall discomfort experienced by the patients during the examination. 134 patients, 69 and 65 receiving iodixanol and iopamidol, respectively, were examined according to the protocol and included in the evaluation. The two groups of patients were judged to be comparative. Statistically significant milder discomfort was felt with iodixanol than with iopamidol (p = 0.0001); mean VAS values 16 mm and 51 mm, respectively. Pain was reported far less frequently after iodixanol than after iopamidol (7.4% versus 50.8%) whereas sensation of warmth was less intense after iodixanol than after iopamidol. Four patients in the iodixanol group and two in the iopamidol group reported transient, non-serious adverse events. The difference was not statistically significant (p = 0.68). Systolic blood pressure was affected to a slightly greater degree after injection of iopamidol than after injection of iodixanol. Measurements of diastolic blood pressure, as well as clinical chemistry parameters in blood, revealed no changes of clinical importance, and all arteriograms performed were of diagnostic value. The conclusion is that iodixanol 270 mgI ml-1 is as efficacious as iopamidol 300 mgI ml-1, but produces less discomfort during arteriography. As such, iodixanol is a good alternative to iopamidol in aorto-femoral angiography.

Tail-flick test. I: Impact of a suprathreshold exposure to radiant heat on pain reactivity in rats

Radiant heat applied to the tail elicits a vigorous tail-flick response in rats. This tail-flick reflex is frequently used to measure pain reactivity. Prior research has shown that a suprathreshold exposure to the radiant heat used to elicit this reflex causes a reduction in tail-flick latencies in pentobarbital anesthetized rats. Experiment 1 replicated this observation and showed that the effect is not due to a change in tail temperature. Experiment 2 showed that reduced latencies (hyperalgesia) are not observed if the spinal cord is transected prior to testing. Experiment 3 revealed that pentobarbital anesthesia is required to observe thermal-induced hyperalgesia, for this effect is not observed in awake subjects. Experiments 4 and 5 extended this observation by showing that awake rats also fail to exhibit hyperalgesia if others measures of pain reactivity are employed (shock-induced vocalization and motor reactivity). Implications of the results are discussed.

Oligogenic determination of morphine analgesic magnitude: a genetic analysis of selectively bred mouse lines

Two ongoing selective breeding projects have produced mice that display divergent analgesic responses to morphine. These two projects have selected for similar phenotypes: high and low levorphanol analgesia (HAR/LAR lines; Portland, OR) and high and low swim stress-induced analgesia (HA/LA lines; Jastrzebiec, Poland). Evidence suggests genetic commonalities between mice of the two projects. Using a Mendelian breeding protocol, we have recently found that one or two genetic loci predominantly determine the high morphine analgesia exhibited by HA mice. In the present study we demonstrate that the differential morphine analgesia (5 mg/kg, i.p.) displayed by HAR and LAR mice is similarly oligogenic, predominantly determined by two unlinked loci. A complementation analysis, in which the analgesic responses to morphine of the recessive homozygotes of each project (HAR and HA) were compared to those of their hybrid offspring (HAR x HA), revealed that different genetic loci have been fixed in each project. An intriguing bimodal distribution was observed in the HAR x HA population: Some HAR x HA hybrids displayed greater morphine analgesia than either HAR or HA mice, whereas others displayed minimal analgesia. LAR x LA hybrids displayed less analgesia than either LAR or LA mice. The analgesic responses of HAR x LA and LAR x HA mice were comparable to those of their low-line parents. These findings indicate not only that different loci were responsible for producing high morphine responders in each selection project but that these distinct loci can interact synergistically to produce "superhigh" and "superlow" responders.

Possible involvement of the L-arginine-nitric oxide pathway in the modulation of stress-induced analgesia

The possible participation of nitric oxide (NO) in pain modulation and stress analgesia was studied in adult Wistar rats. Cerebral citruline as a coproduct of NO from L-arginine increased from the mean value 5.6 +/- 0.4 nM/mg.Pt. to 8.9 +/- 0.5 nM/mg.Pt. in acute restraint stress. In high doses (50 mg/kg body weight), intraperitoneal administration of L-arginine caused a small and transient decrease of the tail-flick latencies to the thermal stimulus, without significant changes of the stress analgesia induced by restraint stress. In animals pretreated with N-nitro-L-arginine methyl ester (NAME) a progressive increase of the latency time was obtained and the increased latencies induced by acute immobilization appeared significantly potentiated. These results offer new indirect evidence in favour of the modulatory role of NO in thermoalgesic sensitivity and stress-induced analgesia.

Sensory irritation and coolness produced by menthol: evidence for selective desensitization of irritation

The temporal characteristics of the oral perception of menthol solutions were explored in two experiments. In Experiment 1, 10 samples of either 0.03% or 0.30% menthol were presented at 1 min intervals and rated for the perceived intensity of cooling and irritation. Reports of sensation quality (burning, tingling, stinging and numbing) and pain were also collected. At the higher concentration, a significant decrease in perceived intensity was observed over time for irritation, but not for cooling. Experiment 2 was designed to explore further the nature of the decline in irritation observed in Experiment 1. Employing 1-min and 5-min inter-stimulus intervals between solutions, it was found that the decrease in menthol irritation more closely resembled desensitization than adaptation. Decreases in the frequency of reports of the burning and stinging qualities, but not the tingling, numbing or cooling qualities, suggested that menthol has a specific desensitizing effect on a population of mucosal nociceptive fibers.

Pain perception in depression: relationships to symptomatology and naloxone-sensitive mechanisms

A decrease in pain sensitivity during acute depression has been observed in several studies, apparently related to the severity of symptomatology. However, the question remains whether this relationship can be found only in heterogeneous groups of depressive patients or also in a single diagnostic group, such as major depression. In the present study, pain thresholds were assessed in 20 patients with major depression (DSM-III-R) and in 20 healthy controls. Two threshold methods with a differing impact of reaction time on the results were used. Contact heat was applied as a natural source of pain. With both methods the pain thresholds were significantly increased in the depressive patients. No relationship was found to the various symptoms of depression assessed by psychopathometric scales. In contrast to the pain thresholds, the thresholds of skin sensitivity for nonnoxious stimuli (warmth, cold, vibration) were only slightly increased. In subsamples (N = 10 in each group), naloxone (5 mg i.v.) and placebo were administered in a double-blind design. No systematic changes in pain thresholds occurred under either treatment. Our findings suggest that the decrease in skin sensitivity in major depression is specific to pain and not due to an increased reaction time. Moreover, the decrease appears to be related neither to a naloxone-sensitive mechanism nor to symptomatology.

Receptor selectivity of icv morphine in the rat cold water tail-flick test

The cold water tail-flick test in the rat is somewhat unique in that it is sensitive to the analgesic effects of delta- and kappa- in addition to mu-opioid agonists. The present study was designed to test whether a component of morphine-induced analgesia in this test might be mediated by delta- or kappa-opioid receptors. Morphine was administered icv in combination with the non-selective opioid antagonist naloxone (NLX), as well as the mu-, delta- and kappa-selective antagonists, D-Phe-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr (CTAP), naltrindole (NTI) and norbinaltorphimine (norBNI), respectively. Morphine induced analgesia in a dose related manner. Administration of NLX (1-10 micrograms) or CTAP (1 microgram) antagonized morphine in a competitive fashion. Neither NTI (1-10 micrograms) nor norBNI (0.1 microgram) had any effect on the morphine dose-effect curve. Thus, morphine appeared to be a selective mu agonist in the cold water tail-flick test, at least by the icv route.