Topographical distribution of warmth, burning and itch sensations in healthy humans

Monitoring of the oxidation of the oil from sacha inchi (

This work focuses on the characterization of the oxidation of the oil from sacha inchi seeds (Plukenetia volubilis) under accelerated conditions at 60 ºC for 15 days. Five samples were monitored: three supplemented with 200 ppm of non-hydrolyzed or partially hydrolyzed (for 4 and 9 hours) extracts from tara (Caesalpinia spinosa) pods, one without antioxidant and one with 200 ppm of BHT. Several conventional tech­niques (induction time, peroxide value, conjugated dienoic acid, p-anisidine value, total unsaturated fatty acids and α-linolenic acid contents) and the MIR spectroscopy coupled with chemometric tools were used and com­pared. The results revealed that whatever the antioxidant added, the oil from sacha inchi is fairly stable over time. The results also pointed out that extracts from tara pods, mainly those partially hydrolyzed, were more efficient than BHT against oil oxidation for up to 7 days. Finally, this paper shows that MIR spectroscopy pres­ents an interesting alternative technique for the monitoring of the oxidation of the oil from sacha inchi.

Topography of itch: evidence of distinct coding for pruriception in the trigeminal nerve

Introduction

Little is known about the topographical distribution of pruriception (in particular for nonhistaminergic itch), although conditions with chronic itch frequently occur in distinct anatomic and often bilateral patterns. This study aimed to investigate regional differences in the sensitivity to itch stimuli by assessing the intensity of itch, pain, and cutaneous neurogenic flare evoked by histamine and cowhage in different anatomic regions in 20 healthy volunteers.

Methods

Itch was induced by 1% histamine applied with a prick lancet or by insertion of 25±5 cowhage spicules in 4 regions: volar/dorsal forearm, lower back, and chin. The duration and intensity of itch and pain following each pruritic stimulus were measured by a continuous visual analogue scale (VAS_0-100). Sensitivity to touch-evoked itch was assessed by von Frey filaments and cutaneous flare was quantified by full-field laser perfusion imaging.

Results

Peak itch intensity was lower at the chin (19.4±3.6) compared with other areas (mean of 3 locations; 41.3±4.4), independently of whether histamine or cowhage was applied (P<0.01). Baseline sensitivity to touch-evoked itch was higher on the chin (P<0.01), but here hyperknesis did not develop in contrast to other areas (P<0.05). Cutaneous flare was more intense but had a smaller dispersion at the chin, compared with other areas (P<0.01).

Discussion

In conclusion, sensitivity to histaminergic and non-histaminergic itch diverges considerably between body regions. Lower density of pruriceptive CMH and CMI-neurons or distinct neuronal substrates for itch in the mandibular part of the trigeminal area may explain the observed reduced itch and vasomotor responses.

Sex differences in itch perception and modulation by distraction--an FMRI pilot study in healthy volunteers

BACKGROUND

Even though itch is a common syndrome of many diseases there is only little knowledge about sex and gender differences in pruritus, especially in central itch perception and modulation. To our knowledge, this is the first fMRI study examining sex differences in perception and its modulation by distraction.

METHODS

Experimental itch was induced by application of histamine (0.1 mM) via microdialysis fibers twice at the left forearm and twice at the left lower leg in 33 healthy volunteers (17 females, 16 males). The brain activation patterns were assessed by fMRI during itch without and with distraction (Stroop task). Between the various conditions, subjects were asked to rate itch intensity, desire to scratch and pain intensity. In a second experiment in 10 of the 33 volunteers histamine was replaced by saline solution to serve as control for the 'Stroop' condition.

RESULTS

Women generally presented higher itch intensities compared to men during itch over the course of the experiment. A more specific analysis revealed higher itch intensities and desire to scratch in women during experimental induced itch that can be reduced by distraction at the lower legs when itch is followed by 'Stroop'. In contrast, men depicted significant reduction of 'itch' by 'Stroop' at the forearms. Women depicted higher brain activation of structures responsible for integration of sensory, affective information and motor integration/planning during 'itch' and 'Stroop' condition when compared to men. No sex differences were seen in the saline control condition.

CONCLUSION

Women and men exhibited localisation dependent differences in their itch perception with women presenting higher itch intensities and desire to scratch. Our findings parallel clinical observations of women reporting higher itch intensities depending on itch localisation and suffering more from itch as compared to men.

"The itching hand"- important differential diagnoses and treatment

Skin diseases affecting the hands receive particular individual attention and constitute a considerable emotional burden. Many dermatoses also present with itching of the hands. Itch is often underestimated when it occurs in a comparably limited body area such as the hands. The high occupational significance of the hands in many professions must, nevertheless, be stressed. One of the most frequent diagnoses in itching of the hands is eczema. In the differential diagnosis, less common diseases such as neurological and systemic diseases and adverse drug reactions must also be taken into consideration. Itching of the hands can also be accompanied by other sensations, such as burning, stinging and pain. A thorough history regarding sensations and dysesthesias already allows for a diagnostic classification of the disease in some cases. Itching of the hands requires a careful and thorough diagnostic approach. This forms the basis of a specific and successful therapy which may be adapted stepwise, depending on the underlying cause, and also may require, in addition to causal therapy, symptomatic antipruritic therapy. Therapy should follow the current guidelines for chronic pruritus and hand eczema. This article reviews over the differential diagnosis and therapy of "itching hands".

Differences in peripheral endocannabinoid modulation of scratching behavior in facial vs. spinally-innervated skin

Cannabinoids suppress nocifensive behaviors in rodents. We presently investigated peripheral endocannabinoid modulation of itch- and pain-related behaviors elicited from facial vs. spinally-innervated skin of rats. Intradermal (id) injection of the pruritogen serotonin (5-HT) elicited significantly more hindlimb scratch bouts, and longer cumulative time scratching, when injected in the rostral back compared to the cheek. Pretreatment of skin with inhibitors of degrading enzymes for the endocannabinoids anandamide (URB597) or 2-arachidonoylglycerol (JZL184) significantly reduced scratching elicited by 5-HT in the rostral back. These effects were prevented by co-treatment with antagonists of the CB₁ (AM251) or CB₂ receptor (AM630), implicating both receptor subtypes in endocannabinoid suppression of scratching in spinally-innervated skin. Conversely, pretreatment with either enzyme inhibitor, or with AM630 alone, increased the number of scratch bouts elicited by id 5-HT injection in the cheek. Moreover, pretreatment with JZL184 also significantly increased pain-related forelimb wipes directed to the cheek following id injection of the algogen, allyl isothiocyanate (AITC; mustard oil). Thus, peripheral endocannabinoids have opposite effects on itch-related scratching behaviors in trigeminally- vs. spinally-innervated skin. These results suggest that increasing peripheral endocannabinoid levels represents a promising therapeutic approach to treat itch arising from the lower body, but caution that such treatment may not relieve, and may even exacerbate, itch and pain arising from trigeminally-innervated skin of the face or scalp.

The itchy scalp--scratching for an explanation

Scalp pruritus is a common complaint that is considered a diagnostically and therapeutically challenging situation. Scalp skin has a unique neural structure that contains densely innervated hair follicles and dermal vasculature. In spite of the recent advances in our understanding of itch pathophysiology, scalp itching has not been studied as yet. In this review, we summarize the current knowledge on the neurobiology of scalp and hair follicles as well as itch mediators and provide a putative mechanism for scalp itch with special emphasis on neuroanatomy and pathophysiology.

The pleasurability of scratching an itch: a psychophysical and topographical assessment

BACKGROUND

Scratching an itch is perceived as being pleasurable. However, an analysis of topographical variations in itch intensity, the effectiveness of scratching to provide itch relief and the associated pleasurability has not been performed at different body sites.

OBJECTIVES

To examine the role of scratching pleasurability in providing itch relief by investigating whether itch intensity is perceived differently at three different sites and to assess a potential correlation between the pleasurability and itch attenuation induced by scratching.

METHODS

Itch was induced on the forearm, ankle and back using cowhage spicules in 18 healthy subjects. These sites were subsequently scratched by an investigator with a cytology brush immediately following itch induction. The intensity of itch with and without scratching at these sites and the pleasurability of scratching were recorded by taking visual analogue scale ratings at 30-s intervals.

RESULTS

Mean itch intensity and scratching pleasurability ratings at the ankle and back were significantly higher than on the forearm. For the forearm and ankle, the greater the itch while scratching, the higher was the pleasurability. A higher baseline itch was linked to a higher itch reduction secondary to scratching in all tested areas. Pleasurability paralleled the curve of itch reduction for the back and forearm; however, scratching pleasurability at the ankle remained elevated and only slightly decreased while itch was diminishing.

CONCLUSIONS

There are topographical differences in itch intensity, the effectiveness of scratching in relieving itch and the associated pleasurability. Experimental itch induced by cowhage was more intensely perceived at the ankle, while scratching attenuated itch most effectively on the back.