Sj. Brull et al., Attenuation of experimental pruritus and mechanically evoked dysesthesiae in an area of cutaneous allodynia, SOMAT MOT R, 16(4), 1999, pp. 299-303
We investigated the effects of tactile allodynia on the itch and mechanical
ly evoked dysesthesiae produced by an intradermal injection of histamine in
human volunteers. After an intradermal injection of capsaicin into the vol
ar surface of one forearm, there developed an area of tactile allodynia to
stroking and hyperalgesia to pricking the skin. Histamine was then injected
simultaneously into the area of allodynia (experimental arm) and into the
opposite forearm (control arm). Magnitude estimates of itch were obtained e
very 15 s for 5 min, and the areas of cutaneous hyperalgesia (pricking-evok
ed pain), alloknesis (stroking-evoked itch), hyperknesis (pricking-evoked i
tch) and wheal and flare were measured. The areas of wheal and flare were n
ot significantly different on the two arms. The magnitude of itch and the a
reas of hyperknesis and alloknesis developed normally on the control arm bu
t were absent or greatly reduced on the experimental arm. Thus, both the it
ch and the alloknesis and hyperknesis normally induced by histamine were ab
sent or greatly reduced when histamine was injected in an area of capsaicin
-induced allodynia. These results are compatible with the hypothesis that a
ctivity in capsaicin-sensitive, nociceptive primary afferent neurons evokes
a central neuronal inhibitory process that prevents or reduces the itch an
d mechanically evoked dysesthesiae normally produced by an intradermal inje
ction of histamine.