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Sustained sensitization and recruitment of rat cutaneous nociceptors by bradykinin and a novel theory of its excitatory action
Author(s) -
Liang YunFei,
Haake Bettina,
Reeh Peter W.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0229g.x
Subject(s) - nociceptor , tachyphylaxis , bradykinin , sensitization , excitatory postsynaptic potential , chemistry , hyperalgesia , radiant heat , mechanosensitive channels , endocrinology , medicine , anesthesia , nociception , biophysics , inhibitory postsynaptic potential , immunology , biology , materials science , receptor , ion channel , composite material
1 Excitation and sensitization to heat of nociceptors by bradykinin (BK) were examined using an isolated rat skin‐saphenous nerve preparation. 2 A total of 52 C‐fibres was tested: 42 were mechano‐heat sensitive (CMH) and 40 % of them were excited and sensitized to heat by BK superfusion (10 −5 m , 5 min) of their receptive fields; heat responses were augmented by more than five times and heat thresholds dropped to 36.4 °C, on average. 3 Sixty per cent of the CMH did not respond to BK itself, but 3/4 of these units showed an increase in their heat responses by more than 100 % following BK exposure. 4 Ten high‐threshold mechanosensitive C‐fibres did not discharge upon BK application but following this five of them responded to heat in a well‐graded manner. 5 In all fibres, the sensitizing effect of BK was abolished within 9 min or less of wash‐out, and it could be reproduced several times at equal magnitude, whereas the excitatory effect of BK regularly showed profound tachyphylaxis. 6 Sustained superfusion (20 min) of BK induced a desensitizing excitatory response while superimposed heat responses showed constant degrees of sensitization. 7 The large extent and high prevalence of BK‐induced sensitization (almost 80 % of all fibres tested) and de novo recruitment of heat sensitivity suggest a prominent role of BK not only in hyperalgesia but also in sustained inflammatory pain which may be driven by body or even lower local temperatures acting on sensitized nociceptors. 8 Based on the latter assumption, a hypothesis is put forward that excludes a direct excitatory effect of BK on nociceptors, but assumes a temperature‐controlled activation as a result of rapid and profound sensitization.