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. 2010 Aug 11;169(1):431-5.
doi: 10.1016/j.neuroscience.2010.04.082. Epub 2010 May 10.

Hyperalgesic priming is restricted to isolectin B4-positive nociceptors

E K Joseph  1 , J D Levine
Affiliations

Hyperalgesic priming is restricted to isolectin B4-positive nociceptors

E K Joseph et al. Neuroscience. .

Abstract

We have previously described a rat model for the contribution of neuroplastic changes in nociceptors to the transition from acute to chronic pain. In this model a prior injury activates protein kinase C epsilon (PKCepsilon), inducing a chronic state characterized by marked prolongation of the hyperalgesia induced by inflammatory cytokines, prototypically prostaglandin E(2) (PGE(2)), referred to as hyperalgesic priming. In this study we evaluated the population of nociceptors involved in priming, by lesioning isolectin B4-positive (IB4(+)) nociceptors with intrathecal administration of a selective neurotoxin, IB4-saporin. To confirm that the remaining, TrkA(+)/IB4(-), nociceptors are still functional, we evaluated if nerve growth factor (NGF) induced hyperalgesia. While pretreatment with IB4-saporin eliminated the acute mechanical hyperalgesia induced by glia-derived neurotrophic factor (GDNF), NGF and PsiepsilonRACK, a highly selective activator of PKCepsilon, induced robust hyperalgesia. After injection of NGF, GDNF or PsiepsilonRACK, at a time at which hyperalgesia induced by PGE(2) is markedly prolonged (hyperalgesic priming) in control rats, in IB4-saporin-pretreated rats PGE(2) failed to produce this prolonged hyperalgesia. Thus, while PKCepsilon is present in most dorsal root ganglion neurons, where it can contribute to acute mechanical hyperalgesia, priming is restricted to IB4(+)-nociceptors, including those that are TrkA(+). While PKCepsilon activation can induce acute hyperalgesia in the IB4(+) population, it fails to induce priming. We suggest that hyperalgesic priming occurs only in IB4(+) nociceptors, and that in the peripheral terminals of nociceptors separate intracellular pools of PKCepsilon mediate nociceptor sensitization and the induction of hyperalgesic priming.

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Figures

Figure 1
Figure 1. Changes in mechanical hyperalgesia in IB4-saporin pretreated rats
A. Changes in mechanical hyperalgesia in IB4-saporin pretreated rats Intradermal injection of glia-derived neurotrophic factor (GDNF) in rats that were pretreated with the neurotoxin isolectin B4 (IB4)-saporin failed to produce mechanical hyperalgesia (n=6), while in groups of rats similarly pretreated with IB4-saporin, nerve growth factor (NGF) and ψεRACK produced robust hyperalgesia (both n=6; p<0.001). B. Hyperalgesia induced by GDNF, NGF and ψεRACK Intradermal administration of GDNF (10 ng), NGF (1 μg) and ψεRACK (1 μg) produced mechanical hyperalgesia in naïve rats. All drugs were injected in a volume of 5 μl and the paw withdrawal thresholds measured 30 min after each injection (n=6/group, p<0.001).
Figure 2
Figure 2. Lack of hyperalgesic priming in IB4-saporin pretreated rats
A. Lack of hyperalgesic priming in IB4-saporin pretreated rats In rats pre-treated with IB4-saporin, 10 days prior, NGF and ψεRACK, as well as GDNF, prostaglandin E2 (PGE2) administered in separate groups of rats, failed to induce hyperalgesic priming. B. GDNF, NGF and ψεRACK-induced hyperalgesic priming Intradermal injection of PGE2 produced priming (prolonged duration of PGE2 hyperalgesia) in rats that were previously treated with GDNF, NGF or ψεRACK (n=6/group, p<0.001).
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