Establishment of bee venom-induced contralateral heat hyperalgesia in the rat is dependent upon central temporal summation of afferent input from the site of injury

The present investigation was designed to study whether central sensitization is determined by a time window of central summation of ongoing primary afferent input from a peripheral injury site. Sensitization was assessed behaviorally in the rat as contralateral heat hyperalgesia induced by injection of bee venom (BV) in the hind paw. The sciatic nerve was transected at various time points following intraplantar BV injection to analyze the time window for contralateral hyperalgesia. The results show that after a dose of 0.2 mg BV, axotomy at 5 min completely prevented contralateral heat hyperalgesia but was without effect at 10 min, whereas after a dose of 0.1 mg BV, axotomy at 10 min was able to prevent the contralateral heat hyperalgesia but remained without effect at 20 min. These findings suggest an important role of the amount of ipsilateral ongoing primary afferent in establishing the contralateral heat hyperalgesia. Moreover, by counting the total amount of paw flinches that is believed to be mediated by ongoing primary afferent input, it was shown that 87.35 +/- 5.36, 170.50 +/- 9.15 and 305.80 +/- 20.13 flinches were induced by 0.2 mg BV for a period of 5, 10 and 20 min, respectively. At the lower dose of 0.1 mg BV significant fewer flinches were elicited with 59.17 +/- 13.54, 133.00 +/- 22.33 and 234.00 +/- 36.42 within the three corresponding time windows before sciatic nerve transection. The results suggest that the amount of primary afferent input determines the time window required to establish central changes that are independent of further afferent input. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.