Nociceptive responses to chronic stress of restraint and noxious stimuli in sucrose fed rats

Stress produces analgesia and sucrose ingestion immediately relieves the st ress in both the rat and human models, however the effect of sucrose feedin g on chronic stress of repeated varying pain is not known. Adult male rats were subjected to a stress regimen of restraint and various degrees of noxi ous stimuli given repeatedly during 58 h in six sessions with a rest of 32 h. In a 4-h session, the rats were subjected to the stress of thermal noxio us stimulation, pin prick and electrical stimulation of nociceptive afferen ts (six, one and nine times at intervals of S min) in addition to the restr aint stress. The effect of this stress on their nociceptive responses was n oted as hind paw lick latency, HPL; tail flick latency, TFL; threshold of t ail flick, TF; vocalization during stimulus, SV and vocalization after disc harge, VA. On the fourth day, the rats received sucrose solution (20 percen t orally) ad libitum, which was withdrawn after session IV. During session IT-IV in pre-sucrose fed state, the TFL remained unaffected as compared to session I, while the HPL decreased (18.53 +/- 4.96 s, 12.01 +/- 4.64 s in s essions I, VI respectively); and the thresholds for TF, SV and VA (0.34 +/- 0.16 and 0.71 +/- 0.32 mA in session I, VI respectively) progressively inc reased. After sucrose ingestion during sessions II-IV, the above-mentioned decrease in HPL and increase in thresholds was not observed. However, they appeared after discontinuation of sucrose during sessions V and VI. The res ults of our experiment suggest that exposure to our novel model of chronic (58 h) albeit intermittent stress of noxious stimuli and restraint produced an analgesic response in the threshold of TF, SV and VA, an hyperalgesic r esponse in HPL and no effect in TFL; which were attenuated by ingesting a p alatable sucrose solution ad libitum. Copyright (C) 2001 John Wiley & Sons, Ltd.