Sweet taste and nonnutritive suckling produce analgesia to transient noxious stimuli in infant rats and humans. The present study evaluated the pain-modulating effects of sucrose and suckling in a rat model of persistent pain and hyperalgesia that mimics the response to tissue injury in humans. Fore- and hindpaw withdrawal latencies from a 30°or 48°C brass stylus were determined in 10-day-old rats following paw inflammation induced by complete Freund's adjuvant (CFA; 1:1 injected s.c, in a 0.01 ml volume). CFA markedly decreased escape latencies to both 48°and 30°C stimulation, thereby demonstrating thermal hyperalgesia and mechanical allodynia. The combination of nonnutritive suckling and sucrose (7.5%, 0.01-0.06 ml/min) infusion markedly increased escape latencies to forepaw stimulation in both CFA- treated and control rats. In contrast, intraoral sucrose and suckling did not increase hindpaw withdrawal latencies in either control or CFA-inflamed rats. The effect was specific to sweet taste because neither water nor isotonic saline infusion affected forepaw escape latencies. Parallel findings were obtained for CFA-induced Fos-like immunoreactivity (Fos-LI), a marker of neuronal activation. Fos-LI was selectively induced in cervical and lumbar regions ipsilateral to forepaw and hindpaw inflammation, respectively. Suckling-sucrose treatment significantly reduced Fos-LI at the cervical but not at the lumbar regions. These findings demonstrate: (i) the development of persistent pain and hyperalgesia in 10-day-old rats that can be attenuated by endogenous pain-modulating systems activated by taste and nonnutritive suckling; (ii) the mediation of the sucrose-suckling analgesia and antihyperalgesia at the spinal level; and (iii) a differential rostrocaudal maturation of descending pain-modulating systems to the spinal cord of 10- day-old rats. These findings may provide new clinical approaches for engaging endogenous analgesic mechanisms in infants following tissue injury and inflammation.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Feb 18 1997|
- Freund's adjuvant
- pain modulation
ASJC Scopus subject areas