Sucrose induced analgesia in the brainstem of neonatal rat pups.
SUCROSE INDUCED ANALGESIA IN THE BRAINSTEM OF NEONATAL RAT PUPS.
Indre Augustinaite, Matthew Ennis, and Yi-Hong Zhang, Christian Brothers
University, Memphis, Tennessee (IA), and University of Tennessee Health
Science Center, Memphis, Tennessee (ME, YHZ). Previous studies show that
nursing produces analgesia in neonatal humans and rats. Sugars in breast
milk stimulate oral cavity sweet-responsive taste buds which triggers
opioid release in the brain. The neural circuits mediating this
analgesia are unknown. The goal of this study was to inactivate a key
brain site involved in opioid analgesia, the rostral ventromedial medulla (RVM), to determine its role in analgesia produced by intraoral
sucrose infusion in neonatal rats (ages P10-P13). Intraoral sucrose
infusion produced analgesia as measured by hindpaw withdrawal responses
to a series of von Frey filaments; i.e., sucrose increased the filament
force needed to produce a withdrawal response. Sucrose analgesia was
unaffected by microinjection of saline into RVM. By contrast,
microinjection of the local anesthetic lidocaine into RVM eliminated
sucrose-induced analgesia. As lidocaine suppresses neural activity,
these findings indicate that sucrose-induced analgesia is mediated, at
least in part, by the RVM.