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GRAVITY STIMULATION CHANGES WITHDRAWAL REFLEX IN RATS.    K. Toda¹ ,Y. Kawauchi^1,2, Y. Kumei³, F.H. Nasution⁴ and K. Makita⁵.  Sect. Congnitive Neurobiol¹, Dept. Anesthesiol²., Sect. Bio-Matrix³, Orthodontic Science, Division of Oral Health Sciences⁴ and Systemic Organ Regulation⁵, Tokyo Med. Dent. Uni., Tokyo 113-8549, Japan. 

The purpose of the present study is to reveal the effect of gravity stimulation on the nociceptive responses in the rat.1.5G or 2.0G gravity stimulation was applied during 10 minutes in Wistar albino rats. We selected eight sites for noxious stimulation using von Frey type filament. The threshold intensities of withdrawal reflex were measured before and after the application of gravity stimulation. Naloxone-HCl (0.1mg/g ip) was used to test whether endogenous-opioids are concerned with those gravity-induced effects.  The threshold value was significantly increased in all the stimulating sites tested after 2.0G stimulation, but not after 1.5 G stimulation. Naloxone blocked analgesic effects in case of 2.0G-gravity stimulation.  The present study indicates that high gravity can provoke naloxone-reversible analgesic effects in rats. This analgesic effects is considered to be a stress-induced analgesia.