The relationship of hyperalgesia in SART (repeated cold)-stressed animals to the autonomic nervous system

1. The mechanism of hyperalgesia observed in SART (repeated cold)-stressed animals (mice and rats) was studied in relation to the autonomic nervous system. 2. SART stress reduced the nociceptive threshold previously increased in vagotomized mice, but failed to change the threshold previously decreased in sympathectomized mice. 3. The nociceptive threshold previously decreased in SART-stressed mice was elevated by vagotomy, but decreased still more by sympathectomy. 4. Lesion of ventromedial (VMH), anterior (AH) or posterior hypothalamus (PH) prevented decrease in the nociceptive threshold of rats by SART stress, but lesion of the lateral hypothalamus (LH) had no such effect. 5. The nociceptive threshold previously decreased in stressed rats did not change by VMH, AH or PH lesion, but increased by LH lesion. 6. The above findings indicate that hyperalgesia in SART-stressed animals apparently bears little relation to the parasympathetic nervous system, but is associated relatively more with reduced tone in the sympathetic nervous system.