Nociceptive thresholds following food restriction and return to free-feeding.

Nine rats were placed on a restricted food diet for 14 days and nociceptive thresholds were measured by the tail-flick procedure. After 24 hr of food restriction nociceptive thresholds increased. This initial increase in nociceptive threshold was followed by a decrease in pain threshold on the second day of food restriction. Nociceptive thresholds returned to pre-deprivation levels on the remaining 11 days of food restriction. When the rats were given free access to food after 14 days of food restriction, nociceptive thresholds increased 24 hr after the reintroduction of food and decreased during the next 24 hr. Thus, the results of the present experiment demonstrate that both food restriction and a return to free feeding after 14 days of food restriction produced the same biphasic pattern of changes in nociceptive thresholds.