Biphasic alterations of nociceptive thresholds induced by food deprivation

Abstract

Acute exposure to such stressful events as inescapable footshock, rotation, or cold-water swims produces a transient analgesia. The physiological effects of food deprivation resemble those of an environmental stressor, in that corticosterone levels increase during food restriction and fall following meals. The present study investigated whether food deprivation, like other stressors, would produce a transient analgesia. Flinch-jump thresholds of 16 rats, maintained on a 14-h-light/10-h-dark cycle, were tested twice daily for 4 baseline, 3 food-deprivation, and 2 recovery days. Deprivation was initiated for eight animals at the beginning of the dark cycle (p.m. group), and for eight animals at the end of the dark cycle (a.m. group). Nociceptive thresholds of the p.m. group increased after 12 h of deprivation and decreased after 36 and 60 h. Thresholds of the a.m. group were increased for up to 36 h of deprivation and decreased after 72 h. Thresholds were higher after the dark cycle on the 1st deprivation day, and lower on the 3rd deprivation day, indicating an important circadian rhythmicity. Changes in weight, water intake, or activity levels could not account for the nociceptive alterations. These results provide further support for the contention that initial exposure to severe environmental stressful events produces a transient analgesia. © 1978, Psychonomic Society, Inc.. All rights reserved.