Feeding is essential for survival, whereas withdrawal and escape reactions are fundamentally protective. These critical behaviors can compete for an animal's resources when an acutely painful stimulus affects the animal during feeding. One solution to the feeding-withdrawal conflict is to optimize feeding by suppressing pain. We examined whether rats continue to feed when challenged with a painful stimulus. During feeding, motor withdrawal responses to noxious paw heat either did not occur or were greatly delayed. To investigate the neural basis of sensory suppression accompanying feeding, we recorded from brainstem pain-modulatory neurons involved in the descending control of pain transmission. During feeding, pain-facilitatory ON cells were inhibited and pain-inhibitory OFF cells were excited. When a nonpainful somatosensory stimulus preactivated ON cells and preinhibited OFF cells, rats interrupted eating to react to painful stimuli. Inactivation of the brainstem region containing ON and OFF cells also blocked pain suppression during eating, demonstrating that brainstem pain-modulatory neurons suppress motor reactions to external stimulation during homeostatic behaviors.homeostasis Í nociceptive modulation Í pain Í raphe magnus Í ON and OFF cells B ehaviors such as eating, drinking, micturition, and defecation are essential for an organism's survival and are affected by exposure to aversive stimuli. Stress-induced eating and defecation occur across species and can be triggered by exposure to a painful stimulus (1-4). Yet, very little is known about the effects of feeding (eating and drinking), micturition, and defecation on pain sensitivity. In food-deprived animals, eating takes precedence over pain-motivated behaviors. During eating, fooddeprived cats were less likely to withdraw from acute noxious cutaneous heat (5), and food-deprived chickens showed fewer pain-motivated behaviors in response to chronic pain induced by sodium urate (6). However, responses to a painful stimulus are affected by the hungerÍsatiation state (7), and it remains to be determined whether these analgesic effects can be generalized to animals that have been fed freely. Consequently, the aim of Experiment 1 was to examine whether the drive to satisfy hunger still overrides the need to avoid pain in non-food-deprived animals. We found that feeding suppressed pain in rats that were fed ad libitum.The suppression of pain during feeding indicates the activation of endogenous pain modulatory pathways. The brainstem ventromedial medulla (VMM) is a critical area in the descending control of pain and is the final common pathway from the brain to the spinal cord (8-11). The VMM modulates pain bidirectionally: its activation can produce either pain facilitation or pain inhibition (10-16). The pain-facilitatory and pain-inhibitory effects are thought to be mediated by two populations of neurons with opposing responses to noxious stimulation and morphine (17)(18)(19)(20). Cells activated by noxious stimulation are inhibited by opioids. These cel...