Sensory suppression during feeding

Abstract

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 ͉ nociceptive modulation ͉ pain ͉ raphe magnus ͉ 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 hunger͞satiation 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...

Intraperiaqueductal Gray Glycine and d-Serine Exert Dual Effects on Rostral Ventromedial Medulla on- and off-Cell Activity and Thermoceptive Threshold in the Rat

“…The present finding that 7-Cl-KYN in the VL-PAG blocked glycine-or D-serine-induced antinociception and the related changes in the RVM cell activity suggests that the effects of glycine or D-serine were related to the enhancement of NMDAR-mediated neurotransmission. Since the ON cells may facilitate nociception (Fields et al 1991), a delayed onset of the ON-cell burst as well as the shortened interval between the onset of the ON-cell burst and tail withdrawal, with either glycine or D-serine, might be expected to be critical events in the occurrence of analgesia (Foo and Mason 2005;Heinricher et al 1989;Jinks et al 2004). Indeed, pain transmission and perception are constantly changing: increasing during periods of ON-cell activity and decreasing when OFF cells are active FIG. 7.…”

Cough, pain and dyspnoea: Similarities and differences

“…the case of urge to breathe in a submerged diving animal). In the case of pain, suppression of normal pain reactions is sometimes required to allow the animal to pursue more important tasks; this has been quantified in animal behaviour experiments [29,30].…”

Chocolate and Pain Tolerance

“…Nutrition is critical for survival, yet many animals place themselves at risk in order to feed. Animals must obtain nutrients while at the same time protecting their well-being; however, feeding seems to trump escape behavior, because it is more essential for survival, and so, more immediately necessary, as opposed to merely protective [ 36 ] . Thus, the body suppresses pain in order to optimize feeding in potentially dangerous situations [ 36,37 ] .…”

“…Animals must obtain nutrients while at the same time protecting their well-being; however, feeding seems to trump escape behavior, because it is more essential for survival, and so, more immediately necessary, as opposed to merely protective [ 36 ] . Thus, the body suppresses pain in order to optimize feeding in potentially dangerous situations [ 36,37 ] . For example, while feeding, rats' withdrawal responses from noxious heat stimuli on the paw were either completely suppressed or greatly delayed [ 36 ] .…”

“…Thus, the body suppresses pain in order to optimize feeding in potentially dangerous situations [ 36,37 ] . For example, while feeding, rats' withdrawal responses from noxious heat stimuli on the paw were either completely suppressed or greatly delayed [ 36 ] . In an animal model of migraine pain, male rats subjected to painful chemical injections continued to eat chocolate chips instead of tending to their injection site [ 38 ] .…”