Analgesia Accompanying Food Consumption Requires Ingestion of Hedonic Foods

Abstract

Animals eat rather than react to moderate pain. Here, we examined the behavioral, hedonic, and neural requirements for ingestion analgesia in ad libitum fed rats. Noxious heat-evoked withdrawals were similarly suppressed during self-initiated chocolate eating and ingestion of intraorally infused water, sucrose, or saccharin, demonstrating that ingestion analgesia does not require feeding motivation, self-initiated food procurement, sucrose, or calories. Rather, food hedonics is important because neither salt ingestion nor quinine rejection elicited analgesia. During quinine-induced nausea and lipopolysaccharide (LPS)-induced illness, conditions when chocolate eating was presumably less pleasurable, analgesia accompanying chocolate consumption was attenuated, yet analgesia during water ingestion was preserved in LPS-injected rats who showed enhanced palatability for water within this context. The dependence of ingestion analgesia on the positive hedonics of an ingestate was confirmed in rats with a conditioned taste aversion to sucrose: after paired exposure to sucrose and LPS, rats no longer showed analgesia during sucrose ingestion but continued to show analgesia during chocolate consumption. Eating pauses tended to occur less often and for shorter durations in the presence of ingestion analgesia than in its absence. Therefore, we propose that ingestion analgesia functions to defend eating from ending. Muscimol inactivation of the medullary raphe magnus blocked the analgesia normally observed during water ingestion, showing the involvement of brainstem endogenous pain inhibitory mechanisms in ingestion analgesia. Brainstem-mediated defense of the consumption of palatable foods may explain, at least in part, why overeating tasty foods is so irresistible even in the face of opposing cognitive and motivational forces.

Sweet Solution Analgesia

“…Activating sensory aferents in the oral cavity leads to pleasurable sensation or efect. This positive hedonic efect of sweet tasting substances induced analgesia further supports the theory that it is the taste of sweetness not the caloric value of the food [46].…”

Sucrose for Procedural Pain Management in Infants

“…38 Furthermore, the ingestion of hedonic foodstuffs (eg, sucrose) is associated with analgesia. 39 This effect has been proposed to be a consequence of suppressed reactions to distracting (ie, painful) stimuli mediated by the raphe nucleus. 39 In the adult rat model, the brainstem-spinal cord projections are an important source of nociceptive processing in the spinal cord.…”

“…39 This effect has been proposed to be a consequence of suppressed reactions to distracting (ie, painful) stimuli mediated by the raphe nucleus. 39 In the adult rat model, the brainstem-spinal cord projections are an important source of nociceptive processing in the spinal cord. In the neonate, however, the descending inhibitory influences are not fully mature, 34,35 and descending inhibitory tone can only be detected after the third postnatal week in rats.…”

Orexin-A and Endocannabinoid Activation of the Descending Antinociceptive Pathway Underlies Altered Pain Perception in Leptin Signaling Deficiency

“…Eating disorders and obesity are accompanied by altered pain perception (Lautenbacher et al, 1990;Papežová et al, 2005;Foo and Mason, 2009;Rodgers et al, 2014). Although this phenomenon might be a consequence of changes in the hypothalamic-pituitary-adrenal (HPA) axis, stress response, and related or unrelated endocrine modifications (Lewis et al, 1980), its exact underlying mechanisms have not been elucidated.…”