Academic literature on the topic 'Palatability-induced feeding'

Infusion of a μ-opioid receptor (MOR) agonist into the nucleus accumbens (NAcc) drives voracious food intake, an effect hypothesized to occur through increased tastant palatability. While intake of many palatable foods is elevated by MOR stimulation, this manipulation has a preferential effect on fatty food ingestion. Consumption of high-fat foods is increased by NAcc MOR stimulation even in rats that prefer a carbohydrate-rich alternative under baseline conditions. This suggests that NAcc MOR stimulation may not simply potentiate palatability signals and raises the possibility that mechanisms mediating fat intake may be distinct from those underlying intake of other tastants. The present study was conducted to investigate the physiological mechanisms underlying the effects of NAcc MOR stimulation on fatty food intake. In experiment 1, we analyzed lick microstructure in rats ingesting Intralipid to identify the changes underlying feeding induced by infusion of a MOR-specific agonist into the NAcc. MOR stimulation in the NAcc core, but not shell, increased burst duration and first-minute licks, while simultaneously increasing the rate and duration of Intralipid ingestion. These results suggest that MOR activation in the core increases Intralipid palatability and attenuates inhibitory postingestive feedback. In experiment 2, we measured the effects of MOR stimulation in the NAcc core on consumption of nonnutritive olestra. A MOR-specific agonist dose dependently increased olestra intake, demonstrating that caloric signaling is not required for hyperphagia induced by NAcc MOR stimulation. Feeding induced by drug infusion in both experiments 1 and 2 was blocked by a MOR antagonist. In experiment 3, we determined whether MOR activation in the NAcc core could attenuate satiety-related signaling caused by infusion of the melanocortin agonist MTII into the third ventricle. Suppression of intake caused by MTII was reversed by MOR stimulation. Together, our results suggest that MOR stimulation in the NAcc core elevates fatty food intake through palatability mechanisms dependent on orosensory cues and suppression of satiety signals inhibiting food intake.

We studied the effect of the opioid receptor antagonist naloxone on intake of three isocaloric diets containing cornstarch, sucrose, or Polycose as the predominant carbohydrate in ad libitum-fed and food-restricted rats. A large body of evidence suggests that opioids affect palatability (reward)-rater than hunger (energy deficit)-driven food intake. We expected food intake to be driven by both energy needs and palatability in ad libitum-fed rats, whereas in food-restricted rats we expected intake to be driven by energy needs with a relatively small palatability component in the preferred sucrose and Polycose diet groups. In the ad libitum-fed rats, naloxone significantly reduced nocturnal intake of all three diets at doses of 0.3, 1.0, and 3.0 mg/kg. In contrast, naloxone failed to alter intake of the cornstarch diet in chronically food-restricted rats. However, naloxone decreased intake of the sucrose diet in food-restricted rats at doses of 0.3, 1.0, and 3.0 mg/kg and decreased intake of the Polycose diet at the 3 mg/kg dose. These data lend further support to the notion that opioids are involved in some other component of feeding than that induced by energy needs.

We tested the hypothesis that early-season defoliation of flowering crabapple, Malus sp., by eastern tent caterpillars, Malacosoma americanum F., induces localized or systemic resistance to Japanese beetles, Popillia japonica Newman, feeding on the same trees in late June. ‘Candymint Sargent’ crabapple trees were inoculated with M. americanum egg masses, resulting in extensive defoliation during March and April. Second flush leaves of defoliated trees were smaller and thinner than those of control trees. In laboratory feeding assays with non-damaged foliage, beetles generally preferred fully expanded leaves over partially expanded ones, regardless of whether or not the source tree had been defoliated. Detached first flush leaves with caterpillar damage were fed upon less than comparable non-damaged leaves, suggesting that early-season wounding causes some within-leaf reduction in palatability to P. japonica. Other assays with detached first- and second-flush leaves, however, indicated absence of induced, systemic resistance. Previously-defoliated and control trees sustained comparable damage from natural beetle populations in the field. Our results suggest that defoliation of Malus sp. by tent caterpillars in early spring is unlikely to reduce feeding damage by Japanese beetles later in the same growing season.