Has a meal trigger been found?

Cue-potentiated feeding in rodents: Implications for weight regulation in obesogenic environments

Cue-potentiated feeding (CPF) describes instances where food intake is increased by exposure to conditioned cues associated with food, often in the absence of hunger. CPF effects have been reported in a range of experimental protocols developed by researchers working across diverse fields spanning behavioural neuroscience, social psychology and ecology. Here we review the evolution of research on cue-potentiated feeding in animal models to identify important behavioural parameters and key neural circuits and pharmacological systems underlying the effect. Overall, evidence indicates that social, discrete and contextual stimuli can be used to elicit CPF effects across multiple species, though effects are often subtle and sensitive to procedural variables. While regular exposure to food cues is thought to be a key risk factor for overeating in so-called 'obesogenic' environments, further work is needed to identify whether CPF promotes positive energy balance and weight gain over the longer term. We suggest several methodological and conceptual areas for inquiry to elucidate the contribution of CPF to the regulation of food choice and energy intake.

On-line continuous measurement of blood glucose and meal pattern in free-feeding rats: the role of glucose in meal initiation

Louis-Sylvestre and LeMagnen have suggested that the premeal decline in blood glucose is or reflects a signal for meal initiation in rats. In order to extend and test this hypothesis, a computer controlled system for continuously and concurrently measuring blood glucose and food intake in free-feeding rats was developed. In 18 experiments (with and without intravenous saline infusions), blood glucose declined about 12 minutes prior to meal onset. During 2-1/2 hours of observation, no decline in blood glucose and no meal occurred in 19 other experiments. In 7 experiments in which 10 percent glucose was infused IV to partially block the premeal decline (average blockade = 46.5%), the subsequent meal was significantly delayed. These results suggest that the pre-meal decline in blood glucose is not only correlated with but is also caudally related to meal onset. These studies suggest that the premeal decline in blood glucose is among the signals for meal initiation.

Meal initiation controlled by learned cues: basic behavioral properties

The behavioral properties of meals initiated in response to the presentation of food-associated external stimuli are examined. A Pavlovian conditioning procedure was used to teach animals an association between an arbitrary external cue and food. Subsequent presentations of the conditioned cue reliably led to the initiation of feeding even though rats were tested under conditions of satiety. Several properties of learned external control of feeding were identified. First, the size of meals motivated by exposure to signals for food resembled the level of ingestion characteristic of spontaneous feeding. Second, the potency of externally-controlled intake was influenced by satiety signals arising from previous meals. Third, although presentation of the conditioned cue could be used to influence meal pattern, rats regulated the amount of calories consumed in a 24-h period. These results establish that learning contributes to meal initiation and that mechanisms based on learning do not require (but may interact with) internal energy depletion signals in the control of feeding. The implications of these findings to models of feeding behavior are discussed.

Meal initiation controlled by learned cues: effects of peripheral cholinergic blockade and cholecystokinin

Sated animals can be induced to initiate meals by exposing them to external stimuli which they have learned, via Pavlovian conditioning, to associate with food. This study examined physiological properties of this control of feeding. The initial hypothesis examined was that conditioned feeding depended on the elaboration of cholinergic cephalic phase responses (e.g., anticipatory insulin secretion). This idea was evaluated by comparing feeding responses to presentation of conditioned cues following an injection of either a peripheral cholinergic blocker, atropine methyl nitrate, or a control substance, physiological saline. Peripheral cholinergic blockade had no effect on the meal initiated by presentation of conditioned cues even though the dose of atropine methyl nitrate used was demonstrated to be sufficient to completely suppress cholinergic cephalic phase responses. These results indicate that cholinergic anticipatory digestive secretions do not contribute to feeding in this preparation. The effects of exogenously administered cholecystokinin on feeding controlled by learned cues were also studied. Cholecystokinin suppressed the size of the meal induced by presentation of conditioned stimuli but did not influence the latency, or initial rate of eating. The implications of these results to a conclusion that cholecystokinin is a satiety factor are discussed.