Enteroendocrine cell types that drive food reward and aversion

Animals must learn through experience which foods are nutritious and should be consumed, and which are toxic and should be avoided. Enteroendocrine cells (EECs) are the principal chemosensors in the GI tract, but investigation of their role in behavior has been limited by the difficulty of selectively targeting these cells in vivo. Here we describe an intersectional genetic approach for manipulating EEC subtypes in behaving mice. We show that multiple EEC subtypes inhibit food intake but have different effects on learning. Conditioned flavor preference is driven by release of cholecystokinin whereas conditioned taste aversion is mediated by serotonin and substance P. These positive and negative valence signals are transmitted by vagal and spinal afferents, respectively. These findings establish a cellular basis for how chemosensing in the gut drives learning about food.

Assessing the inhibitory properties of a latent inhibitor in flavor-aversion learning

In Experiment 1, rats received 16 nonreinforced trials of exposure to a flavor (A) that was subsequently used as the conditioned stimulus in flavor-aversion conditioning. In the critical condition, Flavor A was presented in compound with a different novel flavor on each of the eight daily trials. This treatment produced latent inhibition, in that this preexposure retarded conditioning just as did 16 trials with A alone. Rats in the control conditions, given no preexposure or exposure just to the sequence of novel flavors, learned readily. Experiment 2 examined the effects of these forms of preexposure on performance on a summation test, in which Flavor A was presented in compound with a separately conditioned flavor (X). The preexposure procedure in which A was presented along with novel flavors rendered A effective in inhibiting the response conditioned to X on that test. The conclusion, that this form of training can establish the target stimulus as a conditioned inhibitor, is predicted by the account of latent inhibition put forward by Hall and Rodríguez (2010) which proposes that the latent inhibition effect is a consequence both of a reduction in the associability of the stimulus and of a process of inhibitory associative learning that opposes the initial expectation that a novel event will be followed by some consequence.

Do Prenatally-Conditioned Flavor Preferences Affect Consumption of Creep Feed by Piglets?

Piglets can prefer flavors that are presented to pregnant sows, hence this study intended to estimate the effect of prenatal exposure of piglets to flavors on the intake of flavored creep feed and performance. Gestational sows were fed either a flavored (garlic or aniseed; n24) or an unflavored diet (n24) from days 90 to 114 of gestation. Their litters were offered either garlic, aniseed, or unflavored creep feed during the suckling period, and its intake was measured as well as animal’s final body weight (BW) and average daily gain (ADG). Data was analyzed taking into account the diet offered to both sows and piglets, as well as the interaction between these variables. As previous experiments have shown, flavor learning did not affect a piglet’s performance during the suckling period, finding no differences for creep feed intake, ADG, or BW according to diets (p > 0.05). Repeated exposure of piglets to previously learned flavors without clear post-ingestive benefits could nullify the strategies proposed. Moreover, milk and creep feed diets show a great reward contrast that may accelerate learning extinction. Results of the present and previous experiments suggest that current flavor continuity strategies that are proposed for pig production systems need to be reconsidered.