MC4-R signaling within the nucleus accumbens shell, but not the lateral hypothalamus, modulates ethanol palatability in rats

The Melanocortin (MC) system is one of the crucial neuropeptidergic systems that modulate energy balance. The roles of endogenous MC and MC-4 receptor (MC4-R) signaling within the hypothalamus in the control of homeostatic aspects of feeding are well established. Additional evidence points to a key role for the central MC system in ethanol consumption. Recently, we have shown that nucleus accumbens (NAc), but not lateral hypothalamic (LH), infusion of a selective MC4-R agonist decreases ethanol consumption. Given that MC signaling might contribute to non-homeostatic aspects of feeding within limbic circuits, we assessed here whether MC4-R signaling within the NAc and the lateral hypothalamus (LH) alters normal ingestive hedonic and/or aversive responses to ethanol in rats as measured by a taste reactivity test. Adult male Sprague-Dawley rats were given NAc- or LH- bilateral infusion of the selective MC4-R agonist cyclo (NH-CH2-CH2-CO-His-D-Phe-Arg-Trp-Glu)-NH2 (0, 0.75 or 1.5 µg/0.5µl/site) and following 30 min, the animals received 1 ml of ethanol solution (6% w/v) intraoral for 1 minute and aversive and hedonic behaviors were recorded. We found that NAc-, but not LH-administration, of a selective MC4-R agonist decreased total duration of hedonic reactions and significantly increased aversive reactions relative to saline-infused animals which support the hypothesis that MC signaling within the NAc may contribute to ethanol consumption by modulating non-homeostatic aspects (palatability) of intake

Some Parameters of Stimulus Preexposure that Affect Conditioning and Generalization of Taste Aversions in Infant Rats

The effects of stimulus preexposure on conditioning and generalization of a taste aversion were evaluated in infant rats, manipulating stimulus similarity and duration, and the length and procedure (intermixed vs. blocked) of preexposure. Preexposure to simple tastes retarded conditioning and reduced generalization (Experiment 1a), whereas preexposure to compound tastes facilitated conditioning and increased generalization (Experiment 1b). Increasing the number of preexposure trials retarded conditioning and decreased generalization with compound tastes (Experiment 1c). These experiments failed to find a differential effect of intermixed vs. blocked stimulus preexposure. In Experiment 2, a 15 min exposure to the conditioned stimulus during conditioning resulted in a weak aversion, whereas a 60-min exposure resulted in a strong aversion. In Experiment 3, the strength of the aversion and the duration of the conditioned stimulus were directly related in nonpreexposed pups, but inversely related in preexposed pups. In infant rats, the level of generalization between stimuli is determined by how preexposure affects acquisition rate

Conditioned inhibition in preweanling rats

Inhibitory conditioning is a very well established phenomenon in associative learning that has been demonstrated in both humans and adult animals. But in spite of the fact that this topic has generated much empirical and theoretical work, there are no published studies assessing inhibitory learning during the early ontogeny of the rat. In this study we test the possibility of finding conditioned inhibition in infant rats (Day 10) using a conditioned taste aversion procedure. We tested whether the consumption of saccharin (A) was reduced when paired with a LiCl injection compared to the presentation of saccharin in compound with a lemon odor (AX) without any aversive consequence. After training, retardation, and summation tests were conducted in order to evaluate the inhibitory properties of the lemon odor (X). The results of this study showed that in male pups, after conditioned inhibition training, stimulus X passed both retardation and summation tests. These results indicate that conditioned inhibition can be established in the early development of the rat, suggesting that animals at this stage of ontogeny have the capacity to acquire and to express inhibitory conditioning, although this effect appears to be sex-dependent.Fil: Aranda-Fernandez, Patricio E.. Universidad del País Vasco; EspañaFil: Gaztañaga, Mirari. Universidad del País Vasco; EspañaFil: Arias Grandio, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; Argentina. Universidad del País Vasco; EspañaFil: Chotro, M. Gabriela. Universidad del País Vasco; Españ