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2018 DEC 22 (NewsRx) -- By a News Reporter-Staff News Editor at Obesity, Fitness & Wellness Week -- Research findings on Endocytosis are discussed in a new report. According to [...]

There is increasing focus on the role of the nucleus accumbens (NAc) in learning and memory, but there is little consensus as to how the core and medial shell subregions of the NAc contribute to these processes. In the current experiments, we used spontaneous object recognition to test rats with 6-hydroxydopamine lesions targeted at the core or medial shell of the NAc on a familiarity discrimination task and a location discrimination task. In the object recognition variant, control animals were able to discriminate the novel object at both 24-hr and 5-min delay. However, in the lesion groups, performance was systematically related to dopamine (DA) levels in the core but not the shell. In the location recognition task, sham-operated animals readily detected the object displacement at test. In the lesion groups, performance impairment was systematically related to DA levels in the shell but not the core. These results suggest that dopamine function within distinct subregions of the NAc plays dissociable roles in the modulation of memory for objects and place. Keywords: nucleus accumbens, dopamine, rat, object memory, place memory DOI: 10.1037/a0021114

The authors investigated the contribution of the nucleus accumbens (NAc) core and shell to effort-based decision making using a discounting procedure. Selection of 1 lever delivered a smaller, 2-pellet reward immediately, whereas the other lever delivered a 4-pellet reward after a fixed ratio of presses (2, 5, 10, or 20) that increased over 4 blocks of 10 discrete choice trials. Subsequent testing employed an equivalent delays procedure, whereby the relative delay to reward delivery after selection of either option was equalized. In well-trained rats, inactivation of the core, but not the shell, via infusion of GABA A/B agonists muscimol/baclofen reduced preference for the high-effort option under standard conditions and also when rats were tested using an equivalent delays procedure. However, inactivation of the core did not alter preference for 4-pellet versus 2-pellet rewards when the relative costs of each option were the same (1 press). Thus, the NAc core, but not the shell, appears to be part of a neural circuit that biases choice toward larger rewards associated with a greater effort cost. Furthermore, the contributions by the NAc core to this form of decision making can be dissociated from its role in delay discounting. Keywords: nucleus accumbens, decision making, effort discounting, inactivation, rat DOI: 10.1037/a0018932

Previous work has implicated the cholinergic system in modulating feeding behavior; however, its specific function remains unclear. This work aims to characterize potential dissociations between the central cholinergic modulation of the incentive properties of food and food-associated cues, and consummatory behaviors. Three separate experiments demonstrated that intra-accumbens infusion of the muscarinic antagonist scopolamine 3 hr before the testing session significantly decreased food intake. General motor activity in anticipation of food was not diminished. Experiments also showed that scopolamine did not impair operant responding for a food-associated conditioned reinforcer (CR), nor was d-amphetamine potentiation of CR responding altered by scopolamine pretreatment. This study contributes to the growing evidence that goal-seeking behaviors are mediated by a set of neural processes distinct from those governing food reward. Keywords: scopolamine, muscarinic, accumbens, feeding, acetylcholine DOI: 10.1037/a0018283

The present series of experiments aimed to pinpoint the source of nucleus accumbens core (AcbC) effects on delay discounting. Rats were trained with an impulsive choice procedure between an adjusting smaller sooner reward and a fixed larger later reward. The AcbC-lesioned rats produced appropriate choice behavior when the reward magnitude was equal. An increase in reward magnitude resulted in a failure to increase preference for the larger later reward in the AcbC-lesioned rats, whereas a decrease in the larger later reward duration resulted in normal alterations in choice behavior in AcbC-lesioned rats. Subsequent experiments with a peak timing (Experiments 2 and 3) and a behavioral contrast (Experiment 4) indicated that the AcbC-lesioned rats suffered from decreased incentive motivation during changes in reward magnitude (Experiments 2 and 4) and when expected rewards were omitted (Experiments 2 and 3), but displayed intact anticipatory timing of reward delays (Experiments 2 and 3). The results indicate that the nucleus accumbens core is critical for determining the incentive value of rewards, but does not participate in the timing of reward delays. Keywords: nucleus accumbens, impulsivity, delay discounting, timing, rats DOI: 10.1037/a0018464

Substantial evidence suggests that pharmacological manipulations of neural serotonin pathways influence ingestive behaviors. Despite the known role of the nucleus accumbens in directing appetitive and consummatory behavior, there has been little examination of the influences that serotonin receptors may play in modulating feeding within nucleus accumbens circuitry. In these experiments, the authors examined the effects of bilateral nucleus accumbens infusions of the 5-H[T.sub.1/7] receptor agonist 5-CT (at 0.0, 0.5, 1.0, or 4.0 [micro]g/0.5 [micro]l/side), the 5-HT6 receptor agonist EMD 386088 (at 0.0, 1.0, and 4.0 [micro]g/0.5 [micro]l/side), or the 5-HT2c preferential agonist RO 60-0175 (at 0.0, 2.0, or 5.0 [micro]g/0.5 [micro]l/side) on food intake and locomotor activity in the rat. Intra-accumbens infusions of 5-CT caused a dose- dependent reduction of food intake and rearing behavior, both in food-restricted animals given 2-hr free access to Purina Protab RMH 3000 Chow, as well as in nondeprived rats offered 2-hr access to a highly palatable fat/sucrose diet. In contrast, stimulation of 5-HT6 receptors with EMD 386088 caused a dose-dependent increase of intake under both feeding conditions, without affecting measures of locomotion. Infusions of the moderately selective 5-HT2c receptor agonist RO 60-0175 had no effects on feeding or locomotor measures in food-restricted animals, but did reduce intake of the fat/sucrose in nonrestricted animals at the 2.0 [micro]g, but not the 5.0 [micro]g dose. Intra-accumbens infusions of selective antagonists for the 5-HT7 (SB 269970), 5-H[T.sub.6] (SB 252585), and 5-HT2c (RS 102221) receptors did not affect locomotion, and demonstrated no lasting changes in feeding for any of the groups tested. These data are the first to suggest that the activation of different serotonin receptor subtypes within the feeding circuitry of the medial nucleus accumbens differentially influence consummatory behavior. Keywords: Nucleus accumbens, serotonin, food intake, motivation

by Sheldon Lewis Scientists have long been puzzled by the fact that a placebo - a "sugar pill" or sham treatment - relieves such symptoms as pain for some people, [...]