Postoral Glucose Sensing, Not Caloric Content, Determines Sugar Reward in C57BL/6J Mice

Self Cite

The oral and post-oral actions of sugar and fat stimulate intake and condition flavor preferences in rodents through a process referred to as appetition. Ghrelin is implicated in food reward processing, and this study investigated its involvement in nutrient conditioning in mice. In Exp. 1 ghrelin receptor-null (GHSR-null) and C57BL/6 wildtype (WT) mice learned to prefer a flavor (CS+) mixed into 8% glucose over another flavor (CS−) mixed into a "sweeter" but non-nutritive 0.1% sucralose + saccharin (S+S) solution. In Exp. 2 treating WT mice with a ghrelin receptor antagonist [(D-Lys3)-GHRP-6] during flavor training did not prevent them from learning to prefer the CS+glucose over the CS−S+S flavor. GHSR-null and WT mice were trained in Exp. 3 to drink a CS+ paired with intragastric (IG) infusion of 16% glucose and a CS− paired with IG water. Both groups drank more CS+ than CS− in training and preferred the CS+ to CS− in a choice test. The same (Exp. 4) and new (Exp. 5) GHSR-null and WT mice learned to prefer a CS+ flavor paired with IG fat (Intralipid) over a CS− flavor paired with IG water. GHSR-null and WT mice also learned to prefer a CS+ flavor added to 8% fructose over a CS− added to water. Together, these results indicate that ghrelin receptor signaling is not required for flavor preferences conditioned by the oral or post-oral actions of sugar and fat. This contrasts with other findings implicating ghrelin signaling in food reward processing and food-conditioned place preferences.

Section: Discussionmentioning

confidence: 91%

Ghrelin signaling is not essential for sugar or fat conditioned flavor preferences in mice

Sclafani

Touzani

Ackroff

2015

Self Cite

“…Like Domingo et al (2013), we have investigated post-oral sugar appetition by comparing the preferences for nutritive sugars vs. non-nutritive sweeteners [26,28,29]. In our studies, however, mice were offered an initially preferred non-nutritive sweetener solution and a less preferred sugar solution, and experience-induced changes in sweetener preference were assessed.…”

Section: Experiments 1 Learned Preference For Nutritive Sugar Overmentioning

confidence: 99%

MCH receptor deletion does not impair glucose-conditioned flavor preferences in mice

Sclafani

Adamantidis

Ackroff

2016

Self Cite

The post-oral actions of glucose stimulate intake and condition flavor preferences in rodents. Hypothalamic melanin-concentrating hormone (MCH) neurons are implicated in sugar reward, and this study investigated their involvement in glucose preference conditioning in mice. In Exp. 1 MCH receptor 1 knockout (KO) and C57BL/6 wildtype (WT) mice learned to prefer 8% glucose over an initially more-preferred non-nutritive 0.1% sucralose + saccharin (S+S) solution. In contrast, the KO and WT mice preferred S+S to 8% fructose, which is consistent with this sugar’s weak post-oral reinforcing action. In Exp. 2 KO and WT mice were trained to drink a flavored solution (CS+) paired with intragastric (IG) infusion of 16% glucose and a different flavored solution (CS−) paired with IG water. Both groups drank more CS+ than CS− in training and preferred the CS+ to CS− in a 2-bottle test. These results indicate that MCH receptor signaling is not required for flavor preferences conditioned by the post-oral actions of glucose. This contrasts with other findings implicating MCH signaling in other types of sugar reward processing.

“…Glucose is the most commonly used nutrient in experiments of this kind and other sugars that support conditioning include sucrose, maltose, and polycose [41,46]. Interestingly, in most situations fructose does not support conditioning [47][48][49] suggesting that it is not simply caloric value that drives this process, but rather nutrient-specific signalling mechanisms [50,51]. A number of flavours have been used in this paradigm and flavour-nutrient preferences even develop to innately aversive flavours, such as sour-or bitter-tasting compounds, after pairing with nutrients [43].…”

Section: Post-ingestive Infusionsmentioning

confidence: 99%

The role of dopamine in the pursuit of nutritional value

McCutcheon

2015

Acquiring enough food to meet energy expenditure is fundamental for all organisms. Thus, mechanisms have evolved to allow foods with high nutritional value to be readily detected, consumed, and remembered. Although taste is often involved in these processes, there is a wealth of evidence supporting the existence of taste-independent nutrient sensing. In particular, post-ingestive mechanisms arising from the arrival of nutrients in the gut are able to drive food intake and behavioural conditioning. The physiological mechanisms underlying these effects are complex but are believed to converge on mesolimbic dopamine signalling to translate post-ingestive sensing of nutrients into reward and reinforcement value. Discerning the role of nutrition is often difficult because food stimulates sensory systems and post-ingestive pathways in concert. Thus, in this mini-review, I discuss the various methods that may be used to study post-ingestive processes in isolation including sham-feeding, nonnutritive sweeteners, post-ingestive infusions, and pharmacological and genetic methods. Using this structure, I present the evidence that dopamine is sensitive to nutritional value of certain foods and examine how this affects learning about food, the role of taste, and the implications for human obesity.