Exclusively drinking sucrose or saline early in life alters adult drinking behavior by laboratory rats

Neurobehavioral plasticity in the rodent gustatory system induced by regular consumption of a low-calorie sweetener during adolescence

Habitual consumption of low-calorie sweeteners (LCS) during juvenile-adolescence can lead to greater sugar intake later in life. Here, we investigated if exposure to the LCS Acesulfame Potassium (Ace-K) during this critical period of development reprograms the taste system in a way that would alter hedonic responding for common dietary compounds. Results revealed that early-life LCS intake not only enhanced the avidity for a caloric sugar (fructose) when rats were in a state of caloric need, it increased acceptance of a bitterant (quinine) in Ace-K-exposed rats tested when middle-aged. These behavior shifts, which endured months after the end of Ace-K exposure, were accompanied by widespread changes in the peripheral taste system. The anterior tongue had fewer fungiform taste papillae, and the circumvallate papillae had a reduced anterior to posterior span and diminished expression of genes involved in sweet reception, sweet and bitter intracellular signaling, fructose transport, and cellular progeneration in the Ace-K-exposed rats. Ace-K exposure also led to a significant reduction in dopamine-producing cells of the ventral tegmental area. The collective findings reveal that LCS intake early in life alters the taste-brain axis and the behavioral responsiveness to both positive and negative tastants that are important determinants of dietary preferences.

Early perturbations to fluid homeostasis alter development of hypothalamic feeding circuits with context-specific changes in ingestive behavior

Drinking and feeding are tightly coordinated homeostatic events and the paraventricular nucleus of the hypothalamus (PVH) represents a possible node of neural integration for signals related to energy and fluid homeostasis. We used TRAP2;Ai14 and Fos labeling to visualize neurons in the PVH and median preoptic nucleus (MEPO) responding to both water deprivation and hunger. Moreover, we determined that structural and functional development of dehydration-sensitive inputs to the PVH from the MEPO precedes those of agouti-related peptide (AgRP) neurons, which convey hunger signals and are known to be developmentally programmed by nutrition. We also determined that osmotic hyperstimulation of neonatal mice led to enhanced AgRP inputs to the PVH in adulthood, as well as disruptions to ingestive behaviors during high-fat diet feeding and dehydration-anorexia. Thus, development of feeding circuits is impacted not only by nutritional signals, but also by early perturbations to fluid homeostasis with context-specific consequences for coordination of ingestive behavior.

Fluid transitions

Water is critical for survival and thirst is a powerful way of ensuring that fluid levels remain in balance. Overconsumption, however, can have deleterious effects, therefore optimization requires a need to balance the drive for water with the satiation of that water drive. This review will highlight our current understanding of how thirst is both generated and quenched, with particular focus on the roles of angiotensin II, glucagon like-peptide 1, and estradiol in turning on and off the thirst drive. Our understanding of the roles these bioregulators play has benefited from modern behavioral analyses, which have improved the time resolution of intake measures, allowing for attention to the details of the patterns within a bout of intake. This has led to behavioral interpretation in ways that are helpful in understanding the many controls of water intake and has expanded our understanding beyond the dichotomy that something which increases water intake is simply a "stimulator" while something that decreases water intake is simply a "satiety" factor. Synthesizing the available information, we describe a framework in which thirst is driven directly by perturbations in fluid intake and indirectly modified by several bioregulators. This allows us to better highlight areas that are in need of additional attention to form a more comprehensive understanding of how the system transitions between states of thirst and satiety.

Experience-dependent plasticity of gustatory insular cortex circuits and taste preferences

Early experience with food influences taste preference in adulthood. How gustatory experience influences development of taste preferences and refinement of cortical circuits has not been investigated. Here, we exposed weanling mice to an array of taste solutions and determined the effects on the preference for sweet in adulthood. We demonstrate an experience-dependent shift in sucrose preference persisting several weeks following the termination of exposure. A shift in sucrose palatability, altered neural responsiveness to sucrose, and inhibitory synaptic plasticity in the gustatory portion of the insular cortex (GC) were also induced. The modulation of sweet preference occurred within a restricted developmental window, but restoration of the capacity for inhibitory plasticity in adult GC reactivated the sensitivity of sucrose preference to taste experience. Our results establish a fundamental link between gustatory experience, sweet preference, inhibitory plasticity, and cortical circuit function and highlight the importance of early life nutrition in setting taste preferences.