The role of dopamine D2 receptors in the nucleus accumbens during taste-aversive learning and memory extinction after long-term sugar consumption

Sugar consumption induces the consummatory suppression of sugary ethanol: Differential effects of sugar restriction according to sex and age

Sweet foods activate the reward system that is essential in processing natural reinforcers. Maturation changes in this system during adolescence are linked to heightened impulsivity and risk-seeking behavior, including the use of drugs like ethanol. This usually starts with the consumption of sugary mixtures. However, the influence of sugar exposure on ethanol consumption remains inconclusive. The present research examines the effect of long-term sugar exposure on sugary ethanol (S-EtOH) preference and net intake, exploring the implications of sex, age, accessor restriction of sugar, and its effect during the transition into adulthood. Wistar rats of both sexes were given 24-hour access to a sugar solution for 21 days during adolescence or adulthood. Subsequently, four preference tests of S-EtOH vs. water were carried out every other day, with or without sugar access between each preference test. Our results demonstrate that continuous acute and long-term sugar access induces a consummatory suppression effect on S-EtOH intake, particularly in adult rats, irrespective of sex. This effect becomes more pronounced with more extended periods of exposure to sugar, leading to a higher prevalence of low consumers. Notably, when sugar access was restricted after high familiarization, the suppression effect in adolescent male rats was reduced. Under these conditions, the rats appeared to be more susceptible to developing a preference for S-EtOH consumption. Furthermore, our longitudinal observations reveal that sugar access or restriction conditions during the transition from adolescence to adulthood play a crucial role in shaping S-EtOH consumption patterns in adulthood.

Activation of multiple neuromodulatory systems in alert rats acquiring conditioned taste aversion revealed by positron emission tomography

Conditioned taste aversion (CTA) is an essential ability for animals to consume food safely and is regulated by neuromodulatory systems including the dopamine, noradrenaline, serotonin, and acetylcholine systems. However, because few studies focused on a comprehensive understanding of whole-brain activities, how these neuromodulators contribute to the process of CTA remains an open issue. 18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET) can visualize activated regions within the whole brain simultaneously and noninvasively. This study aimed to understand the mechanisms of CTA, especially focusing on the retrieval process after CTA acquisition by FDG-PET imaging. CTA was established in rats who received an intraoral application of saccharin solution (IOAS) on the first day (Day 1), a LiCl i.p. injection after an IOAS on Day 2, and an IOAS on Day 3 (CTA group). The subtraction images of Day 3 of the SHAM group, which received a 0.9 % NaCl (saline) injection instead of a LiCl on Day 2, from those of Day 3 of the CTA group revealed increases in FDG signals in multiple brain regions including the substantia nigra, ventral tegmental area, locus coeruleus, dorsal raphe, and nucleus basalis magnocellularis, in addition to the hippocampus and nociception-related regions, including the parabrachial nucleus and solitary nucleus. On the other hand, the visceral pain induced by the LiCl injection increased FDG signals in the primary and secondary somatosensory and insular cortices in addition to the parabrachial nucleus and solitary nucleus. These results suggest that the retrieval process of CTA induces brain regions producing neuromodulators and pain-related brainstem.

Adolescent high-fructose corn syrup consumption leads to dysfunction in adult affective behaviors and mesolimbic proteins in male Sprague-Dawley rats

Adolescence is a critical period of development, during which the brain undergoes rapid maturation. Problematically, adolescents are the top consumers of high fructose corn syrup (HFCS) sweetened beverages and snacks, which may have neurodevelopmental consequences. While HFCS consumption has been linked to an increased likelihood of obesity and other physical health impairments, the link between HFCS and persistent behavioral changes is not yet fully established. The present study aimed to assess whether adolescent HFCS consumption could lead to alterations in adult behaviors and protein expression, following cessation. Adolescent HFCS-exposure contributed to deficits in learning and motivation on an effort-related T-Maze procedure, as well as increased immobility time in the forced swim paradigm during adulthood. Molecularly, protracted decreases in accumbal dopamine D1 and D2 receptors and protein kinase G (PKG), as well as increases in tyrosine hydroxylase and GluA2 receptor subunits, were observed following HFCS-exposure. Taken together, these data suggest that adolescent HFCS-consumption leads to protracted dysfunction in affective behaviors and alterations in accumbal proteins which persist following cessation of HFCS-consumption.

Taste Processing: Insights from Animal Models

Taste processing is an adaptive mechanism involving complex physiological, motivational and cognitive processes. Animal models have provided relevant data about the neuroanatomical and neurobiological components of taste processing. From these models, two important domains of taste responses are described in this review. The first part focuses on the neuroanatomical and neurophysiological bases of olfactory and taste processing. The second part describes the biological and behavioral characteristics of taste learning, with an emphasis on conditioned taste aversion as a key process for the survival and health of many species, including humans.

The artificial sweetener Splenda intake promotes changes in expression of c-Fos and NeuN in hypothalamus and hippocampus of rats

BACKGROUND

Obesity is the result of the interaction of multiple variables, including the excessive increase of sugar-sweetened beverages consumption. Diets aimed to treat obesity have suggested the use of artificial sweeteners. However, recent evidence has shown several health deficits after intake of artificial sweeteners, including effects in neuronal activity. Therefore, the influence of artificial sweeteners consumption such as Splenda, on the expression of c-Fos and neuronal nuclear protein (NeuN) in hypothalamus and hippocampus remains to be determined.

OBJECTIVES

We investigated the effects on c-Fos or NeuN expression in hypothalamus and hippocampus of Splenda-treated rats.

METHODS

Splenda was diluted in water (25, 75 or 250 mg/100 mL) and orally given to rats during 2 weeks ad libitum. Next, animals were sacrificed by decapitation and brains were collected for analysis of c-Fos or NeuN immunoreactivity.

RESULTS

Consumption of Splenda provoked an inverted U-shaped dose-effect in c-Fos expression in ventromedial hypothalamic nucleus while similar findings were observed in dentate gyrus of hippocampus. In addition, NeuN immunoreactivity was enhanced in ventromedial hypothalamic nucleus at 25 or 75 mg/100 mL of Splenda intake whereas an opposite effect was observed at 250 mg/100 mL of artificial sweetener consumption. Lastly, NeuN positive neurons were increased in CA2/CA3 fields of hippocampus from Splenda-treated rats (25, 75 or 250 mg/100 mL).

CONCLUSION

Consuming Splenda induced effects in neuronal biomarkers expression. To our knowledge, this study is the first description of the impact of intake Splenda on c-Fos and NeuN immunoreactivity in hypothalamus and hippocampus in rats.

Protective effect of carnosine on white matter damage in corpus striatum induced by chronic cerebral hypoperfusion

Subcortical ischemic vascular dementia caused by chronic cerebral hypoperfusion due to small-artery disease is a common subtype of vascular dementia, which is recognized as the second most prevalent type of dementia. The aim of this study was to determine the effect of carnosine on white matter damage in corpus striatum. Adult male mice (C57BL/6 strain) were subjected to right unilateral common carotid arteries occlusion (rUCCAO), and treated with carnosine or saline. Klüver-Barrera staining, immunohistochemical analyses, Western blots and neurochemical analysis were performed after rUCCAO. The white matter in corpus striatum was damaged at day 37 after rUCCAO, which was largely rescued by carnosine (200, 500 mg/kg). Carnosine (200, 500 mg/kg) significantly recovered the expression of myelin basic protein, suppressed the activation of microglia and reversed the decrease of 5-hydroxytryptamine and dopamine levels in corpus striatum. Moreover, carnosine (200, 500 mg/kg) significantly inhibited the apoptosis in corpus striatum. These data suggest that carnosine has the neuroprotective effect in corpus striatum on rUCCAO in mice, may be due to its protection of neurotransmitters and inhibition of apoptosis.

Inulin fiber dose-dependently modulates energy balance, glucose tolerance, gut microbiota, hormones and diet preference in high-fat-fed male rats

Inulin, a popular prebiotic fiber, has been reported to promote satiety and fat loss; however, the dose-response effects of inulin on energy balance and diet preference, and whether the metabolic effects are independent of calorie restriction are not well characterized. Therefore, we compared the effects of diets varying in inulin concentrations on food intake, energy expenditure, body composition, gut microbiota and hormones, and assessed whether inulin-induced hypophagia was due to reduced diet preference. In experiment 1, male rats were randomized to six high-fat diet groups: control (CON, 0% inulin), 2.5% inulin (2.5IN), 10% inulin (10IN), 25% inulin (25IN), 25% cellulose (25CE) or pair-fed to 25IN (25PF) for 21 days. We demonstrate that inulin dose-dependently decreased caloric intake and respiratory quotient; improved glucose tolerance; increased the abundance of Bacteroidetes and Bifidobacterium spp.; decreased Clostridium clusters I and IV; increased butyryl-CoA:acetate CoA-transferase in cecum; upregulated peptide YY, cholecystokinin and proglucagon transcripts in the cecum and colon; and increased plasma peptide YY and glucagon-like peptide-1 concentrations. Importantly, unlike 25PF, 25IN attenuated the reduction in energy expenditure associated with calorie restriction and decreased adiposity. In experiment 2, following four training periods, diet preferences were determined. Although 10IN and 25IN decreased caloric intake, and 25CE increased caloric intake, during training, all high-fiber diets were less preferred. Taken together, this work demonstrates that inulin dose-dependently decreased caloric intake, modulated gut microbiota and upregulated satiety hormones, with metabolic effects being largely independent of caloric restriction.