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Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus).

ABSTRACT: The effects of light on cognitive function have been well-documented in human studies, with brighter illumination improving cognitive performance in school children, healthy adults, and patients in early stages of dementia. However, the underlying neural mechanisms are not well understood. The present study examined how ambient light affects hippocampal function using the diurnal Nile grass rats (Arvicanthis niloticus) as the animal model. Grass rats were housed in either a 12:12 h bright light-dark (brLD, 1,000 lux) or dim light-dark (dimLD, 50 lux) cycle. After 4 weeks, the dimLD group showed impaired spatial memory in the Morris Water Maze (MWM) task. The impairment in their MWM performance were reversed when the dimLD group were transferred to the brLD condition for another 4 weeks. The results suggest that lighting conditions influence cognitive function of grass rats in a way similar to that observed in humans, such that bright light is beneficial over dim light for cognitive performance. In addition to the behavioral changes, grass rats in the dimLD condition exhibited reduced expression of brain-derived neurotrophic factor (BDNF) in the hippocampus, most notably in the CA1 subregion. There was also a reduction in dendritic spine density in CA1 apical dendrites in dimLD as compared to the brLD group, and the reduction was mostly in the number of mushroom and stubby spines. When dimLD animals were transferred to the brLD condition for 4 weeks, the hippocampal BDNF and dendritic spine density significantly increased. The results illustrate that not only does light intensity affect cognitive performance, but that it also impacts hippocampal structural plasticity. These studies serve as a starting point to further understand how ambient light modulates neuronal and cognitive functions in diurnal species. A mechanistic understanding of the effects of light on cognition can help to identify risk factors for cognitive decline and contribute to the development of more effective prevention and treatment of cognitive impairment in clinical populations.

SUBMITTER: Soler JE

PROVIDER: S-EPMC5820160 | biostudies-literature | 2018 Mar

REPOSITORIES: biostudies-literature

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Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus).

Soler Joel E JE Robison Alfred J AJ Núñez Antonio A AA Yan Lily L

Hippocampus 20171227 3

The effects of light on cognitive function have been well-documented in human studies, with brighter illumination improving cognitive performance in school children, healthy adults, and patients in early stages of dementia. However, the underlying neural mechanisms are not well understood. The present study examined how ambient light affects hippocampal function using the diurnal Nile grass rats (Arvicanthis niloticus) as the animal model. Grass rats were housed in either a 12:12 h bright light- ...[more]

PMID: 29251803

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Project description:BackgroundThe prevalence of Metabolic Syndrome and related chronic diseases, among them non-insulin-dependent (type 2) diabetes mellitus, are on the rise in the United States and throughout the world. Animal models that respond to environmental stressors, such as diet, are useful for investigating the outcome and development of these related diseases.ObjectiveWithin this context, growth and energy relationships were characterized in the Nile rat, an exotic African rodent, as a potential animal model for diet-induced type 2 diabetes mellitus and Metabolic Syndrome.MethodsCompiled data from several studies established the relationship between age, body weight gain (including abdominal adiposity), food and water consumption, and blood glucose levels as determinants of diabetes in male and female Nile rats. Glucose Tolerance Testing, insulin, HbA1c, blood pressure measurements and plasma lipids further characterized the diabetes in relation to criteria of the Metabolic Syndrome, while diet modification with high-fat, low-fiber or food restriction attempted to modulate the disease.ResultsThe Nile rat fed lab chow demonstrates signs of the Metabolic Syndrome that evolve into diet-induced non-insulin-dependent (type 2) diabetes mellitus characterized by hyperinsulinemia with rising blood glucose (insulin resistance), abdominal adiposity, and impaired glucose clearance that precedes increased food and water intake, as well as elevated HbA1c, marked elevation in plasma triglycerides and cholesterol, microalbuminuria, and hypertension. Males are more prone than females with rapid progression to diabetes depending on the challenge diet. In males diabetes segregated into early-onset and late-onset groups, the former related to more rapid growth and greater growth efficiency for the calories consumed. Interestingly, no correlation was found between blood glucose and body mass index (overall adiposity) in older male Nile rats in long term studies, whereas blood glucose and the perirenal fat pad, as well as liver and kidney weight, were positively related to early-onset diabetes. Rats weaned early (4-5 wks) and challenged with a high-fat Western-type diet developed diabetes faster, and body fat accumulation was more apparent, whereas food restriction curtailed it.ConclusionThe Nile rat fed typical rodent diets develops hyperinsulinemia that precedes hyperglycemia (insulin resistance) leading to diet-induced type 2 diabetes associated with hypertriglyceridemia, hypercholesterolemia, and hypertension. Dietary modulation affected growth rate (weight gain and central adiposity) to impact disease progression. This rodent model represents a novel system of gene-diet interactions affecting energy utilization that can provide insight into the prevention and treatment of the type 2 diabetes and Metabolic Syndrome.

Dataset Information

Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus).

Publications

Light modulates hippocampal function and spatial learning in a diurnal rodent species: A study using male nile grass rat (Arvicanthis niloticus).

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