title: Dietary-induced obesity disrupts trace fear conditioning and decreases hippocampal reelin expression.
abstract: Both obesity and over-consumption of palatable high fat/high sugar "cafeteria" diets in rats has been shown to induce cognitive deficits in executive function, attention and spatial memory. Adult male Sprague-Dawley rats were fed a diet that supplemented standard lab chow with a range of palatable foods eaten by people for 8 weeks, or regular lab chow. Memory was assessed using a trace fear conditioning procedure, whereby a conditioned stimulus (CS) is presented for 10s and then 30s after its termination a foot shock (US) is delivered. We assessed freezing to the CS (flashing light) in a neutral context, and freezing in the context associated with footshock. A dissociation was observed between levels of freezing in the context and to the CS associated with footshock. Cafeteria diet fed rats froze less than control chow fed rats in the context associated with footshock (P<0.01), indicating that encoding of a hippocampus-dependent context representation was impaired in these rats. Conversely, cafeteria diet fed rats froze more (P<0.05) to the CS than chow fed rats, suggesting that when hippocampal function was compromised the cue was the best predictor of footshock, as contextual information was not encoded. Dorsal hippocampal mRNA expression of inflammatory and neuroplasticity markers was analysed at the end of the experiment, 10 weeks of diet. Of these, mRNA expression of reelin, which is known to be important in long term potentiation and neuronal plasticity, was significantly reduced in cafeteria diet fed rats (P=0.003). This implicates reductions in hippocampal plasticity in the contextual fear memory deficits seen in the cafeteria diet fed rats.
authors.affiliation: School of Medical Sciences, The University of New South Wales, Sydney, Australia; School of Psychology, The University of New South Wales, Sydney, Australia.
authors.forename: Amy C
authors.initials: AC
authors.lastname: Reichelt
authors.affiliation: School of Medical Sciences, The University of New South Wales, Sydney, Australia.
authors.forename: Jayanthi
authors.initials: J
authors.lastname: Maniam
authors.affiliation: School of Psychology, The University of New South Wales, Sydney, Australia.
authors.forename: R Frederick
authors.initials: RF
authors.lastname: Westbrook
authors.affiliation: School of Medical Sciences, The University of New South Wales, Sydney, Australia. Electronic address: m.morris@unsw.edu.au.
authors.forename: Margaret J
authors.initials: MJ
authors.lastname: Morris
mesh_terms: D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism*; D003214:Conditioning, Classical / Q000502:physiology*; D059305:Diet, High-Fat; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D005239:Fear / Q000502:physiology*; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009473:Neuronal Plasticity / Q000502:physiology; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D000091042:Reelin Protein; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism*
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D016326:Extracellular Matrix Proteins; D009419:Nerve Tissue Proteins; D000091042:Reelin Protein; C000717129:Reln protein, rat; D012697:Serine Endopeptidases
keywords: BDNF; Conditioning; Context fear; Hippocampus; Memory; Neuroinflammation; Neuroplasticity; Obesity; Reelin