Extracellular field potentials from 400µm Coronal Sections of Mouse Brain using the 7000smz.

Abstract

(from: https://doi.org/10.1002/oby.22983)

Objective: This study aimed to investigate both the long‐term and short‐term impacts of high‐fat diets (HFD) or high‐sucrose diets (HSD) on the normal diurnal pattern of cognitive function, protein expression, and the molecular clock in mice.

Methods: This study used both 6‐month and 4‐week feeding strategies by providing male C57BL/6J mice access to either a standard chow, HFD, or HSD. Spatial working memory and synaptic plasticity were assessed both day and night, and hippocampal tissue was measured for changes in NMDA and AMPA receptor subunits (GluN2B, GluA1), as well as molecular clock gene expression.

Results: HFD and HSD both disrupted normal day/night fluctuations in spatial working memory and synaptic plasticity. Mice fed HFD altered their food intake to consume more calories during the day. Both diets disrupted normal hippocampal clock gene expression, and HFD reduced GluN2B levels in hippocampal tissue.

Conclusions: Taken together, these results suggest that both HFD and HSD induce a loss of day/night performance in spatial working memory and synaptic plasticity as well as trigger a cascade of changes that include disruption to the hippocampal molecular clock.

Slice extracellular field potential recordings

Brains were extracted and sliced in ice-cold oxygenated high sucrose artificial cerebrospinal fluid (in mM: 85 NaCl, 2.5 KCl, 4 MgSO4, 0.5 CaCl2, 1.25 NaH2PO4, 25 NaHCO3, 25 glucose, and 75 sucrose saturated in 95% O2 and 5% CO2). Coronal sections (400 µm)

were prepared via a vibratome (Campden 7000SMZ) and transferred to a chamber with standard artificial cerebrospinal fluid (in mM: 119 NaCl, 2.5 KCl, 1.3 MgSO4, 2.5 CaCl2,

1 NaH2PO4, and 11 glucose, saturated in 95% O2 and 5% CO2) and stored at room temperature until recording. Night slices were prepared between ZT 11 and 11.5 and recorded from ZT 13 to 19, whereas day slices were prepared between ZT 2 and 3 and recorded from ZT 4 to 10. Recordings from different times of day and diet were interpolated across the recording days (weeks 24-26 of feeding). Baseline recordings

were established for 20 minutes, and then LTP of the Schaffer collateral pathway was induced using a high-frequency stimulation (HFS) consisting of two trains of 100 Hz (0.5-second duration, 15-second interval) and field excitatory postsynaptic potential slopes were recorded for 60 minutes following HFS.