Animals and treatments

Three-month-old male C57Bl/J mice were purchased (Clear, Japan) and maintained at the National Institute of Radiological Sciences vivarium facilities with food and water available ad libitum. Beginning at 3 months of age, mice were randomly assigned to groups (n = 6/group) and maintained on a standard diet (10 % kCal fat; Research Diets D12450B Harlan Teklad, Indianapolis, IN) or a high-calorie, high-fat diet (60 % kCal fat; Research Diets D12492, Harlan Teklad) for a period of 3 months. Body weights were monitored weekly, and fasting blood glucose was monitored fortnightly.

After 1 month of feeding, mice were anesthetized with isoflurane (3 % v/v for induction, 1.5 % v/v for maintenance), positioned in a stereotaxic apparatus and 0.9 % saline applied to the eyes. The scalp was shaved and cut, the skull exposed, and adhering tissue was removed with acetone. A cannula (Brain Infusion Kit 3, Alzet) was implanted in the left ventricle at the following coordinates: +1.0 medial/lateral, −0.3 anterior/posterior, −2.5 dorsal/ventral. The cannula was fixed to the skull using dental cement and connected to a mini-osmotic pump (Model 1002, Alzet) that was filled with either vehicle (250 μg/mL high-density lipoprotein (HDL) in 4 mM HEPES with 2.5 % DMSO) or 120-μM oligomeric Aβ-42 [32]. Oligomeric Aβ-42 was prepared by solubilizing synthetic human Aβ-42 (Peptide Institute) to 1 mM in hexafluoroisopropanol, then drying under vacuum in a SpeedVac. The peptide film was then resuspended in DMSO to 5 mM and diluted in 4 mM HEPES containing 250 μg/mL HDL (Millipore) to a final concentration of 120 μM. Pumps were partially coated with paraffin to adjust the infusion rate to 3 μL/day for 1 month, then the filled pumps were incubated in sterile phosphate-buffered saline (PBS) at 37 °C for 40 h prior to implantation under the dorsal skin on the back. The incision site on the scalp was closed with suture, and mice were administered buprenorphrine (0.05 mg/kg i.p., Henry Schein Inc.) post-operatively for analgesia. One spontaneous death occurred in the 8 weeks post-surgery treatment duration (obese + Aβ group).

All experimentation was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health and was approved by the Institutional Animal Care and Use Committee of the National Institutes for Quantum and Radiological Science and Technology, Japan.