To prevent the physiological rise in plasma FFA levels that accompany fasting in the control arm, nicotinic acid (NA) was given as Acipimox 250-mg tablets (Olbetam™, Pharmacia, U.K.) (Chen et al. 1999); one dose following the baseline scan, and a further dose 2 h later. Cognitive tests Executive function, cognitive speed and attention were tested using the Trail making A+B test, the dual tasks test (Baddeley Inhibitors,research,lifescience,medical et al. 1997), learn more including the Wechsler Adult Intelligence Scale – Revised (WAIS-R) digit span forwards and backwards (Wechsler 1981), Stroop color word and interference test (Trenerry et al. 1989), and the pattern and letter comparison speed test (Salthouse and Babcock 1991). Visual recall
was tested using the Doors B test from the Doors and People test (Thames Valley Testing Company). Verbal recall was tested using the Hopkins Verbal Learning Inhibitors,research,lifescience,medical Test – Revised (forms 1, 3, 4, and 6) with delayed recall (Brandt 1991) and the Paragraph Recall Test (Rivermead Behavioral test, Versions A, B, C, and D) (Wilson et al. 1985). The delayed recall parts for both verbal recall tests were performed while the subjects were in the scanner. Standardized
meal To prevent the influence of postprandial pulses of insulin, subjects were required to fast for the duration of the visit. In order to limit the physiological responses to prolonged fasting including lipolysis and mild ketosis, a small standardized meal was given following the baseline MRS scan. This was Inhibitors,research,lifescience,medical to provide Inhibitors,research,lifescience,medical enough carbohydrate to stimulate a small pulse of circulating insulin to prevent ketosis. This small amount of insulin would have dissipated within 2 h, and therefore not interfere with assessments 4 h later. Based on data from Juntunen et al. (2002) in healthy volunteers, a 50-g carbohydrate load, in the form of a slice of bread, stimulated a rise in plasma insulin that returned to fasting levels within 3 h. For this study, a smaller carbohydrate load was given. Subjects were given a waffle, a low-fat yogurt, and Inhibitors,research,lifescience,medical a low-sugar fruit juice drink (total carbohydrate 16.3 g, fat 7.3 g, protein 6.2 g). Following
this meal, the intervention was started and subjects were kept fasting for the remainder of the study, but were allowed to drink water freely. Energetics The neuropsychological tasks used in this study stimulate hippocampal activation so 31P MRS data were acquired to assess hippocampal energetics. Scans were performed using a 3 Tesla system (Siemens Trio, Erlangen, Germany) using a dedicated dual tuned 1H/31P quadrature unless birdcage head coil (Rapid Biomedical GmbH, Germany). Proton images for localization and anatomical structural images were obtained using a standard Magnetization Prepared-Rapid Gradient Echo (MP-RAGE) sequence. Spectral data were acquired using a multivoxel acquisition-weighted chemical shift imaging (3D AW-CSI) sequence (Pohmann and von Kienlin 2001). Nuclear overhauser enhancement was employed on all acquisitions to increase signal strength (Li et al.