| Description |
Nuclear magnetic resonance (NMR) studies were performed with a two turn copper foil surface coil employing a unique transposition design that incorporates an explicit center tap ground of a widened bottom layer. Flexibility permitted easy conformation to tissues of interest thereby enhancing coil performance. Dielectric and inductive losses were thus reduced via effective shielding of electric fields and uniform distribution of magnetic fields. Construction details of the crossover coil and performance data for coils of varied dimensions are given. To establish age variant spectral saturation, apparent 31P longitudinal relaxation times, T1, values were measured for brain phosphates in young (5-6 mo), mature (11-12 mo), and aged rats (23-24 mo). Significant differences were found for alpha-, and beta-phosphate groups of adenosine triphosphate (ATP) and bone phosphate. A large, but nonsignificant change between young and mature rats was noted for the T1 of inorganic phosphate. Age related changes in tissue composition and biochemistry are discussed as possible contributors to these results. To assess the senescent response to stress, cerebral phosphate metabolism during mild hypoxia in young, mature and old rats was studied. Young rats displayed a greater drop in phosphocreatine (PCr), an earlier and greater onset of acidosis, and a larger rise in inorganic phosphate (Pi) than either the mature or old animals. PCr and intracellular pH (pHi) levels stayed low while Pi remained elevated after normoxia was reinstated. In contrast, all metabolite levels in the mature and senescent rats return to within 10% of control levels. Thus, young animals appear to maintain adequate ATP levels via increased anaerobic glycolysis thereby developing severe acidosis, while mature and senescent animals appear to maintain ATP levels by increased oxidative respiration rates. Speculations to explain this disparity are discussed in detail. The measurement of cerebral blood flow (CBF) via deuterium washout kinetics was developed in anticipation of calculating cerebral metabolic rates of oxygen (CMR[O2). Initially investigated on a vertical NMR system, the technique was found to have less complications when measured with the animal in a horizontal position. Values of global cerebral blood flow were similar to cited literature. |
