" in vivo " and " in vitro " TWO DIMENSIONAL lH NMR SPECTROSCOPY

15 " in vivo " and " in vitro " TWO DIMENSIONAL lH NMR SPECTROSCOPY. The nucleus most frequently used for Nuclear Magnetic Resonance (NMR) spectroscopy studies in living tissues has, until recently, undoubtedly been 3 1 P. 3 1 P NMR is very sensitive, the spectra are simple because of the wide available spectral range, the relatively few accessible molecules and the small number of 3 *P nuclei present in each molecule. The molecules displayed take part in the energy metabolism of the cell (ATP, ADP, phosphocreatine, inorganic phosphate and sugar phosphates). But *£! proton spectra also have several potential advantages: sensitivity is high and, most important, they provide access to many important molecules (1). In vivo proton NMR has developed more slowly, both because of the major problem of selective suppression of the water signal, and also because of the great complexity of the *H spectra. This nucleus has a narrow spectral width (lOppm) and there are many protonated molecules accessible to measurement. Each molecule contains many *H , and the signals have a fine structure, because of scalar ^H-^H coupling. All these characteristics make the spectrum particularly crowded and complex. II Materials and Methods. We have used two models to study cerebral metabolism by NMR. 11.1 In vitro model : superfused slices of new born rat brain. Detailed descriptions of the superfusion for brain slices have been published elsewhere (2,3,4). Our initial results were obtained using a commercial NMR probe which could accept tubes with a maximum diameter of 5mm (2). We have since constructed a special probe accepting 10mm tubes which is better adapted to tissue perfusion. The l H proton signal detecting coil is closest to the sample in this "reversed" probe, and a larger diameter coil allows verification of sample viability using a 3 1 P spectrum. Samples can be kept for up to 12 h under these conditions without detection of any inorganic phosphate in the 31 P spectrum 11.2 In vivo rat model The animal was positioned vertically in a custom built probe. Emission and detection were via a surface coil assembly placed on the rat's skull. II.3 NMR parameters. All spectra were recorded using a BRUKER AM400 wide-bore 400 MHz spectrometer. The conditions for obtaining !H ID spectra varied according to the model. The *H spectra of superfused brain slices were recorded using the sequence: Select, sat.-90-D-180-D-acquisition with a selective saturation …