Characteristics of monocarboxylates as energy substrates other than glucose in rat brain slices and the effect of selective glial poisoning - a 31P NMR study.

In rat brain slices we examined the differences in the levels of high-energy phosphates in the presence of various energy substrates by using 31P NMR with a time resolution of 4 min at 25 degrees C. In parallel experiments we recorded population excitatory postsynaptic potentials (EPSPs) from granule cells in rat hippocampal slices. During high K(+) stimulation (8 min) phosphocreatine (PCr) decreased to a low level and recovered to the control level in standard artificial cerebrospinal fluid (ACSF) in about 10 min. Population EPSPs disappeared following high-K(+) stimulation and recovered in standard ACSF. In iodoacetic acid (IAA)-pretreated slices, whereas glucose was unable to support energy metabolism, the PCr level, which decreased following high-K(+) stimulation, recovered in ACSF containing lactate or pyruvate. The half-time of recovery of PCr levels in ACSF containing lactate was longer than that containing glucose. Population EPSPs in standard ACSF were maintained for more than 1 h, but those in ACSF containing lactate decreased gradually by about half in 40 min. In IAA-pretreated slices, when further treated with fluorocitrate (100 microM) for 2 h, the recovery of the PCr level in ACSF containing lactate after high-K(+) stimulation was completely abolished, whereas the recovery of the PCr level in ACSF containing pyruvate was unaffected. These results indicate that neurons can utilize pyruvate as well as glucose, but not lactate, as exogenous energy substrates, and that lactate may be metabolized to pyruvate in glial cells and transported to neurons to be utilized as an energy substrate.