Hippocampal slices were prepared under three conditions: (1) in medium containing glucose and oxygen at 4 degrees C; (2) as in (1), but at 37 degrees C; (3) in medium devoid of glucose and oxygen at 37 degrees C. The rates of recovery to roughly steady-state levels and through 8 h of incubation were monitored for energy metabolite levels and related parameters. In vitro stable values are compared with in situ hippocampal levels. Regardless of the conditions under which slices were prepared, metabolite levels required up to 3 h to stabilize, and these levels were maintained or improved through 8 h of incubation. Further, the maximal concentrations of metabolites were independent of the conditions of slice preparation. Total adenylates and total creatine levels reached 55% of those in vivo. Lactate decreased from the decapitation-induced high levels, but stabilized at concentrations about twice those in rapidly frozen brain. Cyclic AMP and cyclic GMP exhibited peak levels at 30 min of incubation, and cyclic GMP remained elevated for 3 h. Although all three methods of slice preparation resulted in similar metabolite profiles on incubation, the initial decreases in high energy phosphates were delayed by chilling. Most striking, the slices prepared in the absence of glucose and oxygen exhibited much smaller orthodromic evoked potentials in the dentate gyrus. The presence of glucose and oxygen during preparation of the slices appears to be critical to the electrophysiological response of the tissue.

The delayed death of CA1 neurons in the gerbil has been reported to occur at 4 days of reflow following 5 min of bilateral ischemia. Samples of the CA1 and CA3 somal region of the hippocampus, as well as of the parietal cortex, were dissected from frozen dried sections of gerbil brains frozen in situ between 1.5 and 96 hr of reflow following 5 min of bilateral ischemia and the concentrations of the adenylates, P-creatine, glucose, glycogen, and lactate were determined. The values for high-energy phosphates were restored by 1.5 hr of recirculation in all three regions and remained at or above control in the CA3 region and cortex for up to 96 hr. In contrast, the P-creatine and ATP decreased in the CA1 region at 48 and 96 hr of reflow, respectively. The total adenylates also decreased in the CA1 region at 96 h, but the normal energy charge in this area indicated that the surviving tissue was metabolically viable. A glucose overshoot was exhibited in the three regions at all time periods except 6 and 96 hr. At 6 hr of reflow, there was a transient return of glucose levels toward those of control. By 96 hr, the glucose in the CA3 region and cortex was not significantly different from control but was elevated in the CA1 region. The lactate levels were depressed from 1.5 to 12 hr of recirculation in all areas, but the decrease was significant only in the cerebral cortex. The concentration of glycogen was significantly elevated at 6 hr in all regions, then was restored by 24 to 48 hr, only to increase once again in the affected CA1 region. The results clearly indicate that metabolic perturbations persist for long periods of time after ischemic durations that are compatible with the survival of the animal but that the loss of the CA1 neurons cannot be attributed to a failure in energy metabolism.