Caloric restriction provided after global ischemia does not reduce hippocampal cornu ammonis injury or improve functional recovery

Since caloric restriction (CR) can modify multiple pathways central to the ischemic cascade and enhance neuroplasticity mechanisms, we hypothesized that CR should exert protective effects following brain ischemia. Previous studies have suggested benefit when CR was administered prior to ischemia. We investigated whether prolonged CR beginning after global ischemia would result in lasting protection as assessed by performance in the open field, as a measure of functional outcome, and hippocampal CA1 neuronal counts. Adult, male Mongolian gerbils were subjected to 5 min bilateral carotid artery occlusion (ISCH) or sham surgery (SHAM) with tympanic temperature maintained at 36.5±0.2 °C during the intra-ischemic period. After screening out gerbils with incomplete ischemia, each of the two surgical groups were randomly assigned to control diet (CON) or 30% CR for the duration of the study (60 d). Gerbils were tested in the open field on d3, 7, 10, 30 and 60. ISCH-CON animals showed a significantly higher level of activity in the open field (impaired habituation) compared to SHAM-CON gerbils on all test days (P<0.001). Open field activity was significantly lower in the ISCH-CR group than in ISCH-CON gerbils only on d7 (P=0.024). Open field activity of the SHAM-CR gerbils showed a trend to increase relative to that of SHAM-CON gerbils during the last 30 d of the study (P=0.055 on d60), raising the question of suitability of the open field test for long-term studies of CR and ischemia. Brain sections obtained at d60 were stained with hematoxylin and eosin. Hippocampal CA1 neuron counts were significantly reduced by ischemia (P<0.001), and there was no sparing effect of CR. Our findings suggest that prolonged 30% CR administered beginning after global ischemia cannot diminish brain injury or enhance long-term recovery.