Structural and functional disorders of hippocampus following ischemia/reperfusion in lower limbs and kidneys

Recent evidence suggests that ischemia/reperfusion (I/R) in an organ may have distance effect on the brain. In this study, the effects of renal I/R, limb I/R or both together on the structural and function of hippocampus were evaluated and compared. Hence, rats were subjected to 2-h bilateral lower limb ischemia, 45-min bilateral renal ischemia, or combined limb and renal ischemia followed by 1-day reperfusion. At 22-h reperfusion, each rat was fixed on a stereotaxic apparatus for performing electrophysiological study on the hippocampus. The long-term potentiation (LTP) was induced by high-frequency stimulation (HFS), and paired-pulse ratio (PPR) was also monitored before and after HFS delivery. After taking blood sample and sacrificing animal, its brain was removed and preserved for stereological study. The limb I/R reduced plasma osmolality that led to synaptic excitement in the hippocampus, where there was a considerable loss of pyramidal cells and markedly impaired short- and long-term synaptic plasticity. The renal I/R largely increased plasma creatinine that might excite basal synaptic transmission. In the rats with combined limb and renal I/R, the hippocampal neuronal loss and impaired synaptic plasticity were the same as those with limb I/R, but basal synaptic transmission was lowered. In conclusion, the 2-h lower limb ischemia compared to 45-min renal ischemia induced more injurious distant effects on the hippocampus after 1-day reperfusion. The combination of renal and limb I/R did not add or potentiate hippocampal neuronal loss and synaptic plasticity impairment, whereas it decreased the basal synaptic transmission with respect to each one alone.