TUNEL-positive neurons of hippocampus in both groups (400x): (a) a control rat, (b) a diabetic rat, (c) control neurons, and (d) 24 h after high glucose treatment neurons. TUNEL positive staining neurons were labeled as brown, the arrows in (b) (diabetic rat) and (d) (neurons of high glucose medium) showed that the number of TUNEL-positive cells was increased when compared with the normal rats (a) and neurons of normal medium (c).