Selective responses of myenteric neurons to oxidative stress and diabetic stimuli

Diabetes has a differential effect on different subpopulations of myenteric neurons. Our aim was to investigate an in vitro model to examine the pathways underlying the development of nerve changes in diabetes.

The proportions of neuronal cell bodies containing vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS) and calbindin relative to the pan-neuronal marker HuC/D were quantified in wholemount preparations of the myenteric plexus of adult rat ileum using double labeling immunohistochemistry. Preparations were maintained in culture for 24 h in the presence and absence of stimuli mimicking the diabetic environment including oxidative stress, carbonyl stress, high glucose and advanced glycation end products (AGEs). Data were compared with the effect of streptozotocin-induced diabetes in vivo. KEY RESULTS Only oxidative stress in vitro produced the same pattern as observed in diabetes with an increase in VIP-, decrease in nNOS-, and no change in calbindin-positive neurons. Carbonyl stress and high glucose caused an increase in VIP-containing neurons without affecting nNOS expression. In contrast, exposure to AGEs only caused a decrease in nNOS-positive neurons. Calbindin expression was unaffected by any of the stimuli. The effects of the stimuli were prevented by the antioxidant, α-lipoic acid, or the carbonyl scavenger, aminoguanidine.

The results provide evidence that oxidative stress is the common factor in the development of neuronal changes in diabetes; however, the mechanism by which oxidative stress occurs depends on the individual subpopulation of myenteric neurons examined. The presence of calbindin appears to protect myenteric neurons against harmful stimuli.