Mitochondrial dysfunction in an animal model of diabetic neuropathy is associated with a reduction of neurosteroid synthesis.

Background : Recent work in a model of diabetic neuropathy revealed that layer 2/3 cortical pyramidal neurones of the pain pathway exhibited reduced endogenous neurosteroid modulation of the GABA (A)R and exogenously applied neurosteroids had an exaggerated impact. It is postulated that this is related to reduced precursor synthesis, due to mitochondrial dysfunction in diabetic neuropathy. Benzodiazepines are also known to activate neurosteroidogenesis by binding to mitochondrial translocator protein (TSPO). This study explored the differential effect of diazepam on GABA (A)R modulation via neurosteroidogenesis in diabetic and wild type (WT) mice. Methods : Whole-cell patch-clamp technique was used on slices of neural tissue. Electrophysiological recordings were obtained from layer 2/3 cortical pyramidal neurons of the pain pathway from mice with type-II diabetic neuropathy ( ob/ob) and WT controls aged 60-80 days. Results : There was a key difference in the response of the WT and ob/ob cortical neurons to simultaneous incubation with diazepam and flumazenil. In contrast, diazepam and the 5a-reductase inhibitor finasteride, individually or in combination, produced the same response in both strains. Conclusions : The exaggerated effect of diazepam on GABAergic inhibitory tone in the ob/ob, despite the presence of the GABA (A)R benzodiazepine antagonist flumazenil is likely observed due to physiological upregulation of key neurosteroidogenic enzymes in response to the reduced pregnenolone synthesis by the mitochondria. By increasing pregnenolone via TSPO activation, it is possible to promote enhanced neurosteroidogenesis and increase GABAergic inhibitory tone via an alternate route. In diabetic neuropathy, mitochondrial dysfunction may play an important role. Enhancing the GABAergic neurosteroid tone could be of potential therapeutic benefit.