M1AChR mediates electroacupuncture effects on hippocampal pro-nerve growth factor release and maturation in a rat model of diabetic encephalopathy

Aims: Diabetic encephalopathy (DE) down-regulates brain cholinergic activity that in turn controls proNGF release and maturation. Electroacupuncture (EA) modulates NGF system in experimental DE. We studied, in the hippocampus (HP) of diabetic rats, EA effects on: proNGF and M1AChR distribution; activity-dependent proNGF release; p75 neurotropin receptor (p75NTR) challenge by proNGF. Methods: DE was induced in young adult rats by streptozotocin (STZ). One week after STZ injection, low frequency EA was started and repeated twice a week for 3 weeks. At the end of the treatments, in HP from control, STZ and STZ/EA rats, we analyzed: the expression of proNGF and M1AChR and their co-localization with glutamatergic and GABAergic markers by confocal microscopy; proNGF isoforms release in slices superfused and stimulated by the muscarinic agonist carbachol (CCh), by Western blot and ELISA; different proNGF isoforms binding to the pro-apoptotic p75NTR, by co-immunoprecipitation. Results: STZ decreased and EA normalized the total cell number and the cells expressing M1AChR in HP tissue. proNGF and M1AChR colocalized with vGlut1 in HP cells. Activity-dependent proNGF release from HP slices increased in STZ rats, while EA counteracted the STZ effects. The enhancement of p75NTR interaction with the 25 kDa proNGF in diabetic brain was also counteracted by EA. Conclusions: EA is effective in restoring diabetes-induced alteration in M1AChR distribution in brain areas that produce and release proNGF. Diabetes affects and EA normalizes the production, release and activity of proNGF, suggesting a possible ability of EA in modulating the activity of cholinergic circuits.