Autonomic nervous system imbalance in diabetic mouse choroids

We investigated neurohomeostasis and its possible underlying mechanisms in the choroids of diabetic mice.

Streptozotocin-induced diabetic mice were used in this study. Choroidal nerve fiber alterations were observed via transmission electron microscopy (TEM). The levels of epinephrine and acetylcholine in the choroid were determined via ultra-high-performance liquid chromatography-tandem mass spectrometry. Tyrosine hydroxylase (TH), choline acetyl transferase (ChAT), and neuronal nitric oxide synthase (nNOS), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) levels were evaluated by western blot or quantitative real-time polymerase chain reaction. In addition, immunofluorescence staining were used to analyze the changes in key enzymes (TH, dopamine beta-hydroxylase (DβH), and CGRP) in the superior cervical sympathetic ganglia (SCG) and trigeminal ganglia (TG).

TEM revealed a loose myelin sheath around nerve fibers, axon atrophy, and cytoplasmic vacuoles in Schwann cells in diabetic choroids. Lower epinephrine levels were observed in diabetic mice. Although no difference was found in acetylcholine level, the epinephrine-to-acetylcholine ratio was greatly decreased. Decreased TH and increased ChAT, nNOS, VIP, NPY, and CGRP were found in diabetic choroids. Fewer TH-positive and DβH-positive neuronal cells were found in the SCGs of diabetic mice. More CGRP-positive and fewer TH-positive neuronal cells were observed in the TG of diabetic mice.

Altered markers of the sympathetic, parasympathetic and sensory systems were present in diabetic mouse choroids. An imbalanced choroidal nervous system might explain the initiation of choroidal neovascularization in diabetic patients.