Diabetes induces early transient changes in the content of vesicular transporters and no major effects in neurotransmitter release in hippocampus and retina

Diabetes induces changes in neurotransmitter release in central nervous system, which depend on the type of neurotransmitter and region studied. In this study, we evaluated the effect of diabetes (two and eight weeks duration) on basal and evoked release of [¹⁴C]glutamate and [³H]GABA in hippocampal and retinal synaptosomes. We also analyzed the effect of diabetes on the protein content of vesicular glutamate and GABA transporters, VGluT-1, VGluT-2 and VGAT, and on the α₁A subunit of P/Q type calcium channels, which are abundant in nerve terminals. The protein content of vesicular glutamate and GABA transporters, and of the α₁A subunit, was differently affected by diabetes in hippocampal and retinal synaptosomes. The changes were more pronounced in the retina than in hippocampus. VGluT-1 and VGluT-2 content was not affected in hippocampus. Moreover, changes occurred early, at two weeks of diabetes, but after eight weeks almost no changes were detected, with the exception of VGAT in the retina. Regarding neurotransmitter release, no major changes were detected. After two weeks of diabetes, neurotransmitter release was similar to controls. After eight weeks of diabetes, the basal release of glutamate slightly increased in hippocampus and the evoked GABA release decreased in retina. In conclusion, diabetes induces early transient changes in the content of glutamate and/or GABA vesicular transporters, and on calcium channels subunit, in retinal or hippocampal synaptosomes, but only minor changes in the release of glutamate or GABA. These results point to the importance of diabetes-induced changes in neural tissues at the presynaptic level, which may underlie alterations in synaptic transmission, particularly if they become permanent during the later stages of the disease.