Transmission electron microscopic examination of synapses and mitochondria within the hippocampus of depressed individuals

Introduction: Major depressive disorder (MDD) is a prevalent, complex condition with an unclear pathophysiology. Studies have shown structural and cellular changes in the hippocampus and reduced synaptic density in the prefrontal cortex of depressed individuals (Kang HJ et al. Nature Medicine 2012;18(9):1413-1417). Additionally, impaired mitochondrial function has been linked to susceptibility to mental health disorders.Objectives: This study aimed to examine synaptic and mitochondrial characteristics in post-mortem hippocampal tissues, specifically in individuals with MDD.Methods: The three study groups were: MDD patients; controls and patients with alcohol dependence as positive control group. Controls were individuals who accidentally deceased and had no neuropsychiatric disorders. Dentate gyrus, CA3 and CA1 areas were investigated. Ultrathin sections were examined, and photomicrographs were taken for further analysis using a JEOL JEM 1400 FLASH transmission electron microscope. Systematic quantitative analysis was conducted with the Neurolucida system using unbiased counting principles.Results: We did not find significant differences in synaptic and mitochondrial densities between the patient groups and the control subjects.Conclusion: These initial findings suggest that synaptic and mitochondrial densities in the hippocampus may remain relatively consistent regardless of MDD or alcohol abuse. Various limitations may have affected results, requiring further exploration of synaptic and mitochondrial interactions in MDD.Acknowledgment: This research was supported by the Hungarian Brain Research Program 3 (NAP-3) and the TKP2021-EGA-16 project, as well as the ÚNKP-23-3-I New National Excellence program of the Ministry for Culture and Innovation from the source of the National Research, Development and Innovation Fund.