NEUROBIOLOGY OF SUICIDE: MORPHOLOGICAL ASSESSMENT OF MICROGLIAL NETWORK IN HUMAN <i>POST-MORTEM</i> PREFRONTAL CORTEX

Neuroinflammation is increasingly recognized as a key factor in the pathophysiology of suicidal behavior. This study investigated the morphological profiles of cortical microglia in depressed individuals who died by suicide, compared to healthy controls. Postmortem samples from the dorsolateral prefrontal cortex (dlPFC) were examined using immunohistochemistry and immunofluorescence with different microglial markers, such as Ionized calcium- Binding Adapter molecule 1 (IBA1), Cluster of Differentiation 68 (CD68) and Purinergic Receptor P2Y, G-Protein Coupled, 12 (P2RY12). To better analyze the gliovascular network, we also used the lectin Lycopersicon esculentum Agglutinin (LEA), which recognizes both microglial and vascular endothelial cells. Microglia predominantly exhibited a ramified morphology (IBA1+, P2RY12+), indicative of a surveillance state, but amoeboid CD68+ cells, revealing activation, were also observed. Preliminary observations suggested how CD68+ activation could be prevalent in female subjects if compared with male ones. Also LEA/IBA1 colocalization analysis revealed sex-specific patterns: in male suicide cases, colocalization was reduced in dlPFC compared to controls, possibly reflecting a functional disconnection between microglia and vasculature. In contrast, female suicide cases showed increased colocalization, suggesting a more pronounced neuroinflammatory response. Densitometric analysis supported this trend, with reduced IBA1 signal intensity in male suicides and increased intensity in females. Although statistical analyses did not yield significant group differences, the observed trends point to a sex-dimorphic microglial response in suicide, potentially modulated by neuroendocrine and immune factors. On the other hand, some clarified samples for 3D analysis showed that LEA+ vessels exhibited a statistically significant reduction in cerebral vascularization in suicide cases compared to controls, with a 52.8% decrease, suggesting a potential role of vascular network dysfunction in the pathophysiology of suicide. The combined use of cellular markers and quantitative approaches provided a multilayered view of glio-vascular interactions in the human cortex, supporting the hypothesis of microglial involvement in suicide vulnerability characterized by sex differences and highlighting the importance of further investigations in larger cohorts to elucidate the neuroinflammatory mechanisms underlying affective disorders.