Table 2.

Summary of the BDNF and major depressive disorder connection.

Aspect	BDNF and Major Depressive Disorder Connection
Levels of BDNF	Reduced BDNF levels have been observed in individuals with major depressive disorder [45].
Changes in structure and function	Deficiencies or imbalances in BDNF levels may contribute to the development of depression by promoting structural and functioning changes [7], such as reduced dendritic complexity [37].
Serotonin influence	BDNF is influenced by serotonin, and serotonin activation can stimulate BDNF synthesis and release. Serotonin receptors can also modulate BDNF expression, influencing neuronal function and, consequently, mood regulation [59].
Neuroplasticity	BDNF is involved in neuroplasticity, which is crucial for synaptic connections and structural changes in the brain related to depressive disorder [37].
Antidepressant effects	Different antidepressants can enhance BDNF gene expression, contributing to their therapeutic effects [7].
Oxidative stress	Oxidative stress can lower BDNF production and damage its signaling pathways. The connection between oxidative stress and BDNF levels plays a significant role in the development and progression of depression [11].
Hypothalamic–pituitary–adrenal (HPA) axis dysregulation	Stress-induced HPA axis hyperactivity and the resulting increase in glucocorticoid levels diminish BDNF expression, playing an important role in the development of depression [10].