Discordant Serum and Salivary Reelin Patterns in Major Depressive Disorder: Evidence From Transcranial Magnetic Stimulation

Background: This study aimed to investigate serum and salivary Reelin levels in patients with major depressive disorder (MDD) and to evaluate their changes following Transcranial Magnetic Stimulation (TMS). Methods: This prospective study included 29 patients with MDD and 30 healthy controls recruited between 2024 and 2025. Depression and anxiety severity were assessed using the Beck Depression Inventory and Beck Anxiety Inventory. Serum and salivary Reelin levels were measured before and after treatment. Pre- and post-treatment comparisons were performed using paired samples t-test, and between-group comparisons were conducted. Results: At baseline, serum Reelin levels were significantly higher in patients than in controls (p = 0.009), whereas salivary levels were significantly lower (p = 0.036). Following treatment, both depression and anxiety scores showed significant reductions (p < 0.001), indicating improvement in clinical symptom severity. Serum Reelin levels showed a non-significant increase, while salivary levels demonstrated a slight, non-significant rise and remained below control values. Conclusions: Serum and salivary Reelin levels demonstrated compartment-specific differences in patients with MDD. Despite improvement in clinical symptom severity after treatment, peripheral Reelin levels showed no significant changes. Because concomitant psychotropic treatments were not systematically documented, the observed biomarker findings cannot be attributed specifically to TMS.