TITLE
Dorsolateral Prefrontal Gamma-Aminobutyric Acid in Patients with Treatment-Resistant Depression after Transcranial Magnetic Stimulation Measured with Magnetic Resonance Spectroscopy
SOURCE
Journal of Psychiatry & Neuroscience. 44(6):386-394, 2019 Nov 01.
AUTHORS
Levitt JG; Kalender G; O’Neill J; Diaz JP; Cook IA; Ginder N; Krantz D; Minzenberg MJ; Vince-Cruz N; Nguyen LD; Alger JR; Leuchter AF.
BACKGROUND
The therapeutic mechanism of repetitive transcranial magnetic stimulation (rTMS) for treatment-resistant depression (TRD) may involve modulation of gamma-aminobutyric acid (GABA) levels. We used proton magnetic resonance spectroscopy (MRS) to assess changes in GABA levels at the site of rTMS in the left dorsolateral prefrontal cortex (DLPFC).
METHODS
In 26 adults with TRD, we used Mescher-Garwood point-resolved spectroscopy (MEGA-PRESS) spectral-editing MRS to measure GABA in the left DLPFC before and after standard clinical treatment with rTMS. All participants but 1 were medicated, including 12 patients on GABA agonist agents.
RESULTS
Mean GABA in the DLPFC increased 10.0% (p = 0.017) post-rTMS in the overall sample. As well, GABA increased significantly in rTMS responders (n = 12; 23.6%, p = 0.015) but not in nonresponders (n = 14; 4.1%, p = not significant). Changes in GABA were not significantly affected by GABAergic agonists, but clinical response was less frequent (p = 0.005) and weaker (p = 0.035) in the 12 participants who were receiving GABA agonists concomitant with rTMS treatment.
LIMITATIONS
This study had an open-label design in a population receiving naturalistic treatment.
CONCLUSION
Treatment using rTMS was associated with increases in GABA levels at the stimulation site in the left DLPFC, and the degree of GABA change was related to clinical improvement. Participants receiving concomitant treatment with a GABA agonist were less likely to respond to rTMS. These findings were consistent with earlier studies showing the effects of rTMS on GABA levels and support a GABAergic model of depression.
