Acute prefrontal rTMS increases striatal dopamine to a similar degree as d-amphetamine

Abstract

Prefrontal repetitive transcranial magnetic stimulation (rTMS) has been shown to increase striatal dopaminergic activity; however, the magnitude of these effects compared with other dopaminergic stimuli is unknown. We have investigated dopaminergic neurotransmission in patients with major depressive episodes using single photon emission computed tomography (SPECT) and [123I] iodobenzamide (IBZM) under a bolus and constant infusion paradigm to indirectly assess the change in endogenous striatal dopamine concentration upon rTMS and d-amphetamine challenge. SPECT imaging was performed twice each in five patients during rTMS, and in two patients who received 0.3mg/kg d-amphetamine. The change in striatal IBZM binding upon challenge was assessed with a region of interest technique. Data sets of 13 SPECT imaging sessions were available for analysis. TMS (9 SPECT assessments) led to a mean relative decrease in striatal IBZM binding by 9.6±6.2%, d-amphetamine challenge (n=4) induced a mean relative reduction by 8±2.95% (difference not statistically significant). The decrease of IBZM binding upon challenge is suggestive of an increase in endogenous dopaminergic stimulation. Acute rTMS challenge showed similar striatal dopaminergic effects as compared to administration of d-amphetamine, a substance known to increase synaptic dopamine.