Duration of transcranial magnetic stimulation effects on the neuroendocrine stress response and coping behavior of adult male rats

Background: Transcranial magnetic stimulation (TMS) is a relatively novel, noninvasive method of altering cerebral electrophysiological activity that produces localized and reversible changes in brain tissue. TMS has been shown to have antidepressant properties in both human trials and animal models. Additionally, TMS may alter hypothalamic-pituitary-adrenal (HPA) function resulting in a normalized dexamethasone suppression test in some depressed subjects and an attenuated stress-induced increase in adrenocorticotropic hormone (ACTH) and a possibly lowered basal corticosterone (CORT) concentration in rats. This research was undertaken to investigate the duration of these behavioral and neuroendocrine effects of TMS in rats. Methods: In this study, serum ACTH, CORT, testosterone, and luteinizing hormone (LH) concentrations following and immobility parameters during a forced-swim test in adult male rats were evaluated immediately and 1, 3, 5, 7, and 14 days subsequent to a 10-day course of once-daily TMS or sham application. Results: TMS animals had significantly higher ACTH and CORT concentrations immediately following the 10-day course of TMS compared to sham controls. Higher CORT concentrations (numerically but not statistically) were displayed by TMS-treated animals I and 3 days after the 10-day application course, although there were no significant differences between TMS and sham groups for ACTH or CORT levels 1, 3, 5, 7, and 14 days following application of sham or TMS. No significant differences were found between groups for serum testosterone and LH levels at any given collection time point. Immobility time, a measure of coping ability that is predictive of human antidepressant response, was significantly decreased (i.e., time spent actively swimming was significantly increased) immediately after the 10-day course of TMS. Thereafter, a nonsignificant numerical trend at I and 3 days after TMS application for immobility times between the TMS and control groups was observed TMS <control values). No significant differences in immobility between TMS and control animals were found at subsequent time points. Conclusions: The present findings suggest that the HPA stress axis is significantly altered immediately following a 10-day course of TMS in that a significant increase in ACTH and CORT levels in TMS-treated animals corresponded to a significant decrease in immobility times in the forced-swim test compared to control values. Finally, based upon the obtained results, the TMS effects in rats appear to be of relatively short duration. (C) 2003 Elsevier Science Inc. All rights reserved.