Long-term effects of repetitive transcranial magnetic stimulation on markers for neuroplasticity: differential outcomes in anesthetized and awake animals

Abstract

Long-term effects of repetitive transcranial magnetic stimulation (rTMS) have been associated with neuroplasticity, but most physiological studies have evaluated only the immediate effects of the stimulation on neurochemical markers. Furthermore, although it is known that baseline excitability state plays a major role in rTMS outcomes, the role of spontaneous neural activity in metaplasticity has not been investigated. The first aim of this study was to evaluate and compare the long-term effects of high- and low-frequency rTMS on the markers of neuroplasticity such as BDNF and GluR1 subunit of AMPA receptor. The second aim was to assess whether these effects depend on spontaneous neural activity, by comparing the neurochemical alterations induced by rTMS in anesthetized and awake rats. Ten daily sessions of high- or low-frequency rTMS were applied over the rat brain, and 3 d later, levels of BDNF, GluR1, and phosphorylated GluR1 were assessed in the hippocampus, prelimbic cortex, and striatum. We found that high-frequency stimulation induced a profound effect on neuroplasticity markers; increasing them in awake animals while decreasing them in anesthetized animals. In contrast, low-frequency stimulation did not induce significant long-term effects on these markers in either state. This study highlights the importance of spontaneous neural activity during rTMS and demonstrates that high-frequency rTMS can induce long-lasting effects on BDNF and GluR1 which may underlie the clinical benefits of this treatment in neuroplasticity-related disorders.

Figures

Figure 1.

Diagram of rat stimulation. The circular coil was positioned over the rat's head so that the coil center was placed over the middle of the interocular line with the handle pointing forward. The awake groups were restrained by hand, whereas the anesthesia in the other groups was performed using the isoflurane system.

Figure 2.

Effects of rTMS on BDNF expression. Data are presented as mean ± SEM of BDNF levels in the hippocampus, prelimbic cortex, and striatum of animals previously treated with 10 daily rTMS or sham rTMS sessions while awake (A) or anesthetized (B). *p < 0.05, **p < 0.01, compared with the sham control group.

Figure 3.

Effects of rTMS on GluR1 and pGluR1 levels. A–D, Data are presented as mean ± SEM of GluR1 (A, B) and pGluR1 (C, D) relative levels in the hippocampus, prelimbic cortex, and striatum of animals previously treated with 10 daily rTMS or sham rTMS sessions while awake (A, C) or anesthetized (B, D). E, Representative Western blots of GluR1, pGluR1, and corresponding actin in the measured areas of all treatment groups are shown. *p < 0.05, **p < 0.01, compared with the sham control group. LF, Low frequency; HF, high frequency.

Figure 4.

Correlations between BDNF and GluR1 or pGluR1 levels in the hippocampus. BDNF levels are plotted as a function of GluR1 (empty circles) or pGluR1 (black circles) relative levels in the hippocampus of animals previously treated with 10 daily rTMS or sham rTMS sessions while awake (A) or anesthetized (B). The corresponding linear fit is presented.