High-frequency repetitive transcranial magnetic stimulation mitigates depression-like behaviors in CUMS-induced rats via FGF2/FGFR1/p-ERK signaling pathway

Repetitive transcranial magnetic stimulation in Alzheimer's disease: effects on neural and synaptic rehabilitation

Alzheimer's disease is a neurodegenerative disease resulting from deficits in synaptic transmission and homeostasis. The Alzheimer's disease brain tends to be hyperexcitable and hypersynchronized, thereby causing neurodegeneration and ultimately disrupting the operational abilities in daily life, leaving patients incapacitated. Repetitive transcranial magnetic stimulation is a cost-effective, neuro-modulatory technique used for multiple neurological conditions. Over the past two decades, it has been widely used to predict cognitive decline; identify pathophysiological markers; promote neuroplasticity; and assess brain excitability, plasticity, and connectivity. It has also been applied to patients with dementia, because it can yield facilitatory effects on cognition and promote brain recovery after a neurological insult. However, its therapeutic effectiveness at the molecular and synaptic levels has not been elucidated because of a limited number of studies. This study aimed to characterize the neurobiological changes following repetitive transcranial magnetic stimulation treatment, evaluate its effects on synaptic plasticity, and identify the associated mechanisms. This review essentially focuses on changes in the pathology, amyloidogenesis, and clearance pathways, given that amyloid deposition is a major hypothesis in the pathogenesis of Alzheimer's disease. Apoptotic mechanisms associated with repetitive transcranial magnetic stimulation procedures and different pathways mediating gene transcription, which are closely related to the neural regeneration process, are also highlighted. Finally, we discuss the outcomes of animal studies in which neuroplasticity is modulated and assessed at the structural and functional levels by using repetitive transcranial magnetic stimulation, with the aim to highlight future directions for better clinical translations.

Repetitive transcranial magnetic stimulation (rTMS) for depressive-like symptoms in rodent animal models

Repetitive transcranial magnetic stimulation (rTMS) emerged as a non-invasive brain stimulation technique in the treatment of psychiatric disorders. Both preclinical and clinical studies as well as systematic reviews provide a heterogeneous picture, particularly concerning the stimulation protocols used in rTMS. Here, we present a review of rTMS effects in rodent models of depressive-like symptoms with the aim to identify the most relevant factors that lead to an increased therapeutic success. The influence of different factors, such as the stimulation parameters (stimulus frequency and intensity, duration of stimulation, shape and positioning of the coil), symptom severity and individual characteristics (age, species and genetic background of the rodents), on the therapeutic success are discussed. Accumulating evidence indicates that rTMS ameliorates a multitude of depressive-like symptoms in rodent models, most effectively at high stimulation frequencies (≥5 Hz) especially in adult rodents with a pronounced pathological phenotype. The therapeutic success of rTMS might be increased in the future by considering these factors and using more standardized stimulation protocols.

High-frequency repetitive transcranial magnetic stimulation improves depressive-like behaviors in CUMS-induced rats by modulating astrocyte GLT-1 to reduce glutamate toxicity

Impaired glutamate recycling plays an important role in the pathophysiology of depression, and it has been demonstrated that glutamate transporter-1 (GLT-1) on astrocytes is involved in glutamate uptake. Studies have shown that repetitive transcranial magnetic stimulation (rTMS) is effective in treating depression, however, the exact mechanism of rTMS treatment remains unclear. Here, we used a chronic unpredictable mild stress (CUMS) protocol to induce depression-like behaviors in rats followed by rTMS treatment. Behavioral assessment was primarily through SPT, FST, OFT and body weight. Histological analysis focused on GFAP and GLT-1 expression, synaptic plasticity, apoptosis and PI3K/Akt/CREB pathway-related proteins. The results showed that rTMS treatment increased sucrose preference, improved locomotor activity, shortened immobility time as well as increased body weight. And rTMS intervention reversed the elevated glutamate concentration in the hippocampus of CUMS rats using an ELISA kit. Moreover, rTMS ameliorated the reduction in GFAP and GLT-1 expression, alleviated the decrease in BDNF, PSD95 and synapsin-1 expression, also reversed the expression levels of BAX and Bcl2 in the hippocampus of CUMS-induced rats. Moreover, rTMS also increased the protein phosphorylation level of PI3K/Akt/CREB pathway. These results suggest that rTMS treatment ameliorates depression-like behaviors in the rat model by reversing the reduction of GLT-1 on astrocytes and reducing glutamate accumulation in the synaptic cleft, which in turn ameliorates synaptic plasticity damage and neuronal apoptosis. The regulation of GLT-1 by rTMS may be through the PI3K/Akt/CREB pathway.

Contribution of glial cells to the neuroprotective effects triggered by repetitive magnetic stimulation: a systematic review

Repetitive transcranial magnetic stimulation has been increasingly studied in different neurological diseases, and although most studies focus on its effects on neuronal cells, the contribution of non-neuronal cells to the improvement triggered by repetitive transcranial magnetic stimulation in these diseases has been increasingly suggested. To systematically review the effects of repetitive magnetic stimulation on non-neuronal cells two online databases, Web of Science and PubMed were searched for the effects of high-frequency-repetitive transcranial magnetic stimulation, low-frequency-repetitive transcranial magnetic stimulation, intermittent theta-burst stimulation, continuous theta-burst stimulation, or repetitive magnetic stimulation on non-neuronal cells in models of disease and in unlesioned animals or cells. A total of 52 studies were included. The protocol more frequently used was high-frequency-repetitive magnetic stimulation, and in models of disease, most studies report that high-frequency-repetitive magnetic stimulation led to a decrease in astrocyte and microglial reactivity, a decrease in the release of pro-inflammatory cytokines, and an increase of oligodendrocyte proliferation. The trend towards decreased microglial and astrocyte reactivity as well as increased oligodendrocyte proliferation occurred with intermittent theta-burst stimulation and continuous theta-burst stimulation. Few papers analyzed the low-frequency-repetitive transcranial magnetic stimulation protocol, and the parameters evaluated were restricted to the study of astrocyte reactivity and release of pro-inflammatory cytokines, reporting the absence of effects on these parameters. In what concerns the use of magnetic stimulation in unlesioned animals or cells, most articles on all four types of stimulation reported a lack of effects. It is also important to point out that the studies were developed mostly in male rodents, not evaluating possible differential effects of repetitive transcranial magnetic stimulation between sexes. This systematic review supports that through modulation of glial cells repetitive magnetic stimulation contributes to the neuroprotection or repair in various neurological disease models. However, it should be noted that there are still few articles focusing on the impact of repetitive magnetic stimulation on non-neuronal cells and most studies did not perform in-depth analyses of the effects, emphasizing the need for more studies in this field.

Thomas F, Battaglia F. High-frequency rTMS modulates emotional behaviors and structural plasticity in layers II/III and V of the mPFC

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive neuromodulation technique, and it has been increasingly used as a nonpharmacological intervention for the treatment of various neurological and neuropsychiatric diseases, including depression. In humans, rTMS over the prefrontal cortex is used to induce modulation of the neural circuitry that regulates emotions, cognition, and depressive symptoms. However, the underlying mechanisms are still unknown. In this study, we investigated the effects of a short (5-day) treatment with high-frequency (HF) rTMS (15 Hz) on emotional behavior and prefrontal cortex morphological plasticity in mice. Mice that had undergone HF-rTMS showed an anti-depressant-like activity as evidenced by decreased immobility time in both the Tail Suspension Test and the Forced Swim Test along with increased spine density in both layer II/III and layer V apical and basal dendrites. Furthermore, dendritic complexity assessed by Sholl analysis revealed increased arborization in the apical portions of both layers, but no modifications in the basal dendrites branching. Overall, these results indicate that the antidepressant-like activity of HF-rTMS is paralleled by structural remodeling in the medial prefrontal cortex.

Antidepressant-like effects of trophic factor receptor signaling

A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).

The enhancing effects of heparin on the biological activity of FGF-2 in heparin-FGF-2-calcium phosphate composite layers

Orthopedic and dental implants coated with fibroblast growth factor-2 (FGF-2)-calcium phosphate composite layers promote dermis formation, bone formation, and angiogenesis because of the biological activity of FGF-2. Enhancing the biological activity of FGF-2 in the composite layers is important for its wider application in orthopedics and dentistry. This study incorporated low-molecular-weight heparin (LMWH) into the FGF-2-calcium phosphate composite layers and clarified the enhancing effects of LMWH on the biological activity of FGF-2 in the composite layers in vitro. LMWH-FGF-2-calcium phosphate composite layers were successfully formed on zirconia in supersaturated calcium phosphate solutions. The composite layers comprised continuous and macroscopically homogeneous layers and particles smaller than 500 nm in size composed of amorphous calcium phosphate. The amounts of Ca and P deposited on zirconia remained almost unchanged with the addition of LMWH under the presence of FGF-2 in the supersaturated calcium phosphate solution. The LMWH in the supersaturated calcium phosphate solution increased the stability of FGF-2 in the solution and the amount of FGF-2 in the composite layers. The LMWH in the composite layers increased the mitogenic and endothelial tube-forming activities of FGF-2, and FGF-2 activity of inducing osteogenic differentiation gene expression pattern in the composite layers. Our results indicate that the enhanced biological activity of FGF-2 in the LMWH-FGF-2-calcium phosphate composite layers is attributed to an LMWH-mediated increase in the amount of FGF-2, which maintains its biological activity in the supersaturated calcium phosphate solution and the composite layers. The LMWH-FGF-2-calcium phosphate composite layer is a promising coating for orthopedic and dental implants. STATEMENT OF SIGNIFICANCE: Orthopedic and dental implants coated with fibroblast growth factor-2 (FGF-2)-calcium phosphate composite layers promote dermis formation, bone formation, and angiogenesis because of the biological activity of FGF-2. Enhancing the biological activity of FGF-2 in the layers is important for wider its application in orthopedics and dentistry. This study demonstrates the enhancing effects of low-molecular-weight heparin (LMWH) contained within LMWH-FGF-2-calcium phosphate composite layers on the biological activity of FGF-2 in vitro. Our results indicate that the enhanced biological activity of FGF-2 within the composite layers arises from an LMWH-mediated increase in the amount of FGF-2, which maintains its biological activity in the LMWH-FGF-2-calcium phosphate composite layers and supersaturated calcium phosphate solutions used for coating the composite layers.