High-frequency repetitive transcranial magnetic stimulation regulates neural oscillations of the hippocampus and prefrontal cortex in mice by modulating endocannabinoid signalling

Theta-gamma phase-amplitude coupling as a promising neurophysiological biomarker for evaluating the efficacy of low-intensity focused ultrasound stimulation on vascular dementia treatment

Low-intensity focused ultrasound stimulation (LIFUS) has garnered attention for its potential in vascular dementia (VD) treatment. However, the lack of sufficient data supporting its efficacy and elucidating its mechanisms of action limits its further clinical translation and application. Considerable researches support the idea that LIFUS can improve the disturbance of neural oscillation modes caused by a variety of neurological diseases. However, the effect of LIFUS on neural oscillation modes in VD remains unclear. Therefore, this study aims to investigate the therapeutic effects of LIFUS on neural oscillation modes in VD. To achieve this purpose, the VD model was established via the bilateral common carotid artery occlusion, followed by two weeks of LIFUS treatment targeting the bilateral hippocampus. The therapeutic effects of LIFUS were evaluated by behavioral tests and cerebral blood flow measurement. Electrophysiological signals were recorded from the hippocampal CA1 and CA3 and medial prefrontal cortex (mPFC). The results indicated LIFUS could effectively improve cognitive dysfunction in VD rats. The underlying electrophysiological mechanisms involved the restoration of phase-amplitude coupling (PAC) of theta-gamma oscillations within both the CA3-CA1 local circuit and the hippocampus-mPFC cross-brain circuit. Classification results based on PAC characteristics suggested that PAC metrics are effective for evaluating the efficacy of LIFUS in treating VD, with optimal recognition performance observed in the hippocampus-mPFC cross-brain circuit. Our findings provide neuroelectrophysiological insights into the mechanisms of LIFUS in VD treatment and propose a promising diagnostic biomarker for evaluating LIFUS efficacy in future applications.

Intermittent theta burst stimulation is superior to 10 Hz-repetitive transcranial magnetic stimulation in promoting episodic-like memory in healthy male rats by enhancing low γ oscillation and glutamate neuronal activities of the anterior cingulate cortex

Intermittent theta-burst stimulation (iTBS) and high-frequency repetitive transcranial magnetic stimulation (rTMS) produce beneficial after-effects on memory performance. The two modalities have modulatory after-effects on the prefrontal neuronal oscillations and neurotransmitters, which are critically involved in episodic memory processing. However, whether iTBS exerts better cognitive effects than high-frequency rTMS through modulating neuronal oscillations and neurotransmitter levels in the prefrontal cortex has not been determined. Thus, iTBS and 10 Hz-rTMS modalities were applied to healthy male rats respectively, and behavior tests, electrophysiological experiments and microdialysis and neurochemistry were performed. We found that iTBS and 10 Hz-rTMS promoted episodic memory in healthy male rats, and iTBS exerted better cognitive effects than 10 Hz-rTMS. Intriguingly, iTBS induced greater effects than 10 Hz-rTMS in enhancing low γ oscillation in the anterior cingulate cortex (ACC) which is a subregion of the prefrontal cortex. Further, compared to sham stimuli, iTBS suppressed δ oscillation and enhanced θ oscillation, while 10 Hz-rTMS did not, suggesting that iTBS induces higher cortical excitability in the ACC than 10 Hz-rTMS. This is supported by a higher increase in glutamate neuronal activities in the ACC following iTBS than 10 Hz-rTMS. Finally, we found that iTBS and 10 Hz-rTMS decreased extracellular gamma-aminobutyric acid levels and increased extracellular glutamate levels in the ACC, thus leading to the activation of ACC glutamate neurons after the two modalities. These findings suggest that iTBS produces better cognitive effects in healthy male rats, which may be attributed to enhanced low γ oscillation and activated glutamatergic neurons in the ACC.

The association between traumatic temporomandibular joint bony ankylosis and depressive disorder in growing rats

BACKGROUND

The psychological symptoms of temporomandibular joint (TMJ) ankylosis were similar to that of depressive disorder, but there were no relevant evidences to confirm that the humans or animals with TMJ ankylosis had depressive disorder. The aim of this study was to investigate the association between TMJ ankylosis and depressive disorder in the rat model.

METHODS

Thirty 3-week-old male Sprague-Dawley (SD) rats were used in this study. The damage of TMJ complexes and narrowed joint space were performed in the unilateral TMJ of test group to induce TMJ bony ankylosis (experimental side). The other TMJ of test group underwent a sham operation (sham side). The TMJs of control group did not undergo any operations. At 8 weeks postoperatively, behavioral tests, body weight, passive maximum mouth opening (PMMO), and TMJ morphological features were evaluated, and the hippocampuses were analyzed using western blotting and immunocytochemistry. The data was compared between the test group and control group by independent t-test, between the experimental side and sham side by paired t-test. The correlations between PMMO/area of bony fusion and duration of immobility, sucrose preference, CB1 receptor protein, mean optical density of CB1 receptor protein, and the number of BrdU-positive cell were evaluated using linear regression analysis. The level of significance was 0.05.

RESULTS

In the test group, the traumatic TMJ complexes with narrowed joint space developed TMJ bony ankylosis, the area of bony mass of experimental side (21.26 mm2) was larger than that of sham side (1.73 mm2) (p < 0.001). There were significant difference with the sucrose preference (test group: 0.36, control group: 0.76, p < 0.001), duration of immobility (test group: 127.36 s, control group: 59.41 s, p < 0.001), body weight (test group: 156.70 g, control group: 270.06 g, p < 0.001), PMMO (test group: 9.98 mm, control group: 28.79 mm, p < 0.001), CB1 receptor protein (test group: 41.00%, control group: 86.69%, p < 0.001), mean optical density of CB1 receptor protein (test group: 29.60 a.u., control group: 54.69 a.u., p < 0.001), and the number of BrdU-positive cell between the test group and control group (test group: 2133.71, control group: 4301.95, p < 0.001). PMMO was negatively correlated with the duration of immobility (r = 0.953, p < 0.001), while the area of bony fusion was positively correlated (r = 0.961, p < 0.001). PMMO was positively correlated with the sucrose preference, CB1 receptor protein, mean optical density of CB1 receptor protein, and the number of BrdU-positive cell (r = 0.955, 0.955, 0.976, 0.958, p < 0.001, all), while the area of bony fusion was negatively correlated (r = 0.970, 0.981, 0.971, 0.958, p < 0.001, all).

CONCLUSIONS

The present study verified that depressive disorder was found in the rat model of traumatic TMJ bony ankylosis. The severity of TMJ bony ankylosis correlated with the severity of depressive disorder.

Acute Intermittent Theta-Burst Stimulation Produces Antidepressant-Like Effects by Modulating Neuronal Oscillations and Serotonin Levels of the Medial Prefrontal Cortex in Experimental Parkinson's Disease

Parkinson's disease (PD)-related depression is associated with aberrant neuronal oscillations and 5-hydroxytryptamine (5-HT) neurotransmission in the medial prefrontal cortex (mPFC). Intermittent theta-burst stimulation (iTBS), an updated pattern of high-frequency repetitive transcranial magnetic stimulation, has possible efficacy in PD-related depression. However, whether iTBS alleviates PD-related depression through modulating neuronal oscillations and 5-HT levels in the mPFC has not been determined. In this study, male Sprague-Dawley rats were used to establish a unilateral 6-hydroxydopamine-induced PD model. Then, acute iTBS was applied to the parkinsonian rats, and behavioral, neurochemical, and electrophysiological experiments were performed. We found that the parkinsonian rats exhibited increased immobility time and decreased sucrose preference accompanied by an increase of δ power and a decrease of θ power in the mPFC compared to sham-operated rats. One block of iTBS (1 block-iTBS, 300 stimuli) alleviated depressive-like behaviors in parkinsonian rats and elevated 5-HT levels in the mPFC compared to sham-iTBS. Additionally, it altered neuronal oscillations in the mPFC in the opposite fashion by suppressing the δ rhythm and enhancing the θ and β rhythms compared to sham-iTBS, suggesting that acute iTBS induces hyperactivity in the mPFC. With this iTBS paradigm, we also observed decreased parvalbumin expression in the mPFC, reflecting reduced cortical inhibition. Finally, correlation analyses showed strong correlation between immobility time and θ power after 1 block-iTBS. These findings suggest that the application of acute iTBS in parkinsonian rats produces antidepressant-like effects, which may be associated with elevated 5-HT levels and normalized neuronal oscillations in the mPFC.

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.

Sex-Specific Differences and the Role of Environmental Enrichment in the Expression of Hippocampal CB1 Receptors following Chronic Unpredictable Stress

Stress-related mental disorders have become increasingly prevalent, thus endangering mental health worldwide. Exploring stress-associated brain alterations is vital for understanding the possible neurobiological mechanisms underlying these changes. Based on existing evidence, the brain endogenous cannabinoid system (ECS) plays a significant role in the stress response, and disruptions in its function are associated with the neurobiology of various stress-related disorders. This study primarily focuses on investigating the impact of chronic unpredictable stress (CUS) on the expression of hippocampal cannabinoid type 1 (CB1) receptors, part of the ECS, in adult male and female Wistar rats. Additionally, it explores whether environmental enrichment (EE) initiated during adolescence could mitigate the CUS-associated alterations in CB1 expression. Wistar rats, shortly after weaning, were placed in either standard housing (SH) or EE conditions for a duration of 10 weeks. On postnatal day 66, specific subgroups of SH or EE animals underwent a 4-week CUS protocol. Western blot (WB) analysis was conducted in the whole hippocampus of the left brain hemisphere to assess total CB1 protein expression, while immunohistochemistry (IHC) was performed on the right hemisphere to estimate the expression of CB1 receptors in certain hippocampal areas (i.e., CA1, CA3 and dentate gyrus-DG). The WB analysis revealed no statistically significant differences in total CB1 protein levels among the groups; however, reduced CB1 expression was found in specific hippocampal sub-regions using IHC. Specifically, CUS significantly decreased CB1 receptor expression in the CA1 and DG of both sexes, whereas in CA3 the CUS-associated decrease was limited to SH males. Interestingly, EE housing proved protective against these reductions. These findings suggest a region and sex-specific endocannabinoid response to chronic stress, emphasizing the role of positive early experiences in the protection of the adolescent brain against adverse conditions later in life.