Improved voiding function by deep brain stimulation in traumatic brain-injured animals with bladder dysfunctions

Electrical stimulation methods and protocols for the treatment of traumatic brain injury: a critical review of preclinical research

BACKGROUND

Traumatic brain injury (TBI) is a leading cause of disabilities resulting from cognitive and neurological deficits, as well as psychological disorders. Only recently, preclinical research on electrical stimulation methods as a potential treatment of TBI sequelae has gained more traction. However, the underlying mechanisms of the anticipated improvements induced by these methods are still not fully understood. It remains unclear in which stage after TBI they are best applied to optimize the therapeutic outcome, preferably with persisting effects. Studies with animal models address these questions and investigate beneficial long- and short-term changes mediated by these novel modalities.

METHODS

In this review, we present the state-of-the-art in preclinical research on electrical stimulation methods used to treat TBI sequelae. We analyze publications on the most commonly used electrical stimulation methods, namely transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS) and vagus nerve stimulation (VNS), that aim to treat disabilities caused by TBI. We discuss applied stimulation parameters, such as the amplitude, frequency, and length of stimulation, as well as stimulation time frames, specifically the onset of stimulation, how often stimulation sessions were repeated and the total length of the treatment. These parameters are then analyzed in the context of injury severity, the disability under investigation and the stimulated location, and the resulting therapeutic effects are compared. We provide a comprehensive and critical review and discuss directions for future research. RESULTS AND CONCLUSION: We find that the parameters used in studies on each of these stimulation methods vary widely, making it difficult to draw direct comparisons between stimulation protocols and therapeutic outcome. Persisting beneficial effects and adverse consequences of electrical simulation are rarely investigated, leaving many questions about their suitability for clinical applications. Nevertheless, we conclude that the stimulation methods discussed here show promising results that could be further supported by additional research in this field.

A time-course study of urodynamic analyses in rat models with dopaminergic depletion induced through unilateral and bilateral 6-hydroxydopamine injections

BACKGROUND

Bladder dysfunction is a common non-motor disorder in Parkinson's disease (PD). This study attempted to determine the bladder dysfunction with disease progression in the PD rat model produced from unilateral/bilateral injections of 6-hydroxydopamine (6-OHDA).

METHODS

Cystometrographic (CMG) and external urethral sphincter electromyographic (EUS-EMG) measurements were scheduled in a time-course manner to determine the disease timing, onset, and severity. Animals were allotted into normal control, unilateral, bilateral 6-OHDA injected groups and subjected to scheduled CMG, EUS-EMG analyses at weeks 1, 2, and 4.

RESULTS

The urodynamic results concluded that voiding efficiency (VE) was reduced in both unilateral and bilateral PD rats at all-time points. VE had decreased from 57 ± 11% to 31 ± 7% in unilateral PD rats and in bilateral PD rats, a decreased VE of 20 ± 6% was observed compared to control and unilateral PD rats. The EMG results in unilateral PD rats indicated declines in bursting period (BP) (3.78-2.94 s), active period (AP) (93.38-88.75 ms), and silent period (SP) (161.62-114.30 ms). A sudden reduction was noticed in BP (3.62-2.82 s), AP (92.21-86.01 ms), and SP (128.61-60.16 ms) of bilateral PD rats than in control and unilateral PD rats. Histological evidence exhibited a progressive dopaminergic neurons (DA) depletion in the substantia nigra (SN) region in 6-OHDA lesioned rats.

CONCLUSION

The experimental outcomes strongly implied that significant variations in bladder function and VE decline were due to the depletion of DA neurons in the SN region of the brain.

Neurostimulation for Functional Recovery After Traumatic Brain Injury: Current Evidence and Future Directions for Invasive Surgical Approaches

We aim to provide a comprehensive review of the current scientific evidence supporting the use of invasive neurostimulation in the treatment of deficits associated with traumatic brain injury (TBI), as well as to identify future directions for research and highlight important questions that remain unaddressed. Neurostimulation is a treatment modality with expanding applications in modern medical practice. Targeted electrical stimulation of specific brain regions has been shown to increase synaptogenesis and enhance structural reorganization of neuronal networks. This underlying therapeutic effect might be of high value for patients suffering from TBI because it could modulate neuronal connectivity and function of areas that are partially or completely spared after injury. The current published literature exploring the application of invasive neurostimulation for the treatment of functional deficits associated with TBI is scarce but promising. Rodent models have shown that targeted stimulation of the hippocampus or connecting structures can result in significant cognitive recovery, while stimulation of the motor cortex and deep cerebellar nuclei is associated with motor improvements. Data from clinical studies are extremely limited; single-patient reports and case series found neurostimulation to be effective in relieving motor symptoms, improving visuospatial memory, and supporting emotional adjustment. Looking forward, it will be important to identify stimulation targets and paradigms that can maximize improvement over multiple functional domains. It will also be important to corroborate the observed behavioral improvements with histological, electrophysiological, and radiological evidence. Finally, the impact of biological variables such as sex and age on the treatment outcomes needs to be explored.

The voiding efficiency in rat models with dopaminergic brain lesions induced through unilateral and bilateral intrastriatal injections

Bladder dysfunction is a common phenomenon in Parkinson’s disease (PD) patients. A research attempt was made to analyze the voiding efficiency (VE) and bladder functions in rats with PD induced by unilateral or bilateral injections of 6-hydroxydopamine (6-OHDA) into the medial forebrain bundle. PD rats were divided into unilateral- and bilateral-injected groups and subjected to rotation and beam walking tests. Further, the experimental rats underwent cystometric measurements for analyses of bladder dysfunction and VE. Immunohistochemical analysis was performed to analyze the dopaminergic neuron depletion on the target area. Outcomes of the rotation and beam walking tests revealed the extent of parkinsonism in the experimental rats. Urodynamic observations denoted that rats with unilateral PD exhibited a significantly decreased VE (from 68.3±3.5% to 32.7±5.8%), while rats with bilateral PD displayed a much-reduced and substantially lower level of VE of 18.3±5.1% compared to the control value and to that of rats with unilateral PD. Rats with bilateral PD showed more-extensive behavioral deficits and urodynamic changes than did rats with unilateral PD. These significant changes in motor, behavioral, bladder function and VE were due to an extensive degeneration of dopaminergic neurons in the substantia nigra region on both sides of the brain. The obtained results were substantiated with appropriate immunohistochemical results.

Efficacy of Deep Brain Stimulation on the Improvement of the Bladder Functions in Traumatic Brain Injured Rats

Objective: Traumatic brain injuries (TBIs) are a prime public health challenge with a high incidence of mortality, and also reflect severe economic impacts. One of their severe symptoms is bladder dysfunction. Conventional therapeutic methods are not effective in managing bladder dysfunction. Henceforth, a research endeavor was attempted to explore a new therapeutic approach for bladder dysfunction through deep brain stimulation (DBS) procedures in a TBI animal model. Methods: TBI in this animal model was induced by the weight-drop method. All rats with an induced TBI were housed for 4 weeks to allow severe bladder dysfunction to develop. Subsequently, an initial urodynamic measurement, the simultaneous recording of cystometric (CMG) and external urethral sphincter electromyography (EUS-EMG) activity was conducted to evaluate bladder function. Further, standard DBS procedures with varying electrical stimulation parameters were executed in the target area of the pedunculopontine tegmental nucleus (PPTg). Simultaneously, urodynamic measurements were re-established to compare the effects of DBS interventions on bladder functions. Results: From the variable combinations of electrical stimulation, DBS at 50 Hz and 2.0 V, significantly reverted the voiding efficiency from 39% to 69% in TBI rats. Furthermore, MRI studies revealed the precise localization of the DBS electrode in the target area. Conclusions: The results we obtained showed an insightful understanding of PPTg-DBS and its therapeutic applications in alleviating bladder dysfunction in rats with a TBI. Hence, the present study suggests that PPTg-DBS is an effective therapeutic strategy for treating bladder dysfunction.

Designing and Implementing an Implantable Wireless Micromanometer System for Real-Time Bladder Pressure Monitoring: A Preliminary Study

Many mini-implantable devices have been developed and fabricated for diagnostic and treatment purposes. Wireless implantable biomicrosystems provide a desirable approach for long-term physiological signal monitoring. In this study, we implemented a wireless implantable biomicrosystem for bladder-cavity pressure measurements in a freely moving rabbit. To manage the power more effectively, a magnetic reed switch was applied to turn on/off the implantable module using a neodymium-iron-boron (NdFeB) magnet. The measured bladder pressure signal was wirelessly transmitted from the implantable module to a host unit. Our results indicated that the implantable biomicrosystem exhibited satisfactory performance and safety, as evidenced by an error percentage of less than ±1% for pressure measurements and less than 2 °C of a temperature rise under normal operation. The wireless biomicrosystem was implanted into the bladder cavity of a rabbit. Bladder pressure was simultaneously measured by both the biomicrosystem and conventional cystometry in the animal. The two signals were similar during the voiding phase, with a correlation coefficient of 0.885. Additionally, the biomicrosystem coated with polydimethylsiloxane in this study showed no cytotoxicity, which confirmed its biocompatibility. In conclusion, we demonstrated a good biocompatible wireless biomicrosystem which showed good reproducibility with respect to pressure monitoring by conventional cystometry. Further studies are needed to confirm the results of this preliminary feasibility study for actual clinical applications.

Cystometric Measurements in Rats with an Experimentally Induced Traumatic Brain Injury and Voiding Dysfunction: A Time-Course Study

Traumatic brain injuries (TBIs) are a serious public health issue worldwide with increased mortality as well as severe disabilities and injuries caused by falls and road accidents. Unfortunately, there is no approved therapy for TBIs, and bladder dysfunction is a striking symptom. Accordingly, we attempted to analyze bladder dysfunction and voiding efficiency in rats with a TBI at different time-course intervals. Time-dependent analyses were scheduled from the next day until four weeks after a TBI. Experimental animals were grouped and analyzed under the above conditions. Cystometric measurements were used for this analysis and were further elaborated as external urethral sphincter electromyographic (EUS-EMG) activity and cystometrogram (CMG) measurements. Moreover, magnetic resonance imaging (MRI) studies were conducted to investigate secondary injury progression in TBI rats, and results were compared to normal control (NC) rats. Results of EUS-EMG revealed that the burst period, active period, and silent period in TBI rats were drastically reduced compared to NC rats, but they increased later and reached a stagnant phase. Likewise, in CMG measurements, bladder function, the voided volume, and voiding efficiency decreased immediately after the TBI, and other parameters like the volume threshold, inter-contraction interval, and residual volume drastically increased. Later, those levels changed, and all observed results were compared to NC rats. MRI results revealed the prevalence of cerebral edema and the progression of secondary injury. All of the above-stated results of the experiments were extensively substantiated. Thus, these innovative findings of our study model will surely pave the way for new therapeutic interventions for TBI treatment and prominently highlight their applications in the field of neuroscience in the future.