Imaging and Quantitative Analysis of the Interstitial Space in the Caudate Nucleus in a Rotenone-Induced Rat Model of Parkinson's Disease Using Tracer-based MRI

Fluids and flows in brain cancer and neurological disorders

Interstitial fluid (IF) and cerebrospinal fluid (CSF) are an integral part of the brain, serving to cushion and protect the brain parenchymal cells against damage and aid in their function. The brain IF contains various ions, nutrients, waste products, peptides, hormones, and neurotransmitters. IF moves primarily by pressure-dependent bulk flow through brain parenchyma, draining into the ventricular CSF. The brain ventricles and subarachnoid spaces are filled with CSF which circulates through the perivascular spaces. It also flows into the IF space regulated, in part, by aquaporin channels, removing waste solutes through a process of IF-CSF mixing. During disease development, the composition, flow, and volume of these fluids changes and can lead to brain cell dysfunction. With the improvement of imaging technology and the help of genomic profiling, more information has been and can be obtained from brain fluids; however, the role of CSF and IF in brain cancer and neurobiological disease is still limited. Here we outline recent advances of our knowledge of brain fluid flow in cancer and neurodegenerative disease based on our understanding of its dynamics and composition. This article is categorized under: Cancer > Biomedical Engineering Neurological Diseases > Biomedical Engineering.

The impairment of intramural periarterial drainage in brain after subarachnoid hemorrhage

Interstitial fluid (ISF) from brain drains along the basement membranes of capillaries and arteries as Intramural Periarterial Drainage (IPAD); failure of IPAD results in cerebral amyloid angiopathy (CAA). In this study, we test the hypothesis that IPAD fails after subarachnoid haemorrhage (SAH). The rat SAH model was established using endovascular perforation method. Fluorescence dyes with various molecular weights were injected into cisterna magna of rats, and the pattern of IPAD after SAH was detected using immunofluorescence staining, two-photon fluorescent microscope, transmission electron microscope and magnetic resonance imaging tracking techniques. Our results showed that fluorescence dyes entered the brain along a periarterial compartment and were cleared from brain along the basement membranes of the capillaries, with different patterns based on individual molecular weights. After SAH, there was significant impairment in the IPAD system: marked expansion of perivascular spaces, and ISF clearance rate was significantly decreased, associated with the apoptosis of endothelial cells, activation of astrocytes, over-expression of matrix metalloproteinase 9 and loss of collagen type IV. In conclusion, experimental SAH leads to a failure of IPAD, clinically significant for long term complications such as CAA, following SAH.

New insight into brain disease therapy: nanomedicines-crossing blood-brain barrier and extracellular space for drug delivery

INTRODUCTION

Brain diseases including brain tumor, Alzheimer's disease, Parkinson's disease, etc. are difficult to treat. The blood-brain barrier (BBB) is a major obstacle for drug delivery into the brain. Although nano-package and receptor-mediated delivery of nanomedicine markedly increases BBB penetration, it yet did not extensively improve clinical cure rate. Recently, brain extracellular space (ECS) and interstitial fluid (ISF) drainage in ECS have been found to determine whether a drug dissolved in ISF can reach its target cells. Notably, an increase in tortuosity of ECS associated with slower ISF drainage induced by the accumulated harmful substances, such as: amyloid-beta (Aβ), α-synuclein, and metabolic wastes, causes drug delivery failure.

AREAS COVERED

The methods of nano-package and receptor-mediated drug delivery and the penetration efficacy of nanomedicines across BBB and ECS are assessed.

EXPERT OPINION

Invasive delivering drug via ECS and noninvasive near-infrared photo-sensitive nanomedicines may provide a promising benefit to patients with brain disease.

The Mechanism of Downregulated Interstitial Fluid Drainage Following Neuronal Excitation

The drainage of brain interstitial fluid (ISF) has been observed to slow down following neuronal excitation, although the mechanism underlying this phenomenon is yet to be elucidated. In searching for the changes in the brain extracellular space (ECS) induced by electrical pain stimuli in the rat thalamus, significantly decreased effective diffusion coefficient (DECS) and volume fraction (α) of the brain ECS were shown, accompanied by the slowdown of ISF drainage. The morphological basis for structural changes in the brain ECS was local spatial deformation of astrocyte foot processes following neuronal excitation. We further studied aquaporin-4 gene (APQ4) knockout rats in which the changes of the brain ECS structure were reversed and found that the slowed DECS and ISF drainage persisted, confirming that the down-regulation of ISF drainage following neuronal excitation was mainly attributable to the release of neurotransmitters rather than to structural changes of the brain ECS. Meanwhile, the dynamic changes in the DECS were synchronized with the release and elimination processes of neurotransmitters following neuronal excitation. In conclusion, the downregulation of ISF drainage following neuronal excitation was found to be caused by the restricted diffusion in the brain ECS, and DECS mapping may be used to track the neuronal activity in the deep brain.

Effect of aquaporin 4 protein overexpression in nigrostriatal system on development of Parkinson's disease

OBJECTS

Recent studies indicated that aquaporin 4 (AQP4), as the main water channel in the central nervous system (CNS), participated in the onset and progression of Parkinson's disease (PD). But how the AQP4 influenced the exacerbation of PD has not been described in detail. In this study, the effect of the AQP4 protein overexpression in nigrostriatal system that include substantia nigra (SN) and striatum (CPu) on the development of PD was investigated.

METHODS

Forty male Sprague Dawley rats were equally divided into two groups at random: PD group and control group, PD group undergoing surgery and receiving 6-hydroxydopamine (6-OHDA). Using MRI tracer-based method, extracellular space (ECS) diffusion parameters of nigrostriatal system for all rats were measured, including the clearance coefficient (k') and the half-life (t_1/2). Immunohistochemistry of AQP4 was performed for 20 rats.

RESULTS

The area of dark-stained AQP4 immunoreactivity increased markedly in SN of PD rats, there were significant differences between two groups (SN: t = 5.809, p < 0.0001; CPu: t = 5.943, p < 0.0001). And the diffusion parameters were significantly greater in PD group than that of control group, including k' (SN: t = 5.519, p < 0.0001; CPu: t = 2.149, p = 0.045) and t_1/2 (SN: t = 6.131, p < 0.0001; CPu: t = 6.708, p < 0.0001). There was a significant positive correlation between the AQP4 expression level and the k' values (SN: r = 0.827, p = 0.0031; CPu: r = 0.641, p = 0.0046), and a significant negative correlation between AQP4 and the t_1/2 values (SN: r=-0.654, p = 0.0403; CPu: r=-0.664, p = 0.0362).

CONCLUSIONS

The results indicated that AQP4 expression was increased in nigrostriatal system of PD rats, therefore, the overexpression of AQP4 led to acceleration of the diffusion and drainage process of drugs in ECS, reduced the effect of drugs for the treatment of PD, inhibited the development of PD.

The Interstitial System of the Brain in Health and Disease

The brain interstitial fluid (ISF) and the cerebrospinal fluid (CSF) cushion and support the brain cells. The ISF occupies the brain interstitial system (ISS), whereas the CSF fills the brain ventricles and the subarachnoid space. The brain ISS is an asymmetrical, tortuous, and exceptionally confined space between neural cells and the brain microvasculature. Recently, with a newly developed in vivo measuring technique, a series of discoveries have been made in the brain ISS and the drainage of ISF. The goal of this review is to confer recent advances in our understanding of the brain ISS, including its structure, function, and the various processes mediating or disrupting ISF drainage in physiological and pathological conditions. The brain ISF in the deep brain regions has recently been demonstrated to drain in a compartmentalized ISS instead of a highly connected system, together with the drainage of ISF into the cerebrospinal fluid (CSF) at the surface of the cerebral cortex and the transportation from CSF into cervical lymph nodes. Besides, accumulation of tau in the brain ISS in conditions such as Alzheimer’s disease and its link to the sleep-wake cycle and sleep deprivation, clearance of ISF in a deep sleep via increased CSF flow, novel approaches to remove beta-amyloid from the brain ISS, and obstruction to the ISF drainage in neurological conditions are deliberated. Moreover, the role of ISS in the passage of extracellular vesicles (EVs) released from neural cells and the rapid targeting of therapeutic EVs into neural cells in the entire brain following an intranasal administration, and the promise and limitations of ISS based drug delivery approaches are discussed

Methods and utility of quantitative brainstem measurements in progressive supranuclear palsy versus Parkinson's disease in a routine clinical setting

Background and Purpose

The clinical diagnosis of progressive supranuclear palsy can be challenging, as the clinical presentation overlaps with that of Parkinson's disease and multiple system atrophy. We sought to examine the practical utility of radiologic markers of progressive supranuclear palsy by investigating whether these markers could distinguish between patients with progressive supranuclear palsy-Richardson syndrome (PSP-RS) and those with Parkinson's disease based on imaging obtained in a typical clinical setting, not in a prospective research environment.

Materials and methods

This retrospective study included 13 patients with PSP-RS and 13 patients with Parkinson's disease who were followed for either condition at our institution at the time of the study and who had MRI records available. Patients were selected without regard to type of imaging obtained. All diagnoses were confirmed by a trained movement disorders specialist using validated diagnostic criteria. Groups were matched for age and disease duration at the time of scanning. MRI records were retrospectively obtained, and image analysis was performed by investigators blinded to disease classification. Midbrain area, midbrain to pons area ratio, midbrain anterior-posterior diameter, and MR parkinsonism index were calculated for each patient.

Results

All established measures of identifying progressive supranuclear palsy (midbrain area, midbrain to pons area ratio, midbrain anterior-posterior diameter, and MR parkinsonism index) were significantly different between patients with PSP-RS and those with Parkinson's disease.

Conclusion

Previously established radiographic markers distinguishing between PSP-RS and Parkinson's disease have practical utility in the clinical setting and not just in well-designed prospective analyses.

The Drainage of Interstitial Fluid in the Deep Brain is Controlled by the Integrity of Myelination

In searching for the drainage route of the interstitial fluid (ISF) in the deep brain, we discovered a regionalized ISF drainage system as well as a new function of myelin in regulating the drainage. The traced ISF from the caudate nucleus drained to the ipsilateral cortex along myelin fiber tracts, while in the opposite direction, its movement to the adjacent thalamus was completely impeded by a barrier structure, which was identified as the converged, compact myelin fascicle. The regulating and the barrier effects of myelin were unchanged in AQP4-knockout rats but were impaired as the integrity of boundary structure of drainage system was destroyed in a demyelinated rat model. We thus proposed that the brain homeostasis was maintained within each ISF drainage division locally, rather than across the brain as a whole. A new brain division system and a new pathogenic mechanism of demyelination are therefore proposed.

Using induced pluripotent stem cells for modeling Parkinson’s disease

Parkinson’s disease (PD) is an age-related neurodegenerative disease caused by the progressive loss of dopaminergic (DA) neurons in the substantia nigra. As DA neurons degenerate, PD patients gradually lose their ability of movement. To date no effective therapies are available for the treatment of PD and its pathogenesis remains unknown. Experimental models that appropriately mimic the development of PD are certainly needed for gaining mechanistic insights into PD pathogenesis and identifying new therapeutic targets. Human induced pluripotent stem cells (iPSCs) could provide a promising model for fundamental research and drug screening. In this review, we summarize various iPSCs-based PD models either derived from PD patients through reprogramming technology or established by gene-editing technology, and the promising application of iPSC-based PD models for mechanistic studies and drug testing.

[Discovery of a new division system in brain and the regionalized drainage route of brain interstitial fluid]

Brain extracellular space (ECS) is a narrow, irregular space, which provides immediate living environment for neural cells and accounts for approximately 15%-20% of the total volume of living brain. Twenty-five years ago, as an interventional radiologist, the author was engaged in investigating early diagnosis and treatment of cerebral ischemic stroke, and the parameters of brain ECS was firstly derived and demonstrated during the study of the permeability of blood-brain barrier (BBB) and its diffusion changes in the cerebral ischemic tissue. Since then, the author and his team had been working on developing a novel measuring method of ECS: tracer-based magnetic resonance imaging (MRI), which could measure brain ECS parameters in the whole brain scale and make the dynamic drainage process of the labelled brain interstitial fluid (ISF) visualized. By using the new method, the team made a series of new findings about the brain ECS and ISF, including the discovery of a new division system in the brain, named regionalized ISF drainage system. We found that the ISF drainage in the deep brain was regionalized and the structural and functional parameters in different interstitial system (ISS) divisions were disparate. The ISF in the caudate nucleus could be drained to ipsilateral cortex and finally into the subarachnoid space, which maintained the pathway of ISF-cerebrospinal fluid (CSF) exchange. However, the ISF in the thalamus was eliminated locally in its anatomical division. After verifying the nature of the barrier structure between different drainage divisions, the author proposed the hypothesis of "regionalized brain homeostasis". Thus, we demonstrated that the brain was protected not only by the BBB, which avoided potential exogenous damage through the vascular system, but was also protected by an internal ISF drainage barrier to avoid potentially harmful interference from other ECS divisions in the deep brain. With the new findings and the proposed hypothesis, an innovative therapeutic method for the treatment of encephalopathy with local drug delivery via the brain ECS pathway was established. By using this new administration method, the drug was achieved directly to the space around neurons or target regions, overwhelming the impendence from the blood-brain barrier, thus solved the obstacles of low efficiency in traditional drug investigation. At present, new methods and discoveries developed by the author and his team have been widely applied in several frontier fields including neuroscience, new drug research and development, neurodevelopment aerospace medicine, clinical encephalopathy treatment,new neural network modeling and so on.

[Temporary acceleration of interstitial fluid drainage in excited brain region induced by movement]

OBJECTIVE

To investigate the changes of brain interstitial fluid (ISF) induced by movement.

METHODS

Twenty mature male Sprague-Dawley rats were randomly divided into two groups: control group and movement group. Electrophysiological neurons in caudate nuclear of additional five rats were recorded and the differences analyzed between under anesthesia and by movement. In the control group, the rats were anesthetized using isoflurane continuously during the experiment process. In the meantime the magnetic tracer was injected into the center of the caudate nucleus and multi-period magnetic resonance scanning was performed at several time points until high signal intensity invisible in the images. In the movement group, the rats were anesthetized for the injection of the tracer, and the first post-injection magnetic resonance scanning was performed. Then the rats were waken and allowed moving voluntarily for 20 minutes. The rats were anesthetized again and multi-period magnetic resonance scanning was performed until the experiment ended. NanoDetect system (Version 1.2, MRI lab, Beijing, China) was used to measure the parameters on ISF, which included the weighed signal intensity (weighed ΔSI) , the term predicting the amount of the tracer, and half-time of the tracer. In movement group, the weighed ΔSI at the time points of pre-movement and 10, 40, 70, 130, and 190 minutes after movement were calculated respectively. In control group, the weighed ΔSI at the same time points also were measured. The weighed ΔSI and half-time were compared between the two groups.

RESULTS

The electrophysiological recording and data analysis showed significant difference in the local field potential of Caudate Nucleus between under anesthesia and by movement. The weighed ΔSI (unit: ΔSI×mm³) values of the two groups, presented by movement group vs. control group, were as followings, 60 257.1±23 069.2 vs. 61 072.0±19 547.3 at pre-move, 83 624.3±21 475.7 vs. 71 218.1±12 586.5 at 10 min after movement, 57 336.0±36 243.4 vs. 69 756.1±13 306.0 at 40 min after movement, 43 705.9±10 246.3 vs. 55 443.2±20 733.3 at 70 min after movement, 7 734.9±2 645.2 vs. 8 967.6±2 007.3 at 130 min after movement and 2 497.3±987.5 vs. 3 013.2±1 760.8 at 190 min after movement. Moreover, at 40 min after movement, the weighed ΔSI of movement group was significantly reduced compared with control group (P<0.05). The half-time was not significantly different [(104.3±54.1) min vs. (113.4±47.3) min, P>0.05].

CONCLUSION

ISF drainage of caudate nuclear can be acclerated temporarily by movement.

[Temporary acceleration of interstitial fluid drainage in excited brain region induced by movement]

OBJECTIVE

To investigate the changes of brain interstitial fluid (ISF) induced by movement.

METHODS

Twenty mature male Sprague-Dawley rats were randomly divided into two groups: control group and movement group. Electrophysiological neurons in caudate nuclear of additional five rats were recorded and the differences analyzed between under anesthesia and by movement. In the control group, the rats were anesthetized using isoflurane continuously during the experiment process. In the meantime the magnetic tracer was injected into the center of the caudate nucleus and multi-period magnetic resonance scanning was performed at several time points until high signal intensity invisible in the images. In the movement group, the rats were anesthetized for the injection of the tracer, and the first post-injection magnetic resonance scanning was performed. Then the rats were waken and allowed moving voluntarily for 20 minutes. The rats were anesthetized again and multi-period magnetic resonance scanning was performed until the experiment ended. NanoDetect system (Version 1.2, MRI lab, Beijing, China) was used to measure the parameters on ISF, which included the weighed signal intensity (weighed ΔSI) , the term predicting the amount of the tracer, and half-time of the tracer. In movement group, the weighed ΔSI at the time points of pre-movement and 10, 40, 70, 130, and 190 minutes after movement were calculated respectively. In control group, the weighed ΔSI at the same time points also were measured. The weighed ΔSI and half-time were compared between the two groups.

RESULTS

The electrophysiological recording and data analysis showed significant difference in the local field potential of Caudate Nucleus between under anesthesia and by movement. The weighed ΔSI (unit: ΔSI×mm3) values of the two groups, presented by movement group vs. control group, were as followings, 60 257.1±23 069.2 vs. 61 072.0±19 547.3 at pre-move, 83 624.3±21 475.7 vs. 71 218.1±12 586.5 at 10 min after movement, 57 336.0±36 243.4 vs. 69 756.1±13 306.0 at 40 min after movement, 43 705.9±10 246.3 vs. 55 443.2±20 733.3 at 70 min after movement, 7 734.9±2 645.2 vs. 8 967.6±2 007.3 at 130 min after movement and 2 497.3±987.5 vs. 3 013.2±1 760.8 at 190 min after movement. Moreover, at 40 min after movement, the weighed ΔSI of movement group was significantly reduced compared with control group (P<0.05). The half-time was not significantly different [(104.3±54.1) min vs. (113.4±47.3) min, P>0.05].

CONCLUSION

ISF drainage of caudate nuclear can be acclerated temporarily by movement.

Advances in the Research of Risk Factors and Prodromal Biomarkers of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disease in the world. With the advent of an aging population and improving life expectancy worldwide, the number of PD patients is expected to increase, which may lead to an urgent need for effective preventive and diagnostic strategies for PD. Although there is increasing research regarding the pathogenesis of PD, there is limited knowledge regarding the prevention of PD. Moreover, the diagnosis of PD depends on clinical criteria, which require the occurrence of bradykinesia and at least one symptom of rest tremor or rigidity. However, converging evidence from clinical, genetic, neuropathological, and imaging studies suggests the initiation of PD-specific pathology prior to the initial presentation of these classical motor clinical features by years or decades. This latent stage of neurodegeneration in PD is a particularly important stage for effective neuroprotective therapies, which might retard the progression or prevent the onset of PD. Therefore, the exploration of risk factors and premotor biomarkers is not only crucial to the early diagnosis of PD but is also helpful in the development of effective neuroprotection and health care strategies for appropriate populations at risk for PD. In this review, we searched and summarized ∼249 researches and 31 reviews focusing on the risk factors and prodromal biomarkers of PD and published in MEDLINE.

Oculomotor Performances Are Associated With Motor and Non-motor Symptoms in Parkinson's Disease

Background: Parkinson's disease (PD) patients exhibit deficits in oculomotor behavior, yet the results are inconsistent across studies. In addition, how these results are associated with clinical symptoms is unclear, especially in China.

Methods: We designed a case-control study in China including 37 PD patients and 39 controls. Clinical manifestations in PD patients were recorded. Oculomotor performance was measured by a video-based eye tracker system.

Results: We found that six oculomotor parameters, including fixation stability, saccadic latency, smooth pursuit gain, saccade frequency, viewing range, and saccade frequency during free-viewing context, were significantly different in PD patients and control group. Combining application of these six parameters could improve diagnostic accuracy to over 90%. Moreover, pursuit gain was significantly associated with PD duration, UPDRS III, in PD patients. Saccade latency was significantly associated with PD duration, Berg balance score, RBD score, and Total LEDD in PD patients.

Conclusions: PD patients commonly exhibit oculomotor deficits in multiple behavioral contexts, which are associated with both motor and non-motor symptoms. Oculomotor test may provide a valuable tool for the clinical assessment of PD.

The Effect of Aquaporin-4 Knockout on Interstitial Fluid Flow and the Structure of the Extracellular Space in the Deep Brain

It has been reported that aquaporin-4 (AQP4) deficiency impairs transportation between the cerebrospinal fluid and interstitial fluid (ISF) as well as the clearance of interstitial solutes in the superficial brain. However, the effect of AQP4 on ISF flow in the deep brain remains unclear. This study compared the brain ISF flow in the caudate nucleus and thalamus of normal rats (NO) and AQP4 knockout rats (KO) using tracer-based magnetic resonance imaging. The rate of brain ISF flow slowed to different degrees in the two regions of KO rats’ brains. Compared with NO rats, the half-life of ISF in the thalamus of KO rats was significantly prolonged, with a corresponding decrease in the clearance coefficient. The tortuosity of the brain extracellular space (ECS) was unchanged in the thalamus of KO rats. In the caudate nucleus of KO rats, the volume fraction of the ECS and the diffusion coefficient were increased, with significantly decreased tortuosity; no significant changes in brain ISF flow were demonstrated. Combined with a change in the expression of glial fibrillary acidic protein and AQP4 in two brain regions, we found that the effect of AQP4 knockout on ISF flow and ECS structure in these two regions differed. This difference may be related to the distribution of astrocytes and the extent of AQP4 decline. This study provides evidence for the involvement of AQP4 in ISF transportation in the deep brain and provides a basis for the establishment of a pharmacokinetic model of the brain’s interstitial pathway.