Gray matter volume alterations in de novo Parkinson's disease: A mediational role in the interplay between sleep quality and anxiety

OBJECTIVE

Parkinson's disease (PD) is increasingly recognized for its non-motor symptoms, among which emotional disturbances and sleep disorders frequently co-occur. The commonality of neuroanatomical underpinnings for these symptoms is not fully understood. This study is intended to investigate the differences in gray matter volume (GMV) between PD patients with anxiety (A-PD) and those without anxiety (NA-PD). Additionally, it seeks to uncover the interplay between GMV variations and the manifestations of anxiety and sleep quality.

METHODS

A total of 37 A-PD patients, 43 NA-PD patients, and 36 healthy controls (HCs) were recruited, all of whom underwent voxel-based morphometry (VBM) analysis. Group differences in GMV were assessed using analysis of covariance (ANCOVA). Partial correlation between GMV, anxiety symptom, and sleep quality were analyzed. Mediation analysis explored the mediating role of the volume of GMV-distinct brain regions on the relationship between sleep quality and anxiety within the PD patient cohort.

RESULTS

A-PD patients showed significantly lower GMV in the fusiform gyrus (FG) and right inferior temporal gyrus (ITG) compared to HCs and NA-PD patients. GMV in these regions correlated negatively with Hamilton Anxiety Rating Scale (HAMA) scores (right ITG: r = -0.690, p < 0.001; left FG: r = -0.509, p < 0.001; right FG: r = -0.576, p < 0.001) and positively with sleep quality in PD patients (right ITG: r = 0.592, p < 0.001; left FG: r = 0.356, p = 0.001; right FG: r = 0.470, p < 0.001). Mediation analysis revealed that GMV in the FG and right ITG mediated the relationship between sleep quality and anxiety symptoms, with substantial effect sizes accounted for by the right ITG (25.74%) and FG (left: 11.90%, right: 15.59%).

CONCLUSION

This study has shed further light on the relationship between sleep disturbances and anxiety symptoms in PD patients. Given the pivotal roles of the FG and the ITG in facial recognition and the recognition of emotion-related facial expressions, our findings indicate that compromised sleep quality, under the pathological conditions of PD, may exacerbate the reduction in GMV within these regions, impairing the recognition of emotional facial expressions and thereby intensifying anxiety symptoms.

The effect of REM-sleep disruption on affective processing: A systematic review of human and animal experimental studies

Evidence on the importance of rapid-eye-movement sleep (REMS) in processing emotions is accumulating. The focus of this systematic review is the outcomes of experimental REMS deprivation (REMSD), which is the most common method in animal models and human studies on REMSD. This review revealed that variations in the applied REMSD methods were substantial. Animal models used longer deprivation protocols compared with studies in humans, which mostly reported acute deprivation effects after one night. Studies on animal models showed that REMSD causes aggressive behavior, increased pain sensitivity, reduced sexual behavior, and compromised consolidation of fear memories. Animal models also revealed that REMSD during critical developmental periods elicits lasting consequences on affective-related behavior. The few human studies revealed increases in pain sensitivity and suggest stronger consolidation of emotional memories after REMSD. As pharmacological interventions (such as selective serotonin reuptake inhibitors [SSRIs]) may suppress REMS for long periods, there is a clear gap in knowledge regarding the effects and mechanisms of chronic REMS suppression in humans.

REM sleep deprivation induced by the modified multi-platform method has detrimental effects on memory: A systematic review and meta-analysis

The modified multi-platform method (MMPM) is used to induce animal models of paradoxical sleep deprivation and impairs memory in rodents. However, variations in MMPM protocols have contributed to inconsistent conclusions across studies. This meta-analysis aimed to assess the variations of the MMPM and their effects on memory in rats and mice. A comprehensive search identified 60 studies, and 50 were included in our meta-analysis. Overall, the meta-analysis showed that the MMPM significantly reduced the percentage of time spent in target quadrants (I2 = 54 %, 95 % confidence interval [CI] = [-1.83, -1.18]) and the number of platform-area crossings (I2 = 26 %, 95 % CI = [-1.71, -1.07]) in the Morris water maze (MWM) and shortened the latency to entering the dark compartment in the passive avoidance task (I2 = 68 %, 95 % CI = [-1.36, -0.57]), but it increased the number of errors in the radial arm water maze (RAWM) (I2 = 59 %, 95 % CI = [1.29, 2.07]). Additionally, mice performed worse on the MWM, whereas rats performed worse on the passive avoidance task. More significant memory deficits were found in cross-learning and post-learning MMPM in the MWM and RAWM, respectively. This study provided evidence that the MMPM can be used in preclinical studies of memory deficits induced by paradoxical sleep deprivation.

Network Neuroscience Untethered: Brain-Wide Immediate Early Gene Expression for the Analysis of Functional Connectivity in Freely Behaving Animals

Studying how spatially discrete neuroanatomical regions across the brain interact is critical to advancing our understanding of the brain. Traditional neuroimaging techniques have led to many important discoveries about the nature of these interactions, termed functional connectivity. However, in animal models these traditional neuroimaging techniques have generally been limited to anesthetized or head-fixed setups or examination of small subsets of neuroanatomical regions. Using the brain-wide expression density of immediate early genes (IEG), we can assess brain-wide functional connectivity underlying a wide variety of behavioural tasks in freely behaving animal models. Here, we provide an overview of the necessary steps required to perform IEG-based analyses of functional connectivity. We also outline important considerations when designing such experiments and demonstrate the implications of these considerations using an IEG-based network dataset generated for the purpose of this review.

The interaction effect of sleep deprivation and cannabinoid type 1 receptor in the CA1 hippocampal region on passive avoidance memory, depressive-like behavior and locomotor activity in rats

Increasing evidence shows the interaction effect of cannabinoids and sleep on cognitive functions. In the present study, we aimed to investigate the interaction effect of cannabinoids type 1 receptor (CB1r) in the CA1 hippocampal region and sleep deprivation (SD) on passive avoidance memory and depressive-like behavior in male Wistar rats. We used water box apparatus to induce total SD (TSD) for 24 h. The shuttle-box was applied to assess passive avoidance memory and locomotion apparatus was applied to assess locomotor activity. Forced swim test (FST) was used to evaluate rat's behavior. ACPA (CB1r agonist) at the doses of 0.01, 0.001 and 0.0001 μg/rat, and AM251 (CB1r antagonist) at the doses of 100, 10 and 1 ng/rat were injected intra-CA1, five minutes after training via stereotaxic surgery. Results showed SD impaired memory. ACPA at the doses of 0.01 and 0.001 μg/rat impaired memory and at all doses did not alter the effect of SD on memory. AM251 by itself did not alter memory, while at lowest dose (1 ng/rat) restored SD-induced memory deficit. Both drugs induced depressive-like behavior in a dose-dependent manner. Furthermore, both drugs decreased swimming at some doses (ACPA at 0.0001 μg/rat, AM251 at 0.001 and 0.01 ng/rat). Also, ACPA at the highest dose increased climbing of SD rats. In conclusion, we suggest CB1r may interact with the effect of SD on memory. Additionally, cannabinoids may show a dose-dependent manner in modulating mood and behavior. Interestingly, CB1r agonists and antagonists may exhibit a similar effect in some behavioral assessments.

Brain mechanisms of insomnia: new perspectives on causes and consequences

While insomnia is the second most common mental disorder, progress in our understanding of underlying neurobiological mechanisms has been limited. The present review addresses the definition and prevalence of insomnia and explores its subjective and objective characteristics across the 24-hour day. Subsequently, the review extensively addresses how the vulnerability to develop insomnia is affected by genetic variants, early life stress, major life events, and brain structure and function. Further supported by the clear mental health risks conveyed by insomnia, the integrated findings suggest that the vulnerability to develop insomnia could rather be found in brain circuits regulating emotion and arousal than in circuits involved in circadian and homeostatic sleep regulation. Finally, a testable model is presented. The model proposes that in people with a vulnerability to develop insomnia, the locus coeruleus is more sensitive to-or receives more input from-the salience network and related circuits, even during rapid eye movement sleep, when it should normally be sound asleep. This vulnerability may ignite a downward spiral of insufficient overnight adaptation to distress, resulting in accumulating hyperarousal, which, in turn, impedes restful sleep and moreover increases the risk of other mental health adversity. Sensitized brain circuits are likely to be subjectively experienced as "sleeping with one eye open". The proposed model opens up the possibility for novel intervention studies and animal studies, thus accelerating the ignition of a neuroscience of insomnia, which is direly needed for better treatment.

The role of sleep disturbances in depressive-like behavior with emphasis on α-ketoglutarate dehydrogenase activity in rats

Sleep disorders may induce anxiety- and depressive-like behaviors. Furthermore, sleep disorders can alter the function of α-KGDH (α-ketoglutarate dehydrogenase), which is involved in the citric acid cycle. In this study, we evaluated the effect of two models of sleep deprivation (SD) including total SD (TSD) and partial SD (PSD), and two models of napping combined with each models of SD on rats' performance in Forced Swim Test (FST) and α-KGDH activity in both hemispheres of the amygdala. 64 male Wistar rats were used in this study. A modified water box was also used to induce SD. The results showed that, immobility was increased in 48-hour PSD group, indicating a possible depressive-like behavior. Swimming time was also increased following 48-hour TSD. However, climbing time was decreased in 48-hour PSD/TSD groups. Additionally, α-KGDH activity was increased in the left amygdala in 48-hour TSD and PSD groups. In conclusion, PSD may increase depressive-like behavior. TSD and PSD can decrease swimming time but increase climbing time, and these effects may be related to serotonergic and noradrenergic transmissions, respectively. Increase in α-KGDH activity in the left amygdala may be related to the brain's need for more energy during prolonged wakefulness. α-KGDH activity in the right amygdala was unaffected probably due to a decrease in alertness following SD.

Meningeal Lymphangiogenesis and Enhanced Glymphatic Activity in Mice with Chronically Implanted EEG Electrodes

Chronic electroencephalography (EEG) is a widely used tool for monitoring cortical electrical activity in experimental animals. Although chronic implants allow for high-quality, long-term recordings in preclinical studies, the electrodes are foreign objects and might therefore be expected to induce a local inflammatory response. We here analyzed the effects of chronic cranial electrode implantation on glymphatic fluid transport and in provoking structural changes in the meninges and cerebral cortex of male and female mice. Immunohistochemical analysis of brain tissue and dura revealed reactive gliosis in the cortex underlying the electrodes and extensive meningeal lymphangiogenesis in the surrounding dura. Meningeal lymphangiogenesis was also evident in mice prepared with the commonly used chronic cranial window. Glymphatic influx of a CSF tracer was significantly enhanced at 30 d postsurgery in both awake and ketamine-xylazine anesthetized mice with electrodes, supporting the concept that glymphatic influx and intracranial lymphatic drainage are interconnected. Altogether, the experimental results provide clear evidence that chronic implantation of EEG electrodes is associated with significant changes in the brain's fluid transport system. Future studies involving EEG recordings and chronic cranial windows must consider the physiological consequences of cranial implants, which include glial scarring, meningeal lymphangiogenesis, and increased glymphatic activity.SIGNIFICANCE STATEMENT This study shows that implantation of extradural electrodes provokes meningeal lymphangiogenesis, enhanced glymphatic influx of CSF, and reactive gliosis. The analysis based on CSF tracer injection in combination with immunohistochemistry showed that chronically implanted electroencephalography electrodes were surrounded by lymphatic sprouts originating from lymphatic vasculature along the dural sinuses and the middle meningeal artery. Likewise, chronic cranial windows provoked lymphatic sprouting. Tracer influx assessed in coronal slices was increased in agreement with previous reports identifying a close association between glymphatic activity and the meningeal lymphatic vasculature. Lymphangiogenesis in the meninges and altered glymphatic fluid transport after electrode implantation have not previously been described and adds new insights to the foreign body response of the CNS.

Regulation of hippocampal dendritic spines following sleep deprivation

Accumulating evidence supports the role of sleep in synaptic plasticity and memory consolidation. One line of investigation, the synaptic homeostasis hypothesis, has emphasized the increase in synaptic strength during waking, and compensatory downsizing of (presumably less frequently used) synapses during sleep. Conversely, other studies have reported downsizing and loss of dendritic spines following sleep deprivation. We wanted to determine the effect of sleep deprivation on dendritic spines of hippocampal CA1 neurons using genetic methods for fluorescent labeling of dendritic spines. Male Vglut2-Cre mice were injected with an AAV-DIO-ChR2-mCherry reporter in CA1 hippocampus. Gentle handling was used to sleep deprive mice for 5 hr, from lights on (7 am) to 12 noon. Control and sleep-deprived mice were euthanized at 12 noon and processed for quantification of dendritic spines. We used confocal microscope imaging and three-dimensional (3D) analysis to quantify thin, mushroom, and stubby spines from CA1 dendrites, distinguishing between branch segments. We observed significantly greater density of spines in CA1 of sleep-deprived mice, driven primarily by greater numbers of thin spines, and significantly larger spine volume and head diameter. Branch and region-specific analysis revealed that spine volume was greater in primary dendrites of apical and basal segments, along with proximal segments on both apical and basal dendrites, and spine density was increased in secondary branches and distal segments on apical dendrites following sleep deprivation. Our 3D quantification suggests sleep contributes to region- and branch-specific synaptic downscaling in the hippocampus, supporting the theory of broad but selective synaptic downscaling during sleep.