Cytology, architecture, development, and connections of the primate striatum: Hints for human pathology

Research progress of the inferior colliculus: from Neuron, neural circuit to auditory disease

The auditory midbrain, also known as the inferior colliculus (IC), serves as a crucial hub in the auditory pathway. Comprising diverse cell types, the IC plays a pivotal role in various auditory functions, including sound localization, auditory plasticity, sound detection, and sound-induced behaviors. Notably, the IC is implicated in several auditory central disorders, such as tinnitus, age-related hearing loss, autism and Fragile X syndrome. Accurate classification of IC neurons is vital for comprehending both normal and dysfunctional aspects of IC function. Various parameters, including dendritic morphology, neurotransmitter synthesis, potassium currents, biomarkers, and axonal targets, have been employed to identify distinct neuron types within the IC. However, the challenge persists in effectively classifying IC neurons into functional categories due to the limited clustering capabilities of most parameters. Recent studies utilizing advanced neuroscience technologies have begun to shed light on biomarker-based approaches in the IC, providing insights into specific cellular properties and offering a potential avenue for understanding IC functions. This review focuses on recent advancements in IC research, spanning from neurons and neural circuits to aspects related to auditory diseases.

From active affordance to active inference: vertical integration of cognition in the cerebral cortex through dual subcortical control systems

In previous papers, we proposed that the dorsal attention system's top-down control is regulated by the dorsal division of the limbic system, providing a feedforward or impulsive form of control generating expectancies during active inference. In contrast, we proposed that the ventral attention system is regulated by the ventral limbic division, regulating feedback constraints and error-correction for active inference within the neocortical hierarchy. Here, we propose that these forms of cognitive control reflect vertical integration of subcortical arousal control systems that evolved for specific forms of behavior control. The feedforward impetus to action is regulated by phasic arousal, mediated by lemnothalamic projections from the reticular activating system of the lower brainstem, and then elaborated by the hippocampus and dorsal limbic division. In contrast, feedback constraint-based on environmental requirements-is regulated by the tonic activation furnished by collothalamic projections from the midbrain arousal control centers, and then sustained and elaborated by the amygdala, basal ganglia, and ventral limbic division. In an evolutionary-developmental analysis, understanding these differing forms of active affordance-for arousal and motor control within the subcortical vertebrate neuraxis-may help explain the evolution of active inference regulating the cognition of expectancy and error-correction within the mammalian 6-layered neocortex.

Abnormalities of cerebral blood flow and the regional brain function in Parkinson's disease: a systematic review and multimodal neuroimaging meta-analysis

Background

Parkinson's disease (PD) is a neurodegenerative disease with high incidence rate. Resting state functional magnetic resonance imaging (rs-fMRI), as a widely used method for studying neurodegenerative diseases, has not yet been combined with two important indicators, amplitude low-frequency fluctuation (ALFF) and cerebral blood flow (CBF), for standardized analysis of PD.

Methods

In this study, we used seed-based d-mapping and permutation of subject images (SDM-PSI) software to investigate the changes in ALFF and CBF of PD patients. After obtaining the regions of PD with changes in ALFF or CBF, we conducted a multimodal analysis to identify brain regions where ALFF and CBF changed together or could not synchronize.

Results

The final study included 31 eligible trials with 37 data sets. The main analysis results showed that the ALFF of the left striatum and left anterior thalamic projection decreased in PD patients, while the CBF of the right superior frontal gyrus decreased. However, the results of multimodal analysis suggested that there were no statistically significant brain regions. In addition, the decrease of ALFF in the left striatum and the decrease of CBF in the right superior frontal gyrus was correlated with the decrease in clinical cognitive scores.

Conclusion

PD patients had a series of spontaneous brain activity abnormalities, mainly involving brain regions related to the striatum-thalamic-cortex circuit, and related to the clinical manifestations of PD. Among them, the left striatum and right superior frontal gyrus are more closely related to cognition.

Systematic review registration

https://www.crd.york.ac.uk/ PROSPERO (CRD42023390914).

Co-exposure to lead, mercury, and cadmium induces neurobehavioral impairments in mice by interfering with dopaminergic and serotonergic neurotransmission in the striatum

Humans are exposed to lead (Pb), mercury (Hg), and cadmium (Cd) through various routes, including drinking water, and such exposure can lead to a range of toxicological effects. However, few studies have investigated the toxic effects of exposure to mixtures of metals, particularly in relation to neurotoxicity. In this study, 7-week-old male mice were exposed to Pb, Hg, and Cd individually or in combination through their drinking water for 28 days. The mice exposed to the metal mixture exhibited significantly reduced motor coordination and impaired learning and memory abilities compared to the control group and each of the single metal exposure groups, indicating a higher level of neurotoxicity of the metal mixture. The dopamine content in the striatum was significantly lower in the metal mixture exposure group than in the single metal exposure groups and the control group. Furthermore, compared to the control group, the metal mixture exposure group showed a significantly lower expression level of tyrosine hydroxylase (TH) and significantly higher expression levels of dopamine transporter (DAT), tryptophan hydroxylase 1 (TPH1), and serotonin reuptake transporter (SERT). Notably, there were no significant differences in SERT expression between the single metal exposure groups and the control group, but SERT expression was significantly higher in the metal mixture exposure group than in the single metal and control groups. These findings suggest that the key proteins involved in the synthesis and reuptake of dopamine (TH and DAT, respectively), as well as in the synthesis and reuptake of serotonin (TPH1 and SERT, respectively), play crucial roles in the neurotoxic effects associated with exposure to metal mixtures. In conclusion, this study demonstrates that simultaneous exposure to different metals can impact key enzymes involved in dopaminergic and serotonergic neurotransmission processes, leading to disruptions in dopamine and serotonin homeostasis and consequently a range of detrimental neurobehavioral effects.

Tunneling Nanotube: An Enticing Cell-Cell Communication in the Nervous System

The field of neuroscience is rapidly progressing, continuously uncovering new insights and discoveries. Among the areas that have shown immense potential in research, tunneling nanotubes (TNTs) have emerged as a promising subject of study. These minute structures act as conduits for the transfer of cellular materials between cells, representing a mechanism of communication that holds great significance. In particular, the interplay facilitated by TNTs among various cell types within the brain, including neurons, astrocytes, oligodendrocytes, glial cells, and microglia, can be essential for the normal development and optimal functioning of this complex organ. The involvement of TNTs in neurodegenerative disorders, such as Alzheimer's disease, Huntington's disease, and Parkinson's disease, has attracted significant attention. These disorders are characterized by the progressive degeneration of neurons and the subsequent decline in brain function. Studies have predicted that TNTs likely play critical roles in the propagation and spread of pathological factors, contributing to the advancement of these diseases. Thus, there is a growing interest in understanding the precise functions and mechanisms of TNTs within the nervous system. This review article, based on our recent work on Rhes-mediated TNTs, aims to explore the functions of TNTs within the brain and investigate their implications for neurodegenerative diseases. Using the knowledge gained from studying TNTs could offer novel opportunities for designing targeted treatments that can stop the progression of neurodegenerative disorders.

Different pieces of the same puzzle: a multifaceted perspective on the complex biological basis of Parkinson's disease

The biological basis of the neurodegenerative movement disorder, Parkinson's disease (PD), is still unclear despite it being 'discovered' over 200 years ago in Western Medicine. Based on current PD knowledge, there are widely varying theories as to its pathobiology. The aim of this article was to explore some of these different theories by summarizing the viewpoints of laboratory and clinician scientists in the PD field, on the biological basis of the disease. To achieve this aim, we posed this question to thirteen "PD experts" from six continents (for global representation) and collated their personal opinions into this article. The views were varied, ranging from toxin exposure as a PD trigger, to LRRK2 as a potential root cause, to toxic alpha-synuclein being the most important etiological contributor. Notably, there was also growing recognition that the definition of PD as a single disease should be reconsidered, perhaps each with its own unique pathobiology and treatment regimen.

Brain-Biomarker Changes in Body Fluids of Patients with Parkinson's Disease

Parkinson's disease (PD) is an incurable neurodegenerative disease that is rarely diagnosed at an early stage. Although the understanding of PD-related mechanisms has greatly improved over the last decade, the diagnosis of PD is still based on neurological examination through the identification of motor symptoms, including bradykinesia, rigidity, postural instability, and resting tremor. The early phase of PD is characterized by subtle symptoms with a misdiagnosis rate of approximately 16-20%. The difficulty in recognizing early PD has implications for the potential use of novel therapeutic approaches. For this reason, it is important to discover PD brain biomarkers that can indicate early dopaminergic dysfunction through their changes in body fluids, such as saliva, urine, blood, or cerebrospinal fluid (CSF). For the CFS-based test, the invasiveness of sampling is a major limitation, whereas the other body fluids are easier to obtain and could also allow population screening. Following the identification of the crucial role of alpha-synuclein (α-syn) in the pathology of PD, a very large number of studies have summarized its changes in body fluids. However, methodological problems have led to the poor diagnostic/prognostic value of this protein and alternative biomarkers are currently being investigated. The aim of this paper is therefore to summarize studies on protein biomarkers that are alternatives to α-syn, particularly those that change in nigrostriatal areas and in biofluids, with a focus on blood, and, eventually, saliva and urine.

Cortical type: a conceptual tool for meaningful biological interpretation of high-throughput gene expression data in the human cerebral cortex

The interpretation of massive high-throughput gene expression data requires computational and biological analyses to identify statistically and biologically significant differences, respectively. There are abundant sources that describe computational tools for statistical analysis of massive gene expression data but few address data analysis for biological significance. In the present article we exemplify the importance of selecting the proper biological context in the human brain for gene expression data analysis and interpretation. For this purpose, we use cortical type as conceptual tool to make predictions about gene expression in areas of the human temporal cortex. We predict that the expression of genes related to glutamatergic transmission would be higher in areas of simpler cortical type, the expression of genes related to GABAergic transmission would be higher in areas of more complex cortical type, and the expression of genes related to epigenetic regulation would be higher in areas of simpler cortical type. Then, we test these predictions with gene expression data from several regions of the human temporal cortex obtained from the Allen Human Brain Atlas. We find that the expression of several genes shows statistically significant differences in agreement with the predicted gradual expression along the laminar complexity gradient of the human cortex, suggesting that simpler cortical types may have greater glutamatergic excitability and epigenetic turnover compared to more complex types; on the other hand, complex cortical types seem to have greater GABAergic inhibitory control compared to simpler types. Our results show that cortical type is a good predictor of synaptic plasticity, epigenetic turnover, and selective vulnerability in human cortical areas. Thus, cortical type can provide a meaningful context for interpreting high-throughput gene expression data in the human cerebral cortex.

Mapping the primate thalamus: systematic approach to analyze the distribution of subcortical neuromodulatory afferents

Neuromodulatory afferents to thalamic nuclei are key for information transmission and thus play critical roles in sensory, motor, and limbic processes. Over the course of the last decades, diverse attempts have been made to map and describe subcortical neuromodulatory afferents to the primate thalamus, including axons using acetylcholine, serotonin, dopamine, noradrenaline, adrenaline, and histamine. Our group has been actively involved in this endeavor. The published descriptions on neuromodulatory afferents to the primate thalamus have been made in different laboratories and are not fully comparable due to methodological divergences (for example, fixation procedures, planes of cutting, techniques used to detect the afferents, different criteria for identification of thalamic nuclei…). Such variation affects the results obtained. Therefore, systematic methodological and analytical approaches are much needed. The present article proposes reproducible methodological and terminological frameworks for primate thalamic mapping. We suggest the use of standard stereotaxic planes to produce and present maps of the primate thalamus, as well as the use of the Anglo-American school terminology (vs. the German school terminology) for identification of thalamic nuclei. Finally, a public repository of the data collected under agreed-on frameworks would be a useful tool for looking up and comparing data on the structure and connections of primate thalamic nuclei. Important and agreed-on efforts are required to create, manage, and fund a unified and homogeneous resource of data on the primate thalamus. Likewise, a firm commitment of the institutions to preserve experimental brain material is much needed because neuroscience work with non-human primates is becoming increasingly rare, making earlier material still more valuable.