The surface ultractructure of the habenular complex of the rat

Engineered Extracellular Vesicles for Drug Delivery in Therapy of Stroke

Extracellular vesicles (EVs) are promising therapeutic modalities for treating neurological conditions. EVs facilitate intercellular communication among brain cells under normal and abnormal physiological conditions. The potential capability of EVs to pass through the blood-brain barrier (BBB) makes them highly promising as nanocarrier contenders for managing stroke. EVs possess several potential advantages compared to existing drug-delivery vehicles. These advantages include their capacity to surpass natural barriers, target specific cells, and stability within the circulatory system. This review explores the trafficking and cellular uptake of EVs and evaluates recent findings in the field of EVs research. Additionally, an overview is provided of the techniques researchers utilize to bioengineer EVs for stroke therapy, new results on EV-BBB interactions, and the limitations and prospects of clinically using EVs for brain therapies. The primary objective of this study is to provide a comprehensive analysis of the advantages and challenges related to engineered EVs drug delivery, specifically focusing on their application in the treatment of stroke.

Engineered extracellular vesicles as brain therapeutics

Extracellular vesicles (EVs) are communication channels between different cell types in the brain, between the brain and the periphery and vice-versa, playing a fundamental role in physiology and pathology. The evidence that EVs might be able to cross the blood-brain barrier (BBB) make them very promising candidates as nanocarriers to treat brain pathologies. EVs contain a cocktail of bioactive factors, yet their content and surface can be further engineered to enhance their biological activity, stability and targeting ability. Native and engineered EVs have been reported for the treatment of different brain pathologies, although issues related to their modest accumulation and limited local therapeutic effect in the brain still need to be addressed. In this review, we cover the therapeutic applications of native and bioengineered EVs for brain diseases. We also review recent data about the interaction between EVs and the BBB and discuss the challenges and opportunities in clinical translation of EVs as brain therapeutics.

The emerging role of exosomes in Alzheimer's disease

Alzheimer's disease (AD), manifested by memory loss and a decline in cognitive functions, is the most prevalent neurodegenerative disease accounting for 60-80 % of dementia cases. But, to-date, there is no effective treatment available to slow or stop the progression of AD. Exosomes are small extracellular vesicles that carry constituents, such as functional messenger RNAs, non-coding RNAs, proteins, lipids, DNA, and other bioactive substances of their source cells. In the brain, exosomes are likely to be sourced by almost all cell types and involve in cell communication to regulate cellular functions. The yet, accumulated evidence on the roles of exosomes and their constituents in the AD pathological process suggests their significance as additional biomarkers and therapeutic targets for AD. This review summarizes the current reported research findings on exosomes roles in the pathogenesis, diagnosis, and treatment of AD.

NeuroEVs: Characterizing Extracellular Vesicles Generated in the Neural Domain

Intercellular communication has recently been shown to occur via transfer of cargo loaded within extracellular vesicles (EVs). Present within all biofluids of the body, EVs can contain various signaling factors, including coding and noncoding RNAs (e.g., mRNA, miRNA, lncRNA, snRNA, tRNA, yRNA), DNA, proteins, and enzymes. Multiple types of cells appear to be capable of releasing EVs, including cancer, stem, epithelial, immune, glial, and neuronal cells. However, the functional impact of these circulating signals among neural networks within the brain has been difficult to establish given the complexity of cellular populations involved in release and uptake, as well as inherent limitations of examining a biofluid. In this brief commentary, we provide an analysis of the conceptual and technical considerations that limit our current understanding of signaling mediated by circulating EVs relative to their impact on neural function.

Scanning electron microscopy of central nervous system cerebrospinal-fluid-contacting surfaces: a bibliography (1963-1995)

This bibliography is compiled to assist in locating papers related to the application of scanning electron microscopy (SEM) to cerebrospinal-fluid-contacting surfaces in vertebrates. The use of SEM by neuroscientists has continued apace since the publication of the first bibliography in 1980. SEM studies now include more than 50 species of vertebrates and range from cyclostomes to humans; they encompass development from embryo to senescence and concern both normal and pathologic morphology. Although remarkable strides have been made toward a greater understanding of many aspects of the structure and function of cerebrospinal-fluid-contacting surfaces, many significant problems await the judicious application of scanning electron microscopy.

GABA and serotonin (5-HT) pattern in the supraependymal fibers of the rat epithalamus: combined radioautographic and immunocytochemical studies. Effect of 5-HT content on [3H]GABA accumulation

Numerous studies have suggested the serotoninergic nature of the supraependymal plexuses; moreover, several supraependymal fibers are also able to take up [3H]GABA and could be GABA-containing fibers. In this approach, by combined immunocytochemistry and radioautography, we analyzed and compared the distribution of endogenous and exogenous GABA and 5-HT in the supraependymal layer, after inhibition of their respective catabolisms. The majority of the supraependymal fibers are reactive to GABA and 5-HT antisera which indicates that they could contain both GABA and 5-HT. Furthermore it is possible to show that endogenous 5-HT containing fibers are able to accumulate [3H]GABA and conversely. These data point to a functional role for both neurotransmitters in these nerve elements. On the other hand, GABA and 5-HT contents may be connected since p-chlorophenylalanine treatment which inhibits 5-HT synthesis increased [3H]GABA labelling of these plexuses. Finally, several supraependymal fibers are also able to take up [3H]glutamate (but not [3H]glutamine); this compound might be accumulated as GABA precursor and/or as neurotransmitter.

Supra-ependymal serotoninergic nerves in mammalian brain: morphological, pharmacological and functional studies

Supra-ependymal nerves in mammals (mainly rats) have been shown to contain serotonin (5-hydroxytryptamine, 5-HT) by combined Falck-Hillarp fluorescence histochemistry, ultrastructural monoamine cytochemistry and pharmacology as well as by immunohistochemistry and autoradiography. Supra-ependymal 5-HT cells do not occur. At least in rats, virtually all supra-ependymal nerves contain 5-HT and in our opinion the occasionally described non-5-HT supra-ependymal nerve cells and their processes contribute little to the supra-ependymal nerve plexus (with the possible exception of those cells above the median eminence). The cells of origin of the supra-ependymal 5-HT nerves are situated in raphe nuclei. The axons and terminals (varicosities) contain small and large dense core vesicles in both of which 5-HT is stored. A co-transmitter has not been found among the candidates investigated so far (leu- and met-enkephalin, substance P and gamma-aminobutyric acid (GABA)). The nerves possess uptake mechanisms specific for 5-HT and possibly GABA. Occasionally desmosome-like junctions are observed between 5-HT nerve terminals and ependymal cells but no true synapses. The function of these nerves is not known. They do not appear to regulate ciliary movement, but might influence the shape of ependymal cells.

Post-mortem modifications of the ependyma of the lateral ventricular wall

The ependymal lining of the lateral ventricles of the brain of rats, rabbits, and man was investigated at several times after death. In contrast to control material that was fixed by the aldehyde perfusing method, the following post-mortem (p.m.) changes were found: (1) Cytoplasmic protrusions of ependymal cells appear 15 min p.m. They are present up to several hours after death. (2) The formation of these protrusions causes the tufts of cilia to clump together and later to become integrated within the ependymal cell. This may simulate an unciliated surface. (3) Small porelike holes, which are present 15 min p.m. in the ependymal cell membrane, enlarge and in later stages produce a meshwork of fibers instead of a closed ependymal lining. (4) TEM observation shows that ependymal cells are separated from each other very soon after death by intercellular gaps. Cell junctions between ependymal cells resist separation over a longer p.m. period. In animal or human material that is fixed at any time after death, such modifications have to be considered very critically. In human p.m. autopsy material they are mostly the expression of a p.m. alteration.

Serotonergic intraventricular axons in the habenular region. Phagocytosis after induced degeneration

Both intracerebroventricular injection of 5,7-dihydroxytryptamine and electrolytical midbrain-raphe lesions in rats induce degeneration of supraependymal axons (SEAs) normally occurring in large numbers upon the ependyma of the medial habenular nucleus and habenular commissure. It is concluded that the intraventricular axon plexus in the epithalamic region is comprised of serotonergic (5-HT) fibers originating in the dorsal and/or median raphe nuclei. Besides the elimination of SEAs, conspicious features were a marked reduction in the number of cilia, degenerative signs in the habenular ependyma, and the emergence of large numbers of supraependymal macrophages, being most probably involved in phagocytosis of the axonal debris. It is suggested that the nucleus habenulae medialis is influenced serotonergically by the midbrain raphe via (1) a direct projection upon its neurons and (2) an indirect projection by way of the intraventricular axon plexus. The origin of intraventricular macrophages is discussed in relation to recent data in the literature.