Astrocytes are crucial for the functioning of the nervous system as they maintain the ion homeostasis via volume regulation. Pathological states, such as amyotrophic lateral sclerosis (ALS), affect astrocytes and might even cause a loss of such functions. In this study, we examined astrocytic swelling/volume recovery in both the brain and spinal cord of the SOD1 animal model to determine the level of their impairment caused by the ALS-like pathology. Astrocyte volume changes were measured in acute brain or spinal cord slices during and after exposure to hyperkalemia. We then compared the results with alterations of extracellular space (ECS) diffusion parameters, morphological changes, expression of the Kir4.1 channel and the potassium concentration measured in the cerebrospinal fluid, to further disclose the link between potassium and astrocytes in the ALS-like pathology. Morphological analysis revealed astrogliosis in both the motor cortex and the ventral horns of the SOD1 spinal cord. The activated morphology of SOD1 spinal astrocytes was associated with the results from volume measurements, which showed decreased swelling of these cells during hyperkalemia. Furthermore, we observed lower shrinkage of ECS in the SOD1 spinal ventral horns. Immunohistochemical analysis then confirmed decreased expression of the Kir4.1 channel in the SOD1 spinal cord, which corresponded with the diminished volume regulation. Despite astrogliosis, cortical astrocytes in SOD1 mice did not show alterations in swelling nor changes in Kir4.1 expression, and we did not identify significant changes in ECS parameters. Moreover, the potassium level in the cerebrospinal fluid did not deviate from the physiological concentration. The results we obtained thus suggest that ALS-like pathology causes impaired potassium uptake associated with Kir4.1 downregulation in the spinal astrocytes, but based on our data from the cortex, the functional impairment seems to be independent of the morphological state.

• Keywords
• SOD1, amyotrophic lateral sclerosis, astrocytes, extracellular space, potassium uptake, volume regulation,
• Publication type
• Journal Article MeSH

Hapln4 is a link protein which stabilizes the binding between lecticans and hyaluronan in perineuronal nets (PNNs) in specific brain regions, including the medial nucleus of the trapezoid body (MNTB). The aim of this study was: (1) to reveal possible age-related alterations in the extracellular matrix composition in the MNTB and inferior colliculus, which was devoid of Hapln4 and served as a negative control, (2) to determine the impact of the Hapln4 deletion on the values of the ECS diffusion parameters in young and aged animals and (3) to verify that PNNs moderate age-related changes in the ECS diffusion, and that Hapln4-brevican complex is indispensable for the correct protective function of the PNNs. To achieve this, we evaluated the ECS diffusion parameters using the real-time iontophoretic method in the selected region in young adult (3 to 6-months-old) and aged (12 to 18-months-old) wild type and Hapln4 knock-out (KO) mice. The results were correlated with an immunohistochemical analysis of the ECM composition and astrocyte morphology. We report that the ECM composition is altered in the aged MNTB and aging is a critical point, revealing the effect of Hapln4 deficiency on the ECS diffusion. All of our findings support the hypothesis that the ECM changes in the MNTB of aged KO animals affect the ECS parameters indirectly, via morphological changes of astrocytes, which are in direct contact with synapses and can be influenced by the ongoing synaptic transmission altered by shifts in the ECM composition.

• Keywords
• Aging, Diffusion, Extracellular matrix, Extracellular space, Hapln4,
• MeSH
• Trapezoid Body metabolism   pathology   MeSH
• Diffusion * MeSH
• Extracellular Matrix Proteins deficiency   MeSH
• Extracellular Matrix metabolism   pathology   MeSH
• Extracellular Space metabolism   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Protein Deficiency metabolism   pathology   MeSH
• Organ Culture Techniques MeSH
• Peripheral Nerves metabolism   pathology   MeSH
• Nerve Tissue Proteins deficiency   MeSH
• Auditory Pathways metabolism   pathology   MeSH
• Aging metabolism   pathology   MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Extracellular Matrix Proteins MeSH
• Hapln4 protein, mouse MeSH Browser
• Nerve Tissue Proteins MeSH

Volume transmission is a form of intercellular communication that does not require synapses; it is based on the diffusion of neuroactive substances across the brain extracellular space (ECS) and their binding to extrasynaptic high-affinity receptors on neurons or glia. Extracellular diffusion is restricted by the limited volume of the ECS, which is described by the ECS volume fraction α, and the presence of diffusion barriers, reflected by tortuosity λ, that are created, for example, by fine astrocytic processes or extracellular matrix (ECM) molecules. Organized astrocytic processes, ECM scaffolds or myelin sheets channel the extracellular diffusion so that it is facilitated in a certain direction, i.e. anisotropic. The diffusion properties of the ECS are profoundly influenced by various processes such as the swelling and morphological rebuilding of astrocytes during either transient or persisting physiological or pathological states, or the remodelling of the ECM in tumorous or epileptogenic tissue, during Alzheimer's disease, after enzymatic treatment or in transgenic animals. The changing diffusion properties of the ECM influence neuron-glia interaction, learning abilities, the extent of neuronal damage and even cell migration. From a clinical point of view, diffusion parameter changes occurring during pathological states could be important for diagnosis, drug delivery and treatment.

• Keywords
• astrocytes, diffusion, extracellular matrix, extracellular space, tortuosity, volume fraction,
• MeSH
• Anisotropy MeSH
• Astrocytes pathology   MeSH
• Diffusion MeSH
• Extracellular Matrix physiology   MeSH
• Humans MeSH
• Cell Communication physiology   MeSH
• Synaptic Transmission physiology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH