The permeation and activation properties of brain sodium channels change during development

Comparative fMRI and MEG localization of cortical sensorimotor function: Bimodal mapping supports motor area reorganization in glioma patients

INTRODUCTION

Preoperative functional mapping in the vicinity of brain lesion is of high importance for avoiding complications in surgical management. However, space-occupying lesions may lead to functional reorganization or decreased BOLD activity.

METHODS

Therefore in 13 patients with cerebral gliomas or brain arterio-venous malformations/ hemangioma fMRI- and MEG-based cortical localizations of motor and somatosensory cortical activation pattern were compared in order to investigate their congruency.

RESULTS

Localization of cortical sensorimotor areas with fMRI and MEG showed good congruency with a mean spatial distance of around 10 mm, with differences depending on the localization method. The smallest mean differences for the centroids were found for MEF with MNE 8 mm and SEF with sLORETA 8 mm. Primary motor area (M1) reorganization was found in 5 of 12 patients in fMRI and confirmed with MEG data. In these 5 patients with M1-reorganization the distance between the border of the fMRI-based cortical M1-localization and the tumor border on T1w MR images varied between 0-4 mm, which was significant (P = 0.025) different to the distance in glioma patients without M1-reorganization (5-26 mm).

CONCLUSION

Our multimodal preoperative mapping approach combining fMRI and MEG reveals a high degree of spatial congruence and provided high evidence for the presence of motor cortex reorganization.

Physiologic and pathophysiologic consequences of altered sialylation and glycosylation on ion channel function

Voltage-gated ion channels are transmembrane proteins that regulate electrical excitability in cells and are essential components of the electrically active tissues of nerves, muscle and the heart. Potassium channels are one of the largest subfamilies of voltage sensitive channels and are among the most-studied of the voltage-gated ion channels. Voltage-gated channels can be glycosylated and changes in the glycosylation pattern can affect ion channel function, leading to neurological and neuromuscular disorders and congenital disorders of glycosylation (CDG). Alterations in glycosylation can also be acquired and appear to play a role in development and aging. Recent studies have focused on the impact of glycosylation and sialylation on ion channels, particularly for voltage-gated potassium and sodium channels. The terminal step of sialylation often affects channel activation and inactivation kinetics. The presence of sialic acids on O or N-glycans can alter the gating mechanism and cause conformational changes in the voltage-sensing domains due to sialic acid's negative charges. This manuscript will provide an overview of sialic acids, potassium and sodium channel function, and the impact of sialylation on channel activation and deactivation.

N-glycosylation in regulation of the nervous system

Protein N-glycosylation can influence the nervous system in a variety of ways by affecting functions of glycoproteins involved in nervous system development and physiology. The importance of N-glycans for different aspects of neural development has been well documented. For example, some N-linked carbohydrate structures were found to play key roles in neural cell adhesion and axonal targeting during development. At the same time, the involvement of glycosylation in the regulation of neural physiology remains less understood. Recent studies have implicated N-glycosylation in the regulation of neural transmission, revealing novel roles of glycans in synaptic processes and the control of neural excitability. N-Glycans were found to markedly affect the function of several types of synaptic proteins involved in key steps of synaptic transmission, including neurotransmitter release, reception, and uptake. Glycosylation also regulates a number of channel proteins, such as TRP channels that control responses to environmental stimuli and voltage-gated ion channels, the principal determinants of neuronal excitability. Sialylated carbohydrate structures play a particularly prominent part in the modulation of voltage-gated ion channels. Sialic acids appear to affect channel functions via several mechanisms, including charge interactions, as well as other interactions that probably engage steric effects and interactions with other molecules. Experiments also indicated that some structural features of glycans can be particularly important for their function. Since glycan structures can vary significantly between different cell types and depend on the metabolic state of the cell, it is important to analyze glycan functions using in vivo approaches. While the complexity of the nervous system and intricacies of glycosylation pathways can create serious obstacles for in vivo experiments in vertebrates, recent studies have indicated that more simple and experimentally tractable model organisms like Drosophila should provide important advantages for elucidating evolutionarily conserved functions of N-glycosylation in the nervous system.

Fetal development of membrane water channel proteins aquaporin-1 and aquaporin-4 in the human brain

Aquaporin-1 and aquaporin-4, water channel membrane proteins reported in both experimental animals and in adult humans, have been detected in different, non-overlapping areas of the central nervous system. This immunohistochemical study describes the developmental expression pattern of the water channel membrane proteins, aquaporin-1 and aquaporin-4, in various structures of human fetal brain over the gestational period of 14-40 weeks. Aquaporin-1 immunostaining was exclusively found in the epithelial cells of the choroid plexus from the 14th gestational week, and the staining pattern altered slightly over time. At week 14, immunostaining appeared only in the apical cell membranes. By the 18th gestational week, the entire plasma membrane of these apical cells was immunopositive, as well as was the cytosol. These changes in immunoreactivity indicate an increasing production of aquaporin-1 in the epithelial cells during the period between the 14th and 24th weeks of gestation. Aquaporin-4 immunostaining was first detected in the archicortex, from gestational week 14 and was detected in the neocortex, 6-7 weeks later. Immunostained structures were always astrocytes, particularly the astrocytic endfeet in the ventricular wall, at the developing ependymal lining, at the pial surface, and around the capillaries. Neuronal labeling was not observed. These results in human fetal brain lend morphological support to the previous findings that aquaporin-1 and aquaporin-4 play different roles in the regulation of the water homeostasis of the brain.