Membrane properties of ameboid microglial cells in the corpus callosum slice from early postnatal mice

Microglial cells in culture are distinct from neurons, macroglial cells, and macrophages of tissues other than brain with respect to their membrane current pattern. To assess these cells in the intact tissue, we have applied the patch-clamp technique to study membrane currents in microglial cells from acute, whole brain slices of 6-9-d-old mice in an area of microglial cell invasion, the cingulum. As strategies to identify microglial cells prior to or after recording, we used binding and incorporation of Dil-acetylated low-density lipoproteins, binding of fluorescein isothiocyanate-coupled IgG via microglial Fc-receptors, and ultrastructural characterization. As observed previously for cultured microglial cells, depolarizing voltage steps activate only minute if any membrane currents, while hyperpolarizing voltage steps induced large inward currents. These currents exhibited properties of the inwardly rectifying K+ channel in that the reversal potential depended on the transmembrane K+ gradient, inactivation time constants decreased with hyperpolarization, and the current was blocked by tetraethylammonium (50 mM). This study represents the first attempt to assess microglial cells in situ using electrophysiological methods. It opens the possibility to address questions related to the function of microglial cells in the intact CNS

Translating the cellular neuropathology of microglia into neuroimaging results

The brain responds to the challenge of disease with marked changes in the functional state of its glial cells. One of the most rapid and obvious events is the activation of microglia, the brain’s resident tissue macrophages. Microglial activation is increasingly recognised as an important, early step in the pathophysiological response to traumatic, inflammatory and degenerative tissue changes and even to neoplastic transformation that may affect the nervous system. Microglia react rapidly and in a territorially highly confined way to subtle, acute as well as chronic pathological stimuli. Microglia have been aptly called a “sensor” of pathology in the CNS by Kreutzberg [1,2]. This unique behaviour, which may be due to a lack of gap junctions in these cells [3] is of great practical diagnostic use. Thus, detection of microglial activation provides useful information on formal parameters of disease, such as accurate spatial localisation of the disease process, rate of disease progression and insights into secondary neurodegenerative or adaptive alterations which may take place quite remote from the actual lesion site. Part of the remarkable structural and functional plasticity of microglia is the de novo expression of the “peripheral benzodiazepine binding site" (PBBS). PBBS is linked to important functions, such as immune modulation, steroid synthesis and mitochondrial activity. The PBBS is bound by the isoquinoline, PK11195, which labelled with carbon-11 can be used for positron emission tomography (PET). This opens up a unique window to study glial activity in the living human brain

Translating the cellular neuropathology of microglia into neuroimaging results

The brain responds to the challenge of disease with marked changes in the functional state of its glial cells. One of the most rapid and obvious events is the activation of microglia, the brain’s resident tissue macrophages. Microglial activation is increasingly recognised as an important, early step in the pathophysiological response to traumatic, inflammatory and degenerative tissue changes and even to neoplastic transformation that may affect the nervous system. Microglia react rapidly and in a territorially highly confined way to subtle, acute as well as chronic pathological stimuli. Microglia have been aptly called a “sensor” of pathology in the CNS by Kreutzberg [1,2]. This unique behaviour, which may be due to a lack of gap junctions in these cells [3] is of great practical diagnostic use. Thus, detection of microglial activation provides useful information on formal parameters of disease, such as accurate spatial localisation of the disease process, rate of disease progression and insights into secondary neurodegenerative or adaptive alterations which may take place quite remote from the actual lesion site. Part of the remarkable structural and functional plasticity of microglia is the de novo expression of the “peripheral benzodiazepine binding site" (PBBS). PBBS is linked to important functions, such as immune modulation, steroid synthesis and mitochondrial activity. The PBBS is bound by the isoquinoline, PK11195, which labelled with carbon-11 can be used for positron emission tomography (PET). This opens up a unique window to study glial activity in the living human brain

HIV-1 Nef protein exhibits structural and functional similarity to scorpion peptides interacting with K+ channels.

The persistent infection of human glial cells with HIV-1 is characterized by prominent expression of the Nef protein. In order to evaluate the possible role of Nef in the development of HIV-1-associated neurological disorders, we compared Nef with known neuroactive proteins. We found that HIV Nef shares sequence and structural features with scorpion peptides known to interact with K+ channels. Sequence similarity encompasses two distinct regions of scorpion peptides. Based on crystallography data, both regions in scorpion peptides cooperate in forming a common domain stabilized by ion pairs between charged amino-acid residues. Recombinant Nef protein, as well as a synthetic part of a scorpion channel active peptide (M10), reversibly increased the total K+ current of chick dorsal root ganglions in patch-clamp experiments without killing the cells. These results indicate that a region conserved in HIV Nef and scorpion peptides concurs in both structure and electrophysiological activity and suggest that Nef, like scorpion peptides, may affect neuronal cell function