Glial cells are now recognized as active communication partners in the central nervous system, and this new perspective has rekindled the question of their role in pathology. In the present study we analysed functional properties of astrocytes in hippocampal specimens from patients with mesial temporal lobe epilepsy without (n = 44) and with sclerosis (n = 75) combining patch clamp recording, K(+) concentration analysis, electroencephalography/video-monitoring, and fate mapping analysis. We found that the hippocampus of patients with mesial temporal lobe epilepsy with sclerosis is completely devoid of bona fide astrocytes and gap junction coupling, whereas coupled astrocytes were abundantly present in non-sclerotic specimens. To decide whether these glial changes represent cause or effect of mesial temporal lobe epilepsy with sclerosis, we developed a mouse model that reproduced key features of human mesial temporal lobe epilepsy with sclerosis. In this model, uncoupling impaired K(+) buffering and temporally preceded apoptotic neuronal death and the generation of spontaneous seizures. Uncoupling was induced through intraperitoneal injection of lipopolysaccharide, prevented in Toll-like receptor4 knockout mice and reproduced in situ through acute cytokine or lipopolysaccharide incubation. Fate mapping confirmed that in the course of mesial temporal lobe epilepsy with sclerosis, astrocytes acquire an atypical functional phenotype and lose coupling. These data suggest that astrocyte dysfunction might be a prime cause of mesial temporal lobe epilepsy with sclerosis and identify novel targets for anti-epileptogenic therapeutic intervention.

Astrocytes are endowed with the machinery to sense and respond to neuronal activity. Recent work has demonstrated that astrocytes play important physiological roles in the CNS, e.g., they synchronize action potential firing, ensure ion homeostasis, transmitter clearance and glucose metabolism, and regulate the vascular tone. Astrocytes are abundantly coupled through gap junctions, which is a prerequisite to redistribute elevated K 1 from sites of excessive neuronal activity to sites of lower extracellular K 1 concentration. Recent studies identified dysfunctional astrocytes as crucial players in epilepsy. Investigation of specimens from patients with pharmacoresistant temporal lobe epilepsy and epilepsy models revealed alterations in expression, localization, and function of astroglial inwardly rectifying K 1 (Kir) channels, particularly Kir4.1, which is suspected to entail impaired K 1 buffering. Gap junctions in astrocytes appear to play a dual role: on the one hand they counteract the generation of hyperactivity by facilitating clearance of elevated extracellular K 1 levels while in contrast, they constitute a pathway for energetic substrate delivery to fuel neuronal (hyper)activity. Recent work suggests that astrocyte dysfunction is causative of the generation or spread of seizure activity. Thus, astrocytes should be considered as promising targets for alternative antiepileptic therapies. V V C 2012 Wiley Periodicals, Inc.

The thalamus plays important roles as a relay station for sensory information in the central nervous system (CNS). Although thalamic glial cells participate in this activity, little is known about their properties. In this study, we characterized the formation of coupled networks between astrocytes and oligodendrocytes in the murine ventrobasal thalamus and compared these properties with those in the hippocampus and cortex. Biocytin filling of individual astrocytes or oligodendrocytes revealed large panglial networks in all 3 gray matter regions. Combined analyses of mice with cell type-specific deletion of connexins (Cxs), semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and western blotting showed that Cx30 is the dominant astrocytic Cx in the thalamus. Many thalamic astrocytes even lack expression of Cx43, while in the hippocampus astrocytic coupling is dominated by Cx43. Deletion of Cx30 and Cx47 led to complete loss of panglial coupling, which was restored when one allele of either Cxs was present. Immunohistochemistry revealed a unique antigen profile of thalamic glia and identified an intermediate cell type expressing both Olig2 and Cx43. Our findings further the emerging concept of glial heterogeneity across brain regions.

Olfactory receptors are the largest group of orphan G protein-coupled receptors with an infinitely small number of agonists identified out of thousands of odorants. The de-orphaning of olfactory receptor (OR) is complicated by its combinatorial odorant coding and thus requires large scale odorant and receptor screening and establishing receptor-specific odorant profiles. Here, we report on the stable reconstitution of OR-specific signaling in HeLa/Olf cells via G protein ␣olf and adenylyl cyclase type-III to the Ca 2؉ influx-mediating olfactory cyclic nucleotide-gated CNGA2 channel. We demonstrate the central role of G␣olf in odorant-specific signaling out of OR. The employment of the non-typical G protein ␣15 dramatically altered the odorant specificities of 3 of 7 receptors that had been characterized previously by different groups. We further show for two OR that an odorant may be an agonist or antagonist, depending on the G protein used. HeLa/Olf cells proved suitable for high-throughput screening in fluorescenceimaging plate reader experiments, resulting in the deorphaning of two new OR for the odorant (؊)citronellal from an expression library of 93 receptors. To demonstrate the G protein dependence of its odorant response pattern, we screened the most sensitive (؊)citronellal receptor Olfr43 versus 94 odorants simultaneously in the presence of G␣15 or G␣olf. We finally established an EC 50 -ranking odorant profile for Olfr43 in HeLa/Olf cells. In summary, we conclude that, in heterologous systems, odorants may function as agonists or antagonists, depending on the G protein used. HeLa/Olf cells provide an olfactory model system for functional expression and de-orphaning of OR.

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