The curious case of NG2 cells: transient trend or game changer?

It has been 10 years since the seminal work of Dwight Bergles and collaborators demonstrated that NG2 (nerve/glial antigen 2)-expressing oligodendrocyte progenitor cells (NG2 cells) receive functional glutamatergic synapses from neurons (Bergles et al., 2000), contradicting the old dogma that only neurons possess the complex and specialized molecular machinery necessary to receive synapses. While this surprising discovery may have been initially shunned as a novelty item of undefined functional significance, the study of neuron-to-NG2 cell neurotransmission has since become a very active and exciting field of research. Many laboratories have now confirmed and extended the initial discovery, showing for example that NG2 cells can also receive inhibitory GABAergic synapses (Lin and Bergles, 2004) or that neuron-to-NG2 cell synaptic transmission is a rather ubiquitous phenomenon that has been observed in all brain areas explored so far, including white matter tracts (Kukley et al., 2007; Ziskin et al., 2007; Etxeberria et al., 2010). Thus, while still being in its infancy, this field of research has already brought many surprising and interesting discoveries, and has become part of a continuously growing effort in neuroscience to re-evaluate the long underestimated role of glial cells in brain function (Barres, 2008). However, this area of research is now reaching an important milestone and its long-term significance will be defined by its ability to uncover the still elusive function of NG2 cells and their synapses in the brain, rather than by its sensational but transient successes at upsetting the old order established by neuronal physiology. To participate in the effort to facilitate such a transition, here we propose a critical review of the latest findings in the field of NG2 cell physiology – discussing how they inform us on the possible function(s) of NG2 cells in the brain – and we present some personal views on new directions the field could benefit from in order to achieve lasting significance

Cellular Bases of Barbiturate and Phenytoin Anticonvulsant Drug Action

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65509/1/j.1528-1157.1982.tb06093.x.pd

Dopaminergic Activation of Estrogen Receptors Induces Fos Expression within Restricted Regions of the Neonatal Female Rat Brain

Steroid receptor activation in the developing brain influences a variety of cellular processes that endure into adulthood, altering both behavior and physiology. Recent data suggests that dopamine can regulate expression of progestin receptors within restricted regions of the developing rat brain by activating estrogen receptors in a ligand-independent manner. It is unclear whether changes in neuronal activity induced by dopaminergic activation of estrogen receptors are also region specific. To investigate this question, we examined where the dopamine D1-like receptor agonist, SKF 38393, altered Fos expression via estrogen receptor activation. We report that dopamine D1-like receptor agonist treatment increased Fos protein expression within many regions of the developing female rat brain. More importantly, prior treatment with an estrogen receptor antagonist partially reduced D1-like receptor agonist-induced Fos expression only within the bed nucleus of the stria terminalis and the central amygdala. These data suggest that dopaminergic activation of estrogen receptors alters neuronal activity within restricted regions of the developing rat brain. This implies that ligand-independent activation of estrogen receptors by dopamine might organize a unique set of behaviors during brain development in contrast to the more wide spread ligand activation of estrogen receptors by estrogen

New Insights in the Contribution of Voltage-Gated Nav Channels to Rat Aorta Contraction

BACKGROUND: Despite increasing evidence for the presence of voltage-gated Na(+) channels (Na(v)) isoforms and measurements of Na(v) channel currents with the patch-clamp technique in arterial myocytes, no information is available to date as to whether or not Na(v) channels play a functional role in arteries. The aim of the present work was to look for a physiological role of Na(v) channels in the control of rat aortic contraction. METHODOLOGY/PRINCIPAL FINDINGS: Na(v) channels were detected in the aortic media by Western blot analysis and double immunofluorescence labeling for Na(v) channels and smooth muscle alpha-actin using specific antibodies. In parallel, using real time RT-PCR, we identified three Na(v) transcripts: Na(v)1.2, Na(v)1.3, and Na(v)1.5. Only the Na(v)1.2 isoform was found in the intact media and in freshly isolated myocytes excluding contamination by other cell types. Using the specific Na(v) channel agonist veratridine and antagonist tetrodotoxin (TTX), we unmasked a contribution of these channels in the response to the depolarizing agent KCl on rat aortic isometric tension recorded from endothelium-denuded aortic rings. Experimental conditions excluded a contribution of Na(v) channels from the perivascular sympathetic nerve terminals. Addition of low concentrations of KCl (2-10 mM), which induced moderate membrane depolarization (e.g., from -55.9+/-1.4 mV to -45.9+/-1.2 mV at 10 mmol/L as measured with microelectrodes), triggered a contraction potentiated by veratridine (100 microM) and blocked by TTX (1 microM). KB-R7943, an inhibitor of the reverse mode of the Na(+)/Ca(2+) exchanger, mimicked the effect of TTX and had no additive effect in presence of TTX. CONCLUSIONS/SIGNIFICANCE: These results define a new role for Na(v) channels in arterial physiology, and suggest that the TTX-sensitive Na(v)1.2 isoform, together with the Na(+)/Ca(2+) exchanger, contributes to the contractile response of aortic myocytes at physiological range of membrane depolarization

Changes in calcium dynamics following the reversal of the sodium-calcium exchanger have a key role in AMPA receptor-mediated neurodegeneration via calpain activation in hippocampal neurons

Proteolytic cleavage of the Na(+)/Ca(2+) exchanger (NCX) by calpains impairs calcium homeostasis, leading to a delayed calcium overload and excitotoxic cell death. However, it is not known whether reversal of the exchanger contributes to activate calpains and trigger neuronal death. We investigated the role of the reversal of the NCX in Ca(2+) dynamics, calpain activation and cell viability, in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor-stimulated hippocampal neurons. Selective overactivation of AMPA receptors caused the reversal of the NCX, which accounted for approximately 30% of the rise in intracellular free calcium concentration ([Ca(2+)](i)). The NCX reverse-mode inhibitor, 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea (KB-R7943), partially inhibited the initial increase in [Ca(2+)](i), and prevented a delayed increase in [Ca(2+)](i). In parallel, overactivation of AMPA receptors strongly activated calpains and led to the proteolysis of NCX3. KB-R7943 prevented calpain activation, cleavage of NCX3 and was neuroprotective. Silencing of NCX3 reduced Ca(2+) uptake, calpain activation and was neuroprotective. Our data show for the first time that NCX reversal is an early event following AMPA receptor stimulation and is linked to the activation of calpains. Since calpain activation subsequently inactivates NCX, causing a secondary Ca(2+) entry, NCX may be viewed as a new suicide substrate operating in a Ca(2+)-dependent loop that triggers cell death and as a target for neuroprotectio

E-cadherin expression and bromodeoxyuridine incorporation during development of ovarian inclusion cysts in age-matched breeder and incessantly ovulated CD-1 mice

BACKGROUND: Female CD-1/Swiss Webster mice subjected to incessant ovulation for 8 months and 12-month breeder mice both developed ovarian inclusion cysts similar to serous cystadenomas. The majority of cysts appeared to be dilated rete ovarii tubules, but high ovulation number resulted in more cortical inclusion cysts. We hypothesized that comparison of inclusion cyst pathology in animals of the same age, but with differences in total lifetime ovulation number, might allow us to determine distinguishing characteristics of the two types of cyst. METHODS: Ovaries from breeder mice (BR) or females subjected to incessant ovulation (IO) were compared at 6-, 9- and 12-months of age. Ovaries were serially sectioned and cysts characterized with regard to location and histology, E-cadherin immunoreactivity and rates of BrdU incorporation. RESULTS: Inclusion cysts developed with age in BR and IO ovaries. The majority of cysts were connected to the ovarian hilus. Two cortical inclusion cysts were observed in ten IO ovaries and one in ten BR ovaries. Low or no E-cadherin immuno-staining was seen in the OSE of all mice studied. Conversely, strong membrane immuno-staining was observed in rete ovarii epithelial cells. Variable E-cadherin immunoreactivity was seen in cells of hilar inclusion cysts, with strong staining observed in cuboidal ciliated cells and little or no staining in flat epithelial cells. Two of the three cortical cysts contained papillae, which showed E-cadherin immuno-staining at the edge of cells. However hilar and cortical cysts were not distinguishable by morphology, cell type or E-cadherin immunoreactivity. BrdU incorporation in cyst cells (1.4% [95% CI: 1.0 to 2.1]) was greater than in OSE (0.7% [95% CI: 0.4 to 1.2]) and very few BrdU-labeled cells were observed in rete ovarii at any age. Incessant ovulation significantly increased BrdU incorporation in OSE of older animals. CONCLUSION: These experiments confirm ovarian inclusion cysts develop with age in the CD-1 mouse strain, irrespective of total ovulation burden. We conclude longer periods of incessant ovulation do not lead to significant changes in inclusion cyst formation or steroidogenesis in CD-1 mice and inclusion cyst type can not be distinguished by morphology, cell proliferation rate or E-cadherin immunoreactivity

Seasonal Pattern of Batrachochytrium dendrobatidis Infection and Mortality in Lithobates areolatus: Affirmation of Vredenburg's “10,000 Zoospore Rule”

To fully comprehend chytridiomycosis, the amphibian disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), it is essential to understand how Bd affects amphibians throughout their remarkable range of life histories. Crawfish Frogs (Lithobates areolatus) are a typical North American pond-breeding species that forms explosive spring breeding aggregations in seasonal and semipermanent wetlands. But unlike most species, when not breeding Crawfish Frogs usually live singly—in nearly total isolation from conspecifics—and obligately in burrows dug by crayfish. Crayfish burrows penetrate the water table, and therefore offer Crawfish Frogs a second, permanent aquatic habitat when not breeding. Over the course of two years we sampled for the presence of Bd in Crawfish Frog adults. Sampling was conducted seasonally, as animals moved from post-winter emergence through breeding migrations, then back into upland burrow habitats. During our study, 53% of Crawfish Frog breeding adults tested positive for Bd in at least one sample; 27% entered breeding wetlands Bd positive; 46% exited wetlands Bd positive. Five emigrating Crawfish Frogs (12%) developed chytridiomycosis and died. In contrast, all 25 adult frogs sampled while occupying upland crayfish burrows during the summer tested Bd negative. One percent of postmetamorphic juveniles sampled were Bd positive. Zoospore equivalents/swab ranged from 0.8 to 24,436; five out of eight frogs with zoospore equivalents near or >10,000 are known to have died. In summary, Bd infection rates in Crawfish Frog populations ratchet up from near zero during the summer to over 25% following overwintering; rates then nearly double again during and just after breeding—when mortality occurs—before the infection wanes during the summer. Bd-negative postmetamorphic juveniles may not be exposed again to this pathogen until they take up residence in crayfish burrows, or until their first breeding, some years later