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In CNS, glucocorticoids (GCs) activate both GC receptor (GR) and mineralocorticoid receptor (MR), whereas GR is widely expressed, the expression of MR is restricted. However, both are present in the microglia, the resident macrophages of the brain and their activation can lead to pro- or anti-inflammatory effects. We have therefore addressed the specific functions of GR in microglia. In mice lacking GR in macrophages/microglia and in the absence of modifications in MR expression, intraparenchymal injection of lipopolysaccharide (LPS) activating Toll-like receptor 4 signaling pathway resulted in exacerbated cellular lesion, neuronal and axonal damage. Global inhibition of GR by RU486 pre-treatment revealed that microglial GR is the principal mediator preventing neuronal degeneration triggered by lipopolysaccharide (LPS) and contributes with GRs of other cell types to the protection of non-neuronal cells. In vivo and in vitro data show GR functions in microglial differentiation, proliferation and motility. Interestingly, microglial GR also abolishes the LPS-induced delayed outward rectifier currents by downregulating Kv1.3 expression known to control microglia proliferation and oxygen radical production. Analysis of GR transcriptional function revealed its powerful negative control of pro-inflammatory effectors as well as upstream inflammatory activators. Finally, we analyzed the role of GR in chronic unpredictable mild stress and aging, both known to prime or sensitize microglia in vivo. We found that microglial GR suppresses rather than mediates the deleterious effects of stress or aging on neuronal survival. Overall, the results show that microglial GR acts on several key processes limiting pro-inflammatory actions of activated microglia. [ABSTRACT FROM AUTHOR]

Slowly inactivating outward currents were examined in neurons from rat anterior cortex dissociated at postnatal day 1 and recorded after 7-48 days in vitro by the use of whole-cell patch-clamp technique, in the presence of 0.5-0.8 μM tetrodotoxin (TTX), 50 μM carbachol and 1-5 mM CsCl. Experiments were often carried out in the additional presence of 1-5 mM CsCl, which blocks the anomalous, inwardly rectifying I, the fast Ca-dependent K current ( I), and 50 μM carbachol, which depresses the I current. These currents were evoked by depolarizing steps to -40+-5 mV from a conditioning hyperpolarization to -110+-10 mV. Their sensitivity to elevation from 2.5 to 12.5 mM in extracellular K concentration, together with their sensitivity to 5-15 mM tetraethylammonium, suggests that they are mainly carried by K ions. Their activation and inactivation curves show that the threshold for activation is -65 mV, that their inactivation is achieved at -75 mV and that potentials more negative than -120 mV are needed to abolish it. The time-dependence of de-inactivation gives a maximal current amplitude for conditioning hyperpolarizations of 2 s and is best described by a monoexponential function with a time constant of 0.7 s. Slow, transient K currents were depressed by low doses of 4-aminopyridine (30-100 μM), which indicates the occurrence of an I-type component in the recorded K currents. No slowly declining K current was expressed when a recording solution containing 10 mM 1,2-bis(2-aminophenoxy)ethane- N, N, N′- N′-tetraacetic acid (BAPTA), instead of 1-5 mM BAPTA, was used. When recorded without Ca chelator in the pipette, slowly declining K currents were blocked by bath-applied 40-50 μM BAPTA-aminoethoxy, revealing a large-amplitude, rapidly inactivating outward current. This residual component is insensitive to 50 μM 4-aminopyridine and may include a current more related to the I-type. Our data provide evidence that, in cultured cortical neurons from rat, the expression of an I-like K current is highly dependent on internal Ca concentration. [ABSTRACT FROM AUTHOR]

The actions of neurotensin (NT) on frontal pyramidal neurons were studied in vitro in slices of rat cerebral cortex using current clamp and single electrode voltage clamp (SEVC) techniques. Bath application of NT (0.1 μM-10 μM) induced a depolarization (2-13 mV) in 88% of the pyramidal cells, this effect was associated with a decrease in input conductance of 5-35% and its reversal potential was estimated at -88 +/-9.7mV. Typically, this depolarizing effect of NT was transient, since no cell responded to a second application of the peptide within 20 min after the first one. NT also induced an increase in the rate of firing of pyramidal cells evoked by direct stimulation, even when an hyperpolarizing current was applied to prevent the depolarization induced by NT. This effect could neither be explained by a decrease of the post-spike after-hyperpolarization, nor by an increase of the persistent sodium current which sustains the spiking of pyramidal cells, since the former was not affected consistently by NT and the later was insensitive to the peptide. This excitation of pyramidal neurons by NT persisted after blockade of synaptic transmission. On the other hand, NT also enhanced the synaptic noise recorded in pyramidal cells in standard perfusing medium. Furthermore, dopaminergic antagonists and noradrenergic antagonists failed to block these effects of NT. Finally, the inactive fragment of the peptide, NT(1-8), did not affect membrane properties of pyramidal cells. All together, these results suggest that NT excites frontal cortical neurons through the activation of specific NT receptors. [ABSTRACT FROM AUTHOR]

By means of the retrograde transport of fluorescent tracers (Fast Blue, True Blue, Fluorogold and Diamidino Yellow), the cortico-cortical connections of prelimbic, insular, anterior and posterior cingulate (retrosplenial) areas have been studied. Our results demonstrate that there are, in the cortex of the adult rat, a few cells which have branched axons with connections in the ipsilateral hemisphere (associational neurons) or in the contralateral hemisphere (callosal neurons). The callosal neurons could be separated into two categories: 'double callosal' neurons which project both axon collaterals to two cortical areas of the contralateral hemisphere, and 'associational-callosal' neurons which send axon collaterals to both hemispheres. [ABSTRACT FROM AUTHOR]