Corticosteroids: way upstream

Studies into the mechanisms of corticosteroid action continue to be a rich bed of research, spanning the fields of neuroscience and endocrinology through to immunology and metabolism. However, the vast literature generated, in particular with respect to corticosteroid actions in the brain, tends to be contentious, with some aspects suffering from loose definitions, poorly-defined models, and appropriate dissection kits. Here, rather than presenting a comprehensive review of the subject, we aim to present a critique of key concepts that have emerged over the years so as to stimulate new thoughts in the field by identifying apparent shortcomings. This article will draw on experience and knowledge derived from studies of the neural actions of other steroid hormones, in particular estrogens, not only because there are many parallels but also because 'learning from differences' can be a fruitful approach. The core purpose of this review is to consider the mechanisms through which corticosteroids might act rapidly to alter neural signaling

Two types of somatostatin-expressing GABAergic interneurons in the superficial layers of the mouse cingulate cortex

Somatostatin-expressing (SOM+), inhibitory interneurons represent a heterogeneous group of cells and given their remarkable diversity, classification of SOM+ interneurons remains a challenging task. Electrophysiological, morphological and neurochemical classes of SOM+ interneurons have been proposed in the past but it remains unclear as to what extent these classes are congruent. We performed whole-cell patch-clamp recordings from 127 GFP-labeled SOM+ interneurons ('GIN') of the superficial cingulate cortex with subsequent biocytin-filling and immunocytochemical labeling. Principal component analysis followed by k-means clustering predicted two putative subtypes of SOM+ interneurons, which we designated as group I and group II GIN. A key finding of our study is the fact that these electrophysiologically and morphologically distinct groups of SOM+ interneurons can be correlated with two neurochemical subtypes of SOM+ interneurons described recently in our laboratory. In particular, all SOM+ interneurons expressing calbindin but no calretinin could be classified as group I GIN, whereas all but one neuropeptide Y- and calretinin-positive interneurons were found in group II

Pumilio2-deficient mice show a predisposition for epilepsy

Epilepsy is a neurological disease that is caused by abnormal hypersynchronous activities of neuronal ensembles leading to recurrent and spontaneous seizures in human patients. Enhanced neuronal excitability and a high level of synchrony between neurons seem to trigger these spontaneous seizures. The molecular mechanisms, however, regarding the development of neuronal hyperexcitability and maintenance of epilepsy are still poorly understood. Here, we show that pumilio RNA-binding family member 2 (Pumilio2;Pum2) plays a role in the regulation of excitability in hippocampal neurons of weaned and 5-month-old male mice. Almost complete deficiency of Pum2 in adult Pum2 gene-trap mice (Pum2 GT) causes misregulation of genes involved in neuronal excitability control. Interestingly, this finding is accompanied by the development of spontaneous epileptic seizures in Pum2 GT mice. Furthermore, we detect an age-dependent increase in Scn1a (Na(v)1.1) and Scn8a (Na(v)1.6) mRNA levels together with a decrease in Scn2a (Na(v)1.2) transcript levels in weaned Pum2 GT that is absent in older mice. Moreover, field recordings of CA1 pyramidal neurons show a tendency towards a reduced paired-pulse inhibition after stimulation of the Schaffer-collateral-commissural pathway in Pum2 GT mice, indicating a predisposition to the development of spontaneous seizures at later stages. With the onset of spontaneous seizures at the age of 5 months, we detect increased protein levels of Na(v)1.1 and Na(v)1.2 as well as decreased protein levels of Na(v)1.6 in those mice. In addition, GABA receptor subunit alpha-2 (Gabra2) mRNA levels are increased in weaned and adult mice. Furthermore, we observe an enhanced GABRA2 protein level in the dendritic field of the CA1 subregion in the Pum2 GT hippocampus. We conclude that altered expression levels of known epileptic risk factors such as Na(v)1.1, Na(v)1.2, Na(v)1.6 and GABRA2 result in enhanced seizure susceptibility and manifestation of epilepsy in the hippocampus. Thus, our results argue for a role of Pum2 in epileptogenesis and the maintenance of epilepsy

Direct neuronal reprogramming of NDUFS4 patient cells identifies the unfolded protein response as a novel general reprogramming hurdle

Mitochondria account for essential cellular pathways, from ATP production to nucleotide metabolism, and their deficits lead to neurological disorders and contribute to the onset of age -related diseases. Direct neuronal reprogramming aims at replacing neurons lost in such conditions, but very little is known about the impact of mitochondrial dysfunction on the direct reprogramming of human cells. Here, we explore the effects of mitochondrial dysfunction on the neuronal reprogramming of induced pluripotent stem cell (iPSC)derived astrocytes carrying mutations in the NDUFS4 gene, important for Complex I and associated with Leigh syndrome. This led to the identification of the unfolded protein response as a major hurdle in the direct neuronal conversion of not only astrocytes and fibroblasts from patients but also control human astrocytes and fibroblasts. Its transient inhibition potently improves reprogramming by influencing the mitochondriaendoplasmic-reticulum-stress-mediated pathways. Taken together, disease modeling using patient cells unraveled novel general hurdles and ways to overcome these in human astrocyte-to-neuron reprogramming

Current-voltage relationship in GIN.

<p><b>A</b>, <b>B</b><i>Left panels</i> Determination of the current-voltage-curve in GIN. A series of de- and hyperpolarizing current steps (upper traces) were injected into the cells and the corresponding voltage responses (lower traces) were measured. The subsequently obtained recordings are shown superimposed. Note the large sag potential in A. <i>Right panels</i> Corresponding <i>I-V</i> curves derived from the recordings shown in A and B. Closed circles depict the IV-relationship at steady state (i.e. at the end of the current pulse) and open circles show the IV-relationship at the time point of occurrence of the maximum negative peak potential. The difference between these two curves corresponds to the sag potential. <b>C-E</b> Differences in the IV-relationship in group I and group II GIN. Scatter plots of sag index (<b>C</b>), time to negative peak (<b>D</b>) and rectification index (<b>E</b>) in both GIN subgroups.</p

Single action potential kinetics in GIN.

<p><b>A</b> Representative recording of a single action potential in GIN. <b>B</b> First derivative of the action potential shown in (A). <b>C-E</b> Scatter plots with mean and SD values in group I and group II GIN showing differences in the action potential rise-to-fall ratio (<b>C</b>), spike duration (<b>D</b>) and spike threshold (<b>E</b>).</p

Properties of spontaneous postsynaptic potentials in GIN.

<p><b>A</b> Representative recordings of spontaneous synaptic activity in different GIN. <b>B</b> Expanded traces of the voltage traces shown in A. <b>C</b> Expanded voltage traces (same recordings as in A) showing spontaneously induced action potentials. <b>D</b> PSP frequencies are similar in both GIN subgroups (scatter plots with mean values ± SD). <b>E</b> Scatter plot showing that PSP amplitudes and <b>F</b> PSP durations are significantly smaller in group II compared to group I GIN.</p

Morphological varieties in group II GIN.

<p>Many group I GIN classified as Martinotti cells with massive axonal arborizations in layer 1 and in the home layer. All scalebars: 50 μm. <b>A-F</b>, <i>left panel</i> Confocal Z-stack images of biocytin-injected GIN as maximum intensity projections. <i>Right panel</i> Corresponding immunolabelings of the cells shown in the <i>left panel</i>. Cells were labeled for GFP (green), CR (white or blue), CB (blue or white), SOM (white) or NPY (red). Fluorescence (GFP, white) and infrared-DIC (grey) images were acquired of cells in A-F prior recording.</p