Modulation of Neuronal Excitability and Plasticity by BHLHE41 Conveys Lithium Non-Responsiveness.

Many bipolar disorder (BD) patients are non-responsive to lithium. The mechanisms underlying lithium (non-)responsiveness are largely unknown. By using gene-set enrichment analysis methods, we found that core clock gene-sets are significantly associated with lithium response.

Polygenic risk for schizophrenia converges on alternative polyadenylation as molecular mechanism underlying synaptic impairment.

Schizophrenia (SCZ) is a genetically heterogenous psychiatric disorder of highly polygenic nature. Correlative evidence from genetic studies indicate that the aggregated effects of distinct genetic risk factor combinations found in each patient converge onto common molecular mechanisms. To prove this on a functional level, we employed a reductionistic cellular model system for polygenic risk by differentiating induced pluripotent stem cells (iPSCs) from 104 individuals with high polygenic risk load and controls into cortical glutamatergic neurons (iNs).

Functional and structural features of L2/3 pyramidal cells continuously covary with pial depth in mouse visual cortex.

Pyramidal cells of neocortical layer 2/3 (L2/3 PyrCs) integrate signals from numerous brain areas and project throughout the neocortex. These PyrCs show pial depth-dependent functional and structural specializations, indicating participation in different functional microcircuits. However, whether these depth-dependent differences result from separable PyrC subtypes or whether their features display a continuum correlated with pial depth is unknown.

Orientation and direction tuning align with dendritic morphology and spatial connectivity in mouse visual cortex.

The functional properties of neocortical pyramidal cells (PCs), such as direction and orientation selectivity in visual cortex, predominantly derive from their excitatory and inhibitory inputs. For layer 2/3 (L2/3) PCs, the detailed relationship between their functional properties and how they sample and integrate information across cortical space is not fully understood. Here, we study this relationship by combining functional in vivo two-photon calcium imaging, in vitro functional circuit mapping, and dendritic reconstruction of the same L2/3 PCs in mouse visual cortex.

Limited functional convergence of eye-specific inputs in the retinogeniculate pathway of the mouse.

Segregation of retinal ganglion cell (RGC) axons by type and eye of origin is considered a hallmark of dorsal lateral geniculate nucleus (dLGN) structure. However, recent anatomical studies have shown that neurons in mouse dLGN receive input from multiple RGC types of both retinae. Whether convergent input leads to relevant functional interactions is unclear.

Inducing Different Neuronal Subtypes from Astrocytes in the Injured Mouse Cerebral Cortex.

Astrocytes are particularly promising candidates for reprogramming into neurons, as they maintain some of the original patterning information from their radial glial ancestors. However, to which extent the position of astrocytes influences the fate of reprogrammed neurons remains unknown. To elucidate this, we performed stab wound injury covering an entire neocortical column, including the gray matter (GM) and white matter (WM), and targeted local reactive astrocytes via injecting FLEx switch (Cre-On) adeno-associated viral (AAV) vectors into mGFAP-Cre mice.

Live cell imaging reveals 3'-UTR dependent mRNA sorting to synapses.

mRNA transport restricts translation to specific subcellular locations, which is the basis for many cellular functions. However, the precise process of mRNA sorting to synapses in neurons remains elusive. Here we use Rgs4 mRNA to investigate 3'-UTR-dependent transport by MS2 live-cell imaging.

Quantitative Analysis of the Spatial Organization of Synaptic Inputs on the Postsynaptic Dendrite.

The spatial organization of synaptic inputs on the dendritic tree of cortical neurons is considered to play an important role in the dendritic integration of synaptic activity. Active electrical properties of dendrites and mechanisms of dendritic integration have been studied for a long time. New technological developments are now enabling the characterization of the spatial organization of synaptic inputs on dendrites.

High-yield in vitro recordings from neurons functionally characterized in vivo.

In vivo two-photon calcium imaging provides detailed information about the activity and response properties of individual neurons. However, in vitro methods are often required to study the underlying neuronal connectivity and physiology at the cellular and synaptic levels at high resolution. This protocol provides a fast and reliable workflow for combining the two approaches by characterizing the response properties of individual neurons in mice in vivo using genetically encoded calcium indicators (GECIs), followed by retrieval of the same neurons in brain slices for further analysis in vitro (e.

Clusters of synaptic inputs on dendrites of layer 5 pyramidal cells in mouse visual cortex.

The spatial organization of synaptic inputs on the dendritic tree of cortical neurons plays a major role for dendritic integration and neural computations, yet, remarkably little is known about it. We mapped the spatial organization of glutamatergic synapses between layer 5 pyramidal cells by combining optogenetics and 2-photon calcium imaging in mouse neocortical slices. To mathematically characterize the organization of inputs we developed an approach based on combinatorial analysis of the likelihoods of specific synapse arrangements.

Balance and stability of synaptic structures during synaptic plasticity.

Subsynaptic structures such as bouton, active zone, postsynaptic density (PSD) and dendritic spine, are highly correlated in their dimensions and also correlate with synapse strength. Why this is so and how such correlations are maintained during synaptic plasticity remains poorly understood. We induced spine enlargement by two-photon glutamate uncaging and examined the relationship between spine, PSD, and bouton size by two-photon time-lapse imaging and electron microscopy.

Function of dendritic spines on hippocampal inhibitory neurons.

The majority of γ-aminobutyric acid (GABA)ergic interneurons have smooth dendrites with no or only few dendritic spines, but certain types of spiny GABAergic interneurons do actually contain substantial numbers of spines. The explanation for such spines has so far been purely structural: They increase the dendritic surface area and thus provide the opportunity to accommodate larger numbers of synapses. We reasoned that there may be specific functional properties for these spines and therefore, undertook to characterize interneuron spines functionally.

Loss of sensory input causes rapid structural changes of inhibitory neurons in adult mouse visual cortex.

A fundamental property of neuronal circuits is the ability to adapt to altered sensory inputs. It is well established that the functional synaptic changes underlying this adaptation are reflected by structural modifications in excitatory neurons. In contrast, the degree to which structural plasticity in inhibitory neurons accompanies functional changes is less clear.

Rapid functional maturation of nascent dendritic spines.

Spine growth and retraction with synapse formation and elimination plays an important role in shaping brain circuits during development and in the adult brain, yet the temporal relationship between spine morphogenesis and the formation of functional synapses remains poorly defined. We imaged hippocampal pyramidal neurons to identify spines of different ages. We then used two-photon glutamate uncaging, whole-cell recording, and Ca(2+) imaging to analyze the properties of nascent spines and their older neighbors.

Characterization and subcellular targeting of GCaMP-type genetically-encoded calcium indicators.

Genetically-encoded calcium indicators (GECIs) hold the promise of monitoring [Ca(2+)] in selected populations of neurons and in specific cellular compartments. Relating GECI fluorescence to neuronal activity requires quantitative characterization. We have characterized a promising new genetically-encoded calcium indicator-GCaMP2-in mammalian pyramidal neurons.

Nonlinear [Ca2+] signaling in dendrites and spines caused by activity-dependent depression of Ca2+ extrusion.

Spine Ca2+ triggers the induction of synaptic plasticity and other adaptive neuronal responses. The amplitude and time course of Ca2+ signals specify the activation of the signaling pathways that trigger different forms of plasticity such as long-term potentiation and depression. The shapes of Ca2+ signals are determined by the dynamics of Ca2+ sources, Ca2+ buffers, and Ca2+ extrusion mechanisms.

Release kinetics, quantal parameters and their modulation during short-term depression at a developing synapse in the rat CNS.

We have characterized developmental changes in the kinetics and quantal parameters of action potential (AP)-evoked neurotransmitter release during maturation of the calyx of Held synapse. Quantal size (q) and peak amplitudes of evoked EPSCs increased moderately, whereas the fraction of vesicles released by single APs decreased. During synaptic depression induced in postnatal day (P) 5-7 synapses by 10-100 Hz stimulation, q declined rapidly to 40-12% of its initial value.

NMDA receptor subunit-dependent [Ca2+] signaling in individual hippocampal dendritic spines.

Ca2+ influx through synaptic NMDA receptors (NMDA-Rs) triggers a variety of adaptive cellular processes. To probe NMDA-R-mediated [Ca2+] signaling, we used two-photon glutamate uncaging to stimulate NMDA-Rs on individual dendritic spines of CA1 pyramidal neurons in rat brain slices. We measured NMDA-R currents at the soma and NMDA-R-mediated [Ca2+] transients in stimulated spines (Delta[Ca2+]).

Allosteric modulation of the presynaptic Ca2+ sensor for vesicle fusion.

Neurotransmitter release is triggered by an increase in the cytosolic Ca2+ concentration ([Ca2+]i), but it is unknown whether the Ca2+-sensitivity of vesicle fusion is modulated during synaptic plasticity. We investigated whether the potentiation of neurotransmitter release by phorbol esters, which target presynaptic protein kinase C (PKC)/munc-13 signalling cascades, exerts a direct effect on the Ca2+-sensitivity of vesicle fusion. Using direct presynaptic Ca2+-manipulation and Ca2+ uncaging at a giant presynaptic terminal, the calyx of Held, we show that phorbol esters potentiate transmitter release by increasing the apparent Ca2+-sensitivity of vesicle fusion.

Imaging calcium concentration dynamics in small neuronal compartments.

Calcium and its regulation play central roles diverse physiologic processes. Quantification of calcium concentrations ([Ca2+]) in small neuronal compartments is crucial to understanding Ca2+-dependent signaling. Here, we describe techniques that are optimized for 2-photon imaging of [Ca2+] dynamics in small compartments such as dendrites and dendritic spines.

Separation of presynaptic and postsynaptic contributions to depression by covariance analysis of successive EPSCs at the calyx of Held synapse.

Synaptic short-term plasticity is considered to result from multiple cellular mechanisms, which may include presynaptic and postsynaptic contributions. We have recently developed a nonstationary EPSC fluctuation analysis (Scheuss and Neher, 2001) to estimate synaptic parameters and their transient changes during short-term synaptic plasticity. Extending the classical variance-mean approach, a short train of stimuli is applied repetitively, and the resulting EPSCs are analyzed for means, variances, and covariances.