Sparsely Distributed, Pre-synaptic Kv3 K Channels Control Spontaneous Firing and Cross-Unit Synchrony via the Regulation of Synaptic Noise in an Auditory Brainstem Circuit.

Spontaneous subthreshold activity in the central nervous system is fundamental to information processing and transmission, as it amplifies and optimizes sub-threshold signals, thereby improving action potential initiation and maintaining reliable firing. This form of spontaneous activity, which is frequently considered noise, is particularly important at auditory synapses where acoustic information is encoded by rapid and temporally precise firing rates. In contrast, when present in excess, this form of noise becomes detrimental to acoustic information as it contributes to the generation and maintenance of auditory disorders such as tinnitus.

Changes in presynaptic calcium signalling accompany age-related deficits in hippocampal LTP and cognitive impairment.

The loss of cognitive function accompanying healthy aging is not associated with extensive or characteristic patterns of cell death, suggesting it is caused by more subtle changes in synaptic properties. In the hippocampal CA1 region, long-term potentiation requires stronger stimulation for induction in aged rats and mice and long-term depression becomes more prevalent. An age-dependent impairment of postsynaptic calcium homeostasis may underpin these effects.

Corrigendum: Imaging Calcium in Hippocampal Presynaptic Terminals With a Ratiometric Calcium Sensor in a Novel Transgenic Mouse.

[This corrects the article DOI: 10.3389/fncel.2018.

Imaging Calcium in Hippocampal Presynaptic Terminals With a Ratiometric Calcium Sensor in a Novel Transgenic Mouse.

Genetically encoded calcium indicators (GECIs) have gained widespread use for measurement of neuronal activity but their low expression levels in transgenic mice tend to limit sensitivity. We have developed a transgenic mouse line (SyG37) that expresses a ratiometric calcium sensor, SyGCaMP2-mCherry, that is expressed throughout the brain but targeted to presynaptic terminals. Within the CA1 and CA3 regions of hippocampus of male and female mice, SyGaMP2 fluorescence responds linearly up to 10 electrical stimuli at frequencies up to 100 Hz and it can detect responses to a single stimulus.

Post-processing strategies in image scanning microscopy.

Image scanning microscopy (ISM) coupled with pixel reassignment offers a resolution improvement of √2 over standard widefield imaging. By scanning point-wise across the specimen and capturing an image of the fluorescent signal generated at each scan position, additional information about specimen structure is recorded and the highest accessible spatial frequency is doubled. Pixel reassignment can be achieved optically in real time or computationally a posteriori and is frequently combined with the use of a physical or digital pinhole to reject out of focus light.

Programmable illumination and high-speed, multi-wavelength, confocal microscopy using a digital micromirror.

Confocal microscopy is routinely used for high-resolution fluorescence imaging of biological specimens. Most standard confocal systems scan a laser across a specimen and collect emitted light passing through a single pinhole to produce an optical section of the sample. Sequential scanning on a point-by-point basis limits the speed of image acquisition and even the fastest commercial instruments struggle to resolve the temporal dynamics of rapid cellular events such as calcium signals.

Voltage-dependent calcium signaling in rat cerebellar unipolar brush cells.

Unipolar brush cells (UBCs) are a class of excitatory interneuron found in the granule cell layer of the vestibulocerebellum. Mossy fibers form excitatory inputs on to the paint brush shaped dendrioles in the form of giant, glutamatergic synapses, activation of which results in prolonged bursts of action potentials in the postsynaptic UBC. The axons of UBCs themselves form mossy fiber contacts with other UBCs and granule cells, forming an excitatory, intrinsic cerebellar network that has the capacity to synchronize and amplify mossy fiber inputs to potentially large populations of granule cells.

Dual involvement of G-substrate in motor learning revealed by gene deletion.

In this study, we generated mice lacking the gene for G-substrate, a specific substrate for cGMP-dependent protein kinase uniquely located in cerebellar Purkinje cells, and explored their specific functional deficits. G-substrate-deficient Purkinje cells in slices obtained at postnatal weeks (PWs) 10-15 maintained electrophysiological properties essentially similar to those from WT littermates. Conjunction of parallel fiber stimulation and depolarizing pulses induced long-term depression (LTD) normally.

The effects of fear conditioning on cerebellar LTP and LTD.

Long-term potentiation (LTP) and depression (LTD) at parallel fibre-Purkinje cell synapses have been described in vitro in the cerebellar cortex, but the physiological roles of these two forms of plasticity have not been well defined. Here we show that, in cerebellar slices taken from rats that had undergone fear conditioning, there was a significant occlusion of electrically induced LTP at parallel fibre-Purkinje cell synapses. This effect was long-lasting and related to associative processes, as LTP was not occluded in unpaired animals.

Simple Windows-based software for the control of laser scanning confocal microscopes.

Rapid advances in computer processing power and the appearance of low cost, high speed multifunction data acquisition hardware makes the control of confocal laser scanning microscopes (CLSMs) with standard laboratory hardware a potentially straightforward task. This paper describes software designed to control a Biorad MRC 600 scan head under Windows 2000 or XP. Using a single high speed, multifunction data acquisition board running under the Igor Pro software environment, waveforms required to drive the scan head galvanometers can be generated and up to two channels of images (768 x 512 pixels at 8 or 12 bit levels) captured live or at set intervals.

Cell uptake, cytoplasmic diffusion and nuclear access of a 6.5 nm diameter dendrimer.

Macromolecular crowding and the presence of organelles in the cytosol present barriers to particle mobility, such that it is unclear how nano-carriers can deliver their active agents to the nucleus. In this work a sixth generation amino terminated polyamide polylysine dendrimer (Gly-Lys(63) (NH(2))(64)) (MW 8149, diameter 6.5 nm) which is fluorescent allowed the study of nuclear uptake and mobility in living lung carcinoma (SK/MES-1) and colon adenocarcinoma (Caco-2) cells.

An intrinsically fluorescent dendrimer as a nanoprobe of cell transport.

Dendrimers, spherical or quasi-spherical synthetic polymers in the nano-size range, have found useful applications as prospective carriers in drug and gene delivery. The investigation of dendrimer uptake by cells has been previously achieved by the incorporation of a fluorescent dye to the dendrimer either by chemical conjugation or by physical interaction. Here we describe the synthesis of two intrinsically fluorescent lysine based cationic dendrimers which lack a fluorophore, but which has sufficient fluorescence intensity to be detected at low concentrations.

Differential susceptibility to synaptic plasticity reveals a functional specialization of ascending axon and parallel fiber synapses to cerebellar Purkinje cells.

Granule cell axons, via their parallel fibers, form synapses with Purkinje cells across large areas of the cerebellar cortex. Evidence for uniform transmission along parallel fibers to Purkinje cells is controversial, however, leading to speculation that the ascending axonal segment plays a dominant role in cerebellar processing. We have compared the relative susceptibilities of ascending axon and parallel fiber synaptic inputs to several forms of synaptic plasticity.

Nitric oxide release is induced by dopamine during illumination of the carp retina: serial neurochemical control of light adaptation.

Several lines of indirect evidence have suggested that nitric oxide may play an important role during light adaptation of the vertebrate retina. We aimed to verify directly the effect of light on nitric oxide release in the isolated carp retina and to investigate the relationship between nitric oxide and dopamine, an established neuromodulator of retinal light adaptation. Using a biochemical nitric oxide assay, we found that steady or flicker light stimulation enhanced retinal nitric oxide production from a basal level.

Differences in transmission properties and susceptibility to long-term depression reveal functional specialization of ascending axon and parallel fiber synapses to Purkinje cells.

An understanding of the patterns of mossy fiber transmission to Purkinje cells, via granule cell axons, is fundamental to models of cerebellar cortical signaling and processing. Early theories assumed that mossy fiber input is widely disseminated across the cerebellar cortex along beams of parallel fibers, which spread for several millimeters across the cerebellar cortex. Direct evidence for this has, however, proved controversial, leading to the development of an alternative hypothesis that mossy fiber inputs to the cerebral cortex are in fact vertically organized such that the ascending segment of the granule axon carries a greater synaptic weight than the parallel fiber segment.

Insulin-stimulated endothelial nitric oxide release is calcium independent and mediated via protein kinase B.

Insulin exerts a vasodilator effect by stimulating endothelial nitric oxide (NO) production. Studies in cultured cells suggest that insulin might activate endothelial nitric oxide synthase (eNOS) by an atypical, calcium-independent mechanism. This study investigates the mechanism of insulin-stimulated endothelial NO production in intact aortic wall.

Parallel fiber plasticity.

Cerebellar long-term depression (LTD) is classically observed when climbing fibers, originating from the inferior olive, and parallel fibers, axons of granule cells, are activated repetitively and synchronously. On the basis that the climbing fiber signals errors in motor performance, LTD provides a mechanism of learning whereby inappropriate motor signals, relayed to the cerebellar cortex by parallel fibers, are selectively weakened through their repeated, close temporal association with climbing fiber activity. LTD therefore provides a cellular substrate for error-driven motor learning in the cerebellar cortex.

Nitric oxide is required for the induction and heterosynaptic spread of long-term potentiation in rat cerebellar slices.

1. In the cerebellar cortex, brief, 8 Hz activation of parallel fibres (PFs) induces a cyclic adenosine 3'5'-monophosphate (cAMP) and protein kinase A (PKA)-dependent form of long-term potentiation between PFs and Purkinje cells. 2.

Intercellular action of nitric oxide increases cGMP in cerebellar Purkinje cells.

cGMP is thought to play a role in cerebellar signalling yet its production within Purkinje cells has never been detected. In the present study, the hydrolysis of a fluorescent substrate analogue, 2'-O-anthranyloyl cyclic GMP, by type 5 phosphodiesterase was monitored within Purkinje cells in slices and in culture. Nitric oxide, either endogenously released from adjacent neurons or pharmacologically applied, accelerated the rate of hydrolysis in a manner that was dependent on soluble guanylyl cyclase, demonstrating that nitric oxide triggers cyclic GMP production in Purkinje cells, which in turn activates type 5 phosphodiesterase.

Roles for nitric oxide and arachidonic acid in the induction of heterosynaptic cerebellar LTD.

In cerebellar slices conjunctive pairing of parallel fibre (PF) stimulation with depolarization of Purkinje cells (PCs) induces a long-term depression (LTD) of PF synaptic transmission that spreads to unpaired PF inputs to the same cell. Inhibitors of NO synthase (7-nitro-indazole), soluble guanylate cyclase (ODQ) and PKG (KT5823) all prevented depression at each of two independent PF pathways to a single PC. Inhibition of NOS also unmasked a platelet activating factor (PAF)-mediated synaptic potentiation of possible presynaptic origin.

Receptors, second messengers and protein kinases required for heterosynaptic cerebellar long-term depression.

Raising the frequency and intensity of stimulation to one of two sets of parallel fibre synaptic inputs to cerebellar Purkinje cells results in a localised calcium influx and a long-term depression (LTD) of parallel fibre-Purkinje cell responses. Although the calcium influx remains spatially constrained, depression spreads heterosynaptically to distant sites. Inhibition of the synthetic enzyme for cGMP, guanylate cyclase, did not significantly affect the overall level of calcium-dependent synaptic depression observed at the site of raised stimulation (test site), but it entirely prevented synaptic depression at the distant (control) site.

An evaluation of the synapse specificity of long-term depression induced in rat cerebellar slices.

Whole-cell excitatory postsynaptic currents (EPSCs) were recorded from single Purkinje cells (PCs) in rat cerebellar slices in response to alternate activation of two separate sets of parallel fibres (PF1 and PF2). Pairing the stimulation of one input (PF1) with PC depolarisation at 1 Hz for 5 min produced varied effects, including a long-term depression (LTD) of subsequent responses, a medium-term potentiation, or no change relative to baseline levels (n = 14). In all but two cases PF2 responses mirrored those in PF1, in both direction and magnitude even though this second pathway was not specifically activated during pairing.

Peptide fragments of beta-amyloid precursor protein: effects on parallel fiber-Purkinje cell synaptic transmission in rat cerebellum.

The effects of peptide fragments of the beta-amyloid precursor protein (betaAPP) on parallel fiber (PF)-Purkinje cell synaptic transmission in the rat cerebellum were examined. Transient inward currents associated with calcium influx were induced by localized applications of the 105-amino acid carboxy-terminal fragment (CT105) of betaAPP to discrete dendritic regions of intact Purkinje cells. betaAPP and the amyloid beta (Abeta) peptide fragments Abeta1-16, Abeta25-35, and Abeta1-42 had little or no effect.

Light dose and time dependency of photodynamic cell membrane damage.

We have investigated the light dose and time dependency of photodynamic cell membrane damage using electrophysiological methods. This study controls the level of cell membrane damage by precisely administration of the light dose. The photosensitizer used was 5',5"-bis(aminomethyl)-2,2':5',2"-terthiophene dihydrochloride (BAT).

Inhibition of cGMP breakdown promotes the induction of cerebellar long-term depression.

The effects of the nonspecific cyclic nucleotide inhibitors 1-methyl-3-isobutylxanthine (IBMX) and dipyridamole, and the cGMP-specific phosphodiesterase inhibitor Zaprinast were studied on parallel fiber-Purkinje cell synaptic responses in rat cerebellar slices. Bath application of all three compounds, at concentrations shown to inhibit cGMP breakdown, led to stable and robust long-term depression of PF responses. Injections of dipyridamole directly into the Purkinje cell dendrites were similarly effective as bath applications, confirming a postsynaptic site of action.