Yoram Ben-Shaul

Unsupervised spike detection and sorting with wavelets and superparamagnetic clustering

This study introduces a new method for detecting and sorting spikes from multiunit recordings. The method combines the wave let transform, which localizes distinctive spike features, with super paramagnetic clustering, which allows automatic classification of the data without assumptions such as low variance or gaussian distributions. Moreover, an improved method for setting amplitude thresholds for spike detection is proposed. We describe several criteria for implementation that render the algorithm unsupervised and fast. The algorithm is compared to other conventional methods using several simulated data sets whose characteristics closely resemble those of in vivo recordings. For these data sets, we found that the proposed algorithm outperformed conventional methods.

In-vivo Vomeronasal Stimulation Reveals Sensory Encoding of Conspecific and Allospecific Cues by the Mouse Accessory Olfactory Bulb

The rodent vomeronasal system plays a critical role in mediating pheromone-evoked social and sexual behaviors. Recent studies of the anatomical and molecular architecture of the vomeronasal organ (VNO) and of its synaptic target, the accessory olfactory bulb (AOB), have suggested that unique features underlie vomeronasal sensory processing. However, the neuronal representation of pheromonal information leading to specific behavioral and endocrine responses has remained largely unexplored due to the experimental difficulty of precise stimulus delivery to the VNO. To determine the basic rules of information processing in the vomeronasal system, we developed a unique preparation that allows controlled and repeated stimulus delivery to the VNO and combined this approach with multisite recordings of neuronal activity in the AOB. We found that urine, a well-characterized pheromone source in mammals, as well as saliva, activates AOB neurons in a manner that reliably encodes the donor animal’s sexual and genetic status. We also identified a significant fraction of AOB neurons that respond robustly and selectively to predator cues, suggesting an expanded role for the vomeronasal system in both conspecific and interspecific recognition. Further analysis reveals that mixed stimuli from distinct sources evoke synergistic responses in AOB neurons, thereby supporting the notion of integrative processing of chemosensory information.

Sex-specific processing of social cues in the medial amygdala

Animal–animal recognition within, and across species, is essential for predator avoidance and social interactions. Despite its essential role in orchestrating responses to animal cues, basic principles of information processing by the vomeronasal system are still unknown. The medial amygdala (MeA) occupies a central position in the vomeronasal pathway, upstream of hypothalamic centers dedicated to defensive and social responses. We have characterized sensory responses in the mouse MeA and uncovered emergent properties that shed new light onto the transformation of vomeronasal information into sex- and species-specific responses. In particular, we show that the MeA displays a degree of stimulus selectivity and a striking sexually dimorphic sensory representation that are not observed in the upstream relay of the accessory olfactory bulb (AOB). Furthermore, our results demonstrate that the development of sexually dimorphic circuits in the MeA requires steroid signaling near the time of puberty to organize the functional representation of sensory stimuli. DOI: http://dx.doi.org/10.7554/eLife.02743.001

Chronic cholinergic imbalances promote brain diffusion and transport abnormalities

Cholinergic imbalances occur after traumatic effects and in the initial stages of neurodegenerative diseases, but their long‐lasting effects remained largely unexplained. To address this, we used TgS transgenic mice constitutively overexpressing synaptic acetylcholinesterase (AChE‐S) and presenting a complex phenotype of progressive neuro‐deterioration. T1‐ and T2‐weighted magnetic resonance (MR) brain images appeared similar. However, diffusion‐weighted MRI showed decreased baseline water apparent diffusion coefficient in the brains of TgS animals. Furthermore, contrast‐enhanced MRI after gadolinium diethylenetriamine‐pentaacetic acid (Gd‐DTPA) injection demonstrated slower recovery of normal signals in the TgS brains than with controls. Perfusion MR imaging and difference T1 maps calculated from pre‐ postcontrast T1‐weighted MR images indicated accumulation of more Gd‐DTPA molecules in the TgS brains than in the parent strain, reflecting impaired blood‐brain barrier (BBB) functioning in these transgenic mice. To explore the molecular mechanism(s) underlying these global phenotypes, we performed microarray analysis in the stress‐controlling prefrontal cortex of TgS vs. strain‐matched wild‐type animals. Profound overexpression of numerous ion channels, transporters, and adhesion genes was confirmed by real time RT‐PCR tests. Immunohistochemical and immuno‐blot analyses revealed corresponding increases in the level and cellular distributions of the chloride channel CLCN3 and the water channel AQP4, both of which contribute to BBB maintenance. Our study attributes to balanced cholinergic neurotransmission, a central role in the brains maintenance of water diffusion and ion transport, and indicates that chronic impairments in this maintenance facilitate neurodeterioration through interference with BBB function. Meshorer, E., Biton, I. E., Ben‐Shaul, Y., Ben‐Ari, S., Assaf, Y., Soreq, H., Cohen, Y. Chronic cholinergic imbalances promote brain diffusion and transport abnormalities. FASEB J. 19, 910–922 (2005)

Trial to trial variability in either stimulus or action causes apparent correlation and synchrony in neuronal activity

In this report we show that the observed inter-neuronal correlation reflects a superposition of correlations associated with the intrinsic correlation between neurons, and correlations associated with variability in the stimuli presented to, or the actions performed by, the subject. We argue that the effects of either stimulus or action variability on the observed correlation, though generally ignored, can be substantial. Specifically, we demonstrate how observed correlations are effected by trial to trial variability in either stimulus or action. In addition, assuming that all relevant stimuli and actions are known, we outline a method for eliminating their effects on the observed correlation. It is also shown that tuning of correlations to a stimulus or an action might be a direct consequence of variability in that stimulus or action, even in the absence of any modulation of direct inter-neuronal interaction. The effects of stimulus and action variability should therefore be carefully considered when designing and interpreting experiments involving multi-neuronal recordings.

A compact representation of drawing movements with sequences of parabolic primitives.

Some studies suggest that complex arm movements in humans and monkeys may optimize several objective functions, while others claim that arm movements satisfy geometric constraints and are composed of elementary components. However, the ability to unify different constraints has remained an open question. The criterion for a maximally smooth (minimizing jerk) motion is satisfied for parabolic trajectories having constant equi-affine speed, which thus comply with the geometric constraint known as the two-thirds power law. Here we empirically test the hypothesis that parabolic segments provide a compact representation of spontaneous drawing movements. Monkey scribblings performed during a period of practice were recorded. Practiced hand paths could be approximated well by relatively long parabolic segments. Following practice, the orientations and spatial locations of the fitted parabolic segments could be drawn from only 2–4 clusters, and there was less discrepancy between the fitted parabolic segments and the executed paths. This enabled us to show that well-practiced spontaneous scribbling movements can be represented as sequences (“words”) of a small number of elementary parabolic primitives (“letters”). A movement primitive can be defined as a movement entity that cannot be intentionally stopped before its completion. We found that in a well-trained monkey a movement was usually decelerated after receiving a reward, but it stopped only after the completion of a sequence composed of several parabolic segments. Piece-wise parabolic segments can be generated by applying affine geometric transformations to a single parabolic template. Thus, complex movements might be constructed by applying sequences of suitable geometric transformations to a few templates. Our findings therefore suggest that the motor system aims at achieving more parsimonious internal representations through practice, that parabolas serve as geometric primitives and that non-Euclidean variables are employed in internal movement representations (due to the special role of parabolas in equi-affine geometry).

Adaptive acetylcholinesterase splicing patterns attenuate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

Balanced dopaminergic cholinergic interactions are crucial for proper basal ganglia function. This is dramatically demonstrated by the worsening of Parkinsons disease symptoms following acetylcholinesterase (AChE) inhibition. Typically, in the brain, the synapse‐anchored synaptic AChE (AChE‐S) variant is prevalent whereas the soluble readthrough AChE (AChE‐R) variant is induced in response to cholinesterase inhibition or stress. Because of the known functional differences between these variants and the fact that AChE‐R expression is triggered by various stimuli that themselves are often associated with Parkinsons disease risk, we hypothesized that the splice shift to AChE‐R plays a functional role in Parkinsonian progression. After establishing that Paraoxon‐induced AChE inhibition indeed aggravates experimental Parkinsonism triggered by the neurotoxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) in mice, we tested the roles of individual AChE variants by exposing transgenic mice overexpressing either the AChE‐S or AChE‐R variant to MPTP. Differential reductions of tyrosine hydroxylase levels in the striatum and substantia nigra indicated that transgenic AChE‐R expression confers resistance as compared with the parent FVB/N strain. In contrast, AChE‐S overexpression accelerated the MPTP‐induced damage. Survival, behavioral measures and plasma corticosterone levels were also compatible with the extent of the dopaminergic damage. Our findings highlight the functional differences between individual AChE variants and indicate that a naturally occurring stress or AChE inhibitor‐induced splicing shift can act to minimize dopaminergic cholinergic imbalances. We propose that inherited or acquired alternative splicing deficits could accelerate Parkinsonism and that, correspondingly, adaptive alternative splicing events may attenuate disease progression.

Modulated splicing‐associated gene expression in P19 cells expressing distinct acetylcholinesterase splice variants

Alternative splicing configurations and acetylcholinesterase (AChE) gene expression are both modified in neurons under stress. However, it is unclear if these phenomena are functionally interrelated. Using a home‐made spotted microarray focused on splicing‐associated transcripts, we tested the effects of excess 3′ splice variants of human AChE on splicing‐related gene expression in semi‐differentiated neuronal P19 cells. Of the tested transcripts, 17.3% and 20.2% showed modified expression levels (log2 of the ratio < − 0.3 or > 0.3) in transfected P19 cells overexpressing the stress‐inducible AChE‐R variant or the synaptic AChE‐S protein, respectively. Multiple transcripts encoding serine‐arginine rich (SR) and SR‐related splicing regulators were suppressed in cells expressing either of these variants, whereas the gene groups including splicing‐related helicases and transcripts involved in apoptosis displayed variant‐specific changes. Our findings are compatible with the assumption that both neuronal overexpression and alternative splicing of pre‐AChE mRNA may be causally involved in initiating global changes in neuronal alternative splicing, causing subsequent modifications in the expression patterns of numerous target genes.

Extracellular pH Regulates Excitability of Vomeronasal Sensory Neurons

The mouse vomeronasal organ (VNO) plays a critical role in semiochemical detection and social communication. Vomeronasal stimuli are typically secreted in various body fluids. Following direct contact with urine deposits or other secretions, a peristaltic vascular pump mediates fluid entry into the recipients VNO. Therefore, while vomeronasal sensory neurons (VSNs) sample various stimulatory semiochemicals dissolved in the intraluminal mucus, they might also be affected by the general physicochemical properties of the “solvent.” Here, we report cycle stage-correlated variations in urinary pH among female mice. Estrus-specific pH decline is observed exclusively in urine samples from sexually experienced females. Moreover, patch-clamp recordings in acute VNO slices reveal that mouse VSNs reliably detect extracellular acidosis. Acid-evoked responses share the biophysical and pharmacological hallmarks of the hyperpolarization-activated current Ih. Mechanistically, VSN acid sensitivity depends on a pH-induced shift in the voltage-dependence of Ih activation that causes the opening of HCN channels at rest, thereby increasing VSN excitability. Together, our results identify extracellular acidification as a potent activator of vomeronasal Ih and suggest HCN channel-dependent vomeronasal gain control of social chemosignaling. Our data thus reveal a potential mechanistic basis for stimulus pH detection in rodent chemosensory communication.

Meta-analysis of genetic and environmental Parkinson's disease models reveals a common role of mitochondrial protection pathways.

Both genetic and environmental factors trigger risks of and protection from Parkinsons disease, the second most common neurodegenerative syndrome, but possible inter-relationships between these risk and protection processes were not yet explored. By examining gene expression changes in the brains of mice under multiple treatments that increase or attenuate PD symptoms we detected underlying disease and protection-associated genes and pathways. In search for potential links between these different genes and pathways, we conducted meta-analysis on 131 brain region transcriptomes from mice over-expressing native or mutated α-synuclein (SNCA) with or without the protective HSP70 chaperone, or exposed to the dopaminergic neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), with or without the protective acetylcholinesterase (AChE-R) variant. All these models showed shared risk-inducible and protection-suppressible transcript modifications. Self-organized map (SOM) classification revealed risk- and protection-associated alterations in nuclear and mitochondrial metal ion-regulated transcripts, respectively; Gene Ontology based analysis validated these pathways. To complement this approach, and identify potential outcome damages, we further searched for shared functional enrichments in the lists of genes detected in young SNCA mutant or in old SNCA mutants and MPTP-exposed mice. This post-hoc functional analysis identified early-onset changes in Parkinsonian, immune and alternative splicing pathways which shifted into late-onset or exposure-associated NFkB-mediated neuro-inflammation. Our study suggests metal ions-mediated cross-talk between nuclear and mitochondrial pathways by both environmental and genetic risk and protective factors involved in Parkinsons disease, which eventually culminates in neuro-inflammation. Together, these findings offer new insights and novel targets for therapeutic interference with the gene-environment interactions underlying sporadic PD.