Scott F. Owen

Oxytocin enhances hippocampal spike transmission by modulating fast-spiking interneurons

Neuromodulatory control by oxytocin is essential to a wide range of social, parental and stress-related behaviours. Autism spectrum disorders (ASD) are associated with deficiencies in oxytocin levels and with genetic alterations of the oxytocin receptor (OXTR). Thirty years ago, Mühlethaler et al. found that oxytocin increases the firing of inhibitory hippocampal neurons, but it remains unclear how elevated inhibition could account for the ability of oxytocin to improve information processing in the brain. Here we describe in mammalian hippocampus a simple yet powerful mechanism by which oxytocin enhances cortical information transfer while simultaneously lowering background activity, thus greatly improving the signal-to-noise ratio. Increased fast-spiking interneuron activity not only suppresses spontaneous pyramidal cell firing, but also enhances the fidelity of spike transmission and sharpens spike timing. Use-dependent depression at the fast-spiking interneuron–pyramidal cell synapse is both necessary and sufficient for the enhanced spike throughput. We show the generality of this novel circuit mechanism by activation of fast-spiking interneurons with cholecystokinin or channelrhodopsin-2. This provides insight into how a diffusely delivered neuromodulator can improve the performance of neural circuitry that requires synapse specificity and millisecond precision.

CaV1 and CaV2 Channels Engage Distinct Modes of Ca2+ Signaling to Control CREB-Dependent Gene Expression

Activity-dependent gene expression triggered by Ca(2+) entry into neurons is critical for learning and memory, but whether specific sources of Ca(2+) act distinctly or merely supply Ca(2+) to a common pool remains uncertain. Here, we report that both signaling modes coexist and pertain to Ca(V)1 and Ca(V)2 channels, respectively, coupling membrane depolarization to CREB phosphorylation and gene expression. Ca(V)1 channels are advantaged in their voltage-dependent gating and use nanodomain Ca(2+) to drive local CaMKII aggregation and trigger communication with the nucleus. In contrast, Ca(V)2 channels must elevate [Ca(2+)](i) microns away and promote CaMKII aggregation at Ca(V)1 channels. Consequently, Ca(V)2 channels are ~10-fold less effective in signaling to the nucleus than are Ca(V)1 channels for the same bulk [Ca(2+)](i) increase. Furthermore, Ca(V)2-mediated Ca(2+) rises are preferentially curbed by uptake into the endoplasmic reticulum and mitochondria. This source-biased buffering limits the spatial spread of Ca(2+), further attenuating Ca(V)2-mediated gene expression.

Mouse model of Timothy syndrome recapitulates triad of autistic traits

Autism and autism spectrum disorder (ASD) typically arise from a mixture of environmental influences and multiple genetic alterations. In some rare cases, such as Timothy syndrome (TS), a specific mutation in a single gene can be sufficient to generate autism or ASD in most patients, potentially offering insights into the etiology of autism in general. Both variants of TS (the milder TS1 and the more severe TS2) arise from missense mutations in alternatively spliced exons that cause the same G406R replacement in the CaV1.2 L-type calcium channel. We generated a TS2-like mouse but found that heterozygous (and homozygous) animals were not viable. However, heterozygous TS2 mice that were allowed to keep an inverted neomycin cassette (TS2-neo) survived through adulthood. We attribute the survival to lowering of expression of the G406R L-type channel via transcriptional interference, blunting deleterious effects of mutant L-type channel overactivity, and addressed potential effects of altered gene dosage by studying CaV1.2 knockout heterozygotes. Here we present a thorough behavioral phenotyping of the TS2-neo mouse, capitalizing on this unique opportunity to use the TS mutation to model ASD in mice. Along with normal general health, activity, and anxiety level, TS2-neo mice showed markedly restricted, repetitive, and perseverative behavior, altered social behavior, altered ultrasonic vocalization, and enhanced tone-cued and contextual memory following fear conditioning. Our results suggest that when TS mutant channels are expressed at levels low enough to avoid fatality, they are sufficient to cause multiple, distinct behavioral abnormalities, in line with the core aspects of ASD.

Optogenetic identification of striatal projection neuron subtypes during in vivo recordings

Optogenetics has revolutionized neuroscience over the past several years by allowing researchers to modulate the activity of specific cell types, both in vitro and in vivo. One promising application of optogenetics is to use channelrhodopsin-2 (ChR2) mediated spiking to identify distinct cell types in electrophysiological recordings from awake behaving animals. In this paper, we apply this approach to in vivo recordings of the two major projection cell types in the striatum: the direct- and indirect-pathway medium spiny neurons. We expressed ChR2 in the neurons of the direct or indirect pathways using a cre-dependent viral strategy and performed electrical recordings together with optical stimulation using an implanted microwire array that included an integrated optical fiber. Despite the apparent simplicity of identifying ChR2-expressing neurons as those that respond to light, we encountered multiple potential confounds when applying this approach. Here, we describe and address these confounds and provide a Matlab tool so that others can implement our analysis methods. This article is part of a Special Issue entitled Optogenetics (7th BRES).

A Genetically Encoded Fluorescent Sensor Enables Rapid and Specific Detection of Dopamine in Flies, Fish, and Mice

Dopamine (DA) is a central monoamine neurotransmitter involved in many physiological and pathological processes. A longstanding yet largely unmet goal is to measure DA changes reliably and specifically with high spatiotemporal precision, particularly in animals executing complex behaviors. Here, we report the development of genetically encoded GPCR-activation-based-DA (GRABDA) sensors that enable these measurements. In response to extracellular DA, GRABDA sensors exhibit large fluorescence increases (ΔF/F0 ∼90%) with subcellular resolution, subsecond kinetics, nanomolar to submicromolar affinities, and excellent molecular specificity. GRABDA sensors can resolve a single-electrical-stimulus-evoked DA release in mouse brain slices and detect endogenous DA release in living flies, fish, and mice. In freely behaving mice, GRABDA sensors readily report optogenetically elicited nigrostriatal DA release and depict dynamic mesoaccumbens DA signaling during Pavlovian conditioning or during sexual behaviors. Thus, GRABDA sensors enable spatiotemporally precise measurements of DA dynamics in a variety of model organisms while exhibiting complex behaviors.

An open-source control system for in vivo fluorescence measurements from deep-brain structures

BACKGROUND Intracranial photometry through chronically implanted optical fibers is a widely adopted technique for measuring signals from fluorescent probes in deep-brain structures. The recent proliferation of bright, photo-stable, and specific genetically encoded fluorescent reporters for calcium and for other neuromodulators has greatly increased the utility and popularity of this technique. NEW METHOD Here we describe an open-source, cost-effective, microcontroller-based solution for controlling optical components in an intracranial photometry system and processing the resulting signal. RESULTS We show proof-of-principle that this system supports high quality intracranial photometry recordings from dorsal striatum in freely moving mice. A single system supports simultaneous fluorescence measurements in two independent color channels, but multiple systems can be integrated together if additional fluorescence channels are required. This system is designed to work in combination with either commercially available or custom-built optical components. Parts can be purchased for less than one tenth the cost of commercially available alternatives and complete assembly takes less than one day for an inexperienced user. COMPARISON WITH EXISTING METHOD(S) Currently available hardware draws on a variety of commercial, custom-built, or hybrid elements for both optical and electronic components. Many of these hardware systems are either specialized and inflexible, or over-engineered and expensive. CONCLUSIONS This open-source system increases experimental flexibility while reducing cost relative to current commercially available components. All software and firmware are open-source and customizable, affording a degree of experimental flexibility that is not available in current commercial systems.

Excitation-transcription coupling mechanisms engaged by specific calcium channel types

mation emerge and disappear at specific time-points. These dynamics are coupled between regions, and appear to reflect the generation and propagation of emotional information from BLA to GC, and from there to CeA. Careful examination of simultaneously recorded neurons demonstrates that taste responses are best thought of as a coherent, unified, multi-regional attractor sequence—that is, taste-specific, non-sparse, informationally rich series of quasi-stable states (with minimal between-state switching delays) that progress inexorably toward the production of emotional behavior, as the animal decides whether to reject or consume the substance in the mouth. The process is remarkably reliable across trials, but the dynamics unfold at different speeds from trial to trial, such that the full richness of the data cannot be seen when averaged across sessions.