Biology subjects

Tiroshi, L.

Publications and source records attributed to Tiroshi, L..

6 recordsLinked to original sources

bioRxiv2026

A red fluorescent sensor for intensity-and lifetime imaging of cAMP in living cells

cAMP (cyclic adenosine monophosphate) is a crucial intracellular messenger involved in neuromodulation and plasticity, but more information on its spatiotemporal regulation is desirable. Here we constructed a red fluorescent indicator based on a truncated cAMP binding site derived from a regulatory PKA subunit of protozoan origin. It contains a single binding site for cAMP highly specific for cAMP over cGMP. chILI (cAMP highly-responsive Intensity and Lifetime Indicator) can be imaged as an intensity-based probe, but alternatively also offers options for fluorescence lifetime imaging. When expressed in the mouse brain using AAV-vector mediated gene transfer, it reports spontaneous and evoked cAMP transients from CA1 neurons in the hippocampus of awake mice. chILI will add valuable options for monitoring cAMP in vitro and in vivo.

neuroscience↗

bioRxiv2022

Striatal neurons are recruited dynamically into collective representations of self-initiated and learned actions in freely-moving mice

Striatal spiny projection neurons are hyperpolarized-at-rest (HaR) and are driven to spike threshold by a small number of powerful inputs - an input-output configuration that is detrimental to response reliability. Because the striatum is important for habitual behaviors and goal-directed learning, we conducted microendoscopic imaging in freely-moving mice that express a genetically-encoded calcium indicator sparsely in striatal HaR neurons to compare their response reliability during self-initiated movements and operant conditioning. The sparse expression was critical for longitudinal studies of response reliability, and for studying correlations among HaR neurons while minimizing spurious correlations arising from contamination by the background neuropil signal. We found that HaR neurons are recruited dynamically into action representation through a moment-by-moment formation of distinct cell assemblies. While individual neurons respond with little reliability, the population response remained reliable. Moreover, we found evidence for the formation of correlated cell assemblies during conditioned (but not innate) behaviors, but this correlation was independent of the distance between neurons.

neuroscience↗

bioRxiv2022

Mechanism of dopamine traveling waves in the striatum: theory and experiment

Striatal dopamine (DA) encodes reward, with recent work showing that DA release occurs in spatiotemporal waves. However, the mechanism of DA waves is unknown. Here we report that the striatal cholinergic neuropil also exhibits wave-like activity, and that the spatial scale of striatal DA release is extended by nicotinic receptors. Based on these findings we hypothesized that the local reciprocal interaction between cholinergic interneurons (CIN) and DA axons suffices to drive endogenous traveling waves. We show that the morphological and physiological properties of the CIN-DA interaction can be modeled as a reaction-diffusion system that gives rise to traveling waves. Analytically-tractable versions of the model show that the structure and the nature of propagation of CIN and DA traveling waves depend on their coupling, and that traveling waves can give rise to empirically observed correlations between these signals. Our model provides a biophysical mechanism for wave formation and predicts that the observed DA and CIN waves are strongly coupled phenomena.

neuroscience↗

bioRxiv2021

Non-uniform distribution of dendritic nonlinearities differentially engages thalamostriatal and corticostriatal inputs onto cholinergic interneurons

The tonic activity of striatal cholinergic interneurons (CINs) is modified differentially by their afferent inputs. Although their unitary synaptic currents are identical, in most CINs cortical inputs onto distal dendrites only weakly entrain them, whereas proximal thalamic inputs trigger abrupt pauses in discharge in response to salient external stimuli. To test whether the dendritic expression of the active conductances that drive autonomous discharge contribute to the CINs capacity to dissociate cortical from thalamic inputs, we used an optogenetics-based method to quantify dendritic excitability. We found that the persistent sodium (NaP) current gave rise to dendritic boosting, and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) current gave rise to a subhertz membrane resonance. This resonance may underlie our novel finding of an association between CIN pauses and internally-generated slow wave events in sleeping non-human primates. Moreover, our method indicated that dendritic NaP and HCN currents were preferentially expressed in proximal dendrites. We validated the non-uniform distribution of NaP currents pharmacologically; with two-photon imaging of dendritic back-propagating action potentials; and by demonstrating boosting of thalamic, but not cortical, inputs by NaP currents. Thus, the localization of active dendritic conductances in CIN dendrites mirrors the spatial distribution of afferent terminals and may promote their differential responses to thalamic vs. cortical inputs.

neuroscience↗

bioRxiv2018

Wave-like activity patterns in the neuropil of striatal cholinergic interneurons in freely moving mice represent their collective spiking dynamics

Cholinergic interneurons (CINs) are believed to form synchronous cell assemblies that modulate the striatal microcircuitry and possibly orchestrate local dopamine release. We expressed GCaMP6s, a genetically encoded calcium indicator (GECIs), selectively in CINs, and used microendoscopes to visualize the putative CIN assemblies in the dorsal striatum of freely moving mice. The GECI fluorescence signal from the dorsal striatum was composed of signals from individual CIN somata that were engulfed by a widespread fluorescent neuropil. Bouts of synchronous activation of the cholinergic neuropil revealed traveling-wave-like patterns of activity that preceded the signal from individual somata. To investigate the nature of the neuropil signal and why it precedes the somatic signal, we target-patched GECI-expressing CINs in acute striatal slices in conjunction with multiphoton imaging or wide-field imaging that emulates the microendoscopes specifications. The ability to detect fluorescent transients associated with individual action potential was constrained by the long decay constant of GECIs (relative to common inorganic dyes) to slowly firing (< 2 spikes/s) CINs. The microendoscopes resolving power and sampling rate further diminished this ability. Additionally, we found that only back-propagating action potentials but not synchronous optogenetic activation of thalamic inputs elicited observable calcium transients in CIN dendrites. Our data suggest that only bursts of CIN activity (but not their tonic firing) are visible using endoscopic imaging, and that the spatiotemporal neuropil patterns are a physiological measure of the collective recurrent CIN network spiking activity.\n\nSignificance StatementCholinergic interneurons (CINs) are key modulators of the striatal microcircuitry that are necessary for assigning action value and behavioral flexibility. We present a first endoscopic imaging study of multiple molecularly identified CINs in freely moving mice. We reveal the presence of traveling-wave-like activity in the CIN neuropil. We then use ex vivo electrophysiological and imaging techniques to show that the neuropil signal is the integrated fluorescence arising from the axo-dendritic arbors of CINs dispersed throughout the striatum. We conclude that the neuropil signal acts as a mean-field readout of the striatal CIN network activity.

neuroscience↗

bioRxiv2018

Population dynamics and entrainment of basal ganglia pacemakers are shaped by their dendritic arbors

The theory of phase oscillators is an essential tool for understanding population dynamics of pacemaking neurons. GABAergic pacemakers in the substantia nigra pars reticulata (SNr), a main basal ganglia (BG) output nucleus, receive inputs from the direct and indirect pathways at distal and proximal regions of their dendritic arbors, respectively. We combine theory, optogenetic stimulation and electrophysiological experiments in acute brain slices to ask how dendritic properties impact the propensity of the various inputs, arriving at different locations along the dendrite, to recruit or entrain SNr pacemakers.\n\nBy combining cable theory with sinusoidally-modulated optogenetic activation of either proximal somatodendritic regions or the entire dendritic arbor of SNr neurons, we construct an analytical model that accurately fits the empirically measured somatic current response to inputs arising from illuminating various portions of the dendritic field. We show that the extent of the dendritic tree that is illuminated generates measurable and systematic differences in the pacemakers phase response curve (PRC), causing a shift in its peak. Finally we show that the divergent PRCs correctly predict differences in two major features of the collective dynamics of SNr neurons: the fidelity of population responses to sudden step-like changes in inputs; and the phase latency at which SNr neurons are entrained by rhythmic stimulation, which can occur in the BG under both physiological and pathophysiological conditions.\n\nOur novel method generates measurable and physiologically meaningful spatial effects, and provides the first empirical demonstration of how the collective responses of SNr pacemakers are determined by the transmission properties of their dendrites. SNr dendrites may serve to delay distal striatal inputs so that they impinge on the spike initiation zone simultaneously with pallidal and subthalamic inputs in order to guarantee a fair competition between the influence of the monosynaptic direct- and polysynaptic indirect pathways.\n\nAuthor SummaryThe substantia nigra pars reticulata (SNr) is a main output nucleus of the basal ganglia (BG), where inputs from the competing direct and indirect pathways converge onto the same neurons. Interestingly, these inputs are differentially distributed with direct and indirect pathway projections arriving at distal and proximal regions of the dendritic arbor, respectively. We employ a novel method combining theory with electrophysiological experiments and optogenetics to study the distinct effects of inputs arriving at different locations along the dendrite.\n\nOur approach represents a useful compromise between complexity and reduction in modelling. Our work addresses the question of high fidelity encoding of inputs by networks of neurons in the new context of pacemaking neurons, which are driven to fire by their intrinsic dynamics rather than by a network state. We provide the first empirical demonstration that dendritic delays can introduce latencies in the responses of a population of neurons that are commensurate with synaptic delays, suggesting a new role for SNr dendrites with implications for BG function.

neuroscience↗