Biology subjects

Holtmaat, A.

Publications and source records attributed to Holtmaat, A..

9 recordsLinked to original sources

bioRxiv2025

A sensitive orange fluorescent calcium ion indicator for imaging neural activity

Genetically encoded calcium indicators (GECIs) are vital tools for fluorescence-based visualization of neuronal activity with high spatial and temporal resolution. However, current highest-performance GECIs are predominantly green or red fluorescent, limiting multiplexing options and efficient excitation with fixed-wavelength femtosecond lasers operating at 1030 nm. Here, we introduce OCaMP (also known as O-GECO2), an orange fluorescent GECI engineered from O-GECO1 through targeted substitutions to improve calcium affinity while retaining the favorable photophysical properties of mOrange2. OCaMP exhibits improved two-photon cross-section, responsiveness, photostability, and calcium affinity relative to O-GECO1. In cultured neurons, zebrafish, and mouse cortex, OCaMP outperforms the red GECIs jRCaMP1a and jRGECO1a in sensitivity, kinetics, and signal-to-noise ratio. These properties establish OCaMP as a robust tool for high-fidelity neural imaging optimized for 1030 nm excitation and a compromise-free option within the spectral gap between existing green and red GECIs.

neuroscience↗

bioRxiv2025

Neurogliaform cells mediate interhemispheric modulation of sensory-evoked activity in cortical pyramidal neurons

Integration of bilateral sensory inputs requires effective communication between brain hemispheres. This interhemispheric communication is essential for sensory perception and involves reciprocal connections between homotopic sensory areas. A key role in this process is attributed to interhemispheric inhibition which, owing to its long-lasting form, is posited to operate largely through neurogliaform cells (NGCs). However, direct evidence on the role of NGCs in interhemispheric inhibition is missing. Here we show that NGCs in the mouse barrel cortex (BC) are engaged by interhemispheric callosal projections to modulate pyramidal neuron (PN) activity and sensory perception. Using optogenetics, ex vivo whole-cell recordings, and in vivo calcium imaging, we found that layer 1 and layer 2/3 (L1-3) NGCs are strongly activated by the callosal and suppressed by the thalamocortical pathway, suggesting that NGCs encode ipsilateral rather than contralateral whisker stimuli. We also found that direct stimulation of L1-3 NGCs modulates whisker-evoked activity in L2/3 and L5b PNs, and increases the perceptual threshold in a whisker-deflection detection task. Furthermore, these effects were recapitulated by direct stimulation of callosal projections and deflection of the ipsilateral whiskers respectively, suggesting that the effect of the callosal pathway on sensory perception is mediated by NGCs. Our results not only prove that NGCs mediate interhemispheric inhibition, but also demonstrate their role in sensory perception via modulation of the main units involved in cortical input and output.

neuroscience↗

bioRxiv2024

Repetitive sensory stimulation potentiates and recruits sensory-evoked cortical population activity

Sensory experience and learning are thought to be associated with plasticity of neocortical circuits. Repetitive sensory stimulation can induce long-term potentiation (LTP) of cortical excitatory synapses in anesthetized mice; however, it is unclear if these phenomena are associated with sustained changes in activity during wakefulness. Here we used time-lapse, calcium imaging of layer (L) 2/3 neurons in the primary somatosensory cortex (S1), in awake male mice, to assess the effects of a bout of rhythmic whisker stimulation (RWS) at a frequency by which rodents sample objects. We found that RWS induced a 1h-increase in whisker-evoked L2/3 neuronal activity. This was not observed for whiskers functionally connected to distant cortical columns. We also found that RWS altered whether individual neurons encoded subsequent stimulus representation by either being recruited or suppressed. Vasoactive intestinal-peptide-expressing (VIP) interneurons, which promote plasticity through disinhibition of pyramidal neurons, were found to exclusively elevate activity during RWS. These findings indicate that cortical neurons representation of sensory input can be modulated over hours through repetitive sensory stimulation, which may be gated by activation of disinhibitory circuits. SIGNIFICANCE STATEMENTSensory experience and learning are thought to be associated with the plasticity of cortical synaptic circuits. Here, we tested how repeated sensory stimulation changes subsequent sensory-evoked responses, using the mouse somatosensory cortex as a model. This cortical area processes, among others, sensory information from the whiskers. We found that rhythmic whisker stimulation potentiated excitatory neuronal activity for an hour, and identified a disinhibitory interneuron-mediated mechanism that could gate this plasticity. This work increases our understanding of sensory learning and experience-dependent plasticity processes by demonstrating that cortical representations of sensory input are dynamic and are effectively modulated by repeated sensory stimulation.

neuroscience↗

bioRxiv2023

Higher-order thalamocortical projections selectively control excitability via NMDAR and mGluRI-mediated mechanisms.

The apical dendrites of layer (L) 2/3 pyramidal neurons in the mouse somatosensory cortex integrate synaptic input from long-range projections. Among those, inputs from the higher-order thalamic posteromedial nucleus may facilitate sensory-evoked cortical activity, but it remains elusive how this role emerges. Here we show using ex vivo dendritic recordings that these projections provide dense synaptic input to broad tufted neurons residing predominantly in L2 and cooperate with other inputs to produce NMDA spikes. They have the unique capacity to block two-pore domain potassium leak channels via group 1 metabotropic glutamate receptor (mGluRI) signaling, which increases excitability. Slender tufted L2/3 neurons and other long-range projections fail to invoke these mechanisms. In vivo imaging of calcium signals confirms the presence of mGluRI-dependent modulation of feedback-mediated spiking in L2. Our results imply that higher-order thalamocortical projections regulate neuronal excitability in a cell type and input-selective manner through fast NMDAR and mGluRI-dependent mechanisms.

neuroscience↗

bioRxiv2021

A brain atlas of synapse protein lifetime across the mouse lifespan.

Protein turnover is required for synapse maintenance and remodelling and may impact memory duration. We quantified the lifetime of postsynaptic protein PSD95 in individual excitatory synapses across the mouse brain and lifespan, generating the Protein Lifetime Synaptome Atlas. Excitatory synapses have a wide range of protein lifetimes that may extend from a few hours to several months, with distinct spatial distributions in dendrites, neuron types and brain regions. Short protein lifetime (SPL) synapses are enriched in developing animals and in regions controlling innate behaviors, whereas long protein lifetime (LPL) synapses accumulate during development, are enriched in the cortex and CA1 where memories are stored, and are preferentially preserved in old age. The protein lifetime synaptome architecture is disrupted in an autism model, with synapse protein lifetime increased throughout the brain. These findings add a further layer to synapse diversity in the brain and enrich prevailing concepts in behavior, development, ageing and brain repair.

neuroscience↗

bioRxiv2020

An increase in dendritic plateau potentials is associated with experience-dependent cortical map reorganization

The organization of sensory maps in the cerebral cortex depends on experience, which drives homeostatic and long-term synaptic plasticity of cortico-cortical circuits. In the mouse primary somatosensory cortex (S1) afferents from the higher-order, posterior medial thalamic nucleus (POm) gate synaptic plasticity in layer (L) 2/3 pyramidal neurons via disinhibition and the production of dendritic plateau potentials. Here we address whether these thalamocortically mediated responses play a role in whisker map plasticity in S1. We find that trimming all but two whiskers causes a partial fusion of the representations of the two spared whiskers, concomitantly with an increase in the occurrence of POm-driven, N-methyl-D-aspartate receptor (NMDAR)-dependent plateau potentials. Blocking the plateau potentials restores the archetypical organization of the sensory map. Our results reveal a novel mechanism for experience-dependent cortical map plasticity in which higher-order thalamocortically mediated plateau potentials facilitate the fusion of normally segregated cortical representations.

neuroscience↗

bioRxiv2019

Dynamic encoding of perceptual features in primary somatosensory cortex upon reversal learning

Neurons in primary sensory cortex encode a variety of stimulus features upon perceptual learning. However, it is unclear whether the acquired stimulus selectivity remains stable when the same input is perceived in a different context. Here, we monitored the activity of individual neurons in the mouse primary somatosensory cortex in a reward-based texture discrimination task. We tracked their stimulus selectivity before and after changing reward contingencies, which allowed us to identify various classes of neurons. We found neurons that stably represented a texture or the upcoming behavioral choice, but the majority was dynamic. Among those, a subpopulation of neurons regained selectivity contingent on stimulus-value. These value-sensitive neurons forecasted the onset of learning by displaying a distinct and transient increase in activity, depending on past behavioral experience. Thus, stimulus selectivity of excitatory neurons during perceptual learning is dynamic and largely relies on behavioral contingencies, even in primary sensory cortex.

neuroscience↗

bioRxiv2019

The mesoSPIM initiative: open-source light-sheet mesoscopes for imaging in cleared tissue

Over the course of the past decade, tissue clearing methods have reached a high level of sophistication with a wide variety of approaches now available1. To image large cleared samples, light-sheet microscopes have proven to be ideal due to their excellent optical sectioning capability in transparent tissue2. Such instruments have recently seen extensive technological and commercial development. However, despite this progress, the community is lacking instruments capable of exploring large samples with near-isotropic resolution within minutes. Here, we introduce the mesoscale selective plane-illumination microscopy (mesoSPIM) initiative, an open-hardware project that provides researchers with instructions and software to easily build and operate light-sheet microscopes for centimeter-sized cleared samples (http://www.mesospim.org).\n\nA wide range of commercial light-sheet microscopes have ...

neuroscience↗

bioRxiv2018

Higher-order thalamocortical inputs gate synaptic long-term potentiation via disinhibiton

Sensory experience and perceptual learning changes the receptive field properties of cortical pyramidal neurons, largely mediated by long-term potentiation (LTP) of synapses. The circuit mechanisms underlying cortical LTP remain unclear. In the mouse somatosensory cortex (S1), LTP can be elicited in layer (L) 2/3 pyramidal neurons by rhythmic whisker stimulation. We combined electrophysiology, optogenetics, and chemogenetics in thalamocortical slices to dissect the synaptic circuitry underlying this LTP. We found that projections from higher-order, posteriormedial thalamic complex (POm) to S1 are key to eliciting NMDAR-dependent LTP of intracortical synapses. Paired activation of intracortical and higher-order thalamocortical pathways increased vasoactive intestinal peptide (VIP) interneuron and decreased somatostatin (SST) interneuron activity, which was critical for inducing LTP. Our results reveal a novel circuit motif in which higher-order thalamic feedback gates plasticity of intracortical synapses in S1 via disinhibition. This motif may allow contextual feedback to shape synaptic circuits that process first-order sensory information.

neuroscience↗