Biology subjects

Martins, G. J.

Publications and source records attributed to Martins, G. J..

3 recordsLinked to original sources

bioRxiv2024

Dynamic representation of appetitive and aversive stimuli in nucleus accumbens shell D1- and D2-medium spiny neurons

The nucleus accumbens (NAc) is a key brain region for motivated behaviors, yet how distinct neuronal populations encode appetitive or aversive stimuli remains undetermined. Using microendoscopic calcium imaging, we tracked NAc shell D1- or D2-medium spiny neurons (MSNs) activity during exposure to stimuli of opposing valence and associative learning. Despite drift in individual neurons coding, both D1- and D2-population activity was sufficient to discriminate opposing valence unconditioned stimuli, but not predictive cues. Notably, D1- and D2-MSNs were similarly co-recruited during appetitive and aversive conditioning, supporting a concurrent role in associative learning. Conversely, when contingencies changed, there was an asymmetric response in the NAc, with more pronounced changes in the activity of D2-MSNs. Optogenetic manipulation of D2-MSNs provided causal evidence of the necessity of this population in the extinction of aversive associations. Our results reveal how NAc shell neurons encode valence, Pavlovian associations and their extinction, and unveil new mechanisms underlying motivated behaviors.

neuroscience↗

bioRxiv2023

RNA- and ATAC-sequencing Reveals a Unique CD83+ Microglial Population Focally Depleted in Parkinson's Disease

All brain areas affected in Parkinsons disease (PD) show an abundance of microglia with an activated morphology together with increased expression of pro-inflammatory cytokines, suggesting that neuroinflammation may contribute to the neurodegenerative process in this common and incurable disorder. We applied a single nucleus RNA- and ATAC-sequencing approach using the 10x Genomics Chromium platform to postmortem PD samples to investigate microglial heterogeneity in PD. We created a multiomic dataset using substantia nigra (SN) tissues from 19 PD donors and 14 non-PD controls (NPCs), as well as three other brain regions from the PD donors which are differentially affected in this disease: the ventral tegmental area (VTA), substantia inominata (SI), and hypothalamus (HypoTs). We identified thirteen microglial subpopulations within these tissues as well as a perivascular macrophage and a monocyte population, of which we characterized the transcriptional and chromatin repertoires. Using this data, we investigated whether these microglial subpopulations have any association with PD and whether they have regional specificity. We uncovered several changes in microglial subpopulations in PD, which appear to parallel the magnitude of neurodegeneration across these four selected brain regions. Specifically, we identified that inflammatory microglia in PD are more prevalent in the SN and differentially express PD-associated markers. Our analysis revealed the depletion of a CD83 and HIF1A-expressing microglial subpopulation, specifically in the SN in PD, that has a unique chromatin signature compared to other microglial subpopulations. Interestingly, this microglial subpopulation has regional specificity to the brainstem in non-disease tissues. Furthermore, it is highly enriched for transcripts of proteins involved in antigen presentation and heat-shock proteins, and its depletion in the PD SN may have implications for neuronal vulnerability in disease.

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↗