Biology subjects

Grant, R. I.

Publications and source records attributed to Grant, R. I..

7 recordsLinked to original sources

bioRxiv2025

Cortical astrocytes flexibly encode reward contingencies and shape conditioned behavior

Learned associations between environmental cues and reward drive motivated behavior, yet how specific cell types support this process remains unclear. Using longitudinal two-photon calcium imaging, we tracked dorsal medial prefrontal cortical astrocytes throughout the acquisition, expression, and reversal of Pavlovian sucrose conditioning. As learning progressed, astrocytes exhibited time-locked, spatially coordinated calcium signals that differentiated correct behavioral action from mistakes, evolving from broad outcome encoding to selective representation of responses associated with the reward-conditioned stimulus. Omission testing revealed that prefrontal astrocytes preferentially respond to the cue-reward association, rather than the conditioned stimulus or reward alone. When reward contingencies were reversed, astrocytic activity rapidly adapted to track the new cue-reward association and encode updated and outdated motivated behavioral actions. Finally, astrocytic ablation attenuated motivated behavior during initial associative learning and prevented persistence of conditioned reward seeking when reward contingencies were updated or unpredictable. These findings reveal prefrontal astrocytes are functionally plastic elements that regulate reward-seeking behavior across associative learning. TeaserPrefrontal astrocytes flexibly encode the cue-reward associations that drive conditioned reward-seeking behavior.

neuroscience↗

bioRxiv2024

Corticostriatal ensemble dynamics across heroin self-administration to reinstatement

Corticostriatal projection neurons from prelimbic medial prefrontal cortex to the nucleus accumbens core critically regulate drug-seeking behaviors, yet the underlying encoding dynamics whereby these neurons contribute to drug seeking remain elusive. Here we use two-photon calcium imaging to visualize the activity of corticostriatal neurons in mice from the onset of heroin use to relapse. We find that the activity of these neurons is highly heterogeneous during heroin self-administration and seeking, with at least 8 distinct neuronal ensembles that display both excitatory and inhibitory encoding dynamics. These neuronal ensembles are particularly apparent during relapse, where excitatory responses are amplified compared to heroin self-administration. Moreover, we find that optogenetic inhibition of corticostriatal projection neurons attenuates heroin seeking regardless of the relapse trigger. Our results reveal the precise corticostriatal activity dynamics underlying drug-seeking behaviors and support a key role for this circuit in mediating relapse to drug seeking.

neuroscience↗

bioRxiv2024

A Model of Ethanol Self-Administration in Head-Fixed Mice

BackgroundSignificant advances in neurotechnology, such as the application of two-photon (2P) imaging of biosensors in vivo, have enabled unparalleled longitudinal and high-resolution access to neural circuits that coordinate behavior in rodents. Integration of these techniques would be groundbreaking for the study of alcohol use disorder (AUD). AUD is rooted in significant neural adaptations that could be functionally monitored and manipulated at the single-cell level across development of dependence in rodents. However, 2P imaging and related methodologies often require or are facilitated by head-fixation, and a lack of head-fixed models have hindered their integration for the study of alcohol dependence. MethodsWe developed a head-fixed model in which animals learned to self-administer ethanol across [~]14 days. Active lever responding resulted in a tone cue and ethanol reward, whereas responding on the inactive lever resulted in neither cue nor ethanol reward. Following acquisition, animals extinguished lever pressing across a minimum of 10 days. And finally, animals were tested separately for both cue- and ethanol-induced reinstatement of lever pressing. ResultsHere we show, for the first time, that in our head-fixed ethanol self-administration model male and female mice reliably pressed an active, but not inactive, lever for an oral ethanol reward. Ethanol rewards positively correlated with blood ethanol concentrations, at pharmacologically relevant levels. Furthermore, mice extinguished ethanol self-administration when the ethanol reward and cue were omitted, suggesting active lever pressing was ethanol directed. Following extinction, presentation of the ethanol-associated cue or priming with ethanol itself invigorated reinstatement of ethanol seeking, modeling relapse in a manner that replicates decades of work in freely-moving rodent studies. ConclusionsOverall, our head-fixed ethanol self-administration model will allow for incorporation of novel technologies that require or are greatly facilitated by head-fixation, improving our ability to study and understand the neural adaptations and computations that underlie alcohol dependence.

animal behavior and cognition↗

bioRxiv2020

Specialized coding patterns among dorsomedial prefrontal neuronal ensembles during conditioned reward seeking.

Non-overlapping cell populations within dorsomedial prefrontal cortex (dmPFC), defined by gene expression or projection target, control dissociable aspects of reward seeking through unique activity patterns. However, even within these defined cell populations considerable cell-to-cell variability is found, suggesting that greater resolution is needed to understand information processing in dmPFC. Here we use two-photon calcium imaging in awake, behaving mice to monitor the activity of dmPFC excitatory neurons throughout Pavlovian sucrose conditioning. We characterize five unique neuronal ensembles that each encode specialized information related to a reward, reward-predictive cues, and behavioral responses to reward-predictive cues. The ensembles differentially emerge across learning - and stabilize after learning - in a manner that improves the predictive validity of dmPFC activity dynamics for deciphering variables related to behavioral conditioning. Our results characterize the complex dmPFC neuronal ensemble dynamics that relay learning-dependent signals for prediction of reward availability and initiation of conditioned reward seeking.

neuroscience↗

bioRxiv2020

Drug self-administration in head-restrained mice for simultaneous multiphoton imaging

Multiphoton microscopy is one of several new technologies providing unprecedented insight into the activity dynamics and function of neural circuits. Unfortunately, many of these technologies require experimentation in head-restrained animals, greatly limiting the behavioral repertoire that can be studied with each approach. This issue is especially evident in drug addiction research, as no laboratories have coupled multiphoton microscopy with simultaneous intravenous drug self-administration, the gold standard of behavioral paradigms for investigating the neural mechanisms of drug addiction. Such experiments would be transformative for addiction research as one could measure or perturb an array of behavior and drug-related adaptations in precisely defined neural circuit elements over time, including but not limited to dendritic spine plasticity, neurotransmitter release, and neuronal activity. Here, we describe a new experimental assay wherein mice self-administer drugs of abuse while head-restrained, allowing for simultaneous multiphoton imaging. We demonstrate that this approach enables longitudinal tracking of activity in single neurons from the onset of drug use to relapse. The assay can be easily replicated by interested labs for relatively little cost with readily available materials and can provide unprecedented insight into the neural underpinnings of substance use disorder.

neuroscience↗

bioRxiv2020

Brain capillary pericytes exert a substantial but slow influence on blood flow

The majority of the brains vasculature is comprised of intricate capillary networks lined by capillary pericytes. However, it remains unclear whether capillary pericytes contribute to blood flow control. Using two-photon microscopy to observe and manipulate single capillary pericytes in vivo, we find their optogenetic stimulation decreases lumen diameter and blood flow, but with slower kinetics than mural cells of upstream pial and pre-capillary arterioles. This slow, optogenetically-induced vasoconstriction was inhibited by the clinically-used vasodilator fasudil, a Rho kinase inhibitor that blocks contractile machinery. Capillary pericytes were also slower to constrict back to baseline following hypercapnia-induced dilation, and relax towards baseline following optogenetically-induced vasoconstriction. In a complementary approach, optical ablation of single capillary pericytes led to sustained local dilation and a doubling of blood cell flux in capillaries lacking pericyte contact. Altogether these data indicate that capillary pericytes contribute to basal blood flow resistance and slow modulation of blood flow throughout the capillary bed.

neuroscience↗

bioRxiv2017

Classification of brain pericytes based on cell structure, location, and α-smooth muscle actin content

Smooth muscle cells and pericytes, together called mural cells, coordinate many distinct vascular functions. Smooth muscle cells are ring-shaped and cover arterioles with circumferential processes, whereas pericytes extend thin processes that run longitudinally along capillaries. In between these canonical mural cell types are cells with mixed phenotype of both smooth muscle cells and pericytes. Recent studies suggest that these transitional cells are critical for controlling blood flow to the capillary bed during health and disease, but there remains confusion on how to identify them and where they are located in the brain microvasculature. To address this issue, we measured the morphology, vascular territory, and -smooth muscle actin content of structurally diverse mural cells in adult mouse cortex. We first imaged intact 3-D vascular networks to establish the locations of major gradations in mural cell appearance as arterioles branched into capillaries. We then imaged individual mural cells occupying the regions within these gradations. This revealed two transitional cells that were often similar in appearance, but with sharply contrasting levels of -smooth muscle actin. Our findings highlight the diversity of mural cell morphologies in brain microvasculature, and provide guidance for identification and categorization of mural cell types.

neuroscience↗