Biology subjects

Alvarez, V. A.

Publications and source records attributed to Alvarez, V. A..

11 recordsLinked to original sources

bioRxiv2026

mTOR inhibition augments antitumor immune effector response by reprogramming the TP53-mutant, immune-cold HNSCC tumor microenvironment.

IntroductionResistance to immunotherapy remains a major clinical challenge in TP53-mutant head and neck squamous cell carcinoma (HNSCC), a disease subset characterized by immune exclusion, high recurrence, and poor outcomes. Given the constitutive activation of PI3K/AKT/mTOR signaling in TP53-mutant HNSCC and its role in disease progression, we investigated whether the mTOR inhibition (mTORi) could overcome immune resistance and improve outcomes. MethodsWe evaluated the effects of mTOR inhibitor everolimus in TP53-mutant, anti-PD-1-resistant syngeneic HNSCC cell lines and syngeneic tumor models. Tumor microenvironment (TME) changes, including immune cell infiltration, immune checkpoint expression, and key pathways associated with immune suppression and angiogenesis were assessed to define the mechanisms underlying TME remodeling. ResultsEverolimus significantly suppressed tumor growth in syngeneic HNSCC models. At the cellular level, everolimus significantly increased intratumoral CD8+ T cell and dendritic cell (DC) infiltration while reducing the accumulation of regulatory T cells (Tregs). Mechanistically, everolimus induced a cytokine/chemokine response, marked by increased TNF-/CXCL10 expression, leading to enhanced immune infiltration. Everolimus also inhibited the HIF-1/VEGFA angiogenic axis, a central driver of immune exclusion and myeloid-derived suppressor cell (MDSC) recruitment. Furthermore, everolimus treatment attenuated PD-1/PD-L1 signaling by reducing PD-1 and PD-L1 expression, respectively, in T cells and tumor cells, thereby restoring T-cell cytotoxic competence. DiscussionThese findings demonstrate that mTORi with everolimus reverses multiple mechanisms of immune resistance in TP53-mutant HNSCC by promoting immune cell recruitment, suppressing immunosuppressive pathways, and enhancing anti-tumor T cell activity. Collectively, these results support mTORi as a mechanistically rational strategy for reprogramming immune resistance in TP53-mutant HNSCC and provide a strong preclinical rationale for combining everolimus with immune therapy in patients who are likely to fail immunotherapy.

cancer biology↗

bioRxiv2026

D2 autoreceptors gate vulnerability to cocaine use disorder

A defining feature of substance use disorder is that repeated drug use does not always lead to addiction, motivating the search for biomarkers of vulnerability1. Reduced striatal dopamine D2/3 receptor availability is a robust PET correlate of problematic stimulant use2-5, but the signal may reflect high endogenous dopamine level, and it conflates presynaptic D2 autoreceptors on dopamine axons with postsynaptic D2/3 heteroreceptors on striatal projection neurons. We dissociated these contributions using cell type-specific Drd2 haploinsufficiency in dopamine neurons (autoD2KD), D2-expressing medium spiny neurons (MSN-D2KD), or both. Autoreceptor haploinsufficiency (autoD2KD) weakened presynaptic control of dopamine release, enhanced phasic gain, and prolonged cocaine-evoked dopamine elevations. This was accompanied by a hyper-exploratory trait and altered cocaine adaptation. Specifically, autoD2KD mice showed greater cocaine-seeking behavior, despite intact responses to sucrose reward and punishment. Although all genotypes showed graded reductions in striatal D2/3 binding, D1-like compensations diverged, resulting in different D1:D2/3 ratio in the striatum. The clinical implication is that striatal D1 density and D1:D2/3 balance may emerge as critical biomarkers for distinguishing cell-type-specific D2 reductions relevant to addiction vulnerability.

neuroscience↗

bioRxiv2026

Scn4b Modulates Huntington's Disease Phenotype Severity in vivo

Although it has been known for over 30 years that CAG trinucleotide repeat expansions in the HTT gene are the cause of Huntingtons disease (HD), it is still not understood how these mutations lead to the loss of striatal spiny projection neurons (SPNs) and other vulnerable neuronal cell types in HD. Here we show that SCN4B, a gene that is enriched in neurons that influence motor function, including striatal SPNs, modulates HD-associated phenotypes in vivo. Loss of Scn4b in wild-type mice mimics and Scn4b overexpression in an HD mouse model rescues several HD-associated phenotypes, including motor and cognitive deficits. Single nucleus RNA sequencing (snRNA-seq) analysis reveals that loss of Scn4b replicates several HD-associated gene expression signatures in the striatum. Conversely, overexpression of Scn4b rescues HD gene expression signatures and improves various SPN electrophysiological properties in HD model mice. Taken together, our results implicate loss of Scn4b expression as an important contributor to HD pathogenesis and therapeutic target in HD.

neuroscience↗

bioRxiv2025

Brain insulin signaling restores deficits in striatal dopamine release in overweight male mice with preexisting low D2-receptor expression

Obesity is characterized by insulin resistance, motivational impairments, and, in some cases, reduced availability of dopamine D2 receptors in the brain. However, whether the low D2 receptor levels represent a predisposing factor or a consequence of obesity, and how these processes are mechanistically linked, remains unclear. Here, we directly tested this causal relationship by selectively reducing D2 receptor density in striatal neurons. Male, but not female, mice with a low density of striatal D2 receptors consumed more food, gained more weight, and developed metabolic features of peripheral insulin resistance despite being maintained on standard chow. Motivational deficits preceded weight gain, manifesting as delayed circadian locomotor onset, reduced physical activity, and diminished effort to obtain food. In the brain, male mice with low D2 receptor density showed reduced dopamine release capacity and age-dependent alterations in brain insulin sensitivity. Prior to weight gain, brain insulin responses were blunted compared to those of controls, in which insulin potentiates dopamine release and enhances striatal acetylcholine signaling. Once overweight, however, these mice exhibited brain insulin hypersensitivity, with insulin strongly restoring dopamine release capacity. Together, these findings demonstrate that low striatal D2 receptor density predisposes male mice to an obesity-like phenotype through early dopaminergic dysfunction that precedes weight gain and is later compensated by insulin hypersensitivity in the brain.

neuroscience↗

bioRxiv2025

Cholinergic-dependent dopamine signals in mouse dorsal striatum are regulated by frontal but not sensory cortices

Everyday decisions depend on linking sensory stimuli with actions and outcomes. The striatum supports these sensorimotor associations through dopamine-dependent plasticity. Thus, the timing and magnitude of dopamine release is critical for learning. Recent work has characterized a local striatal microcircuit in which cholinergic interneurons (CINs) modulate dopamine release via acetylcholine activation of nicotinic receptors on dopamine axons. Here, we show that visual stimuli evoke dopamine responses in the dorsomedial striatum through this cholinergic-dependent mechanism. Using anatomical and functional methods to identify which pathways elicit these signals, we found that visual and auditory cortices that project to the dorsomedial striatum lack robust connectivity to CINs and were unable to drive cholinergic-dependent dopamine release. In contrast, frontal cortical regions, including the prelimbic and anterior cingulate cortices, strongly recruited CINs and acetylcholine, producing robust dopamine release both ex vivo and in vivo. These frontal corticostriatal projections are activated by visual stimuli, representing a possible pathway by which visual information reaches the dorsomedial striatum to evoke dopamine. These findings reveal a fundamental distinction between sensory and frontal cortical inputs to the striatum, demonstrating that only the latter evoke cholinergic-dependent dopamine signaling. This work establishes a framework for understanding how cortical circuits shape striatal dopamine to support reinforcement learning.

neuroscience↗

bioRxiv2025

A synaptic mechanism for encoding the learned value of action-derived safety

Motivated behavior is often framed in terms of biologically grounded outcomes, such as food or threat. Yet many motivated actions, like the pursuit of safety or agency, depend on outcomes that lack explicit sensory value and must instead be inferred from experience. Here, we identify a thalamostriatal circuit mechanism by which such internally constructed outcomes acquire motivational value. In mice performing an active avoidance task, neurons in the paraventricular thalamus (PVT) projecting to the nucleus accumbens (NAc) develop a safety-encoding signal that emerges following successful avoidance. This signal is experience-dependent and value-sensitive, diminishing upon devaluation of the instrumental contingency. Selective silencing of the PVT[->]NAc projection at safety onset disrupts avoidance persistence without impairing action-outcome learning, as confirmed by computational modeling of value updating based on prediction error. Mechanistically, PVT input recruits cholinergic interneurons (CINs) to modulate dopamine release and this influence depends on synaptic potentiation mediated by GluA2-lacking AMPA receptor insertion at PVT-CIN synapses. Disrupting this plasticity selectively impairs the avoidance response by blunting the motivational value of safety without affecting acquisition. These findings reveal how thalamic circuits assign value to abstract, internal outcomes, providing a framework for understanding how goals like safety are inferred, stabilized, and rendered behaviorally effective.

neuroscience↗

bioRxiv2025

Slow synaptic plasticity from the hippocampus underlies gradual mapping and fragmentation of novel spaces by grid cells

Animals construct internal "cognitive maps" of the world during navigation in spatial and non-spatial domains, with grid cells in the medial entorhinal cortex (MEC) playing a key role. This requires associating internal position estimates with external cues to reduce spatial uncertainty over time. However, how grid cell representations evolve in novel spaces to support map formation is unclear. To address this question, we longitudinally imaged calcium dynamics of grid cells over 10 days as mice learn operant tasks in novel virtual linear tracks. We observe that spatial tuning of grid cells is present immediately in novel tracks but evolves as a significant fraction of spatial fields shift backward on a run-by-run basis, within and across days. Backward shifts are more prevalent and persistent in successful learners. The fields gradually stabilize across days, anchored by landmarks, suggesting slow plasticity. The backward shifts partially reset daily, reflecting a slower consolidation timescale. While individual fields of a cell shift differentially, co-active fields of co-modular grid cells shift together, indicating their coupled dynamics on the same two-dimensional torus. Spatial learning leads to systematic changes and stabilization of their population phase trajectory, including lateral shift, rotation, and phase resets at landmarks, forming a landmark-fragmented representation for the environment. Next, we build an entorhinal-hippocampal model that provides a mechanistic explanation of the diverse phenomena - grid field shifts, increasing fidelity, and fragmentation of the spatial map - and predicts slow Hebbian plasticity in the hippocampus-to-entorhinal pathway. Supporting this, electrophysiology demonstrates that learning-performance-correlated weakening of local inhibition facilitates potentiation of indirect hippocampal inputs to superficial MEC. Together, our study provides multifaceted evidence of slow hippocampus-to-MEC plasticity, elucidating the formation of stable and fragmented cognitive maps that combine internal and cue-driven positional estimates in rich environments during learning. This mechanism may extend to broader memory processes involving this circuit.

neuroscience↗

bioRxiv2024

An enhancer-AAV toolbox to target and manipulate distinct interneuron subtypes

In recent years, we and others have identified a number of enhancers that, when incorporated into rAAV vectors, can restrict the transgene expression to particular neuronal populations. Yet, viral tools to access and manipulate specific neuronal subtypes are still limited. Here, we performed systematic analysis of single cell genomic data to identify enhancer candidates for each of the telencephalic interneuron subtypes. We established a set of enhancer-AAV tools that are highly specific for distinct cortical interneuron populations and striatal cholinergic interneurons. These enhancers, when used in the context of different effectors, can target (fluorescent proteins), observe activity (GCaMP) and manipulate (opto-genetics) specific neuronal subtypes. We also validated our enhancer-AAV tools across species. Thus, we provide the field with a powerful set of tools to study neural circuits and functions and to develop precise and targeted therapy.

neuroscience↗

bioRxiv2022

Leucine-Rich Repeat Kinase 2 limits dopamine D1 receptor signaling in the striatum and biases against heavy persistent alcohol drinking

The transition from hedonic alcohol drinking to problematic drinking is a hallmark of alcohol use disorder that occurs only in a subset of drinkers. This transition is known to require long-lasting changes in the synaptic drive and the activity of striatal neurons expressing dopamine D1 receptor (D1R). The molecular mechanisms that generate vulnerability in some individuals to undergo the transition are less understood. Here, we report that the Parkinsons-related protein leucine-rich repeat kinase 2 (LRRK2) modulates striatal D1R function to affect the behavioral response to alcohol and the likelihood that mice transition to heavy, persistent alcohol drinking. Deletion of the Lrrk2 gene specifically from D1R-expressing neurons potentiates D1R signaling at the cellular and synaptic level, enhancing alcohol-related behaviors and drinking. Mice with cell-specific deletion of Lrrk2 are more prone to heavy alcohol drinking and consumption is insensitive to punishment. These findings identify a novel role for LRRK2 function in the striatum in promoting resilience against heavy and persistent alcohol drinking.

neuroscience↗

bioRxiv2021

Loss of muscarinic M5 receptor function manifests disparate impairments in exploratory behavior in male and female mice despite common dopamine regulation

There are five cloned muscarinic acetylcholine receptors (M1-M5). Of these, the muscarinic type 5 receptor (M5) is the only one localized to dopamine neurons in the ventral tegmental area and substantia nigra. Unlike M1-M4, the M5 receptor has relatively restricted expression in the brain, making it an attractive therapeutic target. Here we performed an in-depth characterization of M5-dependent potentiation of dopamine transmission in the nucleus accumbens and accompanying exploratory behaviors in male and female mice. We show that M5 receptors potentiate dopamine transmission by acting directly on the terminals within the nucleus accumbens. Using the agonist oxotremorine, we revealed a unique concentration response curve and a sensitivity to repeated stressor exposure. We found that constitutive deletion of M5 receptors reduced exploration of the center of an open field while at the same time impairing normal habituation only in male mice. In addition, M5 deletion reduced exploration of salient stimuli, especially under conditions of high novelty, yet had no effect on hedonia. We conclude that M5 receptors are critical for both engaging with the environment and updating behavioral output in responses to the environment cues, specifically in male mice. A cardinal feature of mood and anxiety disorders is a withdrawal from the environment. These data indicate that boosting M5 receptor activity may be a useful therapeutic target for ameliorating these symptoms of depression and anxiety. Significance StatementThe basic physiological and behavioral functions of the muscarinic M5 receptor remain understudied. Furthermore, its presence on dopamine neurons, relatively restricted expression in the brain, and recent crystallization make it an attractive target for therapeutic development. Yet, most preclinical studies of M5 receptor function have primarily focused on substance use disorders in male rodents. Here we characterized the role of M5 receptors in potentiating dopamine transmission in the nucleus accumbens, finding impaired functioning after stress exposure. Furthermore, we show that M5 receptors can modulate exploratory behavior in a sex-specific manner, without impacting hedonic behavior. These findings further illustrate the therapeutic potential of the M5 receptor, warranting further research in the context of treating mood disorders.

neuroscience↗

bioRxiv2018

Cholinergic interneurons as a novel target of CRF in the striatum that is spared by repeated stress

Acute stressors can stimulate appetitive and exploratory behaviors, not just produce negative affect that impair performance. Corticotropin releasing factor (CRF), which is released in the brain in response to stress, acts on different targets and circuits to mediate both the negative and positive effects of stress. In the nucleus accumbens, CRF facilitates appetitive behavior through mechanisms not fully understood. Here we report that cholinergic interneurons (CINs) are a novel target for CRF actions in the striatum. CRF enhances the spontaneous firing via activation of CRF-type 1 receptors expressed on CINs. This causes the activation muscarinic acetylcholine receptors type 5, which mediate CRF potentiation of dopamine transmission in the striatum. Repeated stress selectively dampens some CRF functions but spare effect on CINs and changes CRF-R1 expression in a cell-specific manner. These data highlight the existence of diverse CRF targets within the striatum, which vary in their resilience to stress.

neuroscience↗