Identification of ALK in Thinness.

There is considerable inter-individual variability in susceptibility to weight gain despite an equally obesogenic environment in large parts of the world. Whereas many studies have focused on identifying the genetic susceptibility to obesity, we performed a GWAS on metabolically healthy thin individuals (lowest 6th percentile of the population-wide BMI spectrum) in a uniquely phenotyped Estonian cohort. We discovered anaplastic lymphoma kinase (ALK) as a candidate thinness gene. In Drosophila, RNAi mediated knockdown of Alk led to decreased triglyceride levels. In mice, genetic deletion of Alk resulted in thin animals with marked resistance to diet- and leptin-mutation-induced obesity. Mechanistically, we found that ALK expression in hypothalamic neurons controls energy expenditure via sympathetic control of adipose tissue lipolysis. Our genetic and mechanistic experiments identify ALK as a thinness gene, which is involved in the resistance to weight gain.

Glia Accumulate Evidence that Actions Are Futile and Suppress Unsuccessful Behavior.

When a behavior repeatedly fails to achieve its goal, animals often give up and become passive, which can be strategic for preserving energy or regrouping between attempts. It is unknown how the brain identifies behavioral failures and mediates this behavioral-state switch. In larval zebrafish swimming in virtual reality, visual feedback can be withheld so that swim attempts fail to trigger expected visual flow. After tens of seconds of such motor futility, animals became passive for similar durations. Whole-brain calcium imaging revealed noradrenergic neurons that responded specifically to failed swim attempts and radial astrocytes whose calcium levels accumulated with increasing numbers of failed attempts. Using cell ablation and optogenetic or chemogenetic activation, we found that noradrenergic neurons progressively activated brainstem radial astrocytes, which then suppressed swimming. Thus, radial astrocytes perform a computation critical for behavior: they accumulate evidence that current actions are ineffective and consequently drive changes in behavioral states. VIDEO ABSTRACT.

Neuromodulator Signaling Bidirectionally Controls Vesicle Numbers in Human Synapses.

Neuromodulators bind to pre- and postsynaptic G protein-coupled receptors (GPCRs), are able to quickly change intracellular cyclic AMP (cAMP) and Ca2+ levels, and are thought to play important roles in neuropsychiatric and neurodegenerative diseases. Here, we discovered in human neurons an unanticipated presynaptic mechanism that acutely changes synaptic ultrastructure and regulates synaptic communication. Activation of neuromodulator receptors bidirectionally controlled synaptic vesicle numbers within nerve terminals. This control correlated with changes in the levels of cAMP-dependent protein kinase A-mediated phosphorylation of synapsin-1. Using a conditional deletion approach, we reveal that the neuromodulator-induced control of synaptic vesicle numbers was largely dependent on synapsin-1. We propose a mechanism whereby non-phosphorylated synapsin-1 "latches" synaptic vesicles to presynaptic clusters at the active zone. cAMP-dependent phosphorylation of synapsin-1 then removes the vesicles. cAMP-independent dephosphorylation of synapsin-1 in turn recruits vesicles. Synapsin-1 thereby bidirectionally regulates synaptic vesicle numbers and modifies presynaptic neurotransmitter release as an effector of neuromodulator signaling in human neurons.

Neuromodulation and Neurophysiology on the Timescale of Learning and Decision-Making.

Nervous systems evolved to effectively navigate the dynamics of the environment to achieve their goals. One framework used to study this fundamental problem arose in the study of learning and decision-making. In this framework, the demands of effective behavior require slow dynamics-on the scale of seconds to minutes-of networks of neurons. Here, we review the phenomena and mechanisms involved. Using vignettes from a few species and areas of the nervous system, we view neuromodulators as key substrates for temporal scaling of neuronal dynamics.

Sympathetic Neuronal Activation Triggers Myeloid Progenitor Proliferation and Differentiation.

There is a growing body of research on the neural control of immunity and inflammation. However, it is not known whether the nervous system can regulate the production of inflammatory myeloid cells from hematopoietic progenitor cells in disease conditions. Myeloid cell numbers in diabetic patients were strongly correlated with plasma concentrations of norepinephrine, suggesting the role of sympathetic neuronal activation in myeloid cell production. The spleens of diabetic patients and mice contained higher numbers of tyrosine hydroxylase (TH)-expressing leukocytes that produced catecholamines. Granulocyte macrophage progenitors (GMPs) expressed the ß2 adrenergic receptor, a target of catecholamines. Ablation of splenic sympathetic neuronal signaling using surgical, chemical, and genetic approaches diminished GMP proliferation and myeloid cell development. Finally, mice lacking TH-producing leukocytes had reduced GMP proliferation, resulting in diminished myelopoiesis. Taken together, our study demonstrates that catecholamines produced by leukocytes and sympathetic nerve termini promote GMP proliferation and myeloid cell development.

Coordination between circadian neural circuit and intracellular molecular clock ensures rhythmic activation of adult neural stem cells.

The circadian clock throughout the day organizes the activity of neural stem cells (NSCs) in the dentate gyrus (DG) of adult hippocampus temporally. However, it is still unclear whether and how circadian signals from the niches contribute to daily rhythmic variation of NSC activation. Here, we show that norepinephrinergic (NEergic) projections from the locus coeruleus (LC), a brain arousal system, innervate into adult DG, where daily rhythmic release of norepinephrine (NE) from the LC NEergic neurons controlled circadian variation of NSC activation through ß3-adrenoceptors. Disrupted circadian rhythmicity by acute sleep deprivation leads to transient NSC overactivation and NSC pool exhaustion over time, which is effectively ameliorated by the inhibition of the LC NEergic neuronal activity or ß3-adrenoceptors-mediated signaling. Finally, we demonstrate that NE/ß3-adrenoceptors-mediated signaling regulates NSC activation through molecular clock BMAL1. Therefore, our study unravels that adult NSCs precisely coordinate circadian neural circuit and intrinsic molecular circadian clock to adapt their cellular behavior across the day.

Elucidation of a dynamic interplay between a beta-2 adrenergic receptor, its agonist, and stimulatory G protein.

G protein-coupled receptors (GPCRs) represent the largest group of membrane receptors for transmembrane signal transduction. Ligand-induced activation of GPCRs triggers G protein activation followed by various signaling cascades. Understanding the structural and energetic determinants of ligand binding to GPCRs and GPCRs to G proteins is crucial to the design of pharmacological treatments targeting specific conformations of these proteins to precisely control their signaling properties. In this study, we focused on interactions of a prototypical GPCR, beta-2 adrenergic receptor (ß2AR), with its endogenous agonist, norepinephrine (NE), and the stimulatory G protein (Gs). Using molecular dynamics (MD) simulations, we demonstrated the stabilization of cationic NE, NE(+), binding to ß2AR by Gs protein recruitment, in line with experimental observations. We also captured the partial dissociation of the ligand from ß2AR and the conformational interconversions of Gs between closed and open conformations in the NE(+)-ß2AR-Gs ternary complex while it is still bound to the receptor. The variation of NE(+) binding poses was found to alter Gs α subunit (Gsα) conformational transitions. Our simulations showed that the interdomain movement and the stacking of Gsα α1 and α5 helices are significant for increasing the distance between the Gsα and ß2AR, which may indicate a partial dissociation of Gsα The distance increase commences when Gsα is predominantly in an open state and can be triggered by the intracellular loop 3 (ICL3) of ß2AR interacting with Gsα, causing conformational changes of the α5 helix. Our results help explain molecular mechanisms of ligand and GPCR-mediated modulation of G protein activation.

Chronic Desipramine Reverses Deficits in Cell Activity, Norepinephrine Innervation, and Anxiety-Depression Phenotypes in Fluoxetine-Resistant cF1ko Mice.

Selective serotonin (5-HT) reuptake inhibitors are only 30% effective for remission in subjects with major depression, and the best treatments for SSRI-resistant patients remain unclear. To model SSRI resistance, we used cF1ko mice with conditional deletion of the repressor Freud-1/CC2D1A in adult 5-HT neurons. Within weeks, this deletion leads to overexpression of 5-HT1A autoreceptors, reduced serotonergic activity, and fluoxetine-resistant anxiety-depression phenotype. We hypothesized that desipramine (DES), which targets norepinephrine (NE), may be effective in cF1ko mice. The actions of chronic DES treatment on behavior, chronic cellular activation, and NE projections were examined in both sexes of cF1ko and WT mice. In contrast to fluoxetine, chronic DES reversed the behavioral phenotypes in cF1ko mice, while in WT littermates DES slightly increased anxiety and depression-like behaviors. Deficits in FosB+ cell counts were seen in the entorhinal cortex, hippocampal CA2/3 layer, and BLA of cF1ko mice and were reversed by chronic DES treatment, especially in GABAergic neurons. In cF1ko mice, widespread reductions were seen in NE axons, varicosities, and especially 30-60% reductions in NE synaptic and triadic contacts, particularly to inhibitory gephyrin-positive sites. DES treatment also reversed these reductions in NE innervation. These results indicate the dynamic plasticity of the adult noradrenergic system within weeks of altering serotonergic function that can be normalized by DES treatment. Accompanying these changes, DES but not fluoxetine reversed the behavioral alterations in cF1ko mice, suggesting a key role for noradrenergic plasticity in antidepressant response in this model of reduced serotonin activity.

Norepinephrine Drives Sleep Fragmentation Activation of Asparagine Endopeptidase, Locus Ceruleus Degeneration, and Hippocampal Amyloid-ß42 Accumulation.

Chronic sleep disruption (CSD), from insufficient or fragmented sleep and is an important risk factor for Alzheimer's disease (AD). Underlying mechanisms are not understood. CSD in mice results in degeneration of locus ceruleus neurons (LCn) and CA1 hippocampal neurons and increases hippocampal amyloid-ß42 (Aß42), entorhinal cortex (EC) tau phosphorylation (p-tau), and glial reactivity. LCn injury is increasingly implicated in AD pathogenesis. CSD increases NE turnover in LCn, and LCn norepinephrine (NE) metabolism activates asparagine endopeptidase (AEP), an enzyme known to cleave amyloid precursor protein (APP) and tau into neurotoxic fragments. We hypothesized that CSD would activate LCn AEP in an NE-dependent manner to induce LCn and hippocampal injury. Here, we studied LCn, hippocampal, and EC responses to CSD in mice deficient in NE [dopamine ß-hydroxylase (Dbh)-/-] and control male and female mice, using a model of chronic fragmentation of sleep (CFS). Sleep was equally fragmented in Dbh -/- and control male and female mice, yet only Dbh -/- mice conferred resistance to CFS loss of LCn, LCn p-tau, and LCn AEP upregulation and activation as evidenced by an increase in AEP-cleaved APP and tau fragments. Absence of NE also prevented a CFS increase in hippocampal AEP-APP and Aß42 but did not prevent CFS-increased AEP-tau and p-tau in the EC. Collectively, this work demonstrates AEP activation by CFS, establishes key roles for NE in both CFS degeneration of LCn neurons and CFS promotion of forebrain Aß accumulation, and, thereby, identifies a key molecular link between CSD and specific AD neural injuries.

Astrocyte ß-Adrenergic Receptor Activity Regulates NMDA Receptor Signaling of Medial Prefrontal Cortex Pyramidal Neurons.

Glutamate spillover from the synapse is tightly regulated by astrocytes, limiting the activation of extrasynaptically located NMDA receptors (NMDAR). The processes of astrocytes are dynamic and can modulate synaptic physiology. Though norepinephrine (NE) and ß-adrenergic receptor (ß-AR) activity can modify astrocyte volume, this has yet to be confirmed outside of sensory cortical areas, nor has the effect of noradrenergic signaling on glutamate spillover and neuronal NMDAR activity been explored. We monitored changes to astrocyte process volume in response to noradrenergic agonists in the medial prefrontal cortex of male and female mice. Both NE and the ß-AR agonist isoproterenol (ISO) increased process volume by ∼20%, significantly higher than changes seen when astrocytes had G-protein signaling blocked by GDPßS. We measured the effect of ß-AR signaling on evoked NMDAR currents. While ISO did not affect single stimulus excitatory currents of Layer 5 pyramidal neurons, ISO reduced NMDAR currents evoked by 10 stimuli at 50 Hz, which elicits glutamate spillover, by 18%. After isolating extrasynaptic NMDARs by blocking synaptic NMDARs with the activity-dependent NMDAR blocker MK-801, ISO similarly reduced extrasynaptic NMDAR currents in response to 10 stimuli by 18%. Finally, blocking ß-AR signaling in the astrocyte network by loading them with GDPßS reversed the ISO effect on 10 stimuli-evoked NMDAR currents. These results demonstrate that astrocyte ß-AR activity reduces extrasynaptic NMDAR recruitment, suggesting that glutamate spillover is reduced.

Norepinephrine Neurons in the Nucleus of the Solitary Tract Suppress Luteinizing Hormone Secretion in Female Mice.

Stress impairs fertility, at least in part, via inhibition of gonadotropin secretion. Luteinizing hormone (LH) is an important gonadotropin that is released in a pulsatile pattern in males and in females throughout the majority of the ovarian cycle. Several models of stress, including acute metabolic stress, suppress LH pulses via inhibition of neurons in the arcuate nucleus of the hypothalamus that coexpress kisspeptin, neurokinin B, and dynorphin (termed KNDy cells) which form the pulse generator. The mechanism for inhibition of KNDy neurons during stress, however, remains a significant outstanding question. Here, we investigated a population of catecholamine neurons in the nucleus of the solitary tract (NTS), marked by expression of the enzyme dopamine beta-hydroxylase (DBH), in female mice. First, we found that a subpopulation of DBH neurons in the NTS is activated (express c-Fos) during metabolic stress. Then, using chemogenetics, we determined that activation of these cells is sufficient to suppress LH pulses, augment corticosterone secretion, and induce sickness-like behavior. In subsequent studies, we identified evidence for suppression of KNDy cells (rather than downstream signaling pathways) and determined that the suppression of LH pulses was not dependent on the acute rise in glucocorticoids. Together these data support the hypothesis that DBH cells in the NTS are important for regulation of neuroendocrine and behavioral responses to stress.

Dopamine and Norepinephrine Differentially Mediate the Exploration-Exploitation Tradeoff.

Dopamine (DA) and norepinephrine (NE) have been repeatedly implicated in neuropsychiatric vulnerability, in part via their roles in mediating the decision-making processes. Although two neuromodulators share a synthesis pathway and are coactivated under states of arousal, they engage in distinct circuits and modulatory roles. However, the specific role of each neuromodulator in decision-making, in particular the exploration-exploitation tradeoff, remains unclear. Revealing how each neuromodulator contributes to exploration-exploitation tradeoff is important in guiding mechanistic hypotheses emerging from computational psychiatric approaches. To understand the differences and overlaps of the roles of these two catecholamine systems in regulating exploration, a direct comparison using the same dynamic decision-making task is needed. Here, we ran male and female mice in a restless two-armed bandit task, which encourages both exploration and exploitation. We systemically administered a nonselective DA antagonist (flupenthixol), a nonselective DA agonist (apomorphine), a NE beta-receptor antagonist (propranolol), and a NE beta-receptor agonist (isoproterenol) and examined changes in exploration within subjects across sessions. We found a bidirectional modulatory effect of dopamine on exploration. Increasing dopamine activity decreased exploration and decreasing dopamine activity increased exploration. The modulatory effect of beta-noradrenergic receptor activity on exploration was mediated by sex. Reinforcement learning model parameters suggested that dopamine modulation affected exploration via decision noise and norepinephrine modulation affected exploration via sensitivity to outcome. Together, these findings suggested that the mechanisms that govern the exploration-exploitation transition are sensitive to changes in both catecholamine functions and revealed differential roles for NE and DA in mediating exploration.

Selective Enhancement of REM Sleep in Male Rats through Activation of Melatonin MT1 Receptors Located in the Locus Ceruleus Norepinephrine Neurons.

Sleep disorders affect millions of people around the world and have a high comorbidity with psychiatric disorders. While current hypnotics mostly increase non-rapid eye movement sleep (NREMS), drugs acting selectively on enhancing rapid eye movement sleep (REMS) are lacking. This polysomnographic study in male rats showed that the first-in-class selective melatonin MT1 receptor partial agonist UCM871 increases the duration of REMS without affecting that of NREMS. The REMS-promoting effects of UCM871 occurred by inhibiting, in a dose-response manner, the firing activity of the locus ceruleus (LC) norepinephrine (NE) neurons, which express MT1 receptors. The increase of REMS duration and the inhibition of LC-NE neuronal activity by UCM871 were abolished by MT1 pharmacological antagonism and by an adeno-associated viral (AAV) vector, which selectively knocked down MT1 receptors in the LC-NE neurons. In conclusion, MT1 receptor agonism inhibits LC-NE neurons and triggers REMS, thus representing a novel mechanism and target for REMS disorders and/or psychiatric disorders associated with REMS impairments.

Basolateral amygdala activation enhances object recognition memory by inhibiting anterior insular cortex activity.

Noradrenergic activation of the basolateral amygdala (BLA) by emotional arousal enhances different forms of recognition memory via functional interactions with the insular cortex (IC). Human neuroimaging studies have revealed that the anterior IC (aIC), as part of the salience network, is dynamically regulated during arousing situations. Emotional stimulation first rapidly increases aIC activity but suppresses it in a delayed fashion. Here, we investigated in male Sprague-Dawley rats whether the BLA influence on recognition memory is associated with an increase or suppression of aIC activity during the postlearning consolidation period. We first employed anterograde and retrograde viral tracing and found that the BLA sends dense monosynaptic projections to the aIC. Memory-enhancing norepinephrine administration into the BLA following an object training experience suppressed aIC activity 1 h later, as determined by a reduced expression of the phosphorylated form of the transcription factor cAMP response element-binding (pCREB) protein and neuronal activity marker c-Fos. In contrast, the number of perisomatic γ-aminobutyric acid (GABA)ergic inhibitory synapses per pCREB-positive neuron was significantly increased, suggesting a dynamic up-regulation of GABAergic tone. In support of this possibility, pharmacological inhibition of aIC activity with a GABAergic agonist during consolidation enhanced object recognition memory. Norepinephrine administration into the BLA did not affect neuronal activity within the posterior IC, which receives sparse innervation from the BLA. The evidence that noradrenergic activation of the BLA enhances the consolidation of object recognition memory via a mechanism involving a suppression of aIC activity provides insight into the broader brain network dynamics underlying emotional regulation of memory.

Metal-Loaded Synthetic Melanin via Oxidative Polymerization of Neurotransmitter Norepinephrine Exhibiting High Photothermal Conversion.

Polydopamine (PDA)-derived melanin-like materials exhibit significant photothermal conversion owing to their broad-spectrum light absorption. However, their low near-infrared (NIR) absorption and inadequate hydrophilicity compromise their utilization of solar energy. Herein, we developed metal-loaded poly(norepinephrine) nanoparticles (PNE NPs) by predoping metal ions (Fe3+, Mn3+, Co2+, Ca2+, Ga3+, and Mg2+) with norepinephrine, a neuron-derived biomimetic molecule, to address the limitations of PDA. The chelation between catechol and metal ions induces a ligand-to-metal charge transfer (LMCT) through the formation of donor-acceptor pairs, modulating the light absorption behavior and reducing the band gap. Under 1 sun illumination, the Fe-loaded PNE coated wood evaporator achieved a high seawater evaporation rate and efficiency of 1.75 kg m-2 h-1 and 92.4%, respectively, owing to the superior hydrophilicity and photothermal performance of PNE. Therefore, this study offers a comprehensive exploration of the role of metal ions in enhancing the photothermal properties of synthetic melanins.

Human Brainstem and Cerebellum Atlas: Chemoarchitecture and Cytoarchitecture Paired to MRI.

Lesion localization is the basis for understanding neurologic disease, which is predicated on neuroanatomical knowledge carefully cataloged from histology and imaging atlases. However, it is often difficult to correlate clinical images of brainstem injury obtained by MRI scans with the details of human brainstem neuroanatomy represented in atlases, which are mostly based on cytoarchitecture using Nissl stain or a single histochemical stain, and usually do not include the cerebellum. Here, we report a high-resolution (200 µm) 7T MRI of a cadaveric male human brainstem and cerebellum paired with detailed, coregistered histology (at 2 µm single-cell resolution) of the immunohistochemically stained cholinergic, serotonergic, and catecholaminergic (dopaminergic, noradrenergic, and adrenergic) neurons, in relationship to each other and to the cerebellum. These immunohistochemical findings provide novel insights into the spatial relationships of brainstem cell types and nuclei, including subpopulations of melanin and TH+ neurons, and allows for more informed structural annotation of cell groups. Moreover, the coregistered MRI-paired histology helps validate imaging findings. This is useful for interpreting both scans and histology, and to understand the cell types affected by lesions. Our detailed chemoarchitecture and cytoarchitecture with corresponding high-resolution MRI builds on previous atlases of the human brainstem and cerebellum, and makes precise identification of brainstem and cerebellar cell groups involved in clinical lesions accessible for both laboratory scientists and clinicians alike.SIGNIFICANCE STATEMENT Clinicians and neuroscientists frequently use cross-sectional anatomy of the human brainstem from MRI scans for both clinical and laboratory investigations, but they must rely on brain atlases to neuroanatomical structures. Such atlases generally lack both detail of brainstem chemical cell types, and the cerebellum, which provides an important spatial reference. Our current atlas maps the distribution of key brainstem cell types (cholinergic, serotonergic, and catecholaminergic neurons) in relationship to each other and the cerebellum, and pairs this histology with 7T MR images from the identical brain. This atlas allows correlation of the chemoarchitecture with corresponding MRI, and makes the identification of cell groups that are often discussed, but rarely identifiable on MRI scan, accessible to clinicians and clinical researchers.

ß-Adrenergic Signaling Promotes Morphological Maturation of Astrocytes in Female Mice.

Astrocytes play essential roles in the developing nervous system, including supporting synapse function. These astrocyte support functions emerge coincident with brain maturation and may be tailored in a region-specific manner. For example, gray matter astrocytes have elaborate synapse-associated processes and are morphologically and molecularly distinct from white matter astrocytes. This raises the question of whether there are unique environmental cues that promote gray matter astrocyte identity and synaptogenic function. We previously identified adrenergic receptors as preferentially enriched in developing gray versus white matter astrocytes, suggesting that noradrenergic signaling could be a cue that promotes the functional maturation of gray matter astrocytes. We first characterized noradrenergic projections during postnatal brain development in mouse and human, finding that process density was higher in the gray matter and increased concurrently with astrocyte maturation. RNA sequencing revealed that astrocytes in both species expressed α- and ß-adrenergic receptors. We found that stimulation of ß-adrenergic receptors increased primary branching of rodent astrocytes in vitro Conversely, astrocyte-conditional knockout of the ß1-adrenergic receptor reduced the size of gray matter astrocytes and led to dysregulated sensorimotor integration in female mice. These studies suggest that adrenergic signaling to developing astrocytes impacts their morphology and has implications for adult behavior, particularly in female animals. More broadly, they demonstrate a mechanism through which environmental cues impact astrocyte development. Given the key roles of norepinephrine in brain states, such as arousal, stress, and learning, these findings could prompt further inquiry into how developmental stressors impact astrocyte development and adult brain function.SIGNIFICANCE STATEMENT This study demonstrates a role for noradrenergic signaling in the development of gray matter astrocytes. We provide new evidence that the ß1-adrenergic receptor is robustly expressed by both mouse and human astrocytes, and that conditional KO of the ß1-adrenergic receptor from female mouse astrocytes impairs gray matter astrocyte maturation. Moreover, female conditional KO mice exhibit behavioral deficits in two paradigms that test sensorimotor function. Given the emerging interest in moving beyond RNA sequencing to probe specific pathways that underlie astrocyte heterogeneity, this study provides a foundation for future investigation into the effect of noradrenergic signaling on astrocyte functions in conditions where noradrenergic signaling is altered, such as stress, arousal, and learning.

Effects of Adult Age and Functioning of the Locus Coeruleus Norepinephrinergic System on Reward-Based Learning.

Age-related impairments in value representations and updating during decision-making and reward-based learning are often related to age-related attenuation in the catecholamine system such as dopamine (DA) and norepinephrine (NE). However, it is unclear to what extent age-related declines in NE functioning in humans affect reward-based decision-making. We conducted a probabilistic decision-making task and applied a Q-learning model to investigate participants' anticipatory values and value sensitivities. Task-related pupil dilations and locus coeruleus (LC) magnetic resonance imaging (MRI) contrast, which served as a potential window of the LC-NE functions, were assessed in younger and older adults. Results showed that in both choice and feedback phases, younger adults' (N = 42, 22 males) pupil dilations negatively correlated with anticipatory values, indicating uncertainty about outcome probabilities. Uncertainty-evoked pupil dilations in older adults (N = 41, 27 males) were smaller, indicating age-related impairments in value estimation and updating. In both age groups, participants who showed a larger uncertainty-evoked pupil dilation exhibited a higher value sensitivity as reflected in the ß parameter of the reinforcement Q-learning model. Furthermore, older adults (N = 34, 29 males) showed a lower LC-MRI contrast than younger adults (N = 25, 15 males). The LC-MRI contrast positively correlated with value sensitivity only in older but not in younger adults. These findings suggest that task-related pupillary responses can reflect age-related deficits in value estimation and updating during reward-based decision-making. Our evidence with the LC-MRI contrast further showed the age-related decline of the LC structure in modulating value representations during reward-based learning.SIGNIFICANCE STATEMENT Age-related impairments in value representation and updating during reward-based learning are associated with declines in the catecholamine modulation with age. However, it is unclear how age-related declines in the LC-NE system may affect reward-based learning. Here, we show that compared with younger adults, older adults exhibited reduced uncertainty-induced pupil dilations, suggesting age-related deficits in value estimation and updating. Older adults showed a lower structural MRI of the LC contrast than younger adults, indicating age-related degeneration of the LC structure. The association between the LC-MRI contrast and value sensitivity was only observed in older adults. Our findings may demonstrate a pioneering model to unravel the role of the LC-NE system in reward-based learning in aging.

Regulation of the Ca2+ Channel CaV1.2 Supports Spatial Memory and Its Flexibility and LTD.

Widespread release of norepinephrine (NE) throughout the forebrain fosters learning and memory via adrenergic receptor (AR) signaling, but the molecular mechanisms are largely unknown. The ß2 AR and its downstream effectors, the trimeric stimulatory Gs-protein, adenylyl cyclase (AC), and the cAMP-dependent protein kinase A (PKA), form a unique signaling complex with the L-type Ca2+ channel (LTCC) CaV1.2. Phosphorylation of CaV1.2 by PKA on Ser1928 is required for the upregulation of Ca2+ influx on ß2 AR stimulation and long-term potentiation induced by prolonged theta-tetanus (PTT-LTP) but not LTP induced by two 1-s-long 100-Hz tetani. However, the function of Ser1928 phosphorylation in vivo is unknown. Here, we show that S1928A knock-in (KI) mice of both sexes, which lack PTT-LTP, express deficiencies during initial consolidation of spatial memory. Especially striking is the effect of this mutation on cognitive flexibility as tested by reversal learning. Mechanistically, long-term depression (LTD) has been implicated in reversal learning. It is abrogated in male and female S1928A knock-in mice and by ß2 AR antagonists and peptides that displace ß2 AR from CaV1.2. This work identifies CaV1.2 as a critical molecular locus that regulates synaptic plasticity, spatial memory and its reversal, and LTD.SIGNIFICANCE STATEMENT We show that phosphorylation of the Ca2+ channel CaV1.2 on Ser1928 is important for consolidation of spatial memory and especially its reversal, and long-term depression (LTD). Identification of Ser1928 as critical for LTD and reversal learning supports the model that LTD underlies flexibility of reference memory.

DiDBiT-TMT: A Novel Method to Quantify Changes in the Proteomic Landscape Induced by Neural Plasticity.

Direct detection of biotinylated proteins (DiDBiT) is a proteomic method that can enrich and detect newly synthesized proteins (NSPs) labeled with bio-orthogonal amino acids with 20-fold improved detectability compared to conventional methods. However, DiDBiT has currently been used to compare only two conditions per experiment. Here, we present DiDBiT-TMT, a method that can be used to quantify NSPs across many conditions and replicates in the same experiment by combining isobaric tandem mass tagging (TMT) with DiDBiT. We applied DiDBiT-TMT to brain slices to determine changes in the de novo proteome that occur after inducing chemical long-term potentiation (cLTP) or treatment with the neuromodulator norepinephrine. We successfully demonstrated DiDBiT-TMT's capacity to quantitatively compare up to 9 samples in parallel. We showed that there is a minimal overlap among NSPs that are differentially expressed in cLTP-treated organotypic brain slices, norepinephrine-treated organotypic brain slices, and organotypic slices undergoing combinatorial treatment with norepinephrine and cLTP. Our results point to the possible divergence of the molecular mechanisms underlying these treatments and showcase the applicability of DiDBiT-TMT for studying neurobiology.