Journal of Neuroscience最新文献

Natural scenes are filled with groups of similar items. Humans employ ensemble coding to extract the summary statistical information of the environment, thereby enhancing the efficiency of information processing, something particularly useful when observing natural scenes. However, the neural mechanisms underlying the representation of ensemble information in the brain remain elusive. In particular, whether ensemble representation results from the mere summation of individual item representations or it engages other specific processes remains unclear. In this study, we utilized a set of orientation ensembles wherein none of the individual item orientations were the same as the ensemble orientation. We recorded magnetoencephalography (MEG) signals from human participants (both sexes) when they performed an ensemble orientation discrimination task. Time-resolved multivariate pattern analysis (MVPA) and the inverted encoding model (IEM) were employed to unravel the neural mechanisms of the ensemble orientation representation and track its time course. First, we achieved successful decoding of the ensemble orientation, with a high correlation between the decoding and behavioral accuracies. Second, the IEM analysis demonstrated that the representation of the ensemble orientation differed from the sum of the representations of individual item orientations, suggesting that ensemble coding could further modulate orientation representation in the brain. Moreover, using source reconstruction, we showed that the representation of ensemble orientation manifested in early visual areas. Taken together, our findings reveal the emergence of the ensemble representation in the human visual cortex and advance the understanding of how the brain captures and represents ensemble information.

The cell adhesion molecule leucine-rich repeat transmembrane neuronal protein 2 (LRRTM2) is crucial for synapse development and function. However, our understanding of its endogenous trafficking has been limited due to difficulties in manipulating its coding sequence (CDS) using standard genome editing techniques. Instead, we replaced the entire LRRTM2 CDS by adapting a two-guide CRISPR knock-in method, enabling complete control of LRRTM2. In primary rat hippocampal cultures dissociated from embryos of both sexes, N-terminally tagged, endogenous LRRTM2 was found in 80% of synapses, and synaptic LRRTM2 content correlated with PSD-95 and AMPAR levels. LRRTM2 was also enriched with AMPARs outside synapses, demonstrating the sensitivity of this method to detect relevant new biology. Finally, we leveraged total genomic control to increase the synaptic levels of LRRTM2 via simultaneous mutation of its C-terminal domain, which did not correspondingly increase AMPAR enrichment. The coding region of thousands of genes span lengths suitable for whole-CDS replacement, suggesting this simple approach will enable straightforward structure-function analysis in neurons.

Our eyes are never still. Even when we attempt to fixate, the visual gaze is never motionless, as we continuously perform miniature oculomotor movements termed as fixational eye movements. The fastest eye movements during the fixation epochs are termed microsaccades (MSs), that are leading to continual motion of the visual input, affecting mainly neurons in the fovea. Yet our vision appears to be stable. To explain this gap, previous studies suggested the existence of an extra-retinal input (ERI) into the visual cortex that can account for the motion and produce visual stability. Here, we investigated the existence of an ERI to V1 fovea in macaque monkeys (male) while they performed spontaneous MSs, during fixation. We used voltage-sensitive dye imaging (VSDI) to measure and characterize at high spatio-temporal resolution the influence of MSs on neural population activity, in the foveal region of the primary visual cortex (V1). Microsaccades performed over a blank screen, induced a two-phase response modulation: an early suppression followed by an enhancement. A correlation analysis revealed a widespread foveal increase in neural synchronization, peaking around ∼100 ms after MS onset. Next, we investigated the MS effects in the presence of a small visual stimulus, and found that this modulation was different from the blank condition yet both modulations co-existed in the fovea. Finally, the VSD response to an external motion of the fixation point could not explain the MS modulation. These results support an ERI that may be involved in visual stabilization already at the level of V1.Significance statement Microsaccades are tiny fixational saccades, leading to the continual motion of the visual input on the fovea, during visual fixation. Yet our vision appears to be stable. To explain this gap, we investigated the existence of an extra-retinal input into the fovea of the primary visual cortex (V1) in behaving monkeys while they performed microsaccades over a blank screen with a tiny fixation point. The population response aligned on microsacades showed a widespread, transient increased neural synchronization along with a two-phase response modulation. Microsaccades in the presence of a visual stimulus induced distinct spatio-temporal response from that in the blank condition. Our results support the existence of an extra-retinal input that may be involved in visual stabilization at V1 area.

Numerous studies have shown that neuronal representations in sensory pathways are far from static but are instead strongly shaped by the complex properties of the sensory inputs they receive. Adaptation dynamically shapes the neural signaling that underlies our perception of the world yet remains poorly understood. We investigated rapid adaptation across timescales from hundreds of milliseconds to seconds through simultaneous multi-electrode recordings from the ventro-posteromedial nucleus of the thalamus (VPm) and layer 4 of the primary somatosensory cortex (S1) in male and female anesthetized mice in response to controlled, persistent whisker stimulation. Observations in VPm and S1 reveal a degree of adaptation that progresses through the pathway. Under these experimental conditions, signatures of two distinct timescales of rapid adaptation in the firing rates of both thalamic and cortical neuronal populations were revealed, also reflected in the synchrony of the thalamic population and in the thalamocortical synaptic efficacy that was measured in putatively monosynaptically connected thalamocortical pairs. Controlled optogenetic activation of VPm further demonstrated that the longer timescale adaptation observed in S1 is likely inherited from slow decreases in thalamic firing rate and synchrony. Despite the degraded sensory responses, adaptation induced by the controlled repetitive stimulation presented here resulted in a shift in coding strategy that favors theoretical discrimination over detection across the observed timescales of adaptation. Overall, although multiple mechanisms contribute to rapid adaptation at distinct timescales, they support a unifying framework on the role of adaptation in sensory processing.Significance Statement Although the perceptual effects of persistent sensory stimulation have been known for centuries, the rapid sensory adaptation of the underlying neural signaling to these persistent inputs are not well understood. Here, we present evidence for two distinct timescales of adaptation over several seconds across the thalamocortical circuit in mice. We identify both the overall level of neural activity and the corresponding population synchrony of the thalamic inputs to primary somatosensory cortex as key role players shaping the cortical adaptation.

We previously reported that ventral subiculum (vSub) activity is critical to incubation of oxycodone seeking after abstinence induced by adverse consequences of drug seeking. Here, we studied the role of claustrum, a key vSub input, in this incubation.We trained male and female rats to self-administer oxycodone for 2 weeks and then induced abstinence by exposing them to an electric barrier for 2 weeks. We used retrograde tracing (cholera toxin B subunit; CTb) plus the activity marker Fos to identify projections to vSub activated during 'incubated' relapse (abstinence day 15). We then used muscimol+baclofen (GABAa+GABAb receptor agonists) reversible inactivation to determine causal role of claustrum in incubation and the behavioral and anatomical specificity of this role. We also used muscimol+baclofen in an anatomical disconnection procedure to determine the causal role of claustrum-vSub connections in incubation. Finally, we analyzed an existing functional MRI dataset to determine if functional connectivity changes in claustrum-related circuits predict incubation of oxycodone seeking.Claustrum neurons projecting to vSub were activated during relapse tests after electric barrier-induced abstinence. Inactivation of claustrum but not areas dorsolateral to claustrum decreased incubation of oxycodone seeking after electric barrier-induced abstinence; claustrum inactivation had no effect on incubation after food choice-induced abstinence. Both ipsilateral and contralateral inactivation of claustrum-vSub projections decreased incubation after electric barrier-induced abstinence. Functional connectivity changes in claustrum-cortical circuits during electric barrier-induced abstinence predicted incubated oxycodone relapse.Our study identified a novel role of claustrum in relapse to opioid drugs after abstinence induced by adverse consequences of drug seeking.Significance statement We recently reported that vSub is critical to incubation of oxycodone craving after abstinence induced by adverse consequences of drug seeking. Here, we first showed that claustrum projections to vSub are active during tests for incubation of oxycodone seeking after electric barrier-induced abstinence. Next, we used pharmacological inactivation to test the causal roles of claustrum and its anatomical connections with vSub in incubation. Using an existing functional MRI dataset, we also tested if functional connectivity changes in claustrum-related circuits predicted 'incubated' oxycodone relapse after electric barrier-induced abstinence. Our data suggest that claustrum- and claustrum-related circuits contribute to relapse after voluntary abstinence induced by adverse consequences to drug seeking but not abstinence induced by availability of alternative non-drug rewards.

Kv4.2 subunits, which mediate transient A-type K⁺ current, are crucial in regulating neuronal excitability and synaptic responses within the hippocampus. While their contribution to activity-dependent regulation of synaptic response is well-established, the impact of Kv4.2 on basal synaptic strength remains elusive. To address this gap, we introduced Kv4.2-specific antibody (anti-Kv4.2) into hippocampal neurons of mouse of both sexes to selectively inhibit postsynaptic Kv4.2, enabling direct examination of its impact on excitatory postsynaptic potentials (EPSPs) and currents (EPSCs) during basal synaptic activity. Our results demonstrated that blocking Kv4.2 significantly enhanced the amplitude of EPSPs. This amplification was proportional to the increase in the amplitude of EPSCs, which, in turn, correlated with the expression level of Kv4.2 in dendritic regions of the hippocampus. Furthermore, the anti-Kv4.2-induced increase in EPSC amplitude was associated with a decrease in the failure rate of EPSCs evoked by minimal stimulation, suggesting that blocking Kv4.2 facilitates the recruitment of AMPA receptors to both silent and functional synapses to enhance synaptic efficacy. The anti-Kv4.2-induced synaptic potentiation was effectively abolished by intracellular 10 mM BAPTA or by blocking R-type calcium channels (RTCCs) and downstream signaling molecules, including protein kinase A and C. Importantly, Kv4.2 inhibition did not occlude further synaptic potentiation induced by high frequency stimulation, suggesting that anti-Kv4.2 induced synaptic strengthening involves unique mechanisms that are distinct from long-term potentiation pathways. Taken together, these findings underscore the essential role of Kv4.2 in the regulation of basal synaptic strength, which is mediated by inhibition of RTCCs.Significance Statement Synaptic transmission is mediated primarily by AMPA receptors (AMPARs) and there has been considerable interest in elucidating the mechanisms underlying their recruitment during activity-dependent synaptic strengthening. However, the mechanism by which basal synaptic strength is regulated remains elusive. Here, we show that blocking postsynaptic Kv4.2 enhances AMPAR-mediated currents in hippocampal neurons, and that this enhancement is mediated by the signaling mechanisms involving R-type Ca²⁺ channels, protein kinases A and C. Importantly, Kv4.2 inhibition did not occlude activity-dependent synaptic potentiation, suggesting its specific influence in regulating synaptic AMPARs under basal conditions. Thus, our study highlights the critical function of Kv4.2 in regulating Ca²⁺ signaling at subthreshold potentials, thereby regulating basal synaptic strength.

Voltage-gated K⁺ channels of the Kv2 family are highly expressed in brain and play dual roles in regulating neuronal excitability and in organizing endoplasmic reticulum - plasma membrane (ER-PM) junctions. Studies in heterologous cells suggest that Kv2.1 and Kv2.2 co-assemble with "electrically silent" KvS subunits to form heterotetrameric channels with distinct biophysical properties, but the prevalence and localization of these channels in native neurons is unknown. Here, using mass spectrometry-based proteomics, we identified five KvS subunits as components of native Kv2.1 channels immunopurified from mouse brain of both sexes, the most abundant being Kv5.1. We found that Kv5.1 co-immunoprecipitates with Kv2.1 and to a lesser extent with Kv2.2 from brain lysates, and that Kv5.1 protein levels are decreased by 70% in Kv2.1 knockout mice and 95% in Kv2.1/Kv2.2 double knockout mice. RNAscope and immunolabelling revealed that Kv5.1 is prominently expressed in neocortex, where it is detected in a substantial fraction of Kv2.1/Kv2.2 positive neurons in layers 2/3, 5, and 6. At the subcellular level, Kv5.1 protein is co-clustered with Kv2.1 and Kv2.2 at presumptive ER-PM junctions on the soma and proximal dendrites of cortical neurons. Moreover, in addition to modifying channel conductance, we found that Kv2/Kv5.1 channels are less phosphorylated and insensitive to RY785, a potent and selective Kv2 channel inhibitor. Together, these findings demonstrate that KvS subunits create multiple Kv2 channel subtypes in brain. Most notably, Kv2/Kv5.1 channels are highly expressed in cortical neurons, where their unique properties likely modulate the critical conducting and non-conducting roles of Kv2 channels.Significance Statement Voltage-gated Kv2 potassium channels play important roles in regulating neuronal excitability and organizing endoplasmic reticulum - plasma membrane (ER-PM) junctions in brain neurons. Here, we use mass spectrometry to identify five KvS channel subunits as components of native Kv2 channels in brain. The most abundant of these subunits, Kv5.1, is prominently expressed in cortex, where it clusters at ER-PM junctions with Kv2 subunits in a subpopulation of cortical neurons. Kv5.1 expression depends on Kv2 subunits, and Kv2/Kv5.1 heteromeric channels differ in their biophysical and pharmacological properties. We propose that differential expression of Kv5.1 in subclasses of cortical neurons diversifies Kv2 channel function.

Many daily behaviors rely on estimates of our body's motion and orientation in space. Vestibular signals are essential for such estimates but to contribute appropriately two key computations are required. First, ambiguous motion information from the otolith organs must be combined with spatially transformed rotational signals (e.g., from the canals) to distinguish head translation from tilt. Second, tilt and translation estimates must be transformed from a head- to a body-centered reference frame to correctly interpret the body's motion. Studies have shown that cells in the caudal cerebellar vermis (nodulus/ventral uvula, NU) reflect the output of the first set of computations to estimate translation and tilt. However, it remains unknown whether these estimates are encoded exclusively in head-centered coordinates or whether they reflect further transformation towards body-centered coordinates. Here we addressed this question by examining how the 3D spatial tuning of otolith and canal signals on translation- and tilt-selective NU Purkinje cells in male rhesus monkeys varies with changes in head-re-body and body-re-gravity orientation. We show that NU cell tuning properties are consistent with head-centered otolith signal coding during translation. Furthermore, while canal signals in the NU have been transformed into a specific world-referenced rotation signal indicating reorientation relative to gravity (tilt), as needed to resolve the tilt-translation ambiguity, the resulting tilt estimates are encoded in head-centered coordinates. Our results thus suggest that body-centered motion and orientation estimates required for postural control, navigation and reaching are computed elsewhere, either by further transforming NU outputs or via computations in other parallel pathways.Significance statement Estimates of body motion and orientation are essential for daily activities. Vestibular signals contribute vitally to such estimates but must first undergo transformations to distinguish translation from tilt and convert head-centered estimates into body-centered representations. Previous studies implicated the caudal cerebellar vermis (nodulus/uvula, NU) in computing estimates of translation and tilt. However, here we show for the first time that NU cells encode such estimates exclusively in head-centered coordinates. The NU thus reflects motion estimates appropriate for head and gaze stabilization but not the body-centered representations relevant for tasks such as body postural control and reaching. We suggest that head- versus body-centered motion and orientation estimates may be computed via at least partially distinct cerebellar pathways serving different functional roles.

Opioid use disorder constitutes a major health and economic burden, but our limited understanding of the underlying neurobiology impedes better interventions. Alteration in the activity and output of dopamine (DA) neurons in the ventral tegmental area (VTA) contributes to drug effects, but the mechanisms underlying these changes remain relatively unexplored. We used translating ribosome affinity purification and RNA sequencing to identify gene expression changes in mouse VTA DA neurons following chronic morphine exposure. We found that expression of the neuropeptide neuromedin S (Nms) is robustly increased in VTA DA neurons by morphine. Using an NMS-iCre driver line, we confirmed that a subset of VTA neurons express NMS and that chemogenetic modulation of VTA NMS neuron activity altered morphine responses in male and female mice. Specifically, VTA NMS neuronal activation promoted morphine locomotor activity while inhibition reduced morphine locomotor activity and conditioned place preference (CPP). Interestingly, these effects appear specific to morphine, as modulation of VTA NMS activity did not affect cocaine behaviors, consistent with our data that cocaine administration does not increase VTA Nms expression. Chemogenetic manipulation of VTA neurons that express glucagon-like peptide, a transcript also robustly increased in VTA DA neurons by morphine, does not alter morphine-elicited behavior, further highlighting the functional relevance of VTA NMS-expressing neurons. Together, our current data suggest that NMS-expressing neurons represent a novel subset of VTA neurons that may be functionally relevant for morphine responses and support the utility of cell type-specific analyses like TRAP to identify neuronal adaptations underlying substance use disorder.Significance Statement The opioid epidemic remains prevalent in the U.S., with more than 70% of overdose deaths caused by opioids. The ventral tegmental area (VTA) is responsible for regulating reward behavior. Although drugs of abuse can alter VTA dopaminergic neuron function, the underlying mechanisms have yet to be fully explored. This is partially due to the cellular heterogeneity of the VTA. Here, we identify a novel subset of VTA neurons that express the neuropeptide neuromedin S (NMS). Nms expression is robustly increased by morphine and alteration of VTA NMS neuronal activity is sufficient to alter morphine-elicited behaviors. Our findings are the first to implicate NMS-expressing neurons in drug behavior and thereby improve our understanding of opioid-induced adaptations in the VTA.

Because of the important roles of both serotonin (5-HT) and the cerebellum in regulating anxiety, we asked whether 5-HT signaling within the cerebellum is involved in anxiety behavior. Physiological 5-HT levels were measured in vivo by expressing a fluorescent sensor for 5-HT in lobule VII of the cerebellum, while using fiber photometry to measure sensor fluorescence during anxiety behavior on the elevated zero maze. Serotonin increased in lobule VII when male mice were less anxious and decreased when mice were more anxious. To establish a causal role for this serotonergic input in anxiety behavior, we photostimulated or photoinhibited serotonergic terminals in lobule VII while mice were in an elevated zero maze. Photostimulating these terminals reduced anxiety behavior in mice, while photoinhibiting them enhanced anxiety behavior. Our findings add to evidence that cerebellar lobule VII is a topographical locus for anxiety behavior and establish that 5-HT input into this lobule is necessary and sufficient to bidirectionally influence anxiety behavior. These results represent progress toward understanding how the cerebellum regulates anxiety behavior and provide new evidence for a functional connection between the cerebellum and the serotonin system within the anxiety circuit.Significance Statement This is the first analysis of the involvement of the neuromodulator, serotonin, in the cerebellum during anxiety behavior. Our results reveal that serotonin regulates anxiety behavior. This offers new insight into the role of serotonin in the cerebellum, as well as illuminating how the cerebellum interacts with the rest of the brain to produce anxiety. Our results are important for future use of serotonin-related pharmacological therapeutics, such as selective serotonin-reuptake inhibitors, in treating anxiety in humans.