•Studies on the role of serotonergic system in motor control are summarized.•Effect of serotonin varies depending on the type of 5-HT receptor in the target.•Genetic tracing method revealed its ...connectivity with other brain regions.•Large-scale neural activity imaging revealed its internal sensorimotor computation.•The serotonergic system may modulate motor control independent of its other functions.
The serotonergic system in the vertebrate brain is implicated in various behaviors and diseases. Its involvement in motor control has been studied for over half a century, but efforts to build a unified model of its functions have been hampered due to the complexity of serotonergic neuromodulation. This review summarizes the anatomical structure of the serotonergic system, its afferent and efferent connections to other brain regions, and recent insights into the sensorimotor computations in the serotonergic system, and considers future research directions into the roles of serotonergic system in motor control.
Genetically encoded voltage indicators (GEVIs) enable monitoring of neuronal activity at high spatial and temporal resolution. However, the utility of existing GEVIs has been limited by the ...brightness and photostability of fluorescent proteins and rhodopsins. We engineered a GEVI, called Voltron, that uses bright and photostable synthetic dyes instead of protein-based fluorophores, thereby extending the number of neurons imaged simultaneously in vivo by a factor of 10 and enabling imaging for significantly longer durations relative to existing GEVIs. We used Voltron for in vivo voltage imaging in mice, zebrafish, and fruit flies. In the mouse cortex, Voltron allowed single-trial recording of spikes and subthreshold voltage signals from dozens of neurons simultaneously over a 15-minute period of continuous imaging. In larval zebrafish, Voltron enabled the precise correlation of spike timing with behavior.
We developed a new way to engineer complex proteins toward multidimensional specifications using a simple, yet scalable, directed evolution strategy. By robotically picking mammalian cells that were ...identified, under a microscope, as expressing proteins that simultaneously exhibit several specific properties, we can screen hundreds of thousands of proteins in a library in just a few hours, evaluating each along multiple performance axes. To demonstrate the power of this approach, we created a genetically encoded fluorescent voltage indicator, simultaneously optimizing its brightness and membrane localization using our microscopy-guided cell-picking strategy. We produced the high-performance opsin-based fluorescent voltage reporter Archon1 and demonstrated its utility by imaging spiking and millivolt-scale subthreshold and synaptic activity in acute mouse brain slices and in larval zebrafish in vivo. We also measured postsynaptic responses downstream of optogenetically controlled neurons in C. elegans.
To execute accurate movements, animals must continuously adapt their behavior to changes in their bodies and environments. Animals can learn changes in the relationship between their locomotor ...commands and the resulting distance moved, then adjust command strength to achieve a desired travel distance. It is largely unknown which circuits implement this form of motor learning, or how. Using whole-brain neuronal imaging and circuit manipulations in larval zebrafish, we discovered that the serotonergic dorsal raphe nucleus (DRN) mediates short-term locomotor learning. Serotonergic DRN neurons respond phasically to swim-induced visual motion, but little to motion that is not self-generated. During prolonged exposure to a given motosensory gain, persistent DRN activity emerges that stores the learned efficacy of motor commands and adapts future locomotor drive for tens of seconds. The DRN’s ability to track the effectiveness of motor intent may constitute a computational building block for the broader functions of the serotonergic system.
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•The dorsal raphe nucleus (DRN) mediates short-term locomotor learning•DRN responses convey the visual outcomes of swim motor commands•Learning induces a motor memory signal in the DRN that modulates future swimming•DRN ablation/activation abolishes/extends the effect of learning
Animals use environmental feedback to learn the effectiveness of their movements: in larval zebrafish, this motor learning process is mediated by sensorimotor responses and persistent activity in serotonergic neurons in the dorsal raphe nucleus.
Genetic labeling of neurons with a specific response feature is an emerging technology for precise dissection of brain circuits that are functionally heterogeneous at the single-cell level. While ...immediate early gene mapping has been widely used for decades to identify brain regions which are activated by external stimuli, recent characterization of the promoter and enhancer elements responsible for neuronal activity-dependent transcription have opened new avenues for live imaging of active neurons. Indeed, these advancements provided the basis for a growing repertoire of novel experiments to address the role of active neuronal networks in cognitive behaviors. In this review, we summarize the current literature on the usage and development of activity-dependent promoters and discuss the future directions of this expanding new field.
CREB is a pivotal mediator of activity-regulated gene transcription that underlies memory formation and allocation. The contribution of a key CREB cofactor, CREB-regulated transcription coactivator 1 ...(CRTC1), has, however, remained elusive. Here we show that several constitutive kinase pathways and an activity-regulated phosphatase, calcineurin, converge to determine the nucleocytoplasmic shuttling of CRTC1. This, in turn, triggered an activity-dependent association of CRTC1 with CREB-dependent regulatory elements found on IEG promoters. Forced expression of nuclear CRTC1 in hippocampal neurons activated CREB-dependent transcription, and was sufficient to enhance contextual fear memory. Surprisingly, during contextual fear conditioning, we found evidence of nuclear recruitment of endogenous CRTC1 only in the basolateral amygdala, and not in the hippocampus. Consistently, CRTC1 knockdown in the amygdala, but not in the hippocampus, significantly attenuated fear memory. Thus, CRTC1 has a wide impact on CREB-dependent memory processes, but fine-tunes CREB output in a region-specific manner.
The neuronal immediate early gene Arc/Arg-3.1 is widely used as one of the most reliable molecular markers for intense synaptic activity in vivo. However, the cis-acting elements responsible for such ...stringent activity dependence have not been firmly identified. Here we combined luciferase reporter assays in cultured cortical neurons and comparative genome mapping to identify the critical synaptic activity-responsive elements (SARE) of the Arc/Arg-3.1 gene. A major SARE was found as a unique almost equal to100-bp element located at >5 kb upstream of the Arc/Arg-3.1 transcription initiation site in the mouse genome. This single element, when positioned immediately upstream of a minimal promoter, was necessary and sufficient to replicate crucial properties of endogenous Arc/Arg-3.1's transcriptional regulation, including rapid onset of transcription triggered by synaptic activity and low basal expression during synaptic inactivity. We identified the major determinants of SARE as a unique cluster of neuronal activity-dependent cis-regulatory elements consisting of closely localized binding sites for CREB, MEF2, and SRF. Consistently, a SARE reporter could readily trace and mark an ensemble of cells that have experienced intense activity in the recent past in vivo. Taken together, our work uncovers a novel transcriptional mechanism by which a critical 100-bp element, SARE, mediates a predominant component of the synapse-to-nucleus signaling in ensembles of Arc/Arg-3.1-positive activated neurons.
Uninterrupted arousal is important for survival during threatening situations. Activation of orexin/hypocretin neurons is implicated in sustained arousal. However, orexin neurons produce and release ...orexin as well as several co-transmitters including dynorphin and glutamate. To disambiguate orexin-dependent and -independent physiological functions of orexin neurons, we generated a novel Orexin-flippase (Flp) knock-in mouse line. Crossing with Flp-reporter or Cre-expressing mice showed gene expression exclusively in orexin neurons. Histological studies confirmed that orexin was knock-out in homozygous mice. Orexin neurons without orexin showed altered electrophysiological properties, as well as received decreased glutamatergic inputs. Selective chemogenetic activation revealed that both orexin and co-transmitters functioned to increase wakefulness, however, orexin was indispensable to promote sustained arousal. Surprisingly, such activation increased the total time spent in cataplexy. Taken together, orexin is essential to maintain basic membrane properties and input-output computation of orexin neurons, as well as to exert awake-sustaining aptitude of orexin neurons.
Abstract The clinical effectiveness of the newly released neuraminidase inhibitors (NAIs) laninamivir and peramivir has not been sufficiently evaluated in influenza-infected patients in clinical and ...practical settings. In this study, we analyzed the clinical data of 211 patients infected with influenza A virus subtype H3N2 (A(H3N2)) and 45 patients infected with influenza A virus subtype H1N1pdm (A(H1N1)pdm09) who received the NAIs oseltamivir, zanamivir, laninamivir, or peramivir during the 2010-2011 influenza season. The duration of fever from the first dose of the NAI to fever alleviation to <37.5 °C was evaluated as an indicator of the clinical effectiveness of the NAIs in the influenza-infected patients. For the A(H3N2)-infected patients, Kaplan–Meier analysis showed the peramivir treatment group had the fastest time of fever alleviation to <37.5 °C (median 17.0 h, 95 % confidence interval CI 7.2–26.8 h) of the four treatment groups. No significant difference was found in the time to fever alleviation among the other antivirals, oseltamivir, zanamivir, and laninamivir. Results of multivariate analysis, using a Cox proportional-hazards model (hazard ratio 3.321) adjusted for the factors age, sex, body weight, vaccination status, time from onset to the clinic visit, and body temperature showed significantly faster fever alleviation in the peramivir treatment group compared with the oseltamivir treatment group. For the A(H1N1)pdm09-infected patients, only the oseltamivir and zanamivir treatment groups were compared, and no significant difference in time to alleviation of fever was observed between the two groups. Based on a cycling probe real-time polymerase chain reaction (PCR) assay, none of the A(H1N1)pdm09 strains in this study had the H275Y mutation conferring oseltamivir resistance. Further evaluation of the clinical effectiveness of the newly released NAIs for influenza-infected patients, including those infected with A(H1N1)pdm09, is needed.
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