Fluctuation of lysosomal protein degradation in neural stem cells of the postnatal mouse brain.

Lysosomes are intracellular organelles responsible for degrading diverse macromolecules delivered from several pathways, including the endo-lysosomal and autophagic pathways. Recent reports have suggested that lysosomes are essential for regulating neural stem cells in developing, adult and aged brains. However, the activity of these lysosomes has yet to be monitored in these brain tissues. Here, we report the development of a new probe to measure lysosomal protein degradation in brain tissue by immunostaining. Our results indicate that lysosomal protein degradation fluctuates in neural stem cells of the hippocampal dentate gyrus, depending on age and brain disorders. Neural stem cells increase their lysosomal activity during hippocampal development in the dentate gyrus, but aging and aging-related disease reduce lysosomal activity. In addition, physical exercise increases lysosomal activity in neural stem cells and astrocytes in the dentate gyrus. We therefore propose that three different stages of lysosomal activity exist: the state of increase during development, the stable state during adulthood and the state of reduction due to damage caused by either age or disease.

Recurrent rewiring of the adult hippocampal mossy fiber system by a single transcriptional regulator, Id2.

Circuit formation in the central nervous system has been historically studied during development, after which cell-autonomous and nonautonomous wiring factors inactivate. In principle, balanced reactivation of such factors could enable further wiring in adults, but their relative contributions may be circuit dependent and are largely unknown. Here, we investigated hippocampal mossy fiber sprouting to gain insight into wiring mechanisms in mature circuits. We found that sole ectopic expression of Id2 in granule cells is capable of driving mossy fiber sprouting in healthy adult mouse and rat. Mice with the new mossy fiber circuit solved spatial problems equally well as controls but appeared to rely on local rather than global spatial cues. Our results demonstrate reprogrammed connectivity in mature neurons by one defined factor and an assembly of a new synaptic circuit in adult brain.

Young adult males have worse survival than females that is largely independent of treatment received for many types of central nervous system tumors: A National Cancer Database analysis.

BACKGROUND: Central nervous system (CNS) tumors rank among the top 5 cancers diagnosed in young adults aged 20 to 39 years at diagnosis and show a clear male excess in incidence. It is unknown whether sex differences in survival persist across histologic types and depend on the treatment received. METHODS: From the National Cancer Database (2004-2016), young adults (aged 20-39 years) who had been diagnosed with CNS tumors were identified. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated as measures of association between sex and death via Cox regression. An inverse odds weighting mediation analysis was performed with treatment received as a mediator. RESULTS: There were 47,560 cases (47% male). Males had worse overall survival than females for 9 of 16 histologic types, including diffuse astrocytoma, glioblastoma, and meningioma (all P < .05). Males had an increased risk of death after a brain tumor diagnosis overall (HR, 1.47; 95% CI, 1.41-1.53) and for 8 histologies. There was a significant association between male sex and death overall that was mediated by treatment received (indirect-effect HR, 1.17; 95% CI, 1.15-1.18), but no single histology had a significant indirect effect. All histologies examined in mediation analyses had significant direct effects for sex. The excess mortality due to sex was 20% for all CNS tumors combined and 34% among males with CNS tumors. CONCLUSIONS: Overall, treatment received may mediate a portion of the association between sex and death after a CNS tumor, but sex itself appears to be a stronger risk factor for death in this study.

Circuit formation in the adult brain.

Neurons in the mammalian central nervous system display an enormous capacity for circuit formation during development but not later in life. In principle, new circuits could be also formed in adult brain, but the absence of the developmental milieu and the presence of growth inhibition and hundreds of working circuits are generally viewed as unsupportive for such a process. Here, we bring together evidence from different areas of neuroscience-such as neurological disorders, adult-brain neurogenesis, innate behaviours, cell grafting, and in vivo cell reprogramming-which demonstrates robust circuit formation in adult brain. In some cases, adult-brain rewiring is ongoing and required for certain types of behaviour and memory, while other cases show significant promise for brain repair in disease models. Together, these examples highlight that the adult brain has higher capacity for structural plasticity than previously recognized. Understanding the underlying mechanisms behind this retained plasticity has the potential to advance basic knowledge regarding the molecular organization of synaptic circuits and could herald a new era of neural circuit engineering for therapeutic repair.

The Role of the Dopamine Transporter in the Effects of Amphetamine on Sleep and Sleep Architecture in Drosophila.

The dopamine transporter (DAT) mediates the inactivation of released dopamine (DA) through its reuptake, and thereby plays an important homeostatic role in dopaminergic neurotransmission. Amphetamines exert their stimulant effects by targeting DAT and inducing the reverse transport of DA, leading to a dramatic increase of extracellular DA. Animal models have proven critical to investigating the molecular and cellular mechanisms underlying transporter function and its modulation by psychostimulants such as amphetamine. Here we establish a behavioral model for amphetamine action using adult Drosophila melanogaster. We use it to characterize the effects of amphetamine on sleep and sleep architecture. Our data show that amphetamine induces hyperactivity and disrupts sleep in a DA-dependent manner. Flies that do not express a functional DAT (dDAT null mutants) have been shown to be hyperactive and to exhibit significantly reduced sleep at baseline. Our data show that, in contrast to its action in control flies, amphetamine decreases the locomotor activity of dDAT null mutants and restores their sleep by modulating distinct aspects of sleep structure. To begin to explore the circuitry involved in the actions of amphetamine on sleep, we also describe the localization of dDAT throughout the fly brain, particularly in neuropils known to regulate sleep. Together, our data establish Drosophila as a robust model for studying the regulatory mechanisms that govern DAT function and psychostimulant action.

Effects of ß-amyloid (1-42) Administration on the Main Neurogenic Niches of the Adult Brain: Amyloid-Induced Neurodegeneration Influences Neurogenesis.

Alzheimer's disease (AD) is the most prevalent neurodegenerative disorder and warrants further study as well as timely treatment. Additionally, the mechanisms of the brain's intrinsic defense against chronic injury are not yet fully understood. Herein, we examined the response of the main neurogenic niches to amyloid exposure and the associated changes in structure and synaptic activity. Flow cytometry of Nestin-, Vimentin-, Nestin/Vimentin-, NeuN-, GFAP-, NeuN/GFAP-, NSE-, BrdU-, Wnt-, BrdU/Wnt-, VEGF-, Sox14-, VEGF/Sox14-, Sox10-, Sox2-, Sox10/Sox2-, Bax-, and Bcl-xL-positive cells was performed in the subventricular zone (SVZ), hippocampus, and cerebral cortex of rat brains on 90th day after intracerebroventricular (i.c.v.) single injection of a fraction of ß-amyloid (Aß) (1-42). The relative structural changes in these areas and disruptions to synaptic activity in the entorhinal cortex-hippocampus circuit were also evaluated. Our flow analyses revealed a reduction in the numbers of Nestin-, Vimentin-, and Nestin/Vimentin-positive cells in neurogenic niches and the olfactory bulb. These changes were accompanied by an increased number of BrdU-positive cells in the hippocampus and SVZ. The latter changes were strongly correlated with changes in the numbers of VEGF- and VEGF/Sox14-positive cells. The morphological changes were characterized by significant neural loss, a characteristic shift in entorhinal cortex-hippocampus circuit activity, and decreased spontaneous alternation in a behavioral test. We conclude that although an injection of Aß (1-42) induced stem cell proliferation and triggered neurogenesis at a certain stage, this process was incomplete and led to neural stem cell immaturity. We propose the idea of enhancing adult neurogenesis as a promising strategy for preventing dementia at healthy elderly people andpeople at high risk for developing AD, or treating patients diagnosed with AD.

Proliferative Capacity of Adult Mouse Brain.

We studied cell proliferation in the postnatal mouse brain between the ages of 2 and 30 months and identified four compartments with different densities of proliferating cells. The first identified compartment corresponds to the postnatal pallial neurogenic (PPN) zone in the telencephalon; the second to the subpallial postnatal neurogenic (SPPN) zone in the telencephalon; the third to the white matter bundles in the telencephalon; and the fourth to all brain parts outside of the other three compartments. We estimated that about 3.4 million new cells, including 0.8 million in the subgranular zone (SGZ) in the hippocampus, are produced in the PPN zone. About 21 million new cells, including 10 million in the subependymal zone (SEZ) in the lateral walls of the lateral ventricle and 2.7 million in the rostral migratory stream (RMS), are produced in the SPPN zone. The third and fourth compartments together produced about 31 million new cells. The analysis of cell proliferation in neurogenic zones shows that postnatal neurogenesis is the direct continuation of developmental neurogenesis in the telencephalon and that adult neurogenesis has characteristics of the late developmental process. As a developmental process, adult neurogenesis supports only compensatory regeneration, which is very inefficient.

Sexual differentiation of microglia.

Sex plays a role in the incidence and outcome of neurological illnesses, also influencing the response to treatments. Despite sexual differentiation of the brain has been extensively investigated, the study of sex differences in microglia, the brain's resident immune cells, has been largely neglected until recently. To fulfill this gap, our laboratory developed several tools, including cellular and animal models, which bolstered in-depth studies on sexual differentiation of microglia and its impact on brain physiology, as well as on the onset and progression of neurological disorders. Here, we summarize the current status of knowledge on the sex-dependent function of microglia, and report recent evidence linking these cells to the sexual bias in the susceptibility to neurological brain diseases.

Acute alcohol intoxication as a confounding factor for mild traumatic brain injury.

BACKGROUND: Acute alcohol intoxication is universally considered a risk factor for traumatic brain injury (TBI), therefore an indication for head CT scan. There is no evidence in the literature for this attitude. Aim of this study is to assess the need for head CT scan in acutely alcohol-intoxicated subjects with mTBI and the role of Glasgow coma scale (GCS) score in this kind of patients. METHODS: We retrospectively analyzed all 3358 consecutive patients presenting to our department in Switzerland, with TBI as chief complaint between January 2014 and January 2018. RESULTS: Alcohol was a statistically significant factor for presentation with a GCS score lower than 15. As for bleedings in mild TBI patients, the results were somewhat contradictory with GCS 15 patients showing a higher percentage of hemorrhages than GCS 14 patients. By dividing alcohol-intoxicated subjects into groups per blood alcohol concentration, the higher was the alcohol level, the lower the GCS score. CONCLUSIONS: We can affirm that GCS score is underestimated in acutely intoxicated head trauma patients. In this kind of patient, alcohol is a confounding factor and mild TBI could be safely managed by watchful waiting.

Risk factors of radiotherapy-induced cerebral microbleeds and serial analysis of their size compared with white matter changes: A 7T MRI study in 113 adult patients with brain tumors.

BACKGROUND: Although radiation therapy (RT) contributes to survival benefit in many brain tumor patients, it has also been associated with long-term brain injury. Cerebral microbleeds (CMBs) represent an important manifestation of radiation-related injury. PURPOSE: To characterize the change in size and number of CMBs over time and to evaluate their relationship to white matter structural integrity as measured using diffusion MRI indices. STUDY TYPE: Longitudinal, retrospective, human cohort. POPULATION: In all, 113 brain tumor patients including patients treated with focal RT (n = 91, 80.5%) and a subset of nonirradiated controls (n = 22, 19.5%). FIELD STRENGTH/SEQUENCE: Single and multiecho susceptibility-weighted imaging (SWI) and multiband, shell, and direction diffusion tensor imaging (DTI) at 7 T. ASSESSMENT: Patients were scanned either once or serially. CMBs were detected and quantified on SWI images using a semiautomated approach. Local and global fractional anisotropy (FA) were measured from DTI data for a subset of 35 patients. STATISTICAL TESTS: Potential risk factors for CMB development were determined by multivariate linear regression and using linear mixed-effect models. Longitudinal FA was quantitatively and qualitatively evaluated for trends. RESULTS: All patients scanned at 1 or more years post-RT had CMBs. A history of multiple surgical resections was a risk factor for development of CMBs. The total number and volume of CMBs increased by 18% and 11% per year, respectively, although individual CMBs decreased in volume over time. Simultaneous to these microvascular changes, FA decreased by a median of 6.5% per year. While the majority of nonirradiated controls had no CMBs, four control patients presented with fewer than five CMBs. DATA CONCLUSION: Identifying patients who are at the greatest risk for CMB development, with its likely associated long-term cognitive impairment, is an important step towards developing and piloting preventative and/or rehabilitative measures for patients undergoing RT. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2019;50:868-877.

Dexmedetomidine for Refractory Intracranial Hypertension.

Dexmedetomidine (DEX) is a selective α2 adrenergic agonist that is commonly used for sedation in the intensive care unit (ICU). The role of DEX for adjunctive treatment of refractory intracranial hypertension is poorly defined. The primary objective of this study was to determine the effect of DEX on the need for rescue therapy (ie, hyperosmolar boluses, extraventricular drain [EVD] drainages) for refractory intracranial hypertension. Secondary objectives included the number of intracranial pressure (ICP) excursions, bradycardic, hypotensive, and compromised cerebral perfusion pressure episodes. This retrospective cohort study evaluated patients admitted to the neurosurgical ICU from August 1, 2009, to July 29, 2015, and who received DEX for refractory intracranial hypertension. The objectives were compared between the 2 time periods-before (pre-DEX) and during therapy (DEX). Twenty-three patients with 26 episodes of refractory intracranial hypertension met the inclusion criteria. The number of hyperosmolar boluses was decreased after DEX therapy was initiated. Mannitol boluses required were statistically reduced (1 vs 0.5, P = .03); however, reduction in hypertonic boluses was not statistically significant (1.3 vs 0.9, P = .2). The mean number of EVD drainages per 24 hours was not significantly different between the time periods (15.7 vs 14.0, P = .35). The rate of ICP excursions did not differ between the 2 groups (24.3 vs 22.5, P = .62). When compared to pre-DEX data, there was no difference in the median number of hypotensive (0 vs 0), bradycardic (0 vs 0), or compromised cerebral perfusion pressure episodes (0.5 vs 1.0). Dexmedetomidine may avoid increases in the need for rescue therapy when used as an adjunctive treatment of refractory intracranial hypertension without compromising hemodynamics.

Adult hippocampal MeCP2 preserves the genomic responsiveness to learning required for long-term memory formation.

MeCP2 is required both during postnatal neurodevelopment and throughout the adult life for brain function. Although it is well accepted that MeCP2 in the maturing nervous system is critical for establishing normal development, the functions of MeCP2 during adulthood are poorly understood. Particularly, the requirement of hippocampal MeCP2 for cognitive abilities in the adult is not studied. To characterize the role of MeCP2 in adult neuronal function and cognition, we used a temporal and region-specific disruption of MeCP2 expression in the hippocampus of adult male mice. We found that MeCP2 is required for long-term memory formation and that it controls the learning-induced transcriptional response of hippocampal neurons required for memory consolidation. Furthermore, we uncovered MeCP2 functions in the adult hippocampus that may underlie cognitive integrity. We showed that MeCP2 maintains the developmentally established chromatin configuration and epigenetic landscape of CA1 neurons throughout the adulthood, and that it regulates the expression of neuronal and immune-related genes in the adult hippocampus. Overall, our findings identify MeCP2 as a maintenance factor in the adult hippocampus that preserves signal responsiveness of the genome and allows for integrity of cognitive functions. This study provides new insight into how MeCP2 maintains adult brain functions, but also into the mechanisms underlying the cognitive impairments observed in RTT patients and highlights the understudied role of DNA methylation interpretation in adult cognitive processes.

The effect of contextual auditory stimuli on virtual spatial navigation in patients with focal hemispheric lesions.

Topographical disorientation is a frequent deficit among patients suffering from brain injury. Spatial navigation can be explored in this population using virtual reality environments, even in the presence of motor or sensory disorders. Furthermore, the positive or negative impact of specific stimuli can be investigated. We studied how auditory stimuli influence the performance of brain-injured patients in a navigational task, using the Virtual Action Planning-Supermarket (VAP-S) with the addition of contextual ("sonar effect" and "name of product") and non-contextual ("periodic randomised noises") auditory stimuli. The study included 22 patients with a first unilateral hemispheric brain lesion and 17 healthy age-matched control subjects. After a software familiarisation, all subjects were tested without auditory stimuli, with a sonar effect or periodic random sounds in a random order, and with the stimulus "name of product". Contextual auditory stimuli improved patient performance more than control group performance. Contextual stimuli benefited most patients with severe executive dysfunction or with severe unilateral neglect. These results indicate that contextual auditory stimuli are useful in the assessment of navigational abilities in brain-damaged patients and that they should be used in rehabilitation paradigms.

Drosophila intermediate neural progenitors produce lineage-dependent related series of diverse neurons.

Drosophila type II neuroblasts (NBs), like mammalian neural stem cells, deposit neurons through intermediate neural progenitors (INPs) that can each produce a series of neurons. Both type II NBs and INPs exhibit age-dependent expression of various transcription factors, potentially specifying an array of diverse neurons by combinatorial temporal patterning. Not knowing which mature neurons are made by specific INPs, however, conceals the actual variety of neuron types and limits further molecular studies. Here we mapped neurons derived from specific type II NB lineages and found that sibling INPs produced a morphologically similar but temporally regulated series of distinct neuron types. This suggests a common fate diversification program operating within each INP that is modulated by NB age to generate slightly different sets of diverse neurons based on the INP birth order. Analogous mechanisms might underlie the expansion of neuron diversity via INPs in mammalian brain.

Decrease in newly generated oligodendrocytes leads to motor dysfunctions and changed myelin structures that can be rescued by transplanted cells.

NG2-glia in the adult brain are known to proliferate and differentiate into mature and myelinating oligodendrocytes throughout lifetime. However, the role of these newly generated oligodendrocytes in the adult brain still remains little understood. Here we took advantage of the Sox10-iCreERT2 x CAG-eGFP x Esco2fl/fl mouse line in which we can specifically ablate proliferating NG2-glia in adult animals. Surprisingly, we observed that the generation of new oligodendrocytes in the adult brain was severely affected, although the number of NG2-glia remained stable due to the enhanced proliferation of non-recombined cells. This lack of oligodendrogenesis led to the elongation of the nodes of Ranvier as well as the associated paranodes, which could be locally rescued by myelinating oligodendrocytes differentiated from transplanted NG2-glia deriving from wildtype mice. Repetitive measurements of conduction velocity in the corpus callosum of awake animals revealed a progressive deceleration specifically in the mice lacking adult oligodendrogenesis that resulted in progressive motor deficits. In summary, here we demonstrated for the first time that axon function is not only controlled by the reliable organization of myelin, but also requires a dynamic and continuous generation of new oligodendrocytes in the adult brain. GLIA 2016;64:2201-2218.

Increased functional connectivity between language and visually deprived areas in late and partial blindness.

In the congenitally blind, language processing involves visual areas. In the case of normal visual development however, it remains unclear whether later visual loss induces interactions between the language and visual areas. This study compared the resting-state functional connectivity (FC) of retinotopic and language areas in two unique groups of late visually deprived subjects: (1) blind individuals suffering from retinitis pigmentosa (RP), (2) RP subjects without a visual periphery but with preserved central "tunnel vision", both of whom were contrasted with sighted controls. The results showed increased FC between Broca's area and the visually deprived areas in the peripheral V1 for individuals with tunnel vision, and both the peripheral and central V1 for blind individuals. These findings suggest that FC can develop in the adult brain between the visual and language systems in the completely and partially blind. These changes start in the deprived areas and increase in size (involving both foveal and peripheral V1) and strength (from negative to positive FC) as the disease and sensory deprivation progress. These observations support the claim that functional connectivity between remote systems that perform completely different tasks can change in the adult brain in cases of total and even partial visual deprivation.

Trends in alcohol use during moderate and severe traumatic brain injury: 18 years of neurotrauma in Pennsylvania.

PRIMARY OBJECTIVE: Alcohol is a known risk factor for TBI, yet little is known about how rates of alcohol use at time of injury differ across demographics and the stability of alcohol-related injury over time. Further, findings examining the relationship between alcohol and outcome are mixed. This study aimed to examine changes in alcohol-positive moderate-to-severe traumatic brain injury (+aTBI) over two decades with focus on demographic factors, changes in +aTBI frequency over time, mortality and acute outcome. METHODS: This retrospective study examined data collected from 1992-2009 by the Pennsylvania Trauma Outcome Study (PTOS). RESULTS: Results reveal that the proportion of +aTBI has been generally stable across years. However, there is an interaction of +aTBI incidence with mechanism of injury and age, with a downward trend in +aTBI within MVA and fall and individuals 18-30 and 71+ years. Further, consistent with several findings in the literature, alcohol was associated with higher rates of survival and better FSD scores during acute recovery. CONCLUSIONS: This study discusses findings in the context of a greater literature on TBI-related alcohol and outcome. The injury-alcohol profiles highlighted could be used to inform future allocation of resources toward prevention of, intervention for and care of individuals who sustain TBI.

A neuroprotective role of the NMDA receptor subunit GluN3A (NR3A) in ischemic stroke of the adult mouse.

GluN3A or NR3A is a developmentally regulated N-methyl-d-aspartate receptor (NMDAR) subunit, showing a unique inhibitory role that decreases NMDAR current and the receptor-mediated Ca(2+) influx. In the neonatal brain, GluN3A is shown to associate with synaptic maturation and spine formation and plays a neuroprotective role. Its functional role in the adult brain, however, is largely unknown. We tested the hypothesis that, disrespecting the relatively lower expression level of GluN3A in the adult brain, this inhibitory NMDAR subunit shows a protective action against ischemia-induced brain injury. In littermate wild-type (WT) and GluN3A knockout (KO) mice, focal cerebral ischemia was induced by permanent occlusion of right distal branches of the middle cerebral artery (MCA) plus 10-min ligation of both common carotid arteries (CCAs). Twenty-four hours after focal cerebral ischemia, the infarction volume assessed using 2,3,5-triphenyltetrazolium chloride (TTC) staining was significantly larger in GluN3A KO mice compared with WT mice. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining demonstrated enhanced cell death in GluN3A KO mice. Moreover, the deletion of GluN3A hindered sensorimotor functional recovery after stroke. It is suggested that, although the expression level is relatively lower in the adult brain, GluN3A is still a noteworthy regulator in ischemia-induced excitotoxicity and brain injury.

Functional mitochondrial analysis in acute brain sections from adult rats reveals mitochondrial dysfunction in a rat model of migraine.

Mitochondrial dysfunction has been implicated in many neurological disorders that only develop or are much more severe in adults, yet no methodology exists that allows for medium-throughput functional mitochondrial analysis of brain sections from adult animals. We developed a technique for quantifying mitochondrial respiration in acutely isolated adult rat brain sections with the Seahorse XF Analyzer. Evaluating a range of conditions made quantifying mitochondrial function from acutely derived adult brain sections from the cortex, cerebellum, and trigeminal nucleus caudalis possible. Optimization of this technique demonstrated that the ideal section size was 1 mm wide. We found that sectioning brains at physiological temperatures was necessary for consistent metabolic analysis of trigeminal nucleus caudalis sections. Oxygen consumption in these sections was highly coupled to ATP synthesis, had robust spare respiratory capacities, and had limited nonmitochondrial respiration, all indicative of healthy tissue. We demonstrate the effectiveness of this technique by identifying a decreased spare respiratory capacity in the trigeminal nucleus caudalis of a rat model of chronic migraine, a neurological disorder that has been associated with mitochondrial dysfunction. This technique allows for 24 acutely isolated sections from multiple brain regions of a single adult rat to be analyzed simultaneously with four sequential drug treatments, greatly advancing the ability to study mitochondrial physiology in adult neurological disorders.

Real-time in vivo monitoring of circadian E-box enhancer activity: a robust and sensitive zebrafish reporter line for developmental, chemical and neural biology of the circadian clock.

The circadian clock co-ordinates physiology and behavior with the day/night cycle. It consists of a transcriptional-translational feedback loop that generates self-sustained oscillations in transcriptional activity with a roughly 24h period via E-box enhancer elements. Numerous in vivo aspects of core clock feedback loop function are still incompletely understood, including its maturation during development, tissue-specific activity and perturbation in disease states. Zebrafish are promising models for biomedical research due to their high regenerative capacity and suitability for in vivo drug screens, and transgenic zebrafish lines are valuable tools to study transcriptional activity in vivo during development. To monitor the activity of the core clock feedback loop in vivo, we created a transgenic zebrafish line expressing a luciferase reporter gene under the regulation of a minimal promoter and four E-boxes. This Tg(4xE-box:Luc) line shows robust oscillating reporter gene expression both under light-dark cycles and upon release into constant darkness. Luciferase activity starts to oscillate during the first days of development, indicating that the core clock loop is already functional at an early stage. To test whether the Tg(4xE-box:Luc) line could be used in drug screens aimed at identifying compounds that target the circadian clock in vivo, we examined drug effects on circadian period. We were readily able to detect period changes as low as 0.7h upon treatment with the period-lengthening drugs lithium chloride and longdaysin in an assay set-up suitable for large-scale screens. Reporter gene mRNA expression is also detected in the adult brain and reveals differential clock activity across the brain, overlapping with endogenous clock gene expression. Notably, core clock activity is strongly correlated with brain regions where neurogenesis takes place and can be detected in several types of neural progenitors. Our results demonstrate that the Tg(4xE-box:Luc) line is an excellent tool for studying the regulation of the circadian clock and its maturation in vivo and in real time. Furthermore, it is highly suitable for in vivo screens targeting the core clock mechanism that take into account the complexity of an intact organism. Finally, it allows mapping of clock activity in the brain of a vertebrate model organism with prominent adult neurogenesis and high regeneration capacity.