Doublecortin-like expressing astrocytes of the suprachiasmatic nucleus are implicated in the biosynthesis of vasopressin and influences circadian rhythms.

We have recently identified a novel plasticity protein, doublecortin-like (DCL), that is specifically expressed in the shell of the mouse suprachiasmatic nucleus (SCN). DCL is implicated in neuroplastic events, such as neurogenesis, that require structural rearrangements of the microtubule cytoskeleton, enabling dynamic movements of cell bodies and dendrites. We have inspected DCL expression in the SCN by confocal microscopy and found that DCL is expressed in GABA transporter-3 (GAT3)-positive astrocytes that envelope arginine vasopressin (AVP)-expressing cells. To investigate the role of these DCL-positive astrocytes in circadian rhythmicity, we have used transgenic mice expressing doxycycline-induced short-hairpin (sh) RNA's targeting DCL mRNA (DCL knockdown mice). Compared with littermate wild type (WT) controls, DCL-knockdown mice exhibit significant shorter circadian rest-activity periods in constant darkness and adjusted significantly faster to a jet-lag protocol. As DCL-positive astrocytes are closely associated with AVP-positive cells, we analyzed AVP expression in DCL-knockdown mice and in their WT littermates by 3D reconstructions and transmission electron microscopy (TEM). We found significantly higher numbers of AVP-positive cells with increased volume and more intensity in DCL-knockdown mice. We found alterations in the numbers of dense core vesicle-containing neurons at ZT8 and ZT20 suggesting that the peak and trough of neuropeptide biosynthesis is dampened in DCL-knockdown mice compared to WT littermates. Together, our data suggest an important role for the astrocytic plasticity in the regulation of circadian rhythms and point to the existence of a specific DCL+ astrocyte-AVP+ neuronal network located in the dorsal SCN implicated in AVP biosynthesis.

Stress, glucocorticoid receptors, and adult neurogenesis: a balance between excitation and inhibition?

Adult neurogenesis, the birth of new neurons in the mature brain, has attracted considerable attention in the last decade. One of the earliest identified and most profound factors that affect adult neurogenesis both positively and negatively is stress. Here, we review the complex interplay between stress and adult neurogenesis. In particular, we review the role of the glucocorticoid receptor, the main mediator of the stress response in the proliferation, differentiation, migration, and functional integration of newborn neurons in the hippocampus. We review a multitude of mechanisms regulating glucocorticoid receptor activity in relationship to adult neurogenesis. We postulate a novel concept in which the level of glucocorticoid receptor expression directly regulates the excitation-inhibition balance, which is key for proper neurogenesis. We furthermore argue that an excitation-inhibition dis-balance may underlie aberrant functional integration of newborn neurons that is associated with psychiatric and paroxysmal brain disorders.

Reducing the global burden of cerebral venous thrombosis: An international research agenda.

BACKGROUND: Due to the rarity of cerebral venous thrombosis (CVT), performing high-quality scientific research in this field is challenging. Providing answers to unresolved research questions will improve prevention, diagnosis, and treatment, and ultimately translate to a better outcome of patients with CVT. We present an international research agenda, in which the most important research questions in the field of CVT are prioritized. AIMS: This research agenda has three distinct goals: (1) to provide inspiration and focus to research on CVT for the coming years, (2) to reinforce international collaboration, and (3) to facilitate the acquisition of research funding. SUMMARY OF REVIEW: This international research agenda is the result of a research summit organized by the International Cerebral Venous Thrombosis Consortium in Amsterdam, the Netherlands, in June 2023. The summit brought together 45 participants from 15 countries including clinical researchers from various disciplines, patients who previously suffered from CVT, and delegates from industry and non-profit funding organizations. The research agenda is categorized into six pre-specified themes: (1) epidemiology and clinical features, (2) life after CVT, (3) neuroimaging and diagnosis, (4) pathophysiology, (5) medical treatment, and (6) endovascular treatment. For each theme, we present two to four research questions, followed by a brief substantiation per question. The research questions were prioritized by the participants of the summit through consensus discussion. CONCLUSIONS: This international research agenda provides an overview of the most burning research questions on CVT. Answering these questions will advance our understanding and management of CVT, which will ultimately lead to improved outcomes for CVT patients worldwide.

Doublecortin-Like Is Implicated in Adult Hippocampal Neurogenesis and in Motivational Aspects to Escape from an Aversive Environment in Male Mice.

Doublecortin (DCX)-like (DCL) is a microtubule (MT)-associated protein (MAP) that is highly homologous to DCX and is crucially involved in embryonic neurogenesis. Here, we have investigated the in vivo role of DCL in adult hippocampal neurogenesis by generating transgenic mice producing inducible shRNA molecules that specifically target DCL but no other splice variants produced by the DCLK gene. DCL knock-down (DCL-KD) resulted in a significant increase in the number of proliferating BrdU+ cells in the subgranular zone (SGZ) 1 d after BrdU administration. However, the number of surviving newborn adult NeuN+/BrdU+ neurons are significantly decreased when inspected four weeks after BrdU administration suggesting a blockade of neuronal differentiation after DCL-KD. In line with this, we observed an increase in the number of proliferating cells, but a significant decrease in postmitotic DCX+ cells that are characterized by long dendrites spanning all dentate gyrus layers. Behavioral analysis showed that DCL-KD strongly extended the escape latency of mice on the circular hole board (CHB) but did not affect other aspects of this behavioral task. Together, our results indicate a function for DCL in adult neurogenesis and in the motivation to escape from an aversive environment. In contrast to DCX, its pivotal role in the maturation of postmitotic neuronal progenitor cells (NPCs) marks DCL as a genuine adult neurogenesis indicator in the hippocampus.

Delineation of violence from functional aggression in mice: an ethological approach.

The present study aims at delineating violence from aggression, using genetically selected high (SAL, TA, NC900) and low (LAL, TNA NC100) aggressive mouse strains. Unlike aggression, violence lacks intrinsic control, environmental constraints as well as functional endpoints. Conventional measures namely latency, frequency and duration were used initially to accomplish the objective of delineation using the above strains. However, these quantitative measures fail to reveal further details beyond the magnitude of differential aggression, especially within the high aggressive mouse strains. Hence, it was necessary to analyze further, the behavioral sequences that make up the agonistic encounter. Novel measures such as threat/(attack + chase) (T/AC) and offense/withdrawal (O/W) ratios, context dependency and first-order Markov chain analysis were used for the above purpose. Our present analyses reveal clear qualitative behavioral differences between the three high aggressive selection strains based on the following facets namely structure and context in an agonistic interaction. Structure refers to a detailed study of the agonistic interaction components (ritualistic display, offense and sensitivity to the opponent submission cues) between any two subjects (inter-male interaction for the present study). Context refers to the capacity to identify an opponent by nature of its state (free moving/anesthetized), sex and the environment (home/neutral territory). NC900 displayed context dependency and structurally a rich repertoire of agonistic interaction components with an opponent. SAL failed to show discrimination and its inter-male agonistic behavior is restricted to a repetitive and an opponent-insensitive pattern of attack and chase. TA was comparable to SAL in terms of the structure but sensitive to context variables. Thus, SAL seems to display a violent form of aggressive behavior, while NC900 display 'functional' hyperaggression against a docile opponent in an inter-male agonistic interaction.

Silencing of doublecortin-like (DCL) results in decreased mitochondrial activity and delayed neuroblastoma tumor growth.

Doublecortin-like (DCL) is a microtubule-binding protein crucial for neuroblastoma (NB) cell proliferation. We have investigated whether the anti-proliferative effect of DCL knockdown is linked to reduced mitochondrial activity. We found a delay in tumor development after DCL knockdown in vivo in doxycycline-inducible NB tumor xenografts. To understand the mechanisms underlying this tumor growth retardation we performed a series of in vitro experiments in NB cell lines. DCL colocalizes with mitochondria, interacts with the mitochondrial outer membrane protein OMP25/ SYNJ2BP and DCL knockdown results in decreased expression of genes involved in oxidative phosphorylation. Moreover, DCL knockdown decreases cytochrome c oxidase activity and ATP synthesis. We identified the C-terminal Serine/Proline-rich domain and the second microtubule-binding area as crucial DCL domains for the regulation of cytochrome c oxidase activity and ATP synthesis. Furthermore, DCL knockdown causes a significant reduction in the proliferation rate of NB cells under an energetic challenge induced by low glucose availability. Together with our previous studies, our results corroborate DCL as a key player in NB tumor growth in which DCL controls not only mitotic spindle formation and the stabilization of the microtubule cytoskeleton, but also regulates mitochondrial activity and energy availability, which makes DCL a promising molecular target for NB therapy.

Doublecortin and doublecortin-like are expressed in overlapping and non-overlapping neuronal cell population: implications for neurogenesis.

We have characterized the expression of doublecortin-like (DCL), a microtubule-associated protein involved in embryonic neurogenesis that is highly homologous to doublecortin (DCX), in the adult mouse brain. To this end, we developed a DCL-specific antibody and used this to compare DCL expression with DCX. In the neurogenic regions of the adult brain like the subventricular zone (SVZ), the rostral migratory stream (RMS), the olfactory bulb (OB), and the hippocampus, DCL colocalizes with DCX in immature neuronal cell populations. In contrast to DCX, we also found high DCL expression in three other brain regions with suspected neurogenesis or neuronal plasticity. First, the radial glia-like, hypothalamic tanycytes show high DCL expression that partly colocalizes with the neural stem cell marker vimentin. Second, DCL expression is found in cells of the suprachiasmatic nucleus (SCN), which lacks expression of the adult neuron marker NeuN. Third, a novel region exhibiting DCL expression is part of the olfactory tubercle where DCL is found in the neuropil of the islands of Calleja (ICj). Our findings define DCL as a novel marker for specific aspects of adult neurogenesis, which partly overlap with DCX. In addition, we propose unique roles for DCL in adult neurogenesis and we suggest high levels of neuronal plasticity in tanycytes, SCN, and ICj.

Leptin administration restores the fasting-induced increase of hepatic type 3 deiodinase expression in mice.

BACKGROUND: Decreased serum leptin has been proposed as a critical signal initiating the neuroendocrine response to fasting. Leptin administration partially reverses the fasting-induced suppression of the hypothalamus-pituitary-thyroid axis at the central level. It is, however, unknown to what extent leptin affects peripheral thyroid hormone metabolism. The aim of this study was to evaluate the effect of leptin administration on starvation-induced alterations of peripheral thyroid hormone metabolism in mice. METHODS: Three types of experiments were performed: (i) mice were fasted for 24 hours while leptin was administered twice (at 0 and 8 hours, 1 µg/g body weight [BW]), (ii) mice were fasted for 24 hours and, subsequently, leptin was given once at 24 hours (killed at 28 and 32 hours), and (iii) mice were fasted for 48 hours. All groups had appropriate controls. Serum triiodothyronine and thyroxine, liver type 1 deiodinase (D1), type 3 deiodinase (D3), thyroid hormone receptor (TR)ß1, TRα1 and α2 mRNA expression, and liver D1 and D3 activity were measured. RESULTS: Twenty-four hours of fasting decreased liver TRß1 mRNA expression, while liver TRα1, TRα2, and D1 mRNA expression and activity did not change. In contrast, 24 hours of fasting increased liver D3 mRNA. Leptin administration after fasting restored liver D3 expression, while serum thyroid hormone levels and liver TRß1 expression remained low. CONCLUSION: Leptin administration selectively restores starvation-induced increased hepatic D3 expression independently of serum thyroid hormone concentrations. The present study shows that fasting-induced changes in mRNA expression of genes involved in hepatic hormone metabolism are influenced not only by decreased serum thyroid hormone levels but also by serum leptin.

Behavioral responses to combinations of timed light, food availability, and ultradian rhythms in the common vole (Microtus arvalis).

Light is the main entraining signal of the central circadian clock, which drives circadian organization of activity. When food is made available during only certain parts of the day, it can entrain the clock in the liver without changing the phase of the central circadian clock. Although a hallmark of food entrainment is a behavioral anticipation of food availability, the extent of behavioral alterations in response to food availability has not been fully characterized. The authors have investigated interactions between light and temporal food availability in the timing of activity in the common vole. Temporally restricted food availability enhanced or attenuated re-entrainment to a phase advance in light entrainment when it was shifted together with the light or remained at the same time of day, respectively. When light-entrained behavior was challenged with temporal food availability cycles with a different period, two distinct activity components were observed. More so, the present data indicate that in the presence of cycles of different period length of food and light, an activity component emerged that appeared to be driven by a free-running (light-entrainable) clock. Because the authors have previously shown that in the common vole altering activity through running-wheel availability can alter the effectiveness of food availability to entrain the clock in the liver, the authors included running-wheel availability as a parameter that alters the circadian/ultradian balance in activity. In the current protocols, running-wheel availability enhanced the entraining potential of both light and food availability in a differential way. The data presented here show that in the vole activity is a complex of individually driven components and that this activity is, itself, an important modulator of the effectiveness of entraining signals such as light and food.

Age-dependent alterations in human PER2 levels after early morning blue light exposure.

In our modern society, we are exposed to different artificial light sources that could potentially lead to disturbances of circadian rhythms and, hence, represent a risk for health and welfare. Investigating the acute impact of light on clock-gene expression may thus help us to better understand the mechanisms underlying disorders rooted in the circadian system. Here, we show an overall significant reduction in PER2 expression in oral mucosa with aging in the morning, noon, and afternoon. In the afternoon, 10 h after exposure to early morning blue light, PER2 was significantly elevated in the young compared to green light exposure and to older participants. Our findings demonstrate that human buccal samples are a valuable tool for studying clock-gene rhythms and the response of PER2 to light. Additionally, our results indicate that the influence of light on clock-gene expression in humans is altered with age.