ABOUT THIS COLLECTION

Founded in 2001, the Department of Neurobiology at UMass Chan Medical School has evolved into a unique and integrated hub of investigators addressing fundamental problems in neurobiology, from single molecules to behavior, primarily using invertebrate model organisms. Combining cell biological, physiological and behavioral analyses with a critical interventionist angle afforded by cutting-edge genetic approaches, the Department aims to understand the complexity of brain development and function. This collection showcases journal articles and other publications authored by Neurobiology faculty and researchers.

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Recently Published

  • Co-transmission of neuropeptides and monoamines choreograph the C. elegans escape response

    Florman, Jeremy T.; Alkema, Mark J. (2022-03-03)
    Co-localization and co-transmission of neurotransmitters and neuropeptides is a core property of neural signaling across species. While co-transmission can increase the flexibility of cellular communication, understanding the functional impact on neural dynamics and behavior remains a major challenge. Here we examine the role of neuropeptide/monoamine co-transmission in the orchestration of the C. elegans escape response. The tyraminergic RIM neurons, which coordinate distinct motor programs of the escape response, also co-express the neuropeptide encoding gene flp-18. We find that in response to a mechanical stimulus, flp-18 mutants have defects in locomotory arousal and head bending that facilitate the omega turn. We show that the induction of the escape response leads to the release of FLP-18 neuropeptides. FLP-18 modulates the escape response through the activation of the G-protein coupled receptor NPR-5. FLP-18 increases intracellular calcium levels in neck and body wall muscles to promote body bending. Our results show that FLP-18 and tyramine act in different tissues in both a complementary and antagonistic manner to control distinct motor programs during different phases of the C. elegans flight response. Our study reveals basic principles by which co-transmission of monoamines and neuropeptides orchestrate in arousal and behavior in response to stress.
  • Cell-Type-Specific Circadian Bioluminescence Rhythms in Dbp Reporter Mice

    Smith, Ciearra B.; van der Vinne, Vincent; McCartney, Eleanor; Stowie, Adam C.; Leise, Tanya L.; Martin-Burgos, Blanca; Molyneux, Penny C.; Garbutt, Lauren A.; Brodsky, Michael H.; Davidson, Alec J.; et al. (Sage Publishers, 2022-02-01)
    Circadian rhythms are endogenously generated physiological and molecular rhythms with a cycle length of about 24 h. Bioluminescent reporters have been exceptionally useful for studying circadian rhythms in numerous species. Here, we report development of a reporter mouse generated by modification of a widely expressed and highly rhythmic gene encoding D-site albumin promoter binding protein (Dbp). In this line of mice, firefly luciferase is expressed from the Dbp locus in a Cre recombinase-dependent manner, allowing assessment of bioluminescence rhythms in specific cellular populations. A mouse line in which luciferase expression was Cre-independent was also generated. The Dbp reporter alleles do not alter Dbp gene expression rhythms in liver or circadian locomotor activity rhythms. In vivo and ex vivo studies show the utility of the reporter alleles for monitoring rhythmicity. Our studies reveal cell-type-specific characteristics of rhythms among neuronal populations within the suprachiasmatic nuclei ex vivo. In vivo studies show Dbp-driven bioluminescence rhythms in the liver of Albumin-Cre;DbpKI/+ "liver reporter" mice. After a shift of the lighting schedule, locomotor activity achieved the proper phase relationship with the new lighting cycle more rapidly than hepatic bioluminescence did. As previously shown, restricting food access to the daytime altered the phase of hepatic rhythmicity. Our model allowed assessment of the rate of recovery from misalignment once animals were provided with food ad libitum. These studies confirm the previously demonstrated circadian misalignment following environmental perturbations and reveal the utility of this model for minimally invasive, longitudinal monitoring of rhythmicity from specific mouse tissues.
  • A conserved neuropeptide system links head and body motor circuits to enable adaptive behavior

    Ramachandran, Shankar; Banerjee, Navonil; Bhattacharya, Raja; Lemons, Michele L.; Florman, Jeremy; Lambert, Christopher M.; Touroutine, Denis; Alexander, Kellianne; Schoofs, Liliane; Alkema, Mark J.; et al. (2021-11-12)
    Neuromodulators promote adaptive behaviors that are often complex and involve concerted activity changes across circuits that are often not physically connected. It is not well understood how neuromodulatory systems accomplish these tasks. Here, we show that the Caenorhabditis elegans NLP-12 neuropeptide system shapes responses to food availability by modulating the activity of head and body wall motor neurons through alternate G-protein coupled receptor (GPCR) targets, CKR-1 and CKR-2. We show ckr-2 deletion reduces body bend depth during movement under basal conditions. We demonstrate CKR-1 is a functional NLP-12 receptor and define its expression in the nervous system. In contrast to basal locomotion, biased CKR-1 GPCR stimulation of head motor neurons promotes turning during local searching. Deletion of ckr-1 reduces head neuron activity and diminishes turning while specific ckr-1 overexpression or head neuron activation promote turning. Thus, our studies suggest locomotor responses to changing food availability are regulated through conditional NLP-12 stimulation of head or body wall motor circuits.
  • Distinct neuropeptide-receptor modules regulate a sex-specific behavioral response to a pheromone

    Reilly, Douglas K.; McGlame, Emily J.; Vandewyer, Elke; Robidoux, Annalise N.; Muirhead, Caroline S.; Northcott, Haylea T.; Joyce, William; Alkema, Mark J.; Gegear, Robert J.; Beets, Isabel; et al. (2021-08-31)
    Dioecious species are a hallmark of the animal kingdom, with opposing sexes responding differently to identical sensory cues. Here, we study the response of C. elegans to the small-molecule pheromone, ascr#8, which elicits opposing behavioral valences in each sex. We identify a novel neuropeptide-neuropeptide receptor (NP/NPR) module that is active in males, but not in hermaphrodites. Using a novel paradigm of neuropeptide rescue that we established, we leverage bacterial expression of individual peptides to rescue the sex-specific response to ascr#8. Concurrent biochemical studies confirmed individual FLP-3 peptides differentially activate two divergent receptors, NPR-10 and FRPR-16. Interestingly, the two of the peptides that rescued behavior in our feeding paradigm are related through a conserved threonine, suggesting that a specific NP/NPR combination sets a male state, driving the correct behavioral valence of the ascr#8 response. Receptor expression within pre-motor neurons reveals novel coordination of male-specific and core locomotory circuitries.
  • The transcription factor LAG-1/CSL plays a Notch-independent role in controlling terminal differentiation, fate maintenance, and plasticity of serotonergic chemosensory neurons

    Maicas, Miren; Jimeno-Martin, Angela; Millan-Trejo, Andrea; Alkema, Mark J.; Flames, Nuria (2021-07-07)
    During development, signal-regulated transcription factors (TFs) act as basal repressors and upon signalling through morphogens or cell-to-cell signalling shift to activators, mediating precise and transient responses. Conversely, at the final steps of neuron specification, terminal selector TFs directly initiate and maintain neuron-type specific gene expression through enduring functions as activators. C. elegans contains 3 types of serotonin synthesising neurons that share the expression of the serotonin biosynthesis pathway genes but not of other effector genes. Here, we find an unconventional role for LAG-1, the signal-regulated TF mediator of the Notch pathway, as terminal selector for the ADF serotonergic chemosensory neuron, but not for other serotonergic neuron types. Regulatory regions of ADF effector genes contain functional LAG-1 binding sites that mediate activation but not basal repression. lag-1 mutants show broad defects in ADF effector genes activation, and LAG-1 is required to maintain ADF cell fate and functions throughout life. Unexpectedly, contrary to reported basal repression state for LAG-1 prior to Notch receptor activation, gene expression activation in the ADF neuron by LAG-1 does not require Notch signalling, demonstrating a default activator state for LAG-1 independent of Notch. We hypothesise that the enduring activity of terminal selectors on target genes required uncoupling LAG-1 activating role from receiving the transient Notch signalling.
  • A phase transition enhances the catalytic activity of SARM1, an NAD(+) glycohydrolase involved in neurodegeneration

    Loring, Heather S.; Czech, Victoria L.; Icso, Janneke D.; O'Connor, Lauren C.; Parelkar, Sangram; Byrne, Alexandra B.; Thompson, Paul R. (2021-06-29)
    Sterile alpha and toll/interleukin receptor (TIR) motif-containing protein 1 (SARM1) is a neuronally expressed NAD(+) glycohydrolase whose activity is increased in response to stress. NAD(+) depletion triggers axonal degeneration, which is a characteristic feature of neurological diseases. Notably, loss of SARM1 is protective in murine models of peripheral neuropathy and traumatic brain injury. Herein, we report that citrate induces a phase transition that enhances SARM1 activity by ~2000-fold. This phase transition can be disrupted by mutating a residue involved in multimerization, G601P. This mutation also disrupts puncta formation in cells. We further show that citrate induces axonal degeneration in C. elegans that is dependent on the C. elegans orthologue of SARM1 (TIR-1). Notably, citrate induces the formation of larger puncta indicating that TIR-1/SARM1 multimerization is essential for degeneration in vivo. These findings provide critical insights into SARM1 biology with important implications for the discovery of novel SARM1-targeted therapeutics.
  • Neuronal post-developmentally acting SAX-7S/L1CAM can function as cleaved fragments to maintain neuronal architecture in C. elegans

    Desse, Virginie E.; Blanchette, Cassandra R.; Nadour, Malika; Perrat, Paola N.; Rivollet, Lise; Khandekar, Anagha; Benard, Claire Y. (2021-06-11)
    Whereas remarkable advances have uncovered mechanisms that drive nervous system assembly, the processes responsible for the lifelong maintenance of nervous system architecture remain poorly understood. Subsequent to its establishment during embryogenesis, neuronal architecture is maintained throughout life in the face of the animal's growth, maturation processes, the addition of new neurons, body movements, and aging. The C. elegans protein SAX-7, homologous to the vertebrate L1 protein family of neural adhesion molecules, is required for maintaining the organization of neuronal ganglia and fascicles after their successful initial embryonic development. To dissect the function of sax-7 in neuronal maintenance, we generated a null allele and sax-7S-isoform-specific alleles. We find that the null sax-7(qv30) is, in some contexts, more severe than previously described mutant alleles, and that the loss of sax-7S largely phenocopies the null, consistent with sax-7S being the key isoform in neuronal maintenance. Using a sfGFP::SAX-7S knock-in, we observe sax-7S to be predominantly expressed across the nervous system, from embryogenesis to adulthood. Yet, its role in maintaining neuronal organization is ensured by post-developmentally acting SAX-7S, as larval transgenic sax-7S(+) expression alone is sufficient to profoundly rescue the null mutants' neuronal maintenance defects. Moreover, the majority of the protein SAX-7 appears to be cleaved, and we show that these cleaved SAX-7S fragments together, not individually, can fully support neuronal maintenance. These findings contribute to our understanding of the role of the conserved protein SAX-7/L1CAM in long-term neuronal maintenance, and may help decipher processes that go awry in some neurodegenerative conditions.
  • Corollary discharge promotes a sustained motor state in a neural circuit for navigation

    Ji, Ni; Venkatachalam, Vivek; Rodgers, Hillary Denise; Hung, Wesley; Kawano, Taizo; Clark, Christopher M.; Lim, Maria; Alkema, Mark J.; Zhen, Mei; Samuel, Aravinthan D. T. (2021-04-21)
    Animals exhibit behavioral and neural responses that persist on longer timescales than transient or fluctuating stimulus inputs. Here, we report that Caenorhabditis elegans uses feedback from the motor circuit to a sensory processing interneuron to sustain its motor state during thermotactic navigation. By imaging circuit activity in behaving animals, we show that a principal postsynaptic partner of the AFD thermosensory neuron, the AIY interneuron, encodes both temperature and motor state information. By optogenetic and genetic manipulation of this circuit, we demonstrate that the motor state representation in AIY is a corollary discharge signal. RIM, an interneuron that is connected with premotor interneurons, is required for this corollary discharge. Ablation of RIM eliminates the motor representation in AIY, allows thermosensory representations to reach downstream premotor interneurons, and reduces the animal's ability to sustain forward movements during thermotaxis. We propose that feedback from the motor circuit to the sensory processing circuit underlies a positive feedback mechanism to generate persistent neural activity and sustained behavioral patterns in a sensorimotor transformation.
  • Flexible motor sequence generation during stereotyped escape responses

    Wang, Yuan; Zhang, Xiaoqian; Xin, Qi; Hung, Wesley; Florman, Jeremy; Huo, Jing; Xu, Tianqi; Xie, Yu; Alkema, Mark J.; Zhen, Mei; et al. (2020-06-05)
    Complex animal behaviors arise from a flexible combination of stereotyped motor primitives. Here we use the escape responses of the nematode Caenorhabditis elegans to study how a nervous system dynamically explores the action space. The initiation of the escape responses is predictable: the animal moves away from a potential threat, a mechanical or thermal stimulus. But the motor sequence and the timing that follow are variable. We report that a feedforward excitation between neurons encoding distinct motor states underlies robust motor sequence generation, while mutual inhibition between these neurons controls the flexibility of timing in a motor sequence. Electrical synapses contribute to feedforward coupling whereas glutamatergic synapses contribute to inhibition. We conclude that C. elegans generates robust and flexible motor sequences by combining an excitatory coupling and a winner-take-all operation via mutual inhibition between motor modules.
  • A highly efficient method for single-cell electroporation in mouse organotypic hippocampal slice culture

    Keener, David G.; Cheung, Amy; Futai, Kensuke (2020-05-01)
    BACKGROUND: Exogenous gene introduction by transfection is one of the most important approaches for understanding the function of specific genes at the cellular level. Electroporation has a long-standing history as a versatile gene delivery technique in vitro and in vivo. However, it has been underutilized in vitro because of technical difficulty and insufficient transfection efficiency. NEW METHOD: We have developed an electroporation technique that combines the use of large glass electrodes, tetrodotoxin-containing artificial cerebrospinal fluid and mild electrical pulses. Here, we describe the technique and compare it with existing methods. RESULTS: Our method achieves a high transfection efficiency ( approximately 80 %) in both excitatory and inhibitory neurons with no detectable side effects on their function. We demonstrate this method is capable of transferring at least three different genes into a single neuron. In addition, we demonstrate the ability to transfect different genes into neighboring cells. COMPARISON WITH EXISTING METHODS: The majority of existing methods use fine-tipped glass electrodes (i.e. > 10MOmega) and apply high voltage (10V) pulses with high frequency (100Hz) for 1s. These parameters contribute to practical difficulties thus lowering the transfection efficiency. Our unique method minimizes electrode clogging and therefore procedure duration, increasing transfection efficiency and cellular viability. CONCLUSIONS: Our modifications, relative to current methods, optimize electroporation efficiency and cell survival. Our approach offers distinct research strategies not only in elucidating cell-autonomous functions of genes but also for assessing genes contributing to intercellular functions, such as trans-synaptic interactions.
  • Deconstructing circadian disruption: Assessing the contribution of reduced peripheral oscillator amplitude on obesity and glucose intolerance in mice

    van der Vinne, Vincent; Martin Burgos, Blanca; Harrington, Mary E.; Weaver, David R. (2020-04-03)
    Disturbing the circadian regulation of physiology by disruption of the rhythmic environment is associated with adverse health outcomes but the underlying mechanisms are unknown. Here, the response of central and peripheral circadian clocks to an advance or delay of the light-dark cycle was determined in mice. This identified transient damping of peripheral clocks as a consequence of an advanced light-dark cycle. Similar depression of peripheral rhythm amplitude was observed in mice exposed to repeated phase shifts. To assess the metabolic consequences of such peripheral amplitude depression in isolation, temporally chimeric mice lacking a functional central clock (Vgat-Cre(+) Bmal1(fl/fl) ) were housed in the absence of environmental rhythmicity. In vivo PER2::LUC bioluminescence imaging of anesthetized and freely moving mice revealed that this resulted in a state of peripheral amplitude depression, similar in severity to that observed transiently following an advance of the light-dark cycle. Surprisingly, our mice did not show alterations in body mass or glucose tolerance in males or females on regular or high-fat diets. Overall, our results identify transient damping of peripheral rhythm amplitude as a consequence of exposure to an advanced light-dark cycle but chronic damping of peripheral clocks in isolation is insufficient to induce adverse metabolic outcomes in mice.
  • In Situ Regulated Dopamine Transporter Trafficking: There's No Place Like Home

    Fagan, Rita R.; Kearney, Patrick J.; Melikian, Haley E. (2020-03-07)
    Dopamine (DA) is critical for motivation, reward, movement initiation, and learning. Mechanisms that control DA signaling have a profound impact on these important behaviors, and additionally play a role in DA-related neuropathologies. The presynaptic SLC6 DA transporter (DAT) limits extracellular DA levels by clearing released DA, and is potently inhibited by addictive and therapeutic psychostimulants. Decades of evidence support that the DAT is subject to acute regulation by a number of signaling pathways, and that endocytic trafficking strongly regulates DAT availability and function. DAT trafficking studies have been performed in a variety of model systems, including both in vitro and ex vivo preparations. In this review, we focus on the breadth of DAT trafficking studies, with specific attention to, and comparison of, how context may influence DAT's response to different stimuli. In particular, this overview highlights that stimulated DAT trafficking not only differs between in vitro and ex vivo environments, but also is influenced by both sex and anatomical subregions.
  • HIF-1 Has a Central Role in Caenorhabditis elegans Organismal Response to Selenium

    Romanelli-Credrez, Laura; Doitsidou, Maria; Alkema, Mark J.; Salinas, Gustavo (2020-02-25)
    Selenium is a trace element for most organisms; its deficiency and excess are detrimental. Selenium beneficial effects are mainly due to the role of the 21(st) genetically encoded amino acid selenocysteine (Sec). Selenium also exerts Sec-independent beneficial effects. Its harmful effects are thought to be mainly due to non-specific incorporation in protein synthesis. Yet the selenium response in animals is poorly understood. In Caenorhabditis elegans, Sec is genetically incorporated into a single selenoprotein. Similar to mammals, a 20-fold excess of the optimal selenium requirement is harmful. Sodium selenite (Na2SeO3) excess causes development retardation, impaired growth, and neurodegeneration of motor neurons. To study the organismal response to selenium we performed a genetic screen for C. elegans mutants that are resistant to selenite. We isolated non-sense and missense egl-9/EGLN mutants that confer robust resistance to selenium. In contrast, hif-1/HIF null mutant was highly sensitive to selenium, establishing a role for this transcription factor in the selenium response. We showed that EGL-9 regulates HIF-1 activity through VHL-1, and identified CYSL-1 as a key sensor that transduces the selenium signal. Finally, we showed that the key enzymes involved in sulfide and sulfite stress (sulfide quinone oxidoreductase and sulfite oxidase) are not required for selenium resistance. In contrast, knockout strains in the persulfide dioxygenase ETHE-1 and the sulfurtransferase MPST-7 affect the organismal response to selenium. In sum, our results identified a transcriptional pathway as well as enzymes possibly involved in the organismal selenium response.
  • Periodic Parasites and Daily Host Rhythms

    Prior, Kimberley F.; Rijo-Ferreira, Filipa; Assis, Patricia A.; Hirako, Isabella C.; Weaver, David R.; Gazzinelli, Ricardo T.; Reece, Sarah E. (2020-02-12)
    Biological rhythms appear to be an elegant solution to the challenge of coordinating activities with the consequences of the Earth's daily and seasonal rotation. The genes and molecular mechanisms underpinning circadian clocks in multicellular organisms are well understood. In contrast, the regulatory mechanisms and fitness consequences of biological rhythms exhibited by parasites remain mysterious. Here, we explore how periodicity in parasite traits is generated and why daily rhythms matter for parasite fitness. We focus on malaria (Plasmodium) parasites which exhibit developmental rhythms during replication in the mammalian host's blood and in transmission to vectors. Rhythmic in-host parasite replication is responsible for eliciting inflammatory responses, the severity of disease symptoms, and fueling transmission, as well as conferring tolerance to anti-parasite drugs. Thus, understanding both how and why the timing and synchrony of parasites are connected to the daily rhythms of hosts and vectors may make treatment more effective and less toxic to hosts.
  • Drosophila Cryptochrome: Variations in Blue

    Foley, Lauren E.; Emery, Patrick (2020-02-01)
    CRYPTOCHROMES (CRYs) are structurally related to ultraviolet (UV)/blue-sensitive DNA repair enzymes called photolyases but lack the ability to repair pyrimidine dimers generated by UV exposure. First identified in plants, CRYs have proven to be involved in light detection and various light-dependent processes in a broad range of organisms. In Drosophila, CRY's best understood role is the cell-autonomous synchronization of circadian clocks. However, CRY also contributes to the amplitude of circadian oscillations in a light-independent manner, controls arousal and UV avoidance, influences visual photoreception, and plays a key role in magnetic field detection. Here, we review our current understanding of the mechanisms underlying CRY's various circadian and noncircadian functions in fruit flies.
  • Structure of an Arc-ane virus-like capsid

    Budnik, Vivian; Thomson, Travis (2020-02-01)
    Recent findings unveil a viral-like mechanism for the transmission of synaptic plasticity signals involving the activity-regulated cytoskeleton-associated protein (Arc). Arc forms capsid-like particles that package RNA and are transported across synapses. Here Erlendsson et al. present a high-resolution structural representation of Arc capsids, enabling deeper analysis of their function.
  • Targeted Complement Inhibition at Synapses Prevents Microglial Synaptic Engulfment and Synapse Loss in Demyelinating Disease

    Werneburg, Sebastian; Jung, Jonathan; Kunjamma, Rejani B.; Ha, Seung-Kwon; Luciano, Nicholas J.; Willis, Cory M.; Gao, Guangping; Biscola, Natalia P.; Havton, Leif A.; Crocker, Stephen J.; et al. (2020-01-14)
    Multiple sclerosis (MS) is a demyelinating, autoimmune disease of the central nervous system. While work has focused on myelin and axon loss in MS, less is known about mechanisms underlying synaptic changes. Using postmortem human MS tissue, a preclinical nonhuman primate model of MS, and two rodent models of demyelinating disease, we investigated synapse changes in the visual system. Similar to other neurodegenerative diseases, microglial synaptic engulfment and profound synapse loss were observed. In mice, synapse loss occurred independently of local demyelination and neuronal degeneration but coincided with gliosis and increased complement component C3, but not C1q, at synapses. Viral overexpression of the complement inhibitor Crry at C3-bound synapses decreased microglial engulfment of synapses and protected visual function. These results indicate that microglia eliminate synapses through the alternative complement cascade in demyelinating disease and identify a strategy to prevent synapse loss that may be broadly applicable to other neurodegenerative diseases. VIDEO ABSTRACT.
  • Polymodal Nociception in Drosophila Requires Alternative Splicing of TrpA1

    Gu, Pengyu; Gong, Jiaxin; Shang, Ye; Wang, Fei; Takle, Kendra; Ma, Zhiguo; Sheehan, Amy E.; Freeman, Marc R.; Xiang, Yang (2019-12-02)
    Transcripts of noxious stimulus-detecting TrpA1 channels are alternatively spliced. Despite the importance of nociception for survival, the in vivo significance of expressing different TrpA1 isoforms is largely unknown. Here, we develop a novel genetic approach to generate Drosophila knockin strains expressing single TrpA1 isoforms. Drosophila TrpA1 mediates heat and UVC-triggered nociception. We show that TrpA1-C and TrpA1-D, two alternative isoforms, are co-expressed in nociceptors. When examined in heterologous cells, both TrpA1-C and TrpA1-D are activated by heat and UVC. By contrast, analysis of knockin flies reveals the striking functional specificity; TrpA1-C mediates UVC-nociception, whereas TrpA1-D mediates heat-nociception. Therefore, in vivo functions of TrpA1-C and TrpA1-D are different from each other and are different from their in vitro properties. Our results indicate that a given sensory stimulus preferentially activates a single TrpA1 isoform in vivo and that polymodal nociception requires co-expression of TrpA1 isoforms, providing novel insights of how alternative splicing regulates nociception.
  • Reassessing the Role of Histaminergic Tuberomammillary Neurons in Arousal Control

    Venner, Anne; Mochizuki, Takatoshi; De Luca, Roberto; Anaclet, Christelle; Scammell, Thomas E.; Saper, Clifford B.; Arrigoni, Elda; Fuller, Patrick M. (2019-11-06)
    The histaminergic neurons of the tuberomammillary nucleus (TMN(HDC)) of the posterior hypothalamus have long been implicated in promoting arousal. More recently, a role for GABAergic signaling by the TMN(HDC) neurons in arousal control has been proposed. Here, we investigated the effects of selective chronic disruption of GABA synthesis (via genetic deletion of the GABA synthesis enzyme, glutamic acid decarboxylase 67) or GABAergic transmission (via genetic deletion of the vesicular GABA transporter (VGAT)) in the TMN(HDC) neurons on sleep-wake in male mice. We also examined the effects of acute chemogenetic activation and optogenetic inhibition of TMN(HDC) neurons upon arousal in male mice. Unexpectedly, we found that neither disruption of GABA synthesis nor GABAergic transmission altered hourly sleep-wake quantities, perhaps because very few TMN(HDC) neurons coexpressed VGAT. Acute chemogenetic activation of TMN(HDC) neurons did not increase arousal levels above baseline but did enhance vigilance when the mice were exposed to a behavioral cage change challenge. Similarly, acute optogenetic inhibition had little effect upon baseline levels of arousal. In conclusion, we could not identify a role for GABA release by TMN(HDC) neurons in arousal control. Further, if TMN(HDC) neurons do release GABA, the mechanism by which they do so remains unclear. Our findings support the view that TMN(HDC) neurons may be important for enhancing arousal under certain conditions, such as exposure to a novel environment, but play only a minor role in behavioral and EEG arousal under baseline conditions.SIGNIFICANCE STATEMENT The histaminergic neurons of the tuberomammillary nucleus of the hypothalamus (TMN(HDC)) have long been thought to promote arousal. Additionally, TMN(HDC) neurons may counter-regulate the wake-promoting effects of histamine through co-release of the inhibitory neurotransmitter, GABA. Here, we show that impairing GABA signaling from TMN(HDC) neurons does not impact sleep-wake amounts and that few TMN(HDC) neurons contain the vesicular GABA transporter, which is presumably required to release GABA. We further show that acute activation or inhibition of TMN(HDC) neurons has limited effects upon baseline arousal levels and that activation enhances vigilance during a behavioral challenge. Counter to general belief, our findings support the view that TMN(HDC) neurons are neither necessary nor sufficient for the initiation and maintenance of arousal under baseline conditions.
  • The flight response impairs cytoprotective mechanisms by activating the insulin pathway

    De Rosa, Maria Jose; Veuthey, Tania; Florman, Jeremy; Grant, Jeff; Blanco, Maria Gabriela; Andersen, Natalia; Donnelly, Jamie L.; Rayes, Diego; Alkema, Mark J. (2019-08-28)
    An animal's stress response requires different adaptive strategies depending on the nature and duration of the stressor. Whereas acute stressors, such as predation, induce a rapid and energy-demanding fight-or-flight response, long-term environmental stressors induce the gradual and long-lasting activation of highly conserved cytoprotective processes(1-3). In animals across the evolutionary spectrum, continued activation of the fight-or-flight response weakens the animal's resistance to environmental challenges(4,5). However, the molecular and cellular mechanisms that regulate the trade-off between the flight response and long-term stressors are poorly understood. Here we show that repeated induction of the flight response in Caenorhabditis elegans shortens lifespan and inhibits conserved cytoprotective mechanisms. The flight response activates neurons that release tyramine, an invertebrate analogue of adrenaline and noradrenaline. Tyramine stimulates the insulin-IGF-1 signalling (IIS) pathway and precludes the induction of stress response genes by activating an adrenergic-like receptor in the intestine. By contrast, long-term environmental stressors, such as heat or oxidative stress, reduce tyramine release and thereby allow the induction of cytoprotective genes. These findings demonstrate that a neural stress hormone supplies a state-dependent neural switch between acute flight and long-term environmental stress responses and provides mechanistic insights into how the flight response impairs cellular defence systems and accelerates ageing.

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