Neuroendocrine Modulation of Complex Behavior and Physiology in C. elegans

To survive, animals must adapt to a complex and challenging world in a way that is flexible and responsive, while maintaining internal homeostasis. Neuromodulators provide a means to systemically alter behavioral or physiological state based on intrinsic or extrinsic cues, however dysregulated neuroendocrine signaling has negative consequences for fitness and survival. Here I examine neuroendocrine function and dysfunction using the escape response in Caenorhabditis elegans. The RFamide neuropeptide FLP-18 is a co-transmitter with the monoamine tyramine and functions both synergistically and antagonistically to tyramine in coordinating escape behavior. Using behavioral analysis and calcium imaging, I show that FLP-18 functions primarily through the G-protein coupled receptor (GPCR) NPR-5 to increase calcium levels in muscle, enhancing locomotion rate, bending and reversal behavior during the escape response. Furthermore, I examine the relationship between persistent acute stress and resilience using repeated activation of the escape response as a model of neuroendocrine dysregulation. Repeated activation of the escape response shortens lifespan and renders animals more susceptible to thermal, oxidative, and nutritional stress. Tyramine release is necessary and sufficient for this effect and activity of the tyraminergic RIM neurons is differentially regulated by acute versus long-term stressors. Impaired stress resistance requires both the GPCR TYRA-3 in the intestine and intestinal neuropeptide release. Activation of the insulin receptor DAF-2 is downstream of TYRA-3 and inhibits the transcription factors DAF-16/FOXO, SKN-1/Nrf2 and HSF-1, linking monoamine signaling in acute stress to the insulin signaling pathway and impaired resilience to long-term stressors

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

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

Neural modulation of behavioral state transitions in foraging strategies in C. elegans

Adequate feeding behavior is essential for animal survival and it is regulated not only by the digestive system but also by the nervous system (NS). The NS allows the animal to respond flexibly to changes in the environment depending on the availability of food and the nutritional internal state. Despite feeding behaviors have been studied for decades, understanding the mechanisms involved in different animals´ responses to food depending on its internal state (satiated or fasted/stressed) is still a major challenge. Referred to as the “happiness hormone”, serotonin (5-HT) has been shown to increase with food stimulus and modulate feeding in different animals, suggesting that the role of 5-HT is conserved in nature. On the other hand, noradrenaline (NA), implicated in triggering a stress response, is involved in appetite control by reducing food ingestion. Interestingly, there are reports showing that a lesion of the serotonergic system enhances the effect of noradrenergic drugs. These findings indicate an interaction between serotonergic and noradrenergic signaling. However, the mechanism and relevance of this interplay are not entirely clear. Therefore, our goal is to investigate the molecular processes underlying this interaction. The complexity of the mammalian brain complicates the study of neuronal processes. The nematode Caenorhabditis elegans is suitable for understanding neuronal signaling because of its simple and well-described nervous system. We found that during prolonged fasting, animals decrease their locomotion, which can be resumed by adding tyramine (TA), the analog of NA in invertebrates. 5-HT produces the opposite effect by reducing locomotion, suggesting that 5-HT acts antagonistically to TA. Moreover, it has been shown that when the environment improves and fasted animals encounter food, they release 5-HT to slow their locomotion and promote feeding. Interestingly, we found that this slowing response and the activity of the serotonergic neurons upon food encounter are enhanced in TA-deficient mutants compared to wild-type animals. Given that we also show that TA levels decrease during fasting, we hypothesize that this disinhibits the serotonergic neurons and favors their activity upon refeeding, allowing the animal to exploit the new source of food. Considering the conservation of neuronal components, we believe that our results may contribute to the understanding of the nervous control of state dependent foraging strategiesFil: Blanco, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Florman, Jeremy. University of Massachusetts; Estados UnidosFil: Alkema, Mark. University of Massachusetts; Estados UnidosFil: de Rosa, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Rayes, Diego Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina24th International C. elegans ConferenceGlasgowReino UnidoGenetics Society of Americ

Neurexin Directs Partner-Specific Synaptic Connectivity in \u3cem\u3eC. elegans\u3c/em\u3e

In neural circuits, individual neurons often make projections onto multiple postsynaptic partners. Here, we investigate molecular mechanisms by which these divergent connections are generated, using dyadic synapses in C. elegans as a model. We report that C. elegans nrx-1/neurexin directs divergent connectivity through differential actions at synapses with partnering neurons and muscles. We show that cholinergic outputs onto neurons are, unexpectedly, located at previously undefined spine-like protrusions from GABAergic dendrites. Both these spine-like features and cholinergic receptor clustering are strikingly disrupted in the absence of nrx-1. Excitatory transmission onto GABAergic neurons, but not neuromuscular transmission, is also disrupted. Our data indicate that NRX-1 located at presynaptic sites specifically directs postsynaptic development in GABAergic neurons. Our findings provide evidence that individual neurons can direct differential patterns of connectivity with their post-synaptic partners through partner-specific utilization of synaptic organizers, offering a novel view into molecular control of divergent connectivity

Neurexin directs partner-specific synaptic connectivity in C. elegans

In neural circuits, individual neurons often make projections onto multiple postsynaptic partners. Here, we investigate molecular mechanisms by which these divergent connections are generated, using dyadic synapses in C. elegans as a model. We report that C. elegans nrx-1/neurexin directs divergent connectivity through differential actions at synapses with partnering neurons and muscles. We show that cholinergic outputs onto neurons are, unexpectedly, located at previously undefined spine-like protrusions from GABAergic dendrites. Both these spine-like features and cholinergic receptor clustering are strikingly disrupted in the absence of nrx-1. Excitatory transmission onto GABAergic neurons, but not neuromuscular transmission, is also disrupted. Our data indicate that NRX-1 located at presynaptic sites specifically directs postsynaptic development in GABAergic neurons. Our findings provide evidence that individual neurons can direct differential patterns of connectivity with their post-synaptic partners through partner-specific utilization of synaptic organizers, offering a novel view into molecular control of divergent connectivity

Cannabinoids activate the insulin pathway to modulate mobilization of cholesterol in C. elegans

The nematode Caenorhabditis elegans requires exogenous cholesterol to survive and its depletion leads to early developmental arrest. Thus, tight regulation of cholesterol storage and distribution within the organism is critical. Previously, we demonstrated that the endocannabinoid (eCB) 2-arachidonoylglycerol (2-AG) plays a key role in C. elegans since it modulates sterol mobilization. However, the mechanism remains unknown. Here we show that mutations in the ocr-2 and osm-9 genes, coding for transient receptors potential V (TRPV) ion channels, dramatically reduce the effect of 2-AG in cholesterol mobilization. Through genetic analysis in combination with the rescue of larval arrest induced by sterol starvation, we found that the insulin/IGF-1signaling (IIS) pathway and UNC-31/CAPS, a calcium-activated regulator of neural dense-core vesicles release, are essential for 2-AG-mediated stimulation of cholesterol mobilization. These findings indicate that 2-AG-dependent cholesterol trafficking requires the release of insulin peptides and signaling through the DAF-2 insulin receptor. These results suggest that 2-AG acts as an endogenous modulator of TRPV signal transduction to control intracellular sterol trafficking through modulation of the IGF-1 signaling pathwayFil: Hernández Cravero, Bruno. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario. Laboratorio de Fisiología Microbiana (IBR-CONICET); Argentina.Fil: Vranych, Cecilia V. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario. Laboratorio de Fisiología Microbiana (IBR-CONICET); Argentina.Fil: De Mendoza, Diego. Universidad Nacional de Rosario. Facultad de Ciencias Bioquímicas y Farmacéuticas. Instituto de Biología Molecular y Celular de Rosario. Laboratorio de Fisiología Microbiana (IBR-CONICET); Argentina.Fil: GallinoI, Sofía. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres". Laboratorio de Fisiología y Genética de la Audición (INGEBI-CONICET); Argentina.Fil: Elgoyhen, Ana Belén. Instituto de Investigaciones en Ingeniería Genética y Biología Molecular "Dr. Héctor N. Torres". Laboratorio de Fisiología y Genética de la Audición (INGEBI-CONICET); Argentina.Fil: Florman, Jeremy. University of Massachusetts Medical School. Department of Neurobiology; United States.Fil: AlkemaI, Mark J. University of Massachusetts Medical School. Department of Neurobiology; United States.Fil: Diaz, Philippe. University of Montana. Department of Biomedical and Pharmaceutical Sciences; United States

The flight response impairs cytoprotective mechanisms through neural inhibition of the insulin pathway

An animal uses different survival strategies to cope with life-threatening situations. For instance, it can engage in a rapid and energy-demanding “fightor-flight” response when encountering a predator, or it can induce the gradual and long-lasting activation of highly conserved cytoprotective processes in response to environmental stressors such as hypoxia, heat, oxidative stress, or food shortage. In animals across the evolutionary spectrum the continued activation of the fight-or-flight response weakens the animal’s resistance to environmental challenges. In humans, for instance, the recurrent experience of stress in patients that suffer from post-traumatic stress disorder (PTSD) has been associated with decreased antioxidant capacity, accelerated aging and increased susceptibility to metabolic, cardiovascular and infectious diseases. However, the molecular and cellular mechanisms that regulate the trade-off between flight response and long-term stressors are poorly understood. Here we show that repeated induction of the C. elegans flight response shortens lifespan and inhibits conserved cytoprotective mechanisms. The flight response activates neurons that release tyramine, the invertebrate analog of adrenaline/noradrenaline. Tyramine stimulates the DAF-2/Insulin/IGF-1 pathway and precludes the induction of stress response genes by activating an adrenergic-like receptor in the intestine. In contrast, long-term environmental stressors, such as heat or oxidative stress, reduce tyramine release allowing 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 defense systems and accelerates aging.Fil: Rayes, Diego Hernán. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; ArgentinaFil: de Rosa, Maria Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Veuthey, Tania Vanesa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Florman, Jeremy. University Of Massachussets. Medical School. Department Of Neurobiology; Estados UnidosFil: Grant, Jeff. University Of Massachussets. Medical School. Department Of Neurobiology; Estados UnidosFil: Blanco, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Andersen, Natalia Denise. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Investigaciones Bioquímicas de Bahía Blanca. Universidad Nacional del Sur. Instituto de Investigaciones Bioquímicas de Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Biología, Bioquímica y Farmacia; ArgentinaFil: Alkema, Mark. University Of Massachussets. Medical School. Department Of Neurobiology; Estados Unidos22nd International C. elegans ConferenceLos AngelesEstados UnidosGenetics Society of Americ

Flexible motor sequence generation during stereotyped escape responses

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 conserved neuropeptide system links head and body motor circuits to enable adaptive behavior

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