Transcription factor Creb3l1 maintains proteostasis in neuroendocrine cells

OBJECTIVES: Dynamic changes to neuropeptide hormone synthesis and secretion by hypothalamic neuroendocrine cells is essential to ensure metabolic homeostasis. The specialised molecular mechanisms that allow neuroendocrine cells to synthesise and secrete vast quantities of neuropeptides remain ill defined. The objective of this study was to identify novel genes and pathways controlled by transcription factor and endoplasmic reticulum stress sensor Creb3l1 which is robustly activated in hypothalamic magnocellular neurones in response to increased demand for protein synthesis. METHODS: We adopted a multiomic strategy to investigate specific roles of Creb3l1 in rat magnocellular neurones. We first performed chromatin immunoprecipitation followed by genome sequencing (ChIP-seq) to identify Creb3l1 genomic targets and then integrated this data with RNA sequencing data from physiologically stimulated and Creb3l1 knockdown magnocellular neurones. RESULTS: The data converged on Creb3l1 targets that code for ribosomal proteins and endoplasmic reticulum proteins crucial for the maintenance of cellular proteostasis. We validated genes that compose the PERK arm of the unfolded protein response pathway including Eif2ak3, Eif2s1, Atf4 and Ddit3 as direct Creb3l1 targets. Importantly, knockdown of Creb3l1 in the hypothalamus led to a dramatic depletion in neuropeptide synthesis and secretion. The physiological outcomes from studies of paraventricular and supraoptic nuclei Creb3l1 knockdown animals were changes to food and water consumption. CONCLUSION: Collectively, our data identify Creb3l1 as a comprehensive controller of the PERK signalling pathway in magnocellular neurones in response to physiological stimulation. The broad regulation of neuropeptide synthesis and secretion by Creb3l1 presents a new therapeutic strategy for metabolic diseases

Decreased parenchymal arteriolar tone uncouples vessel-to-neuronal communication in a mouse model of vascular cognitive impairment

Chronic hypoperfusion is a key contributor to cognitive decline and neurodegenerative conditions, but the cellular mechanisms remain ill-defined. Using a multidisciplinary approach, we sought to elucidate chronic hypoperfusion-evoked functional changes at the neurovascular unit. We used bilateral common carotid artery stenosis (BCAS), a well-established model of vascular cognitive impairment, combined with an ex vivo preparation that allows pressurization of parenchymal arterioles in a brain slice. Our results demonstrate that mild (~ 30%), chronic hypoperfusion significantly altered the functional integrity of the cortical neurovascular unit. Although pial cerebral perfusion recovered over time, parenchymal arterioles progressively lost tone, exhibiting significant reductions by day 28 post-surgery. We provide supportive evidence for reduced adenosine 1 receptor-mediated vasoconstriction as a potential mechanism in the adaptive response underlying the reduced baseline tone in parenchymal arterioles. In addition, we show that in response to the neuromodulator adenosine, the action potential frequency of cortical pyramidal neurons was significantly reduced in all groups. However, a significant decrease in adenosine-induced hyperpolarization was observed in BCAS 14 days. At the microvascular level, constriction-induced inhibition of pyramidal neurons was significantly compromised in BCAS mice. Collectively, these results suggest that BCAS uncouples vessel-to-neuron communication—vasculo-neuronal coupling—a potential early event in cognitive decline.Fil: Kim, Ki Jung. Augusta University. Departament of Physiology; Estados UnidosFil: Diaz, Juan Ramiro. Augusta University. Departament of Physiology; Estados UnidosFil: Presa, Jessica Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Augusta University. Departament of Physiology; Estados UnidosFil: Muller, P. Robinson. Augusta University. Departament of Physiology; Estados UnidosFil: Brands, Michael W.. Augusta University. Departament of Physiology; Estados UnidosFil: Khan, Mohammad B.. Augusta University. Medical College of Georgia; Estados UnidosFil: Hess, David C.. Augusta University. Medical College of Georgia; Estados UnidosFil: Althammer, Ferdinand. Georgia State University; Estados UnidosFil: Stern, Javier E.. Georgia State University; Estados UnidosFil: Filosa, Jessica A.. Augusta University. Departament of Physiology; Estados Unido

Oxytocin-based therapies for treatment of Prader-Willi and Schaaf-Yang syndromes: evidence, disappointments, and future research strategies

International audienceAbstract The prosocial neuropeptide oxytocin is being developed as a potential treatment for various neuropsychiatric disorders including autism spectrum disorder (ASD). Early studies using intranasal oxytocin in patients with ASD yielded encouraging results and for some time, scientists and affected families placed high hopes on the use of intranasal oxytocin for behavioral therapy in ASD. However, a recent Phase III trial obtained negative results using intranasal oxytocin for the treatment of behavioral symptoms in children with ASD. Given the frequently observed autism-like behavioral phenotypes in Prader-Willi and Schaaf-Yang syndromes, it is unclear whether oxytocin treatment represents a viable option to treat behavioral symptoms in these diseases. Here we review the latest findings on intranasal OT treatment, Prader-Willi and Schaaf-Yang syndromes, and propose novel research strategies for tailored oxytocin-based therapies for affected individuals. Finally, we propose the critical period theory, which could explain why oxytocin-based treatment seems to be most efficient in infants, but not adolescents

Emerging role of astrocytes in oxytocin-mediated control of neural circuits and brain functions

International audienceThe neuropeptide oxytocin has been in the focus of scientists for decades due to its profound and pleiotropic effects on physiology, activity of neuronal circuits and behaviors, among which sociality. Until recently, it was believed that oxytocinergic action exclusively occurs through direct activation of neuronal oxytocin receptors. However, several studies demonstrated the existence and functional relevance of astroglial oxytocin receptors in various brain regions in the mouse and rat brain. Astrocytic signaling and activity is critical for many important physiological processes including metabolism, neurotransmitter clearance from the synaptic cleft and integrated brain functions. While it can be speculated that oxytocinergic action on astrocytes predominantly facilitates neuromodulation via the release of specific gliotransmitters, the precise role of astrocytic oxytocin receptors remains elusive. In this review, we discuss the latest studies on the interaction between the oxytocinergic system and astrocytes, including detailed information about intracellular cascades, and speculate about future research directions on astrocytic oxytocin signaling

Changes in neuropeptide large dense core vesicle trafficking dynamics contribute to adaptive responses to a systemic homeostatic challenge

Summary: Neuropeptides are packed into large dense core vesicles (LDCVs) that are transported from the soma out into their processes. Limited information exists regarding mechanisms regulating LDCV trafficking, particularly during challenges to bodily homeostasis. Addressing this gap, we used 2-photon imaging in an ex vivo preparation to study LDCVs trafficking dynamics in vasopressin (VP) neurons, which traffic and release neuropeptide from their dendrites and axons. We report a dynamic bidirectional trafficking of VP-LDCVs with important differences in speed and directionality between axons and dendrites. Acute, short-lasting stimuli known to alter VP firing activity and axonal/dendritic release caused modest changes in VP-LDCVs trafficking dynamics. Conversely, chronic/sustained systemic osmotic challenges upregulated VP-LDCVs trafficking dynamic, with a larger effect in dendrites. These results support differential regulation of dendritic and axonal LDCV trafficking, and that changes in trafficking dynamics constitute a novel mechanism by which peptidergic neurons can efficiently adapt to conditions of increased hormonal demand

Chemogenetic activation of oxytocin neurons: Temporal dynamics, hormonal release, and behavioral consequences

Chemogenetics provides cell type-specific remote control of neuronal activity. Here, we describe the application of chemogenetics used to specifically activate oxytocin (OT) neurons as representatives of a unique class of neuroendocrine cells. We injected recombinant adeno-associated vectors, driving the stimulatory subunit hM3Dq of a modified human muscarinic receptor into the rat hypothalamus to achieve cell type-specific expression in OT neurons. As chemogenetic activation of OT neurons has not been reported, we provide systematic analysis of the temporal dynamics of OT neuronal responses in vivo by monitoring calcium fluctuations in OT neurons, and intracerebral as well as peripheral release of OT. We further provide evidence for the efficiency of chemogenetic manipulation at behavioral levels, demonstrating that evoked activation of OT neurons leads to social motivation and anxiolysis. Altogether, our results will be profitable for researchers working on the physiology of neuroendocrine systems, peptidergic modulation of behaviors and translational psychiatry

Oxytocin Signaling in the Lateral Septum Prevents Social Fear during Lactation

Oxytocin (OXT)-mediated behavioral responses to social and stressful cues have extensively been studied in male rodents. Here, we investigated the capacity of brain OXT receptor (OXTR) signaling in the lateral septum (LS) to prevent social fear expression in female mice using the social-fear-conditioning paradigm. Utilizing the activated OXT system during lactation, we show that lactating mice did not express fear 24 hr after social fear conditioning. Supporting the role of OXTR signaling in the LS in attenuation of social fear, synthetic OXT infusion or overexpression of OXTR in the LS diminished social fear expression, whereas constitutive OXTR knockout severely impaired social fear extinction in virgin mice. Subsequently, both pharmacological blockade of local OXTRs in the LS and chemogenetic silencing of supraoptic nucleus OXTergic afferents to the LS increased social fear expression in lactating mice. Hence, LS-projecting OXT neurons suppress social fear in female mice

A Fear Memory Engram and Its Plasticity in the Hypothalamic Oxytocin System

International audienceOxytocin (OT) release by axonal terminals onto the central nucleus of the amygdala exerts anxiolysis. To investigate which subpopulation of OT neurons contributes to this effect, we developed a novel method: virus-delivered genetic activity-induced tagging of cell ensembles (vGATE). With the vGATE method, we identified and permanently tagged a small subpopulation of OT cells, which, by optogenetic stimulation, strongly attenuated contextual fear-induced freezing, and pharmacogenetic silencing of tagged OT neurons impaired context-specific fear extinction, demonstrating that the tagged OT neurons are sufficient and necessary, respectively, to control contextual fear. Intriguingly, OT cell terminals of fear-experienced rats displayed enhanced glutamate release in the amygdala. Furthermore, rats exposed to another round of fear conditioning displayed 5-fold more activated magnocellular OT neurons in a novel environment than a familiar one, possibly for a generalized fear response. Thus, our results provide first evidence that hypothalamic OT neurons represent a fear memory engram

A New Population of Parvocellular Oxytocin Neurons Controlling Magnocellular Neuron Activity and Inflammatory Pain Processing

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Social touch promotes interfemale communication via activation of parvocellular oxytocin neurons

Oxytocin (OT) is a great facilitator of social life but, although its effects on socially relevant brain regions have been extensively studied, OT neuron activity during actual social interactions remains unexplored. Most OT neurons are magnocellular neurons, which simultaneously project to the pituitary and forebrain regions involved in social behaviors. In the present study, we show that a much smaller population of OT neurons, parvocellular neurons that do not project to the pituitary but synapse onto magnocellular neurons, is preferentially activated by somatosensory stimuli. This activation is transmitted to the larger population of magnocellular neurons, which consequently show coordinated increases in their activity during social interactions between virgin female rats. Selectively activating these parvocellular neurons promotes social motivation, whereas inhibiting them reduces social interactions. Thus, parvocellular OT neurons receive particular inputs to control social behavior by coordinating the responses of the much larger population of magnocellular OT neurons. Charlet, Grinevich et al. show that social touch between female rats activates parvocellular oxytocin neurons; these neurons control social behavior by coordinating the responses of the much larger population of magnocellular oxytocin neurons