Sensory neurons promote immune homeostasis in the lung.

Cytokines employ downstream Janus kinases (JAKs) to promote chronic inflammatory diseases. JAK1-dependent type 2 cytokines drive allergic inflammation, and patients with JAK1 gain-of-function (GoF) variants develop atopic dermatitis (AD) and asthma. To explore tissue-specific functions, we inserted a human JAK1 GoF variant (JAK1GoF) into mice and observed the development of spontaneous AD-like skin disease but unexpected resistance to lung inflammation when JAK1GoF expression was restricted to the stroma. We identified a previously unrecognized role for JAK1 in vagal sensory neurons in suppressing airway inflammation. Additionally, expression of Calcb/CGRPß was dependent on JAK1 in the vagus nerve, and CGRPß suppressed group 2 innate lymphoid cell function and allergic airway inflammation. Our findings reveal evolutionarily conserved but distinct functions of JAK1 in sensory neurons across tissues. This biology raises the possibility that therapeutic JAK inhibitors may be further optimized for tissue-specific efficacy to enhance precision medicine in the future.

A GPCR-neuropeptide axis dampens hyperactive neutrophils by promoting an alternative-like polarization during bacterial infection.

The notion that neutrophils exist as a homogeneous population is being replaced with the knowledge that neutrophils adopt different functional states. Neutrophils can have a pro-inflammatory phenotype or an anti-inflammatory state, but how these states are regulated remains unclear. Here, we demonstrated that the neutrophil-expressed G-protein-coupled receptor (GPCR) Mrgpra1 is a negative regulator of neutrophil bactericidal functions. Mrgpra1-mediated signaling was driven by its ligand, neuropeptide FF (NPFF), which dictated the balance between pro- and anti-inflammatory programming. Specifically, the Mrgpra1-NPFF axis counter-regulated interferon (IFN) γ-mediated neutrophil polarization during acute lung infection by favoring an alternative-like polarization, suggesting that it may act to balance overzealous neutrophilic responses. Distinct, cross-regulated populations of neutrophils were the primary source of NPFF and IFNγ during infection. As a subset of neutrophils at steady state expressed NPFF, these findings could have broad implications in various infectious and inflammatory diseases. Therefore, a neutrophil-intrinsic pathway determines their cellular fate, function, and magnitude of infection.

Timed receptor tyrosine kinase signaling couples the central and a peripheral circadian clock in Drosophila.

Circadian clocks impose daily periodicities to behavior, physiology, and metabolism. This control is mediated by a central clock and by peripheral clocks, which are synchronized to provide the organism with a unified time through mechanisms that are not fully understood. Here, we characterized in Drosophila the cellular and molecular mechanisms involved in coupling the central clock and the peripheral clock located in the prothoracic gland (PG), which together control the circadian rhythm of emergence of adult flies. The time signal from central clock neurons is transmitted via small neuropeptide F (sNPF) to neurons that produce the neuropeptide Prothoracicotropic Hormone (PTTH), which is then translated into daily oscillations of Ca2+ concentration and PTTH levels. PTTH signaling is required at the end of metamorphosis and transmits time information to the PG through changes in the expression of the PTTH receptor tyrosine kinase (RTK), TORSO, and of ERK phosphorylation, a key component of PTTH transduction. In addition to PTTH, we demonstrate that signaling mediated by other RTKs contributes to the rhythmicity of emergence. Interestingly, the ligand to one of these receptors (Pvf2) plays an autocrine role in the PG, which may explain why both central brain and PG clocks are required for the circadian gating of emergence. Our findings show that the coupling between the central and the PG clock is unexpectedly complex and involves several RTKs that act in concert and could serve as a paradigm to understand how circadian clocks are coordinated.

Drosophila neuronal Glucose-6-Phosphatase is a modulator of neuropeptide release that regulates muscle glycogen stores via FMRFamide signaling.

Neuropeptides (NPs) and their cognate receptors are critical effectors of diverse physiological processes and behaviors. We recently reported of a noncanonical function of the Drosophila Glucose-6-Phosphatase (G6P) gene in a subset of neurosecretory cells in the central nervous system that governs systemic glucose homeostasis in food-deprived flies. Here, we show that G6P-expressing neurons define six groups of NP-secreting cells, four in the brain and two in the thoracic ganglion. Using the glucose homeostasis phenotype as a screening tool, we find that neurons located in the thoracic ganglion expressing FMRFamide NPs (FMRFaG6P neurons) are necessary and sufficient to maintain systemic glucose homeostasis in starved flies. We further show that G6P is essential in FMRFaG6P neurons for attaining a prominent Golgi apparatus and secreting NPs efficiently. Finally, we establish that G6P-dependent FMRFa signaling is essential for the build-up of glycogen stores in the jump muscle which expresses the receptor for FMRFamides. We propose a general model in which the main role of G6P is to counteract glycolysis in peptidergic neurons for the purpose of optimizing the intracellular environment best suited for the expansion of the Golgi apparatus, boosting release of NPs and enhancing signaling to respective target tissues expressing cognate receptors.

Two C-terminal isoforms of Aplysia tachykinin-related peptide receptors exhibit phosphorylation-dependent and phosphorylation-independent desensitization mechanisms.

Diversity, a hallmark of G protein-coupled receptor (GPCR) signaling, partly stems from alternative splicing of a single gene generating more than one isoform for a receptor. Additionally, receptor responses to ligands can be attenuated by desensitization upon prolonged or repeated ligand exposure. Both phenomena have been demonstrated and exemplified by the deuterostome tachykinin signaling system, although the role of phosphorylation in desensitization remains a subject of debate. Here, we describe the signaling system for tachykinin-related peptides (TKRPs) in a protostome, mollusk Aplysia. We cloned the Aplysia TKRP precursor, which encodes three TKRPs (apTKRP-1, apTKRP-2a, and apTKRP-2b) containing the FXGXR-amide motif. In situ hybridization and immunohistochemistry showed predominant expression of TKRP mRNA and peptide in the cerebral ganglia. TKRPs and their posttranslational modifications were observed in extracts of central nervous system ganglia using mass spectrometry. We identified two Aplysia TKRP receptors (apTKRPRs), named apTKRPR-A and apTKRPR-B. These receptors are two isoforms generated through alternative splicing of the same gene and differ only in their intracellular C termini. Structure-activity relationship analysis of apTKRP-2b revealed that both C-terminal amidation and conserved residues of the ligand are critical for receptor activation. C-terminal truncates and mutants of apTKRPRs suggested that there is a C-terminal phosphorylation-independent desensitization for both receptors. Moreover, apTKRPR-B also exhibits phosphorylation-dependent desensitization through the phosphorylation of C-terminal Ser/Thr residues. This comprehensive characterization of the Aplysia TKRP signaling system underscores the evolutionary conservation of the TKRP and TK signaling systems, while highlighting the intricacies of receptor regulation through alternative splicing and differential desensitization mechanisms.

A novel series of metazoan L/D peptide isomerases.

The function of endogenous cell-cell signaling peptides relies on their interactions with cognate receptors, which in turn are influenced by the peptides' structures, necessitating a comprehensive understanding of the suite of post-translational modifications of the peptide. Herein, we report the initial characterization of putative peptide isomerase enzymes extracted from R. norvegicus, A. californica, and B. taurus tissues. These enzymes are both tissue and substrate-specific across all three organisms. Notably, the lungs of the mammalian species, and the central nervous system of the mollusk displayed the highest isomerase activity among the examined tissues. In vitro enzymatic conversion was observed for several endogenous peptides, such as the tetrapeptide GFFD in A. californica, and mammalian neuropeptide FF in R. norvegicus and B. taurus. To understand their mode of action, we explored the effects of several inhibitors on these enzymes, which suggest common active site residues. While further characterization of these enzymes is required, the investigations emphasize a widespread and overlooked enzyme activity related to the creation of bioactive peptides.

Long-term enhancements in antidepressant efficacy and neurogenesis: Effects of intranasal co-administration of neuropeptide Y 1 receptor (NPY1R) and galanin receptor 2 (GALR2) agonists in the ventral hippocampus.

This study evaluates the sustained antidepressant-like effects and neurogenic potential of a 3-day intranasal co-administration regimen of galanin receptor 2 (GALR2) agonist M1145 and neuropeptide Y Y1 receptor (NPY1R) agonist [Leu31, Pro34]NPY in the ventral hippocampus of adult rats, with outcomes analyzed 3 weeks post-treatment. Utilizing the forced swimming test (FST), we found that this co-administration significantly enhances antidepressant-like behaviors, an effect neutralized by the GALR2 antagonist M871, highlighting the synergistic potential of these neuropeptides in modulating mood-related behaviors. In situ proximity ligation assay (PLA) indicated a significant increase in GALR2/NPYY1R heteroreceptor complexes in the ventral hippocampal dentate gyrus, suggesting a molecular basis for the behavioral outcomes observed. Moreover, proliferating cell nuclear antigen (PCNA) immunolabeling revealed increased cell proliferation in the subgranular zone of the dentate gyrus, specifically in neuroblasts as evidenced by co-labeling with doublecortin (DCX), without affecting quiescent neural progenitors or astrocytes. The study also noted a significant uptick in the number of DCX-positive cells and alterations in dendritic morphology in the ventral hippocampus, indicative of enhanced neuronal differentiation and maturation. These morphological changes highlight the potential of these agonists to facilitate the functional integration of new neurons into existing neural circuits. By demonstrating the long-lasting effects of a brief, 3-day intranasal administration of GALR2 and NPY1R agonists, our findings contribute significantly to the understanding of neuropeptide-mediated neuroplasticity and herald novel therapeutic strategies for the treatment of depression and related mood disorders, emphasizing the therapeutic promise of targeting neurogenesis and neuronal maturation processes.

In vivo photocontrol of orexin receptors with a nanomolar light-regulated analogue of orexin-B.

Orexinergic neurons are critically involved in regulating arousal, wakefulness, and appetite. Their dysfunction has been associated with sleeping disorders, and non-peptide drugs are currently being developed to treat insomnia and narcolepsy. Yet, no light-regulated agents are available to reversibly control their activity. To meet this need, a photoswitchable peptide analogue of the endogenous neuroexcitatory peptide orexin-B was designed, synthesized, and tested in vitro and in vivo. This compound - photorexin - is the first photo-reversible ligand reported for orexin receptors. It allows dynamic control of activity in vitro (including almost the same efficacy as orexin-B, high nanomolar potency, and subtype selectivity to human OX2 receptors) and in vivo in zebrafish larvae by direct application in water. Photorexin induces dose- and light-dependent changes in locomotion and a reduction in the successive induction reflex that is associated with sleep behavior. Molecular dynamics calculations indicate that trans and cis photorexin adopt similar bent conformations and that the only discriminant between their structures and activities is the positioning of the N-terminus. This, in the case of the more active trans isomer, points towards the OX2 N-terminus and extra-cellular loop 2, a region of the receptor known to be involved in ligand binding and recognition consistent with a "message-address" system. Thus, our approach could be extended to several important families of endogenous peptides, such as endothelins, nociceptin, and dynorphins among others, that bind to their cognate receptors through a similar mechanism: a "message" domain involved in receptor activation and signal transduction, and an "address" sequence for receptor occupation and improved binding affinity.

Signaling mechanisms underlying activity-dependent integration of adult-born neurons in the mouse olfactory bulb.

Adult neurogenesis has fascinated the field of neuroscience for decades given the prospects of harnessing mechanisms that facilitate the rewiring and/or replacement of adult brain tissue. The subgranular zone of the hippocampus and the subventricular zone of the lateral ventricle are the two main areas in the brain that exhibit ongoing neurogenesis. Of these, adult-born neurons within the olfactory bulb have proven to be a powerful model for studying circuit plasticity, providing a broad and accessible avenue into neuron development, migration, and continued circuit integration within adult brain tissue. This review focuses on some of the recognized molecular and signaling mechanisms underlying activity-dependent adult-born neuron development. Notably, olfactory activity and behavioral states contribute to adult-born neuron plasticity through sensory and centrifugal inputs, in which calcium-dependent transcriptional programs, local translation, and neuropeptide signaling play important roles. This review also highlights areas of needed continued investigation to better understand the remarkable phenomenon of adult-born neuron integration.

A crustacean neuropeptide spectral library for data-independent acquisition (DIA) mass spectrometry applications.

Neuropeptides have tremendous potential for application in modern medicine, including utility as biomarkers and therapeutics. To overcome the inherent challenges associated with neuropeptide identification and characterization, data-independent acquisition (DIA) is a fitting mass spectrometry (MS) method of choice to achieve sensitive and accurate analysis. It is advantageous for preliminary neuropeptidomic studies to occur in less complex organisms, with crustacean models serving as a popular choice due to their relatively simple nervous system. With spectral libraries serving as a means to interpret DIA-MS output spectra, and Cancer borealis as a model of choice for neuropeptide analysis, we performed the first spectral library mapping of crustacean neuropeptides. Leveraging pre-existing data-dependent acquisition (DDA) spectra, a spectral library was built using PEAKS Online. The library is comprised of 333 unique neuropeptides. The identification results obtained through the use of this spectral library were compared with those achieved through library-free analysis of crustacean brain, pericardial organs (PO), and thoracic ganglia (TG) tissues. A statistically significant increase (Student's t-test, P value < 0.05) in the number of identifications achieved from the TG data was observed in the spectral library results. Furthermore, in each of the tissues, a distinctly different set of identifications was found in the library search compared to the library-free search. This work highlights the necessity for the use of spectral libraries in neuropeptide analysis, illustrating the advantage of spectral libraries for interpreting DIA spectra in a reproducible manner with greater neuropeptidomic depth.

Neuropeptidomics of the American Lobster Homarus americanus.

The American lobster, Homarus americanus, is not only of considerable economic importance but has also emerged as a premier model organism in neuroscience research. Neuropeptides, an important class of cell-to-cell signaling molecules, play crucial roles in a wide array of physiological and psychological processes. Leveraging the recently sequenced high-quality draft genome of the American lobster, our study sought to profile the neuropeptidome of this model organism. Employing advanced mass spectrometry techniques, we identified 24 neuropeptide precursors and 101 unique mature neuropeptides in Homarus americanus. Intriguingly, 67 of these neuropeptides were discovered for the first time. Our findings provide a comprehensive overview of the peptidomic attributes of the lobster's nervous system and highlight the tissue-specific distribution of these neuropeptides. Collectively, this research not only enriches our understanding of the neuronal complexities of the American lobster but also lays a foundation for future investigations into the functional roles that these peptides play in crustacean species. The mass spectrometry data have been deposited in the PRIDE repository with the identifier PXD047230.

EndoGenius: Optimized Neuropeptide Identification from Mass Spectrometry Datasets.

Neuropeptides represent a unique class of signaling molecules that have garnered much attention but require special consideration when identifications are gleaned from mass spectra. With highly variable sequence lengths, neuropeptides must be analyzed in their endogenous state. Further, neuropeptides share great homology within families, differing by as little as a single amino acid residue, complicating even routine analyses and necessitating optimized computational strategies for confident and accurate identifications. We present EndoGenius, a database searching strategy designed specifically for elucidating neuropeptide identifications from mass spectra by leveraging optimized peptide-spectrum matching approaches, an expansive motif database, and a novel scoring algorithm to achieve broader representation of the neuropeptidome and minimize reidentification. This work describes an algorithm capable of reporting more neuropeptide identifications at 1% false-discovery rate than alternative software in five Callinectes sapidus neuronal tissue types.

Hypothalamic transcriptome response to simulated diel earthen pond hypoxia cycles in channel catfish (Ictalurus punctatus).

Commercial culture of channel catfish (Ictalurus punctatus) occurs in earthen ponds that are characterized by diel swings in dissolved oxygen concentration that can fall to severe levels of hypoxia, which can suppress appetite and lead to suboptimal growth. Given the significance of the hypothalamus in regulating these processes in other fishes, an investigation into the hypothalamus transcriptome was conducted to identify specific genes and expression patterns responding to hypoxia. Channel catfish in normoxic water were compared with catfish subjected to 12 h of hypoxia (20% oxygen saturation; 1.8 mg O2/L; 27°C) followed by 12 h of recovery in normoxia to mimic 24 h in a catfish aquaculture pond. Fish were sampled at 0-, 6-, 12-, 18-, and 24-h timepoints, with the 6- and 12-h samplings occurring during hypoxia. A total of 190 genes were differentially expressed during the experiment, with most occurring during hypoxia and returning to baseline values within 6 h of normoxia. Differentially expressed genes were sorted by function into Gene Ontology biological processes and revealed that most were categorized as "response to hypoxia," "sprouting angiogenesis," and "cellular response to xenobiotic stimulus." The patterns of gene expression reported here suggest that transcriptome responses to hypoxia are broad and quickly reversibly with the onset of normoxia. Although no genes commonly reported to modulate appetite were found to be differentially expressed in this experiment, several candidates were identified for future studies investigating the interplay between hypoxia and appetite in channel catfish, including adm, igfbp1a, igfbp7, and stc2b.NEW & NOTEWORTHY Channel catfish are an economically important species that experience diel episodic periods of hypoxia that can reduce appetite. This is the first study to investigate their transcriptome from the hypothalamus in a simulated 24-h span in a commercial catfish pond, with 12 h of hypoxia and 12 h of normoxia. The research revealed functional groups of genes relating to hypoxia, angiogenesis, and glycolysis as well as individual target genes possibly involved in appetite regulation.

Circulating noradrenaline leads to release of neuropeptide Y from cardiac sympathetic nerve terminals via activation of ß-adrenergic receptors.

Cardiac disease is marked by sympathoexcitation and elevated levels of noradrenaline (NA) and cotransmitter neuropeptide Y (NPY). Increased NPY levels are associated with a greater risk of ventricular arrhythmias and mortality. Nonetheless, the factors that cause NPY release remain poorly understood. We hypothesized that circulating catecholamines might lead to NPY release from myocardial sympathetic nerve terminals via a ß-receptor-mediated mechanism that enhances sympathoexcitation. Ventricular interstitial NA and NPY levels were measured in six Yorkshire pigs after i.v. administration of NA (1 mg) and before and after propranolol infusion (1 mg/kg). Real-time interstitial NPY levels were measured using ventricular capacitive immunoprobes (CIs) affixed with NPY antibodies and quantified as the change in CI input current (INPY ) upon binding of NPY. Interstitial NA was measured with adjacent fast-scan cyclic voltammetry probes (INA ). A left ventricular pressure catheter and continuous ECGs were used for haemodynamic recordings, and an epicardial 56-electrode sock was used for measurements of activation recovery interval, a surrogate of action potential duration. Upon administration of NA, heart rate and left ventricular pressure increased, and activation recovery interval shortened. Notably, NA significantly increased interstitial myocardial NPY levels. After propranolol, changes in heart rate and activation recovery interval were largely mitigated. The INA increased to a similar extent post-propranolol vs. pre-propranolol, but changes in INPY were significantly reduced post-propranolol. Coronary sinus plasma analyses confirmed fast-scan cyclic voltammetry and CI findings. Hence, this study demonstrates that circulating NA induces NPY release from ventricular sympathetic nerve terminals, the mechanism for which is mediated via ß-adrenergic receptors and can be blocked by the non-selective ß-blocker, propranolol. KEY POINTS: Cardiovascular disease is characterized by sympathovagal imbalance, with increased plasma noradrenaline (NA) and neuropeptide Y (NPY) concentrations. Increased NPY levels are associated with increased ventricular arrhythmias and mortality in heart failure. Limited data are available on the specific factors that cause NPY release. In this study, fast-scan cyclic voltammetry and capacitive immunoprobes were used to allow for real-time in vivo measurements of interstitial myocardial neurotransmitters and neuropeptides, respectively. Using an in vivo porcine model with cardiac fast-scan cyclic voltammetry and capacitive immunoprobes, it was shown that systemic NA can increase ventricular interstitial NPY levels, suggesting that NA induces NPY release from postganglionic sympathetic nerves. The release of NPY was blocked by administration of the non-selective ß-blocker propranolol, suggesting that release of NPY is dependent on activation of ß-adrenergic receptors by NA.

Bayliss Starling Prize Lecture 2023: Neuropeptide-Y being 'unsympathetic' to the broken hearted.

William Bayliss and Ernest Starling are not only famous as pioneers in cardiovascular physiology, but also responsible for the discovery of the first hormone (from the Greek 'excite or arouse'), the intestinal signalling molecule and neuropeptide secretin in 1902. Our research group focuses on neuropeptides and neuromodulators that influence cardiovascular autonomic control as potential biomarkers in disease and tractable targets for therapeutic intervention. Acute myocardial infarction (AMI) and chronic heart failure (CHF) result in high levels of cardiac sympathetic stimulation, which is a poor prognostic indicator. Although beta-blockers improve mortality in these conditions by preventing the action of the neurotransmitter noradrenaline, a substantial residual risk remains. Recently, we have identified the sympathetic co-transmitter neuropeptide-Y (NPY) as being released during AMI, leading to larger infarcts and life-threatening arrhythmia in both animal models and patients. Here, we discuss recently published data demonstrating that peripheral venous NPY levels are associated with heart failure hospitalisation and mortality after AMI, and all cause cardiovascular mortality in CHF, even when adjusting for known risk factors (including brain natriuretic peptide). We have investigated the mechanistic basis for these observations in human and rat stellate ganglia and cardiac tissue, manipulating NPY neurochemistry at the same time as using state-of-the-art imaging techniques, to establish the receptor pathways responsible for NPY signalling. We propose NPY as a new mechanistic biomarker in AMI and CHF patients and aim to determine whether specific NPY receptor blockers can prevent arrhythmia and attenuate the development of heart failure.

Elucidating the ecophysiology of soybean pod-sucking stinkbug Riptortus pedestris (Hemiptera: Alydidae) based on de novo genome assembly and transcriptome analysis.

Food security is important for the ever-growing global population. Soybean, Glycine max (L.) Merr., is cultivated worldwide providing a key source of food, protein and oil. Hence, it is imperative to maintain or to increase its yield under different conditions including challenges caused by abiotic and biotic stresses. In recent years, the soybean pod-sucking stinkbug Riptortus pedestris has emerged as an important agricultural insect pest in East, South and Southeast Asia. Here, we present a genomics resource for R. pedestris including its genome assembly, messenger RNA (mRNA) and microRNA (miRNA) transcriptomes at different developmental stages and from different organs. As insect hormone biosynthesis genes (genes involved in metamorphosis) and their regulators such as miRNAs are potential targets for pest control, we analyzed the sesquiterpenoid (juvenile) and ecdysteroid (molting) hormone biosynthesis pathway genes including their miRNAs and relevant neuropeptides. Temporal gene expression changes of these insect hormone biosynthesis pathways were observed at different developmental stages. Similarly, a diet-specific response in gene expression was also observed in both head and salivary glands. Furthermore, we observed that microRNAs (bantam, miR-14, miR-316, and miR-263) of R. pedestris fed with different types of soybeans were differentially expressed in the salivary glands indicating a diet-specific response. Interestingly, the opposite arms of miR-281 (-5p and -3p), a miRNA involved in regulating development, were predicted to target Hmgs genes of R. pedestris and soybean, respectively. These observations among others highlight stinkbug's responses as a function of its interaction with soybean. In brief, the results of this study not only present salient findings that could be of potential use in pest management and mitigation but also provide an invaluable resource for R. pedestris as an insect model to facilitate studies on plant-pest interactions.

Identification of the principal neuropeptide MIP and its action pathway in larval settlement of the echiuran worm Urechis unicinctus.

BACKGROUND: Larval settlement and metamorphosis represent critical events in the life history of marine benthic animals. Myoinhibitory peptide (MIP) plays a pivotal role in larval settlement of marine invertebrates. However, the molecular mechanisms of MIP involved in this process are not well understood. RESULTS: In this study, we evaluated the effects of thirteen MIP mature peptides on triggering the larval settlement of Urechis unicinctus (Xenopneusta, Urechidae), and determined that MIP2 was the principal neuropeptide. Transcriptomic analysis was employed to identify differentially expressed genes (DEGs) between the MIP2-treated larvae and normal early-segmentation larvae. Both cAMP and calcium signaling pathways were enriched in the DEGs of the MIP2-treated larvae, and two neuropeptide receptor genes (Spr, Fmrfar) were up-regulated in the MIP2-treated larvae. The activation of the SPR-cAMP pathway by MIP2 was experimentally validated in HEK293T cells. Furthermore, fourteen cilia-related genes, including Tctex1d2, Cfap45, Ift43, Ift74, Ift22, Cav1 and Mns1, etc. exhibited down-regulated expression in the MIP2-treated larvae. Whole-mount in situ hybridization identified two selected ciliary genes, Tctex1d2 and Cfap45, were specially expressed in circumoral ciliary cells of the early-segmentation larvae. Knocking down Tctex1d2 mRNA levels by in vivo RNA interference significantly increased the larval settlement rate. CONCLUSION: Our findings suggest that MIP2 inhibits the function of the cilia-related genes, such as Tctex1d2, through the SPR-cAMP-PKA pathway, thereby inducing larval settlement in U. unicinctus. The study contributes important data to the understanding of neuropeptide regulation in larval settlement.

Switching neuron contributions to second network activity.

Network flexibility is important for adaptable behaviors. This includes neuronal switching, where neurons alter their network participation, including changing from single- to dual-network activity. Understanding the implications of neuronal switching requires determining how a switching neuron interacts with each of its networks. Here, we tested 1) whether "home" and second networks, operating via divergent rhythm generation mechanisms, regulate a switching neuron and 2) if a switching neuron, recruited via modulation of intrinsic properties, contributes to rhythm or pattern generation in a new network. Small, well-characterized feeding-related networks (pyloric, ∼1 Hz; gastric mill, ∼0.1 Hz) and identified modulatory inputs make the isolated crab (Cancer borealis) stomatogastric nervous system (STNS) a useful model to study neuronal switching. In particular, the neuropeptide Gly1-SIFamide switches the lateral posterior gastric (LPG) neuron (2 copies) from pyloric-only to dual-frequency pyloric/gastric mill (fast/slow) activity via modulation of LPG-intrinsic properties. Using current injections to manipulate neuronal activity, we found that gastric mill, but not pyloric, network neurons regulated the intrinsically generated LPG slow bursting. Conversely, selective elimination of LPG from both networks using photoinactivation revealed that LPG regulated gastric mill neuron-firing frequencies but was not necessary for gastric mill rhythm generation or coordination. However, LPG alone was sufficient to produce a distinct pattern of network coordination. Thus, modulated intrinsic properties underlying dual-network participation may constrain which networks can regulate switching neuron activity. Furthermore, recruitment via intrinsic properties may occur in modulatory states where it is important for the switching neuron to actively contribute to network output.NEW & NOTEWORTHY We used small, well-characterized networks to investigate interactions between rhythmic networks and neurons that switch their network participation. For a neuron switching into dual-network activity, only the second network regulated its activity in that network. In addition, the switching neuron was sufficient but not necessary to coordinate second network neurons and regulated their activity levels. Thus, regulation of switching neurons may be selective, and a switching neuron is not necessarily simply a follower in additional networks.

Lineage-tracing reveals an expanded population of NPY neurons in the inferior colliculus.

Growing evidence suggests that neuropeptide signaling shapes auditory computations. We previously showed that neuropeptide Y (NPY) is expressed in the inferior colliculus (IC) by a population of GABAergic stellate neurons and that NPY regulates the strength of local excitatory circuits in the IC. NPY neurons were initially characterized using the NPY-hrGFP mouse, in which humanized renilla green fluorescent protein (hrGFP) expression indicates NPY expression at the time of assay, i.e., an expression-tracking approach. However, studies in other brain regions have shown that NPY expression can vary based on several factors, suggesting that the NPY-hrGFP mouse might miss NPY neurons not expressing NPY on the experiment date. Here, we hypothesized that neurons with the ability to express NPY represent a larger population of IC GABAergic neurons than previously reported. To test this hypothesis, we used a lineage-tracing approach to irreversibly tag neurons that expressed NPY at any point prior to the experiment date. We then compared the physiological and anatomical features of neurons labeled with this lineage-tracing approach to our prior data set, revealing a larger population of NPY neurons than previously found. In addition, we used optogenetics to test the local connectivity of NPY neurons and found that NPY neurons provide inhibitory synaptic input to other neurons in the ipsilateral IC. Together, our data expand the definition of NPY neurons in the IC, suggest that NPY expression might be dynamically regulated in the IC, and provide functional evidence that NPY neurons form local inhibitory circuits in the IC.NEW & NOTEWORTHY Across brain regions, neuropeptide Y (NPY) expression is dynamic and influenced by extrinsic and intrinsic factors. We previously showed that NPY is expressed by a class of inhibitory neurons in the auditory midbrain. Here, we find that this neuron class also includes neurons that previously expressed NPY, suggesting that NPY expression is dynamically regulated in the auditory midbrain. We also provide functional evidence that NPY neurons contribute to local inhibitory circuits in the auditory midbrain.

Influence of the gut microbiome on appetite-regulating neuropeptides in the hypothalamus: Insight from conventional, antibiotic-treated, and germ-free mouse models of anorexia nervosa.

Recent research highlights the profound impact of the gut microbiome on neuropsychiatric disorders, shedding light on its potential role in shaping human behavior. In this study, we investigate the role of the gut microbiome in appetite regulation using activity-based anorexia (ABA) mouse model of anorexia nervosa (AN) - a severe eating disorder with significant health consequences. ABA was induced in conventional, antibiotic-treated, and germ-free mice. Our results show the clear influence of the gut microbiome on the expression of four orexigenic (neuropeptide Y, agouti-related peptide, melanin-concentrating hormone, and orexin) and four anorexigenic peptides (cocaine- and amphetamine-regulated transcript, corticotropin-releasing hormone, thyrotropin-releasing hormone, and pro-opiomelanocortin) in the hypothalamus. Additionally, we assessed alterations in gut barrier permeability. While variations were noted in germ-free mice based on feeding and activity, they were not directly attributable to the gut microbiome. This research emphasizes that the gut microbiome is a pivotal factor in AN's appetite regulation beyond just dietary habits or physical activity.