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Graphical Abstract Highlights d Excitatory NPYR1 Cre (Y1 Cre ) neurons are required for mechanical itch transmission d Spinal Y1 Cre neurons receive LTMR input and mediate light punctate touch d NPY::Cre interneurons inhibit Y1-expressing neurons in the dorsal horn d NPY signaling via dorsal horn Y1-expressing neurons gates mechanical itch In Brief Acton et al. identify the excitatory neurons in the dorsal spinal cord that drive mechanical itch. These cells mediate responses to light punctate touch and are inhibited by neuropeptide Y (NPY)::Cre interneurons. Light touch sensitivity and mechanical itch responses are gated by NPY signaling mediated by Y1-expressing neurons in the dorsal horn. Mechanical itch Disrupted inhibitory gating Normal inhibitory gating Y1 + Low-threshold mechanoreceptors NPY + Normal touch discrimination NPY Y1 + NPY + Mechanical itch NPY Low-threshold mechanoreceptors SUMMARYAcute itch can be generated by either chemical or mechanical stimuli, which activate separate pathways in the periphery and spinal cord. While substantial progress has been made in mapping the transmission pathway for chemical itch, the central pathway for mechanical itch remains obscure. Using complementary genetic and pharmacological manipulations, we show that excitatory neurons marked by the expression of the neuropeptide Y1 receptor (Y1 Cre neurons) form an essential pathway in the dorsal spinal cord for the transmission of mechanical but not chemical itch. Ablating or silencing the Y1 Cre neurons abrogates mechanical itch, while chemogenetic activation induces scratching. Moreover, using Y1 conditional knockout mice, we demonstrate that endogenous neuropeptide Y (NPY) acts via dorsalhorn Y1-expressing neurons to suppress light punctate touch and mechanical itch stimuli. NPY-Y1 signaling thus regulates the transmission of innocuous tactile information by establishing biologically relevant thresholds for touch discrimination and mechanical itch reflexes.

The primary motor cortex has an important role in the precise execution of learned motor responses. During motor learning, synaptic efficacy between sensory and primary motor cortical neurons is enhanced, possibly involving long-term potentiation and N-methyl-D-aspartate (NMDA)-specific glutamate receptor function. To investigate whether NMDA receptor in the primary motor cortex can act as a coincidence detector for activity-dependent changes in synaptic strength and associative learning, here we generate mice with deletion of the Grin1 gene, encoding the essential NMDA receptor subunit 1 (GluN1), specifically in the primary motor cortex. The loss of NMDA receptor function impairs primary motor cortex long-term potentiation in vivo. Importantly, it impairs the synaptic efficacy between the primary somatosensory and primary motor cortices and significantly reduces classically conditioned eyeblink responses. Furthermore, compared with wild-type littermates, mice lacking primary motor cortex show slower learning in Skinner-box tasks. Thus, primary motor cortex NMDA receptors are necessary for activity-dependent synaptic strengthening and associative learning.

Neuropeptide Y (NPY) plays an important role in stress, anxiety, obesity, and energy homeostasis via activation of NPY-Y1 receptors (Y1Rs) in the brain. However, global knockout of the Npy1r gene has low or no impact on anxiety and body weight. To uncover the role of limbic Y1Rs, we generated conditional knockout mice in which the inactivation of the Npy1r gene was restricted to excitatory neurons of the forebrain, starting from juvenile stages (Npy1r rfb ). Npy1r rfb mice exhibited increased anxiety and reduced body weight, less adipose tissue, and lower serum leptin levels. Npy1r rfb mutants also had a hyperactive hypothalamic-pituitaryadrenocortical axis, as indicated by higher peripheral corticosterone and higher density of NPY immunoreactive fibers and corticotropin releasing hormone immunoreactive cell bodies in the paraventricular hypothalamic nucleus. Importantly, through fostering experiments, we determined that differences in phenotype between Npy1r rfb and Npy1r 2lox mice became apparent when both genotypes were raised by FVB/J but not by C57BL/6J dams, suggesting that limbic Y1Rs are key targets of maternal care-induced programming of anxiety and energy homeostasis. where it is involved in the regulation of anxiety, stress reactions, energy balance, circadian rhythms, and cognition (1-3). Clinical studies suggest that NPY plays an important role in the response to stress and in psychiatric disorders (4). In humans, NPY haploinsufficiency is correlated with characteristic brain responses to emotional and stress challenges and with trait anxiety (5). Intracerebroventricular injection of NPY reduces both anxiety-and stress-related behavior in several animal models, an effect that is primarily mediated by Y1 receptors (Y1Rs) expressed in amygdala, hippocampus, and locus coeruleus (6-9). The implications of a role of endogenous NPY in acting via Y1R to control emotionality, mood, and stress reactions have been probed with Y1R-selective antagonists and antisense oligonucleotides (1). NPY exerts its anxiolytic-like effect in the brain via interactions with the hypothalamic-pituitaryadrenocortical (HPA) axis and corticosteroids. Indeed, a functional antagonism between NPY and corticotropin releasing hormone (CRH) has been demonstrated in various CNS nuclei along the stress/anxiety circuits (10).In addition to its crucial role in emotional behavior, NPY potently stimulates feeding, reduces energy expenditure, and induces obesity via the activation of Y1R expressed in the hypothalamus (1). However, global Npy1r gene knockout mice showed only minor deficiencies in energy homeostasis, feeding, and anxiety (11)(12)(13)(14).To study the function of Y1R expressed in the limbic system and to exclude effects induced by the Npy1r gene inactivation in early development, we restricted the ablation of Y1R to excitatory neurons in the postnatal forebrain of mice by using the Cre-loxP system (Fig. 1A). In addition, because early postnatal environment can modulate NPY levels (15), gene-targeted pups were reared by two diffe...

COVID-19, the illness caused by SARS-CoV-2, has a wide-ranging clinical spectrum that, in the worst-case scenario, involves a rapid progression to severe acute respiratory syndrome and death. Epidemiological data show that obesity and diabetes are among the main risk factors associated with high morbidity and mortality. The increased susceptibility to SARS-CoV-2 infection documented in obesity-related metabolic derangements argues for initial defects in defence mechanisms, most likely due to an elevated systemic metabolic inflammation ("metaflammation"). The NLRP3 inflammasome is a master regulator of metaflammation and has a pivotal role in the pathophysiology of either obesity or diabetes. Here, we discuss the most recent findings suggesting contribution of NLRP3 inflammasome to the increase in complications in COVID-19 patients with diabesity. We also review current pharmacological strategies for COVID-19, focusing on treatments whose efficacy could be due, at least in part, to interference with the activation of the NLRP3 inflammasome.

The NMDA receptor-mediated Ca2+ signaling during simultaneous pre- and postsynaptic activity is critically involved in synaptic plasticity and thus has a key role in the nervous system. In GRIN2-variant patients alterations of this coincidence detection provoked complex clinical phenotypes, ranging from reduced muscle strength to epileptic seizures and intellectual disability. By using our gene-targeted mouse line (Grin2aN615S), we show that voltage-independent glutamate-gated signaling of GluN2A-containing NMDA receptors is associated with NMDAR-dependent audiogenic seizures due to hyperexcitable midbrain circuits. In contrast, the NMDAR antagonist MK-801-induced c-Fos expression is reduced in the hippocampus. Likewise, the synchronization of theta- and gamma oscillatory activity is lowered during exploration, demonstrating reduced hippocampal activity. This is associated with exploratory hyperactivity and aberrantly increased and dysregulated levels of attention that can interfere with associative learning, in particular when relevant cues and reward outcomes are disconnected in space and time. Together, our findings provide (i) experimental evidence that the inherent voltage-dependent Ca2+ signaling of NMDA receptors is essential for maintaining appropriate responses to sensory stimuli and (ii) a mechanistic explanation for the neurological manifestations seen in the NMDAR-related human disorders with GRIN2 variant-meidiated intellectual disability and focal epilepsy.

Heat-processed diets contain high amounts of advanced glycation end products (AGEs). Here we explore the impact of an AGE-enriched diet on markers of metabolic and inflammatory disorders as well as on gut microbiota composition and plasma proteins glycosylation pattern. C57BL/6 mice were allocated into control diet (CD, n = 15) and AGE-enriched diet (AGE-D, n = 15) for 22 weeks. AGE-D was prepared replacing casein by methylglyoxal hydroimidazolone-modified casein. AGE-D evoked increased insulin and a significant reduction of GIP/GLP-1 incretins and ghrelin plasma levels, altered glucose tolerance, and impaired insulin signaling transduction in the skeletal muscle. Moreover, AGE-D modified the systemic glycosylation profile, as analyzed by lectin microarray, and increased Nε-carboxymethyllysine immunoreactivity and AGEs receptor levels in ileum and submandibular glands. These effects were associated to increased systemic levels of cytokines and impaired gut microbial composition and homeostasis. Significant correlations were recorded between changes in bacterial population and in incretins and inflammatory markers levels. Overall, our data indicates that chronic exposure to dietary AGEs lead to a significant unbalance in incretins axis, markers of metabolic inflammation, and a reshape of both the intestinal microbiota and plasma protein glycosylation profile, suggesting intriguing pathological mechanisms underlying AGEs-induced metabolic derangements.

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