Probes for SST

The superficial superior colliculus (sSC) carries out diverse roles in visual processing and behaviors, but how these functions are delegated among collicular neurons remains unclear. Here, using single-cell transcriptomics, we identified 28 neuron subtypes and subtype-enriched marker genes from tens of thousands of adult mouse sSC neurons. We then asked whether the sSC's molecular subtypes are tuned to different visual stimuli. Specifically, we imaged calcium dynamics in single sSC neurons in vivo during visual stimulation and then mapped marker gene transcripts onto the same neurons ex vivo. Our results identify a molecular subtype of inhibitory neuron accounting for ∼50% of the sSC's direction-selective cells, suggesting a genetic logic for the functional organization of the sSC. In addition, our studies provide a comprehensive molecular atlas of sSC neuron subtypes and a multimodal mapping method that will facilitate investigation of their respective functions, connectivity, and development.

Exposure to irregular lighting schedules leads to deficits in affective behaviors. The retino-recipient perihabenular nucleus (PHb) of the dorsal thalamus has been shown to mediate these effects in mice. However, the mechanisms of how light information is processed within the PHb remains unknown. Here, we show that the PHb contains a distinct cluster of GABAergic neurons that receive direct retinal input. These neurons are part of a larger inhibitory network composed of the thalamic reticular nucleus and zona incerta, known to modulate thalamocortical communication. In addition, PHbGABA neurons locally modulate excitatory-relay neurons, which project to limbic centers. Chronic exposure to irregular light-dark cycles alters photo-responsiveness and synaptic output of PHbGABA neurons, disrupting daily oscillations of genes associated with inhibitory and excitatory PHb signaling. Consequently, selective and chronic PHbGABA manipulation results in mood alterations that mimic those caused by irregular light exposure. Together, light-mediated disruption of PHb inhibitory networks underlies mood deficits.

Dopamine (DA) neurons in the ventral tier of the substantia nigra pars compacta (SNc) degenerate prominently in Parkinson's disease, while those in the dorsal tier are relatively spared. Defining the molecular, functional, and developmental characteristics of each SNc tier is crucial to understand their distinct susceptibility. We demonstrate that Sox6 expression distinguishes ventrally and dorsally biased DA neuron populations in the SNc. The Sox6+ population in the ventral SNc includes an Aldh1a1+ subset and is enriched in gene pathways that underpin vulnerability. Sox6+ neurons project to the dorsal striatum and show activity correlated with acceleration. Sox6- neurons project to the medial, ventral, and caudal striatum and respond to rewards. Moreover, we show that this adult division is encoded early in development. Overall, our work demonstrates a dual origin of the SNc that results in DA neuron cohorts with distinct molecular profiles, projections, and functions.

Sensory neurons relay gut-derived signals to the brain, yet the molecular and functional organization of distinct populations remains unclear. Here, we employed intersectional genetic manipulations to probe the feeding and glucoregulatory function of distinct sensory neurons. We reconstruct the gut innervation patterns of numerous molecularly defined vagal and spinal afferents and identify their downstream brain targets. Bidirectional chemogenetic manipulations, coupled with behavioral and circuit mapping analysis, demonstrated that gut-innervating, glucagon-like peptide 1 receptor (GLP1R)-expressing vagal afferents relay anorexigenic signals to parabrachial nucleus neurons that control meal termination. Moreover, GLP1R vagal afferent activation improves glucose tolerance, and their inhibition elevates blood glucose levels independent of food intake. In contrast, gut-innervating, GPR65-expressing vagal afferent stimulation increases hepatic glucose production and activates parabrachial neurons that control normoglycemia, but they are dispensable for feeding regulation. Thus, distinct gut-innervating sensory neurons differentially control feeding and glucoregulatory neurocircuits and may provide specific targets for metabolic control.

Background The neuropeptide PACAP is a master regulator of central and peripheral stress responses, yet it is not clear how PACAP projections throughout the brain execute endocrine and behavioral stress responses. Methods We used AAV neuronal tracing, an acute restraint stress (ARS) paradigm, and intersectional genetics, in C57Bl6 mice, to identify PACAP-containing circuits controlling stress-induced behavior and endocrine activation. Results PACAP deletion from forebrain excitatory neurons, including a projection directly from medial prefrontal cortex (mPFC) to hypothalamus, impairs c-fos activation and CRH mRNA elevation in PVN after 2 hr of restraint, without affecting ARS-induced hypophagia, or c-fos elevation in non-hypothalamic brain. Elimination of PACAP within projections from lateral parabrachial nucleus to extended amygdala (EA), on the other hand, attenuates ARS-induced hypophagia, along with EA fos induction, without affecting ARS-induced CRH mRNA elevation in PVN. PACAP projections to EA terminate at PKCδ neurons in both central amygdala (CeA) and oval nuclei of bed nucleus of stria terminalis (BNSTov). Silencing of PKCδ neurons in CeA, but not in BNSTov, attenuates ARS-induced hypophagia. Experiments were carried out in mice of both sexes with n>5 per group. Conclusions A frontocortical descending PACAP projection controls PVN CRH mRNA production, to maintain hypothalamo-pituitary adrenal (HPA) axis activation, and regulate the endocrine response to stress. An ascending PACAPergic projection from eLPBn to PKCδ neurons in central amygdala regulates behavioral responses to stress. Defining two separate limbs of the acute stress response provides broader insight into the specific brain circuitry engaged by the psychogenic stress response.

Therapies based on glucagon-like peptide-1 receptor (GLP-1R) agonism are highly effective in treating type 2 diabetes and obesity, but the localization of GLP-1Rs mediating the antidiabetic and other possible actions of GLP-1 is still debated. The purpose with this study was to identify sites of GLP-1R mRNA and protein expression in the mouse gastrointestinal system by means of GLP-1R antibody immunohistochemistry, Glp1r mRNA fluorescence in situ hybridization, and 125I-exendin (9-39) autoradiography. As expected, GLP-1R staining was observed in almost all β-cells in the pancreatic islets, but more rarely in α- and δ-cells. In the stomach, GLP-1R staining was found exclusively in the gastric corpus mucous neck cells, known to protect the stomach mucosa. The Brunner glands were strongly stained for GLP-1R, and pretreatment with GLP-1 agonist exendin-4 caused internalization of the receptor and mucin secretion, while pretreatment with phosphate-buffered saline or antagonist exendin (9-39) did not. In the intestinal mucosa, GLP-1R staining was observed in intraepithelial lymphocytes, lamina propria lymphocytes, and enteroendocrine cells containing secretin, peptide YY, and somatostatin, but not cholecystokinin. GLP-1R staining was seen in nerve fibers within the choline acetyl transferase- and nitric oxide-positive myenteric plexuses from the gastric corpus to the distal large intestine being strongest in the mid- and hindgut area. Finally, intraperitoneal administration of radiolabeled exendin (9-39) strongly labeled myenteric fibers. In conclusion, this study expands our knowledge of GLP-1R localization and suggests that GLP-1 may serve an important role in modulating gastrointestinal health and mucosal protection.

The growth hormone receptor (GHR) is expressed in brain regions that are known to participate in the regulation of energy homeostasis and glucose metabolism. We generated a novel transgenic mouse line (GHRcre) to characterize GHR-expressing neurons specifically in the arcuate nucleus of the hypothalamus (ARC). Here, we demonstrate that ARCGHR+ neurons are co-localized with agouti-related peptide (AgRP), growth hormone releasing hormone (GHRH), and somatostatin neurons, which are activated by GH stimulation. Using the designer receptors exclusively activated by designer drugs (DREADD) technique to control the ARCGHR+ neuronal activity, we demonstrate that the activation of ARCGHR+ neurons elevates a respiratory exchange ratio (RER) under both fed and fasted conditions. However, while the activation of ARCGHR+ promotes feeding, under fasting conditions, the activation of ARCGHR+ neurons promotes glucose over fat utilization in the body. This effect was accompanied by significant improvements in glucose tolerance, and was specific to GHR+ versus GHRH+ neurons. The activation of ARCGHR+ neurons increased glucose turnover and whole-body glycolysis, as revealed by hyperinsulinemic-euglycemic clamp studies. Remarkably, the increased insulin sensitivity upon the activation of ARCGHR+ neurons was tissue-specific, as the insulin-stimulated glucose uptake was specifically elevated in the skeletal muscle, in parallel with the increased expression of muscle glycolytic genes. Overall, our results identify the GHR-expressing neuronal population in the ARC as a major regulator of glycolysis and muscle insulin sensitivity in vivo.

Pancreatic islets depend on cytosolic calcium (Ca2+) to trigger the secretion of glucoregulatory hormones and trigger transcriptional regulation of genes important for islet response to stimuli. To date, there has not been an attempt to profile Ca2+-regulated gene expression in all islet cell types. Our aim was to construct a large single-cell transcriptomic dataset from human islets exposed to conditions that would acutely induce or inhibit intracellular Ca2+ signalling, while preserving biological heterogeneity.We exposed intact human islets from three donors to the following conditions: (1) 2.8 mmol/l glucose; (2) 16 mmol/l glucose and 40 mmol/l KCl to maximally stimulate Ca2+ signalling; and (3) 16 mmol/l glucose, 40 mmol/l KCl and 5 mmol/l EGTA (Ca2+ chelator) to inhibit Ca2+ signalling, for 1 h. We sequenced 68,650 cells from all islet cell types, and further subsetted the cells to form an endocrine cell-specific dataset of 59,373 cells expressing INS, GCG, SST or PPY. We compared transcriptomes across conditions to determine the differentially expressed Ca2+-regulated genes in each endocrine cell type, and in each endocrine cell subcluster of alpha and beta cells.Based on the number of Ca2+-regulated genes, we found that each alpha and beta cell cluster had a different magnitude of Ca2+ response. We also showed that polyhormonal clusters expressing both INS and GCG, or both INS and SST, are defined by Ca2+-regulated genes specific to each cluster. Finally, we identified the gene PCDH7 from the beta cell clusters that had the highest number of Ca2+-regulated genes, and showed that cells expressing cell surface PCDH7 protein have enhanced glucose-stimulated insulin secretory function.Here we use our large-scale, multi-condition, single-cell dataset to show that human islets have cell-type-specific Ca2+-regulated gene expression profiles, some of them specific to subpopulations. In our dataset, we identify PCDH7 as a novel marker of beta cells having an increased number of Ca2+-regulated genes and enhanced insulin secretory function.A searchable and user-friendly format of the data in this study, specifically designed for rapid mining of single-cell RNA sequencing data, is available at https://lynnlab.shinyapps.io/Human_Islet_Atlas/ . The raw data files are available at NCBI Gene Expression Omnibus (GSE196715).