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Neuronal diversity of neuropeptide signaling, including galanin, in the mouse locus coeruleus

ABSTRACT: Purpose: The locus coeruleus (LC) is a small nucleus in the pons, with norepinephrine (NE) as its major transmitter. It plays key roles in wakefulness and is associated with disorders like depression. The study aims to analyze single-cell RNA-seq data to subdivide neurons in the LC and chart their neuropeptide, co-transmitter, and receptor profiles. It also seeks to build a precise map of galanin and its receptors in the mouse LC, and understand the role of neuropeptide expression and signaling. Results: The study identified 24 clusters in total, with 3 NE, 17 glutamate, and 5 GABA subtypes. NE neurons expressed at least 19 neuropeptide transcripts, mainly galanin (Gal) but not Npy, and >30 neuropeptide receptors. Among galanin receptors, Galr1 was expressed in ~19% of NE neurons, and highly expressed in GABA neurons surrounding the NE ensemble. Patch-clamp electrophysiology and cell-type-specific Ca2+-imaging using GCaMP6s revealed that a GalR1 agonist inhibits no more than ~35% of NE neurons, with the effect being direct and not relying on feed-forward GABA inhibition. Conclusions: The results define a role for the galanin system in NE functions and provide a conceptual framework for the action of many other peptides and their receptors. The study found that most NE neurons express mRNA transcripts for galanin, at least 19 neuropeptides (but not Npy), and >30 neuropeptide receptors, including Galr1 at low levels. Selective activation of GalR1 inhibited the spontaneous activity of a subset of NE neurons possibly through the activation of Kv currents. These findings offer new insights into the role of neuropeptide expression and signaling in mouse LC.

ORGANISM(S): Mus musculus

PROVIDER: GSE236349 | GEO | 2023/07/03

REPOSITORIES: GEO

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Project description:Purpose: We aimed to resolve if there is a matched expression of neuropeptide receptor(s) and their ligand(s) between the sensory trunk of the trigeminal nerve (Pr5) and the ventrobasal hypothalamus on postnatal day 7 (P7) in mice. We hypothesized that a coincidence of neuropeptide expression and release from the ventrobasal thalamus and the cognate receptor(s) for the specific neuropeptide(s) in trigeminal neurons could allow for novel hypotheses be built on intercellular communication between peripheral axons and their postsynaptic targets in the thalamus. Thereby, this work can be informative of the developmental integration of the whisker pathway, one of the major sensory modalities in laboratory rodents. To this end, we used single-cell RNA-seq on cells dissociated from the ventrobasal thalamus and Pr5 on P7. Results: We tested this hypothesis by single-nucleus RNA-seq performed in parallel on the ventrobasal thalamus and Pr5 at P7. At this developmental stage, the ventrobasal thalamus contained two subtypes of Slc17a6+(glutamatergic) neurons, one subtype of Gad1/Gad2+ (GABA) neurons, astroglia, oligodendrocytes, and vascular components (n = 923 nuclei isolated from n = 3 pups of mixed sex). Slc17a6+ neurons, which we recognize as cortically projecting glutamate neurons, co-expressed molecular components underpinning barrel map formation (e.g., Grin1, Adcy1, Prkaca,99 Ache, Slc6a4) and a significant amount of the thalamocortical neuronal marker Cck, while other neuropeptides/hormones were absent or barely present (e.g., Npy, Sst). At the same time, we harvested n = 731 nuclei from the Pr5 by micro-excision at P7, of which ∼98% expressed Slc17a6, thus qualifying, in total or in part, as centrally-projecting sensory neurons. This neuronal cohort harbored axon guidance molecules, and neuropeptide receptors. Conclusions: We suggest that neuropeptides, particularly galanin, could participate in guidance decisions of Pr5 axons given the complementarity of ligand-receptor expression patterns, and that Galr1 expression could be a time locked feature for those neurons that actively undergo neuritogenesis at a given time.