title: Central relaxin-3 receptor (RXFP3) activation increases ERK phosphorylation in septal cholinergic neurons and impairs spatial working memory.
abstract: The medial septum/diagonal band (MS/DB) is a relay region connecting the hypothalamus and brainstem with the hippocampus, and both the MS/DB and dorsal/ventral hippocampus receive strong topographic GABA/peptidergic projections from the nucleus incertus of the pontine tegmentum. The neuropeptide relaxin-3, released by these neurons, is the cognate ligand for a Gi/o-protein-coupled receptor, RXFP3, which is highly expressed within the MS/DB, and both cholinergic and GABAergic neurons in this region of rat brain receive relaxin-3 positive terminals/boutons. Comprehensive in vitro studies have demonstrated that the cell signaling pathways altered by RXFP3 stimulation, include inhibition of forskolin-activated cAMP levels and activation of ERK phosphorylation. In this study we investigated whether intracerebroventricular (icv) injection of RXFP3-A2, a selective relaxin-3 receptor agonist, altered ERK phosphorylation levels in the MS/DB of adult male rats. We subsequently assessed the neurochemical phenotype of phosphorylated (p) ERK-positive neurons in MS/DB after icv RXFP3-A2 administration by dual-label immunostaining for pERK and neuronal markers for cholinergic and GABAergic neurons. Central RXFP3-A2 injection significantly increased levels of pERK immunoreactivity (IR) in MS/DB at 20 and 90 min post-injection, compared to vehicle and naive levels. In addition, RXFP3-A2 increased the number of cells expressing pERK-IR in the MS/DB at 90 (but not 20) min post-injection in cholinergic (but not GABAergic) neurons, which also expressed putative RXFP3-IR. Moreover, icv injection of RXFP3-A2 impaired alternation in a delayed spontaneous T-maze test of spatial working memory. The presence of RXFP3-like IR and the RXFP3-related activation of the MAPK/ERK pathway in MS/DB cholinergic neurons identifies them as a key target of ascending relaxin-3 projections with implications for the acute and chronic modulation of cholinergic neuron activity and function by relaxin-3/RXFP3 signaling.
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain.
authors.forename: Héctor
authors.initials: H
authors.lastname: Albert-Gascó
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain.
authors.forename: Álvaro
authors.initials: Á
authors.lastname: García-Avilés
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain.
authors.forename: Salma
authors.initials: S
authors.lastname: Moustafa
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain.
authors.forename: Sandra
authors.initials: S
authors.lastname: Sánchez-Sarasua
authors.affiliation: The Florey Institute of Neuroscience and Mental Health, Parkville, VIC, 3052, Australia.|Florey Department of Neuroscience and Mental Health, The University of Melbourne, Melbourne, VIC, 3010, Australia.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Gundlach
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain.
authors.forename: Francisco E
authors.initials: FE
authors.lastname: Olucha-Bordonau
authors.affiliation: Department of Medicine, School of Medical Sciences, University Jaume I, 12071, Castellón de la Plana, Spain. sanchean@uji.es.
authors.forename: Ana M
authors.initials: AM
authors.lastname: Sánchez-Pérez
mesh_terms: D000818:Animals; D059329:Cholinergic Neurons / Q000378:metabolism*; D059330:GABAergic Neurons / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D020935:MAP Kinase Signaling System; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D010455:Peptides / Q000008:administration & dosage; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000502:physiology*; D012686:Septal Nuclei / Q000378:metabolism / Q000502:physiology*; D065852:Spatial Memory / Q000502:physiology*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D010455:Peptides; C583617:RXFP3-a2 peptide; D043562:Receptors, G-Protein-Coupled; C505050:SALPR protein, mouse
keywords: Calcium-binding proteins; Choline acetyltransferase; GABA neurons; MAPK/ERK pathway; Nucleus incertus; RXFP3-like immunoreactivity; Septum; Working spatial memory