title: Somatostatin interneurons delineate the inner part of the external plexiform layer in the mouse main olfactory bulb.
abstract: Neuropeptides play a major role in the modulation of information processing in neural networks. Somatostatin, one of the most concentrated neuropeptides in the brain, is found in many sensory systems including the olfactory pathway. However, its cellular distribution in the mouse main olfactory bulb (MOB) is yet to be characterized. Here we show that approximately 95% of mouse bulbar somatostatin-immunoreactive (SRIF-ir) cells describe a homogeneous population of interneurons. These are restricted to the inner lamina of the external plexiform layer (iEPL) with dendritic field strictly confined to the region. iEPL SRIF-ir neurons share some morphological features of Van Gehuchten short-axon cells, and always express glutamic acid decarboxylase, calretinin, and vasoactive intestinal peptide. One-half of SRIF-ir neurons are parvalbumin-ir, revealing an atypical neurochemical profile when compared to SRIF-ir interneurons of other forebrain regions such as cortex or hippocampus. Somatostatin is also present in fibers and in a few sparse presumptive deep short-axon cells in the granule cell layer (GCL), which were previously reported in other mammalian species. The spatial distribution of somatostatin interneurons in the MOB iEPL clearly outlines the region where lateral dendrites of mitral cells interact with GCL inhibitory interneurons through dendrodendritic reciprocal synapses. Symmetrical and asymmetrical synaptic contacts occur between SRIF-ir dendrites and mitral cell dendrites. Such restricted localization of somatostatin interneurons and connectivity in the bulbar synaptic network strongly suggest that the peptide plays a functional role in the modulation of olfactory processing.
authors.affiliation: Inserm UMR 894, Center for Psychiatry and Neurosciences, F-75014 Paris, France.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Lepousez
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Csaba
authors.forename: Véronique
authors.initials: V
authors.lastname: Bernard
authors.forename: Catherine
authors.initials: C
authors.lastname: Loudes
authors.forename: Catherine
authors.initials: C
authors.lastname: Videau
authors.forename: Joelle
authors.initials: J
authors.lastname: Lacombe
authors.forename: Jacques
authors.initials: J
authors.lastname: Epelbaum
authors.forename: Cécile
authors.initials: C
authors.lastname: Viollet
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D064032:Calbindin 2; D006801:Humans; D007150:Immunohistochemistry; D007395:Interneurons / Q000166:cytology / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009830:Olfactory Bulb / Q000033:anatomy & histology*; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D013004:Somatostatin / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D015415:Biomarkers; C576764:CALB2 protein, human; C576511:Calb2 protein, mouse; D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G; D013004:Somatostatin