title: Lipopolysaccharide-induced up-regulation of activated macrophages in the degenerating taste system.
abstract: Unilateral chorda tympani (CT) nerve section and maintenance on a sodium-restricted diet leads to a rapid decrease in neurophysiological taste responses to sodium in the contralateral, intact CT nerve. Up-regulation of immune function with lipopolysaccharide (LPS; 100 microg i.p.) induces a recovery of normal sodium taste responses, suggesting that the sodium-deficient diet is immunosuppressive. In fact, there is a bilateral increase in the number of lingual, activated macrophages in control-fed rats receiving CT nerve section that does not occur in sodium-deficient rats after sectioning. In the current study, we hypothesized that the LPS-induced recovery of normal taste function in sodium-deficient rats is based on an increase in the activated macrophage response to denervation. Rats receiving a unilateral CT nerve section, a sodium-restricted diet, and/or an injection of LPS (100 microg; i.p.) were overdosed with pentobarbital at day 2 postsectioning, and tongues were rapidly dissected and frozen. Cryosections were then immunohistochemically stained to determine the percentage of ED1 staining for activated macrophages or the number of alphabeta or gammadelta T cells. Activated macrophage levels were significantly increased in sodium-restricted rats that received LPS following unilateral CT nerve section, supporting our hypothesis. These novel findings suggest that LPS overcomes the immunosuppression induced by the sodium-restricted diet and also indicate that the immune system plays a role in regulating taste function after neural injury.
authors.affiliation: Department of Physiology/CA 2093, Medical College of Georgia, Augusta, Georgia 30912, USA. mcavallings@students.mcg.edu
authors.forename: Melissa Ann
authors.initials: MA
authors.lastname: Cavallin
authors.forename: Lynnette Phillips
authors.initials: LP
authors.lastname: McCluskey
mesh_terms: D000818:Animals; D019771:Axotomy; D002814:Chorda Tympani Nerve / Q000293:injuries; D004039:Diet, Sodium-Restricted; D005260:Female; D005434:Flow Cytometry; D007839:Functional Laterality; D007091:Image Processing, Computer-Assisted; D007150:Immunohistochemistry; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008262:Macrophage Activation / Q000187:drug effects*; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D013649:Taste / Q000276:immunology*; D014059:Tongue / Q000276:immunology* / Q000294:innervation; D015854:Up-Regulation
chemical_list: D008070:Lipopolysaccharides