title: Functional heterogeneity of the responses of histaminergic neuron subpopulations to various stress challenges.
abstract: In rats, the cell bodies of the histaminergic neuronal system are clustered in five distinct cell groups (E1-E5) within the posterior hypothalamus. On the basis of tract tracing studies, these histaminergic subgroups have been regarded as one functional unit. In addition to its well-characterized role in arousal, locomotor activity, metabolism, feeding, drinking and behaviour, as well as in coordination of autonomic functions, histamine has been implicated in regulation of the hypothalamo-pituitary-adrenocortical axis during stress. To address the capacity of different histaminergic subgroups to respond to various challenges, we revealed c-Fos, the immediate early gene marker of activated neurons, in histamine synthesizing neurons by combining c-Fos immunocytochemistry with in situ hybridization of histidine decarboxylase (HDC) mRNA. Compared to the negligible colocalization of these markers in control rats, restraint, insulin-induced hypoglycaemia and foot shock resulted in specific activation of histamine synthesizing neurons of the E4 and E5 subgroup in the tuberomammillary region. Up to 36% of HDC mRNA-expressing cells show c-Fos immunoreactivity in the E5 region. In addition, some neurons of the E1, E2 and E3 histaminergic groups were activated after restraint stress. Many less c-Fos-positive histaminergic neurons were detected after immobilization and dehydration. Ether stress, acute hyperosmotic stimulus or injection of bacterial lipopolysaccharide did not activate hypothalamic HDC-positive neurons. These results suggest, for the first time, the functional heterogeneity of histaminergic neuron population, the components of which are recruited in a stressor- and subgroup-specific manner.
authors.affiliation: Laboratory of Molecular Neuroendocrinology, Institute of Experimental Medicine, Szigony u. 43. H-1083, Budapest, Hungary.
authors.forename: I H
authors.initials: IH
authors.lastname: Miklós
authors.forename: K J
authors.initials: KJ
authors.lastname: Kovács
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D002452:Cell Count; D003681:Dehydration; D004597:Electroshock; D006632:Histamine / Q000378:metabolism*; D006640:Histidine Decarboxylase / Q000235:genetics / Q000378:metabolism; D049690:History, Ancient; D007003:Hypoglycemia / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D007026:Hypothalamic Area, Lateral / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology; D007103:Immobilization; D007150:Immunohistochemistry / Q000379:methods; D017403:In Situ Hybridization / Q000379:methods; D007328:Insulin; D008070:Lipopolysaccharides / Q000633:toxicity; D008297:Male; D009474:Neurons / Q000145:classification / Q000378:metabolism*; D010286:Paraventricular Hypothalamic Nucleus / Q000166:cytology / Q000378:metabolism / Q000503:physiopathology; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012149:Restraint, Physical / Q000379:methods; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D013312:Stress, Physiological / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology
chemical_list: D007328:Insulin; D008070:Lipopolysaccharides; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger; D012462:Saline Solution, Hypertonic; D006632:Histamine; D006640:Histidine Decarboxylase