title: Anxiogenic effect of median raphe nucleus lesion in stressed rats.
abstract: Serotonin (5-HT) neurons located in the median raphe nucleus (MRN) may have a role in the development of behavioral changes to stress. The objective of the present work was to investigate the effects of a selective lesion of 5-HT neurons located in the MRN in previously stressed male Wistar rats submitted to the elevated plus maze (EPM). In an initial experiment, the animals (n=20-22) were submitted to one (acute) or seven (chronic) daily restraint stress periods (2 h) and tested in the EPM 24 h later. Results showed that acute restraint caused a significant decrease in the number of entries into the open arms, as compared to nonstressed controls. This effect disappeared when the animals were submitted to chronic restraint. In the next set of experiments, animals (n=6-8) received, 1 week before the behavioral studies, intra-MRN injection of 5,7-dihydroxytryptamine (5,7-DHT; 8 microg/1 microl). Neurochemical analysis showed that this treatment significantly decreases 5-HT and 5-hydroxy-indoleacetic acid (5-HIAA) levels in the hippocampus, but not in the striatum. No difference between lesioned and sham-operated animals in EPM performance was found in nonstressed animals or in those submitted to acute restraint. In chronically restrained animals, however, lesioned rats showed a significant decrease in the number of entries and time spent in the open arms. These results suggest that lesions of 5-HT neurons located in the MRN cause anxiogenic-like behavior in animals that have been chronically restrained.
authors.affiliation: Faculdade de Filosofia, Laboratório de Psicobiologia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, 14049-900, Ribeirdo Preto, SP, Brazil.
authors.forename: Sueli Mendonça
authors.initials: SM
authors.lastname: Netto
authors.forename: Rodolfo
authors.initials: R
authors.lastname: Silveira
authors.forename: Norberto Cysne
authors.initials: NC
authors.lastname: Coimbra
authors.forename: Sâmia Regiane Lourenço
authors.initials: SR
authors.lastname: Joca
authors.forename: Francisco Silveira
authors.initials: FS
authors.lastname: Guimarães
mesh_terms: D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology; D000208:Acute Disease; D000818:Animals; D001007:Anxiety / Q000503:physiopathology* / Q000523:psychology*; D015306:Biogenic Monoamines / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002908:Chronic Disease; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D011903:Raphe Nuclei / Q000033:anatomy & histology / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D012149:Restraint, Physical; D012701:Serotonin / Q000502:physiology; D018490:Serotonin Agents / Q000494:pharmacology; D013315:Stress, Psychological / Q000523:psychology*
chemical_list: D015306:Biogenic Monoamines; D018490:Serotonin Agents; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D009638:Norepinephrine