Document Detail

5-HT mechanisms of median raphe nucleus in the conditioned freezing caused by light/foot-shock association.
MedLine Citation:
PMID:  12676284     Owner:  NLM     Status:  MEDLINE    
We have shown that 5-HT mechanisms of the median raphe nucleus (MRN) are involved in contextual fear-conditioning processes as electrolytic or neurotoxic lesions with N-methyl-D-aspartate (NMDA) or injections of 8-hydroxy-2-(di-n-propilamino)-tetralin (8-OH-DPAT) into this structure inhibit freezing behavior in a contextual fear paradigm. In this work, we extend these studies by analyzing the behavioral responses in a classical fear-conditioning paradigm (light or tone/foot-shock association) in rats with either neurochemical lesion with NMDA or injected with 8-OH-DPAT into the MRN. The animals received NMDA or 8-OH-DPAT or saline microinjections into the MRN and were submitted to conditioning trials in an experimental chamber, where they received 10 foot-shocks (0.6 mA, 1 s, variable interval between 10 and 50 s) paired with tone or light (CS). On the next day, they were tested in a different experimental chamber, with or without CS presentation, where the duration of freezing and the number of rearing episodes were recorded. Light or tone alone caused a significant amount of freezing. NMDA lesions or 8-OH-DPAT injections into the MRN clearly inhibited freezing behavior in rats conditioned to light/foot-shock association, but not in the conditioning sessions with tones. Besides the proposed role in contextual fear conditioning, these results clearly show that MRN is involved in the fear conditioning with light as conditioned stimuli. Distinct neural substrates seem to subserve conditioning fear with acoustic stimuli.
V Avanzi; R C B Silva; C E Macedo; M L Brandão
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Physiology & behavior     Volume:  78     ISSN:  0031-9384     ISO Abbreviation:  Physiol. Behav.     Publication Date:  2003 Mar 
Date Detail:
Created Date:  2003-04-04     Completed Date:  2003-08-20     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0151504     Medline TA:  Physiol Behav     Country:  United States    
Other Details:
Languages:  eng     Pagination:  471-7     Citation Subset:  IM    
Laboratório de Psicobiologia, FFCLRP, Campus USP, Av Bandeirantes 3900, 14049-901, Ribeirão Preto, SP, Brazil.
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MeSH Terms
8-Hydroxy-2-(di-n-propylamino)tetralin / pharmacology
Analysis of Variance
Association Learning / drug effects,  physiology*
Conditioning, Classical / drug effects,  physiology*
Electroshock / psychology
Fear / drug effects,  physiology
Motor Activity / drug effects
N-Methylaspartate / pharmacology
Raphe Nuclei / drug effects,  physiology*
Rats, Wistar
Serotonin / physiology*
Reg. No./Substance:
50-67-9/Serotonin; 6384-92-5/N-Methylaspartate; 78950-78-4/8-Hydroxy-2-(di-n-propylamino)tetralin

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