Document Detail

Effects of apomorphine and clozapine on conditioned freezing and latent inhibition.
MedLine Citation:
PMID:  14499310     Owner:  NLM     Status:  MEDLINE    
Consistent evidence has shown that learning may be produced in paradigms using electrical stimulation of the inferior colliculus as unconditioned stimulus (US). Much evidence has also been provided for the involvement of dopamine in the setting up of adaptive responses to aversive states generated at this mesencephalic level. The aim of the present study was to determine whether dopaminergic mechanisms are involved in the conditioned freezing behavior and latent inhibition (LI) using either foot shocks (Experiment 1) or inferior colliculus stimulation (Experiment 2) as US and light as conditioned stimulus (CS). To this end, the authors examined the effects of the dopaminergic agonist apomorphine (AP; 0, 0.5, 1.0, and 2.0 mg/kg) and the atypical antipsychotic clozapine (CLZ 0, 1.0, 2.5, and 5.0 mg/kg) on the acquisition of conditioned freezing and LI. Rats were either simply placed in the experimental chamber non-preexposed (NPE) or preexposed (PE) to 50 light presentations. Next, they were submitted to 10 light plus foot shock (or inferior colliculus stimulation) pairings. In the testing session, conditioned freezing under the CS was measured. In both experiments, conditioned freezing was highly significant in the NPE group while previous exposure to nonreinforced light (PE) weakened the strength of the conditioning. Although weaker than that caused by foot shock/light pairings, the occurrence of freezing and LI with the use of inferior colliculus stimulation as US gives additional support to the participation of this structure in the filtering processes of relevant information to higher brain regions. The drug effects depended on whether foot shock or inferior colliculus stimulation was used as US. In Experiment 1, AP produced a dose dependent increase in conditioned freezing without changing LI. On the other hand, CLZ did not change freezing and LI. In Experiment 2 while AP did not change freezing and LI, CLZ clearly increased freezing without changing LI with the use of inferior colliculus as US. The selective effect of AP on conditioned freezing due to light/foot shocks association is consistent with the heightened attentional and cognitive functions of dopaminergic mechanisms of the mesocorticolimbic systems in the setting up of adaptive responses aimed at coping with or signaling the presence of stimuli of aversive nature. The selective effect of CLZ on conditioned freezing is due to light/IC stimulation and may also be due to the known antagonism of 5-HT(2) receptors produced by low doses of this atypical antipsychotic.
Sueli Masson; Viviane Avanzi; Ana Cristina Troncoso; Marcus Lira Brandão
Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Progress in neuro-psychopharmacology & biological psychiatry     Volume:  27     ISSN:  0278-5846     ISO Abbreviation:  Prog. Neuropsychopharmacol. Biol. Psychiatry     Publication Date:  2003 Sep 
Date Detail:
Created Date:  2003-09-22     Completed Date:  2004-01-05     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  8211617     Medline TA:  Prog Neuropsychopharmacol Biol Psychiatry     Country:  England    
Other Details:
Languages:  eng     Pagination:  935-43     Citation Subset:  IM    
Laboratório de Psicobiologia, Depto de Psicologia, FFCLRP, Campus da USP, Av., Bandeirantes, 3900, 14049-901, Ribeirão Preto, São Paulo, Brazil.
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MeSH Terms
Apomorphine / pharmacology*
Clozapine / pharmacology*
Conditioning (Psychology) / drug effects*,  physiology
Electric Stimulation / methods
Immobilization / physiology
Inferior Colliculi / drug effects,  physiology
Inhibition (Psychology)*
Rats, Wistar
Reg. No./Substance:
5786-21-0/Clozapine; 58-00-4/Apomorphine

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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