Differential effects of selective opioid peptide antagonists on the acquisition of Pavlovian fear conditioning
1991; Elsevier BV; Volume: 12; Issue: 5 Linguagem: Inglês
10.1016/0196-9781(91)90056-u
ISSN1873-5169
AutoresMichael S. Fanselow, Jeansok J. Kim, Stacey L. Young, Daniel J. Calcagnetti, Joseph P. DeCola, Fred J. Helmstetter, J. Landeira‐Fernandez,
Tópico(s)Biochemical effects in animals
ResumoPretreatment with opioid antagonists enhances acquisition of Pavlovian fear conditioning. The present experiments attempted to characterize the type of opioid receptor responsible for this effect using a procedure that assessed the fear of rats to a chamber previously associated with electric shock (1 mA, 0.75 s). Freezing, a species-typical immobility, was employed as an index of fear. Two μ opioid antagonists, CTOP (40 ng) and naloxonazine (10 μg), enhanced conditioning. On the other hand, the κ antagonist nor-binaltorphimine reduced conditioning. Two δ antagonist treatments (16-methyl cyprenorphine and naltrindole) had no reliable effect on acquisition. Thus the enhancement of conditioning appears to be mediated by μ receptors. Previous research has shown that the conditional fear produced by these procedures caused an analgesia that is also mediated by μ receptors. It is argued that the enhancement effect occurs because of an antagonism of this analgesia and that the analgesia normally acts to regulate the level of fear conditioning.
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