5-HT2- and D1-mechanisms of the basolateral nucleus of the amygdala enhance conditioned fear and impair unconditioned fear.
The inferior colliculus (IC) is involved in processing of auditory information, but also integrates acoustic information of aversive nature. In fact, chemical stimulation of the IC with semicarbazide (SMC) - an inhibitor of the GABA synthesizing enzyme glutamic acid decarboxylase - has been found to cause defensive behavior in an open-field test and functions as an unconditioned stimulus in the place conditioned aversion test (PCA). A question has arisen regarding whether the basolateral nucleus of the amygdala (BLA) is involved in the acquisition of the aversive information ascending from the IC and whether dopaminergic and serotoninergic mechanisms of the BLA regulate this process. Recent evidence has shown that inactivation of the BLA with muscimol inhibits the PCA and causes an increase in the aversiveness of the chemical stimulation of the IC. Based on this, we examined the effects of ketanserin and SCH-23390, antagonists of the 5HT(2) and D(1) receptors, respectively, on the conditioned and unconditioned fear elicited by IC stimulation with SMC. The results obtained confirm the crucial role of 5-HT(2)- and D(1)-mechanisms of the BLA on conditioned fear in that ketanserin and SCH-23390 injections into the BLA caused a reduction in the PCA. On the other hand, ketanserin and SCH-23390 injections into the BLA enhanced the aversiveness of the IC injections of SMC. These findings suggest that while 5-HT(2) and DA(1) mechanisms in the BLA appear to facilitate the conditioned fear they inhibit the unconditioned fear triggered by IC activation.
Macedo
Carlos Eduardo
CE
Laboratório de Psicobiologia, Faculdade Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo (USP), 14040-901 Ribeirão Preto, SP, Brasil.
Martinez
Raquel Chacon Ruiz
RC
Albrechet-Souza
Lucas
L
Molina
Victor Alejandro
VA
Brandão
Marcus Lira
ML
D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D001552:Benzazepines / Q000494:pharmacology; D003213:Conditioning, Psychological / Q000187:drug effects / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005106:Exploratory Behavior / Q000187:drug effects; D005239:Fear; D007650:Ketanserin / Q000494:pharmacology; D007859:Learning Disabilities / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000502:physiology*; D044348:Receptors, Serotonin, 5-HT2 / Q000502:physiology*; D012702:Serotonin Antagonists / Q000494:pharmacology
D001552:Benzazepines; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D044348:Receptors, Serotonin, 5-HT2; D012702:Serotonin Antagonists; D007650:Ketanserin