title: Basolateral amygdala inactivation impairs learned (but not innate) fear response in rats.
abstract: Numerous studies have suggested that the amygdala is involved in the formation of aversive memories, but the possibility that this structure is merely related to any kind of fear sensation or response could not be ruled out in previous studies. The present study investigated the effects of bilateral inactivation of the amygdaloid complex in rats tested in the plus-maze discriminative avoidance task. This task concomitantly evaluates aversive memory (by discrimination of the two enclosed arms) and innate fear (by open-arm exploration). Wistar rats (3-5 months-old) were implanted with bilateral guide cannulae into basolateral amygdala. After surgery, all subjects were given 1 week to recover before behavioral experiments. Afterwards, in experiment 1, 15 min prior to training, 0.5 μl of saline or muscimol (1 mg/ml) was infused in each side via microinjection needles. In experiment 2 the animals received injections immediately after the training session and in experiment 3 rats were injected prior to testing session (24 h after training). The main results showed that (1) pre-training muscimol prevented memory retention (evaluated by aversive arm exploration in the test session), but did not alter innate fear (evaluated by percent time in open arms); (2) post-training muscimol impaired consolidation, inducing increased percent in aversive arm exploration in the test session and (3) pre-testing muscimol did not affect retrieval (evaluated by aversive enclosed arm exploration in the test session). The results suggest that amygdala inactivation specifically modulated the learning of the aversive task, excluding a possible secondary effect of amygdala inactivation on general fear responses. Additionally, our data corroborate the hypothesis that basolateral amygdala is not the specific site of storage of aversive memories, since retention of the previously learned task was not affected by pre-testing inactivation.
authors.affiliation: Memory Studies Laboratory, Physiology Department, Federal University of Rio Grande do Norte, Natal, Brazil.
authors.forename: A M
authors.initials: AM
authors.lastname: Ribeiro
authors.forename: F F
authors.initials: FF
authors.lastname: Barbosa
authors.forename: H
authors.initials: H
authors.lastname: Munguba
authors.forename: M S M O
authors.initials: MS
authors.lastname: Costa
authors.forename: J S
authors.initials: JS
authors.lastname: Cavalcante
authors.forename: R H
authors.initials: RH
authors.lastname: Silva
mesh_terms: D000679:Amygdala / Q000187:drug effects / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D003214:Conditioning, Classical / Q000187:drug effects / Q000502:physiology*; D004193:Discrimination Learning / Q000187:drug effects / Q000502:physiology*; D005106:Exploratory Behavior / Q000187:drug effects / Q000502:physiology; D005239:Fear / Q000187:drug effects / Q000502:physiology*; D046352:Freezing Reaction, Cataleptic / Q000502:physiology*; D058785:GABA-A Receptor Agonists / Q000494:pharmacology; D008297:Male; D018782:Maze Learning / Q000187:drug effects / Q000502:physiology; D011939:Mental Recall / Q000187:drug effects / Q000502:physiology; D009118:Muscimol / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018709:Statistics, Nonparametric; D013997:Time Factors
chemical_list: D058785:GABA-A Receptor Agonists; D009118:Muscimol