Retrograde abolition of conditional fear after excitotoxic lesions in the basolateral amygdala of rats: Absence of a temporal gradient.

Abstract

The role of the basolateral amygdala (BLA) in the acquisition and expression of Pavlovian fear conditioning was examined in 80 rats. Excitotoxic lesions were made in the BLA using N-methyl-o-aspartate 7 days before or 1, 14, or 28 days after Pavlovian fear conditioning. Conditioning consisted of three pairings of a tone with an aversive footshock in a novel chamber, and freezing behavior served as an index of conditional fear. BLA lesions abolished conditional freezing to both the contextual and acoustic conditional stimuli at all training-to-lesion intervals, and the magnitude of the impairment did not vary as a function of the training-to-lesion interval. Reacquisition training elevated levels of freezing in rats with BLA lesions but did not reduce the magnitude of their deficit in relation to that of controls. These results reveal that neurons in the BLA have an enduring role in the expression of conditional fear.

The Amygdala Modulates Memory Consolidation of Fear-Motivated Inhibitory Avoidance Learning But Not Classical Fear Conditioning

“…Indeed, a number of lesion studies have implicated the entorhinal and parietal cortex in late memory phases of inhibitory avoidance learning Zanatta et al, 1997), whereas, for example, Pavlovian fear conditioning is spared after entorhinal cortex lesions (Phillips and LeDoux, 1995). Furthermore, although lesion studies have consistently implicated the amygdala in Pavlovian fear conditioning (LeDoux et al, 1990;Maren et al, 1996a;Maren, 1998), lesions of the amygdala appear to have less clear-cut effects on inhibitory avoidance learning, especially if given after training (Liang et al, 1982;Parent et al, 1995). Although this latter finding has been used as evidence in favor of the view that the amygdala is not the site of memory consolidation of conditioned fear, it is equally consistent with the notion that the amygdala plays a fundamentally different role in Pavlovian fear conditioning and inhibitory avoidance learning.…”

Scopolamine and Pavlovian Fear Conditioning in Rats Dose-Effect Analysis

“…Lesions directed at the amygdala produce a severe anterograde amnesia of contextual and tone fear (Phillips and LeDoux 1992), as well as a severe, temporally-stable retrograde amnesia of both types of conditioning (Maren et al 1996a). As such, scopolamine did not nearly have as great an effect as do lesions of the amygdala, even at 50-100 mg/kg.…”

“…Tone fear conditioning, which is typically intact in animals with hippocampal dysfunction Phillips and LeDoux 1992), but readily disrupted by manipulations directed at the amygdala (Maren et al 1996a;Davis 1986), was mildly but nonsignificantly impaired (Anagnostaras et al 1995). Because the amygdala receives cholinergic innervation from the nucleus basalis magnocellularis a milder amygdala impairment may have been present as well.…”

Hippocampus and contextual fear conditioning: Recent controversies and advances

“…Kainic acid injection in one region is known to produce damage in distal areas that the region projects to (e.g., Mintz and Knowlton, 1993). Because we have reported a similar complete loss of context and tone conditional fear after basolateral amygdala damage (Maren et al, 1996a), exploration of this possibility is a necessity. Indeed, Jarrard (1983Jarrard ( , 1989) abandoned the use of kainic acid for selective hippocampal lesions because of cell loss in areas a considerable distance from the site of injection.…”