The Ontogeny of Fear-Potentiated Startle: Effects of Earlier-Acquired Fear Memories

School of Psychology, University of New South Wales, Sydney, NSW, Australia.
Behavioral Neuroscience (Impact Factor: 2.73). 10/2007; 121(5):1053-62. DOI: 10.1037/0735-7044.121.5.1053
Source: PubMed


Research has shown that learned fear emerges in a response-specific sequence. For example, freezing is observed at a younger age than is potentiated startle (P. Hunt & B. A. Campbell, 1997). The present study shows that the age at which a specific learned fear response emerges is influenced by the animal's early experiences. Specifically, fear potentiation of startle emerges earlier in development if the rat is given prior fear conditioning to a different stimulus. Some constraints of this "facilitation" effect are determined in follow-up experiments. This facilitation effect may provide a novel way of testing the development of the neural circuits underlying learned fear.

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    • "In animal testing, the majority of fear conditioning studies has applied foot shocks as the aversive promoter event (Campeau et al, 1992; Davis, 1989; Delgado et al, 2008; Kroon and Carobrez, 2009; Schafe et al, 2005; Yap and Richardson, 2007). However, interventions able to modify the internal mood of the subject (eg thirst, hunger, and nausea-inducing drugs) could also be used as unconditioned stimulus (US) and bring new insights to understand the modulation of fear conditioning acquisition and its behavioral expression (Barnett, 1964; Lal and Emmett-Oglesby, 1983; Parker, 2006; Wood et al, 2007). "
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    ABSTRACT: In the present work, we sought to mimic the internal state changes in response to a predator threat by pharmacologically stimulating the brain circuit involved in mediating predator fear responses, and explored whether this stimulation would be a valuable unconditioned stimulus (US) in an olfactory fear conditioning paradigm (OFC). The dorsal premammillary nucleus (PMd) is a key brain structure in the neural processing of anti-predatory defensive behavior and has also been shown to mediate the acquisition and expression of anti-predatory contextual conditioning fear responses. Rats were conditioned by pairing the US, which was an intra-PMd microinjection of isoproterenol (ISO; β-adrenoceptor agonist), with amyl acetate odor-the conditioned stimulus (CS). ISO (10 and 40 nmol) induced the acquisition of the OFC and the second-order association by activation of β-1 receptors in the PMd. Furthermore, similar to what had been found for contextual conditioning to a predator threat, atenolol (β-1 receptor antagonist) in the PMd also impaired the acquisition and expression of OFC promoted by ISO. Considering the strong glutamatergic projections from the PMd to the dorsal periaqueductal gray (dPAG), we tested how the glutamatergic blockade of the dPAG would interfere with the OFC induced by ISO. Accordingly, microinjections of NMDA receptor antagonist (AP5, 6 nmol) into the dPAG were able to block both the acquisition, and partially, the expression of the OFC. In conclusion, we have found that PMd β-1 adrenergic stimulation is a good model to mimic predatory threat-induced internal state changes, and works as a US able to mobilize the same systems involved in the acquisition and expression of predator-related contextual conditioning.
    Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology 01/2011; 36(5):926-39. DOI:10.1038/npp.2010.231 · 7.05 Impact Factor
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    • "In animal testing, the majority of studies concerning fear conditioning have applied footshocks as an aversive promoter event (e.g. Campeau, Miserendino, & Davis, 1992; Davis, 1989; Delgado, Nearing, Ledoux, & Phelps, 2008; Kroon & Carobrez, 2009; Schafe et al., 2005; Yap & Richardson, 2007). However, it is not known if the neural system that underlies an array of defensive behaviors to external threat stimuli is similar to that involved in the aversion induced by interoceptive aversive stimuli (Canteras, 2003). "
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    ABSTRACT: The association of five footshocks with a neutral odor is able to establish an olfactory fear conditioning in rats. The present study sought to investigate whether the systemic administration of pentylenetetrazole (PTZ; 3.75–15 mg/kg) would turn the coffee odor in a conditioned stimulus in the fear conditioning paradigm. The results showed that rats started to display risk assessment and avoidance after PTZ (15 mg/kg)–coffee odor pairing. When three mild footshocks (0.4 mA for 2 s) were delivered during this pairing, the conditioned response exhibited was greater than before. In both cases, however, pretreatment with the benzodiazepine midazolam (MDZ. 0.5 mg/kg i.p.) fully counteracted the expression of these defensive behaviors. Moreover, after being paired with 15 mg/kg of PTZ alone or combined with footshocks, the coffee odor was able to promote a new fear conditioning related to the context where it was re-exposed. The present findings point out the usefulness of PTZ as an unconditioned stimulus to promote fear conditioning to olfactory and contextual cues in rats.
    Neurobiology of Learning and Memory 11/2009; 92(4-92):512-518. DOI:10.1016/j.nlm.2009.06.010 · 3.65 Impact Factor
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    ABSTRACT: The ontogeny of the temporal context modulation of conditioned taste aversion was studied in male Wistar rats using a palatable 1% NaCl solution. A procedure that included two saline preexposures, a single pairing saline-lithium chloride (0.15 M; 1% b.w.) either at the same or a different time of day of preexposures and a one-bottle test at the same time than preexposure was applied. Four age groups (PN32, PN48, PN64, and PN100) covering the complete range from adolescence to the adult period were tested. The results showed no effect of a temporal context shift in PN32. A peculiar enhancement of temporal context-specific saline aversions was exhibited by PN48 and PN64 rats, while the adult typical temporal context specificity of latent inhibition was only evident in PN100 rats. The results are discussed in terms of the peculiar brain functional organization during a protracted adolescence period.
    Developmental Psychobiology 03/2009; 51(2):147-57. DOI:10.1002/dev.20354 · 3.31 Impact Factor
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