Article

Rau V, Fanselow MS. Exposure to a stressor produces a long lasting enhancement of fear learning in rats. Stress 12: 125-133

Department of Anesthesia, University of California, San Francisco, CA 94143, USA.
Stress (Amsterdam, Netherlands) (Impact Factor: 2.72). 07/2008; 12(2):125-33. DOI: 10.1080/10253890802137320
Source: PubMed

ABSTRACT

In contextual fear conditioning, footshock is given in a context, and re-exposure to this context elicits the conditional defensive response of freezing, a reliable behavioral index of conditional fear. Normally, the amount of contextual freezing is directly proportional to the number of shocks an animal receives in the context. However, pre-exposure to a stressor can produce an enhancement in conditional freezing. Pre-exposure to repeated footshock in one context produces an enhancement of conditional freezing to cues associated with a single shock in a second distinct context. This model of stress-enhanced fear learning (SEFL) can be utilized to study how stress affects learning of future aversive events. The experiments in this paper characterize the magnitude and longevity of SEFL. In the first experiment, the number of footshocks given during the pre-exposure session was varied and conditional fear to the single shock was assessed. Pre-exposure to 1 shock did not produce an enhancement in fear learning in the second context, but pre-exposure to 4 or 15 shocks did. The time-course of the enhancement was examined in the next two experiments. These experiments show that SEFL persists for at least 3 months.

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    • "In this model, rats receive a series of 15 shocks, randomly distributed over 90 min. This experience produces behavioral changes lasting at least 90 days unabated (Rau and Fanselow, 2009). After this experience, rats acquire exaggerated contextual and cued fear in novel situations using a single shock. "
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    ABSTRACT: Fear promotes adaptive responses to threats. However, when the level of fear is not proportional to the level of threat, maladaptive fear-related behaviors characteristic of anxiety disorders result. Post-traumatic stress disorder develops in response to a traumatic event, and patients often show sensitized reactions to mild stressors associated with the trauma. Stress-enhanced fear learning (SEFL) is a rodent model of this sensitized responding, in which exposure to a 15-shock stressor nonassociatively enhances subsequent fear conditioning training with only a single trial. We examined the role of corticosterone (CORT) in SEFL. Administration of the CORT synthesis blocker metyrapone prior to the stressor, but not at time points after, attenuated SEFL. Moreover, CORT co-administered with metyrapone rescued SEFL. However, CORT alone without the stressor was not sufficient to produce SEFL. In these same animals, we then looked for correlates of SEFL in terms of changes in excitatory receptor expression. Western blot analysis of the basolateral amygdala (BLA) revealed an increase in the GluA1 AMPA receptor subunit that correlated with SEFL. Thus, CORT is permissive to trauma-induced changes in BLA function.Neuropsychopharmacology advance online publication, 2 September 2015; doi:10.1038/npp.2015.224.
    No preview · Article · Aug 2015 · Neuropsychopharmacology: official publication of the American College of Neuropsychopharmacology
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    • "(A.P. Carobrez). exposure to diverse threatening situations facilitates the encoding of fear memory during acquisition [1] [2] [3] [4]. These reports, in fact, support the widespread notion that emotionally driven experiences results in stronger and long-lasting memories [1,4–6]. "
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    ABSTRACT: The association of a neutral context with an aversive stimulus, such as foot-shock, result in a contextual fear memory. A growing number of evidence have revealed that prior exposure to diverse threatening situations facilitates the encoding of fear memory during acquisition and such reports support the widespread notion that emotionally arousal results in stronger and long-lasting memories. However, few studies have investigated if a threatening experience can affect the recall and the persistence of such fear memory trace. To test the hypothesis that an emotionally negative experience could modify the retrieval of a memory and potentiate the expression of a fear memory, the present study used the chemical stimulation (microinjection of NMDA) of the dorsolateral periaqueductal gray matter (dlPAG) of rats in order to induce an aversive emotional state. Such stimulation was performed one day after a weak fear training protocol, and the fear expression was analyzed in subsequent re-exposures to the conditioned context. The results showed that the negative emotional state induced by the dlPAG stimulation enhanced the fear memory trace when this trace was reactivated one day after this aversive experience. Additionally, the potentiation of the fear response was contingent to the associated context since no potentiation was evident when NMDA-stimulated animals were subsequently placed in a non-associated context. Finally, the model suggests that the enhancement of fear responses is long-lasting since NMDA-treated animals performed a robust fear response six days after memory retrieval.
    Full-text · Article · Sep 2012 · Behavioural brain research
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    • "Fear conditioning is a well-characterized and widely studied phenomenon. It occurs when an animal is exposed to an aversive stimulus and an unconditioned fear response becomes associated with an environmental cue such as the context in which the aversive stimuli occurred [4] [5]. Fear conditioning is typically studied by placing an animal in a conditioning chamber (e.g. "
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    ABSTRACT: Repeated exposure to laboratory stressors often results in behavioral changes that are commonly referred to as depressive-like behaviors. Here, we examined the contribution fear conditioning may play in altering an animals' behavior in a repeated stress paradigm. Fischer rats were exposed daily to different stressors in a complex environment (context A). After four days of stressor exposure, exploratory behavior (10 min in new cage) and social interaction (5 min with juvenile) were tested on day 5 in either the same environment or a new environment (context B). Rats showed decreased exploration and social interaction when tested in context A compared to control rats or rats tested in context B. Additionally, chronic infusion of propranolol (beta-adrenergic receptor antagonist that crosses the blood-brain barrier), but not nadolol (beta-adrenergic receptor antagonist that does not readily cross the blood-brain barrier), prevented the behavioral changes following repeated stressor exposure. Propranolol treatment did not affect the acute or chronic elevation of corticosterone, the decrease in body weight gain, or adrenal hypertrophy observed in animals exposed to stress. These data demonstrate that conditioned fear responses can contribute to behavioral changes in a repeated stress paradigm. Additional studies revealed, Sprague-Dawley rats do not demonstrate decreased exploration or social interaction when testing occurs in the same context as repeated stressor exposure suggesting Fischer rats may have a greater propensity to associate distal cues with aversive events in a complex environment. This may be due to greater stress responses in Fischer animals that are known to enhance consolidation of emotionally arousing events.
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