Vasopressinergic modulation of stress responses in the central amygdala of the Roman high-avoidance and low-avoidance rat

The central nucleus of the amygdala (CEA) is selectively involved in the passive component of the behavioral (immobility) and the accompanying parasympathetic response during conditioned, stressful environmental challenges. Vasopressinergic mechanisms in the brain seem to play a role in these stress responses. The effects of the neuropeptides arginine-8-vasopressin (AVP) and oxytocin (OXT) on modulating CEA activity during conditioned stress of inescapable footshock were studied in male Roman high-avoidance (RHA/Verh) and low-avoidance (RLA/Verh) rats, psychogenetically selected on the basis of shuttle-box acquisition behavior. In RLA/Verh rats, the cardiac and behavioral responses to the conditioned emotional stressor were bradycardia and immobility, suggesting an important role for the CEA in these rats. The RHA/Verh rats, however, failed to show any change in heart rate or immobility in response to a conditioned stress situation. The low dose of AVP (20 pg) in the CEA of conscious RLA/Verh rats caused an enhancement of the stress-induced bradycardiac and immobility response. However, the high dose of AVP (2 ng) and OXT (200 pg) attenuated the bradycardiac and immobility responses in the RLA/Verh rats. Infusion of AVP and OXT in the RHA/Verh rats failed to induce any change in heart rate nr immobility. Binding studies revealed that the AVP receptor selectively binds AVP with high affinity. In contrast, the OXT receptor recognizes both AVP and OXT with a similar (but lower) affinity. This suggests that the behavioral and autonomic responses of the high dose of AVP may be caused by OXT receptor stimulation. In conclusion, on the basis of the present results one may hypothesize that CEA differences in AVP and OXT innervation and/or receptor densities may contribute to the differences in coping strategy found in these animals.

Stress Hormones Receptors in the Amygdala Mediate the Effects of Stress on the Consolidation, but Not the Retrieval, of a Non Aversive Spatial Task

This study examined the effects of the arousal level of the rat and exposure to a behavioral stressor on acquisition, consolidation and retrieval of a non-aversive hippocampal-dependent learning paradigm, the object location task. Learning was tested under two arousal conditions: no previous habituation to the experimental context (high novelty stress/arousal level) or extensive prior habituation (reduced novelty stress/arousal level). Results indicated that in the habituated rats, exposure to an out-of-context stressor (i.e, elevated platform stress) impaired consolidation and retrieval, but not acquisition, of the task. Non-habituated animals under both stressed and control conditions did not show retention of the task. In habituated rats, RU-486 (10 ng/side), a glucocorticoid receptor (GR) antagonist, or propranolol (0.75 µg/side), a beta-adrenergic antagonist, injected into the basolateral amygdala (BLA), prevented the impairing effects of the stressor on consolidation, but not on retrieval. The CB1/CB2 receptor agonist WIN55,212-2 (WIN, 5 µg/side) microinjected into the BLA did not prevent the effects of stress on either consolidation or retrieval. Taken together the results suggest that: (i) GR and β-adrenergic receptors in the BLA mediate the impairing effects of stress on the consolidation, but not the retrieval, of a neutral, non-aversive hippocampal-dependent task, (ii) the impairing effects of stress on hippocampal consolidation and retrieval are mediated by different neural mechanisms (i.e., different neurotransmitters or different brain areas), and (iii) the effects of stress on memory depend on the interaction between several main factors such as the stage of memory processing under investigation, the animal's level of arousal and the nature of the task (neutral or aversive)

Glucocorticoid enhancement of memory requires arousal-induced noradrenergic activation in the basolateral amygdala

Considerable evidence indicates that glucocorticoid hormones enhance the consolidation of long-term memories for emotionally arousing experiences but not that for less arousing or neutral information. However, previous studies have not determined the basis of such arousal-induced selectivity. Here we report the finding that endogenous noradrenergic activation of the basolateral complex of the amygdala (BLA) induced by emotional arousal is essential in enabling glucocorticoid memory enhancement. Corticosterone administered immediately after object recognition training enhanced 24-h memory of naïve male rats but not that of rats previously habituated to the training context in order to reduce novelty-induced emotional arousal. The β-adrenoceptor antagonist propranolol administered either systemically or into the BLA blocked the corticosterone-induced memory enhancement. Further, in habituated rats, corticosterone activated BLA neurons, as assessed by phosphorylated cAMP response element binding (pCREB) immunoreactivity levels, and enhanced memory only when norepinephrine release was stimulated by administration of the α2-adrenoceptor antagonist yohimbine. These findings strongly suggest that synergistic actions of glucocorticoids and emotional arousal-induced noradrenergic activation of the BLA constitute a neural mechanism by which glucocorticoids may selectively enhance memory consolidation for emotionally arousing experiences.

Determination of interaction effects in expectations for post-event information on memory for items in a service encounter

Our minds are not a blank canvas onto which experiences leave their independent and indelible impression. Consumers, therefore, would rarely enter a service encounter without prior knowledge to guide their expectations. The importance of prior knowledge – in the form of schemas – while acknowledged in the study of post-event misinformation effects on memory has received limited attention. Outside of studies investigating misinformation effects, the literature indicates that inconsistency between our expectations and what we experience, improves recall accuracy. Whether this effect translates into reduced susceptibility to misinformation effects and that schema consistency increases susceptibility, is unclear. The main contribution of this thesis is the demonstration that consistency between schema and the experience, and its interaction with encoding goals, changes a person’s susceptibility to misinformation and their subsequent store quality perceptions. The effects of encoding goals – whether someone is trying to form an impression or remember the details of their experience – while used in previous misinformation studies, has not been previously investigated. To investigate the effects of schema consistency and encoding goals on misinformation acceptance, and the subsequent impact of misinformation acceptance on store quality perceptions, a three-way between participant design was undertaken using a café service encounter as the context. The three factors – independent variables – and their levels included in the study were schema consistency (consistent/ inconsistent), encoding goal (impression/ recall) and post-event information (misinformation/ neutral). Results from the study showed that misinformation effects are most likely when people are paying less attention to the service environment. The explanation provided in the study is that when there is a match between what people expect and what they experience they pay less attention to the details of the experience, which results in less diagnostic information encoded into memory. If, however, they were paying attention due to an inconsistency, the information would be attended and result in reduced misinformation acceptance. Where a person was instructed to try and remember the details of their experience rather than form an impression, they paid greater attention to detail than those who were forming an impression. When their expectations were not met in an experience, subsequent exposure to misinformation causes these people to accurately recall their original experience and escape the effect of misinformation. Significant results were also observed for changes to store quality perceptions, revealing that consumers who accept the misinformation have store quality perceptions that reflect its inclusion. Also observed was an interaction with the initial expectations that meant merchandise quality perceptions improved when a person’s memory for the experience was consistent with their original expectations, and lower when inconsistent

Identification of mineralocorticoid receptor target genes in the mouse hippocampus

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