Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Effects of Acute Stress on Pavlovian-Instrumental Transfer in Rats

Academic journal article Cognitive, Affective and Behavioral Neuroscience

The Effects of Acute Stress on Pavlovian-Instrumental Transfer in Rats

Article excerpt

Published online: 13 October 2012

© Psychonomic Society, Inc. 2012

Abstract Pavlovian stimuli invigorate ongoing instrumental action, a phenomenon termed the Pavlovian-instrumental transfer (PIT) effect. Acute stressors can markedly enhance the release of corticotropin-releasing factor (CRF), and CRF injection into the nucleus accumbens increases the PIT effect. However, it is unknown whether acute stressors by themselves would amplify the PIT effect. Here, we examined the effects of acute stressors on PIT. Rats first received Pavlovian and instrumental training, and then the impact of the Pavlovian stimuli on instrumental responding was analyzed in the subsequent PIT test. Acute stressors were applied prior to the PIT test. Because the effects of acute stressors critically depend on stressor type and time of day, we used two acute stressors that involved one or several distinct stressors (denoted here as "single" vs. "multiple" stressors) applied either in the light or the dark period of the light:dark cycle. The results revealed that single and multiple stressors applied in the light period did not alter the PIT effect-that is, the ability of an appetitive Pavlovian stimulus to enhance leverpressing-or the basal leverpress rate. When applied in the dark period, single and multiple stressors also did not alter the PIT effect, but they did markedly reduce the basal leverpress rate. Diazepam pretreatment did not counteract the declines in basal instrumental responding in the PIT test that were induced by either a single or multiple stressors. Our findings suggest that acute stressors were unable to amplify the incentive salience of rewardpredictive Pavlovian stimuli to activate instrumental responding, but, depending on the time of day of stressor exposure, they did reduce basal instrumental responding.

Keywords Acute stress * Incentive motivation * Anxiety * Pavlovian-instrumental transfer * Rat

Pavlovian stimuli predictive of natural rewards such as food can increase leverpressing for food, a phenomenon termed the Pavlovian-instrumental transfer effect (PIT effect) (Estes, 1948; Lovibond, 1983). One important mechanism by which Pavlovian stimuli influence the vigor of an action is to create a general appetitive arousal that elevates instrumental responding (Rescorla & Solomon, 1967). The central nucleus of the amygdala (Corbit & Balleine, 2005; Holland & Gallagher, 2003), the nucleus accumbens core (Corbit & Balleine, 2011; Hall, Parkinson, Connor, Dickinson, & Everitt, 2001), the ventral tegmental area (Corbit, Janak, & Balleine, 2007; Murschall & Hauber, 2006), and the mesoaccumbens dopamine system (Hall, et al., 2001; Lex & Hauber, 2008; Wyvell & Berridge, 2000) are major components of a neural circuitry mediating the PIT effect. Notably, Pecina, Schulkin, and Berridge (2006) demonstrated that the PIT effect was markedly enhanced not only by intraaccumbens amphetamine infusion but also by intraaccumbens infusion of corticotropin-releasing factor (CRF), and they concluded that activation of CRF subsystems in the nucleus accumbens-and, thus, acute stress-could amplify positive motivation for signaled rewards. Importantly, such paradoxical positive incentive effects could explain why acute stress can produce stimulustriggered bursts of binge eating, drug relapse, or other excessive pursuits of reward (Pecina et al., 2006).

It is well known that acute stress is associated with increased brain CRF and dopamine release (Bale & Vale, 2004; Imperato, Puglisiallegra, Casolini, Zocchi, & Angelucci, 1989). However, although CRF plays a crucial role (Bale & Vale, 2004), it is important to note that acute stress responses involve the release of multiple stress mediators, including a number of other neuropeptides, such as vasopressin or dynorphin, as well as monoamine neurotransmitters and steroids (Joels & Baram, 2009) and entail complex interacting circuits, in particular in the limbic forebrain, the hypothalamus, and the brainstem (Ulrich-Lai & Herman, 2009). …

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