Abstract
Environmental stimuli have the ability to generate specific representations of the rewards they predict and in so doing alter the selection and performance of reward-seeking actions. The basolateral amygdala participates in this process, but precisely how is unknown. To rectify this, we monitored, in near-real time, basolateral amygdala glutamate concentration changes during a test of the ability of reward-predictive cues to influence reward-seeking actions (Pavlovian-instrumental transfer). Glutamate concentration was found to be transiently elevated around instrumental reward seeking. During the Pavlovian-instrumental transfer test these glutamate transients were time-locked to and correlated with only those actions invigorated by outcome-specific motivational information provided by the reward-predictive stimulus (i.e., actions earning the same specific outcome as predicted by the presented CS). In addition, basolateral amygdala AMPA, but not NMDA glutamate receptor inactivation abolished the selective excitatory influence of reward-predictive cues over reward seeking. These data the hypothesis that transient glutamate release in the BLA can encode the outcome-specific motivational information provided by reward-predictive stimuli.
Highlights
Environmental stimuli have the ability to generate specific representations of the rewards they predict and in so doing alter the selection and performance of reward-seeking actions
If basolateral amygdala (BLA) glutamate transients reflect outcome-specific motivational information because glutamate biosensors record from BLA microenvironments, recorded glutamate transients for a given subject/recording location should be specific to CS-Same responding for only one outcome type
The data collected here indicate that transient fluctuations in BLA glutamate release are time-locked to and correlate with instrumental reward seeking and that during Pavlovian-instrumental transfer (PIT) these glutamate transients are time-locked to and correlate with only those actions invigorated by outcome-specific motivational information provided by a reward-predictive stimulus. This correlational relationship was bolstered by evidence that blockade of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), but not NMDA ionotropic glutamate receptors (iGluRs) attenuates the selective invigorating influence of reward-predictive stimuli over reward seeking
Summary
Environmental stimuli have the ability to generate specific representations of the rewards they predict and in so doing alter the selection and performance of reward-seeking actions. We monitored, in near-real time, basolateral amygdala glutamate concentration changes during a test of the ability of reward-predictive cues to influence reward-seeking actions (Pavlovian-instrumental transfer). Basolateral amygdala AMPA, but not NMDA glutamate receptor inactivation abolished the selective excitatory influence of reward-predictive cues over reward seeking. These data support the hypothesis that transient glutamate release in the BLA can encode the outcome-specific motivational information provided by reward-predictive stimuli. Assessment of this hypothesis requires a method to selectively measure BLA glutamate signaling with fast temporal resolution in order to distinguish chemical messages related to individual reward-seeking behaviors. BLA neurons can fire in response to reward-predictive cues[33,34,35,36,37] and in anticipation of reward[38], but the chemical message driving this neuronal activity and whether it encodes the motivational value of specific reward representations has yet to be clarified
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