Behavioural brain research
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Comparative Study
Noradrenergic signaling in the medial prefrontal cortex and amygdala differentially regulates vicarious trial-and-error in a spatial decision-making task.
In uncertain choice situations, we deliberately search and evaluate possible options before taking an action. Once we form a preference regarding the current situation, we take an action more automatically and with less deliberation. In rats, the deliberation process can be seen in vicarious trial-and-error behavior (VTE), which is a head-orienting behavior toward options at a choice point. ⋯ Injection of clonidine into either region impaired selection of the advantageous choice in the task. Furthermore, clonidine injection into the mPFC suppressed occurrence of VTE in the early phase of the task, whereas injection into the AMY inhibited the decrease in VTE in the later phase and thus maintained a high level of VTE throughout the task. These results suggest that the mPFC and AMY play a role in the increase and decrease in VTE, respectively, and that noradrenergic mechanisms mediate the dynamic regulation of VTE over experiences.
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Comparative Study
The neural substrates for the rewarding and dopamine-releasing effects of medial forebrain bundle stimulation have partially discrepant frequency responses.
Midbrain dopamine neurons have long been implicated in the rewarding effect produced by electrical brain stimulation of the medial forebrain bundle (MFB). These neurons are excited trans-synaptically, but their precise role in intracranial self-stimulation (ICSS) has yet to be determined. This study assessed the hypothesis that midbrain dopamine neurons are in series with the directly stimulated substrate for self-stimulation of the MFB and either perform spatio-temporal integration of synaptic input from directly activated MFB fibers or relay the results of such integration to efferent stages of the reward circuitry. ⋯ Whereas the psychometric functions decline monotonically over a broad range of pulse frequencies and level off only at high frequencies, the chemometric functions obtained with the same rats and electrodes are either U-shaped or level off at lower pulse frequencies. This discrepancy was observed when the dopamine transients were recorded in either anesthetized or awake subjects. The lack of correspondence between the psychometric and chemometric functions is inconsistent with the hypothesis that dopamine neurons projecting to the NAc shell constitute an entire series stage of the neural circuit subserving self-stimulation of the MFB.
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The elevated plus maze (EPM) is used to assess anxiety in rodents. Beam-walking tasks are used to assess vestibulomotor function. Brain injury in rodents can disrupt performance on both of these tasks. ⋯ Further, these effects were dissociated from the effects of bTBI on motor function simultaneously measured on MBW. Over the course of 168h post-bTBI, rats gradually recovered on both EPM and MBW. The MBW apparatus succeeded at capturing and dissociating two separate facets of rat behavior, motor function and anxiety, simultaneously.