Evaluation of Possible "Impulsivity" Following Ventromedial Thalamic Nucleus Deactivation in the Rat Using a Fixed Consecutive Number Task Open Access
Goswami, Akshay (2015)
Abstract
This project was designed to assess the role of ventromedial thalamic nucleus (VMT), a thalamic structure which projects to prefrontal cortex, in impulse control as assessed by a fixed consecutive number (FCN) procedure. McGee (unpublished dissertation, 2014) demonstrated that transient deactivation via injection of the GABAA agonist muscimol into the VMT resulted in decreased efficiency of performance on a 5-choice serial reaction time test (5-CSRTT). Specifically, McGee observed an increase in premature responding, which was interpreted as an increase in impulsivity. This interpretation would be strengthened if premature responding could be demonstrated in a behavioral task other than the 5-CSRTT. The experiment reported here utilized the fixed consecutive number (FCN-8) task, in which the rat must complete 8 responses on one lever before a single response on a second lever in order to receive food reward; responding on the second lever before completion of 8 responses on the first lever does not deliver the reward, and the rat must start over. Stereotaxic procedures were used to implant bilateral guide cannulae above the medial VMT of six adult male Sprague-Dawley rats. These rats were subsequently food deprived and trained to perform the FCN-8 procedure. Doses of 5, 10, and 20 ng muscimol HBr, in a saline vehicle, or the vehicle alone, were injected into the VMT prior to some test sessions. The muscimol resulted in a dose-related, statistically significant, increase in premature responding. However, the muscimol also resulted in a marked, dose-related decrease in overall responding. These results support the hypothesis that medial VMT modulates impulse control in the rat, although the decrease in overall responding indicates that the nature of the behavioral change is more complex than simply a change in impulse control.
Table of Contents
INTRODUCTION 1
FIGURE 1: SCHEMATIC OF THE ANATOMY OF A COGNITIVE LOOP IN RATS 4
MATERIALS AND METHODS 5
SUBJECTS 5
DRUGS 6
APPARATUS 6
SURGICAL AND INFUSION PROCEDURE 7
BEHAVIORAL PROCEDURE: FCN-8 TRAINING 8
PERFORMANCE MEASURES 9
EVALUATION OF RESULTS AND HISTOLOGY 9
RESULTS 10
FIGURE 2: HISTOLOGIC INJECTION SITES IN THE RAT VMT 10
FIGURE 3: AVERAGE CHAIN LENGTH 11
FIGURE 4: RESPONSES ON THE FCN LEVER 12
FIGURE 5: RESPONSES ON THE REWARD LEVER 13
FIGURE 6: PELLETS RECEIVED 14
DISCUSSION 15
SUMMARY OF RESULTS 15
INTERPRETATION OF RESULTS 16
FIGURE 7: DETAIL OF AXONAL CONNECTIONS 21
REFRENCES 25
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