Coover, Gary D.
M.A. (Master of Arts)
Department of Psychology
Based on previous research implicating the medial forebrain bundle (MFB) in behavioral inhibitory processes, and the fact that the MFB is known to have fiber interconnections with limbic system and forebrain structures classically thought to be involved in inhibitory processes, the present study investigated the avoidance behavior of rats with electrolytic lesions of the MFB. In Experiment I, rats with lesions of either the MFB or septal nuclei, and operated controls were tested for passive avoidance of a water spout following 48 hours of water deprivations. Contact with the water spout was punished with footshock. The rats with MFB lesions took a significantly greater number of shocks to reach the five minute passive avoidance criterion than those with septal lesions and operated controls, which did not differ from each other. Analysis of the various responses to shock during the task indicated that the MFB group took a significantly greater number of shocks to the final criterion following the first active avoidance of the water spout. The MFB group drank significantly less water under ad libitum conditions when measured seven days pre-test. In Experiment II, similar lesion groups were tested in the same manner, but post-operative recovery periods were lengthened and the shock parameters were changed. Rats with lesions of the MFB again took a significantly greater number of shocks to reach the final criterion, with the deficit due to the greater number of shocks following the first disruption of drinking, and also the greater number of shocks following the first active avoidance. No groups differed in amount of water consumption ad libitum, when measured pre-test. Independent flinch-jump tests for the determination of sensitivity to electric footshock showed that both the MFB and septal lesion groups had significantly lower jump thresholds than operated controls. In Experiment III, rats with lesions of the MFB and operated controls were tested in the same manner as in the previous experiments. Pretreatment with 5-HTP (5-hydroxytryptophan), which has been shown to return jump thresholds to normal in rats with lesions of the MFB, had no effect on the deficit found in this group. As in Experiment II, the deficit appeared due to both the greater number of shocks before exhibiting an active avoidance and in the greater number of shocks following the first active avoidance. It is concluded that lesions of the MFB render a rat less able to inhibit a previously rewarded response, and that the deficit is relatively independent of thirst, sensitivity to shock, and the serotonergic component of the MFB.
Heybach, John P., "Deficit in passive avoidance behavior following bilateral medial forebrain bundle lesions in rats" (1974). Graduate Research Theses & Dissertations. 2054.
54 pages, 3 unnumbered pages
Northern Illinois University
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