Prahlad, K. V.||Lints, Carlton E.
M.S. (Master of Science)
Department of Biological Sciences
After rats have been given bilateral medial forebrain bundle lesions (MFB) it has been observed that there is a decrease in forebrain serotonin (5-HT) concentration and an increase in shock sensitivity as measured by a lowered jump threshold. Thus it has been suggested that forebrain 5-HT modulates shock sensitivity. Therefore when the nuclei of origin (median and dorsal midbrain raphe nuclei) of the serotonergic fibers are lesioned, it is reasonable to expect a greater decrease in forebrain 5-HT content and a greater increase in shock sensitivity than that produced by NFB lesions. These results have not been obtained. A lesion in the raphe nuclei produces a decrease in forebrain 5-HT and no effect on shock sensitivity. The possibility that raphe lesions also destroy an algebraically interacting, excitatory pain system has been suggested to account for this effect. The present study examined this possibility by creating NFB and raphe lesions in experimental animals. These animals were then tested by the flinch-jump method. After behavioral testing, a sub-group of MFB-lesioned animals were reoperated to produce a MFB-raphe combined lesion. All the animals were then retested by the flinch-jump method. The animal's brains were then assayed for 5-HT and NE content and the brainstems were checked for lesion extent and location. It was found that lesions of the MFB, dorsal plus median midbrain raphe nuclei and the combined MFB-raphe areas produced significant reductions in forebrain 5-HT and failed to affect flinch thresholds significantly. One sub-group of MFB-lesioned subjects had significantly lowered jump thresholds on the first test but this effect was not replicated in the second test. MFB-raphe combined lesions produced analgesia as indexed by elevated jump thresholds. This elevation occurred in spite of the fact that this sub-group of MFE-lesioned rats did not have a significantly lowered jump threshold on the first test. Although not clear-cut because of the lack of an increase in shock sensitivity following the initial surgery in this sub-group of MFB-lesioned animals, these results suggest that the failure to find increased pain sensitivity following raphe lesions that significantly deplete forebrain 5-HT could be due to the fact that these same lesions are destroying a non-serotonergic, excitatory pain system in this part of the brain.
Ferguson, Ruthe A., "Effects of lesions in the medial forebrain bundle and median plus dorsal midbrain raphe nuclei on shock sensitivity and forebrain serotonin" (1979). Graduate Research Theses & Dissertations. 2782.
vii, 63 pages
Northern Illinois University
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