Posterior lateral hypothalamus stimulation confirms brain reward site stimulation-induced hyperalgesia
Oh, Jeremy Jaehwan
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Pain is known as one of the most important physical sensations that contribute to animal survival. Kornetsky and colleagues (201 0) established mesencephalic reticular formation (MRF) and midbrain forebrain bundle (MFB) thresholds separately and found that simultaneous stimulation of the sites significantly lowered MRF escape thresholds. They also found that the simultaneous stimulation of the sites eliminated the analgesic effect--that is, raising the MRF threshold--of morphine. In an effort to better understand the interaction between rewarding brain stimulation and nociceptive pain, this study expands upon the previous experiment by implanting an electrode in the ventral tegmental area (VTA). However, during the post-mortem histological review, it was found that the rewarding electrodes were implanted in the posterior lateral hypothalamus (PLH), not in the VTA. Our overall results of this experiment demonstrate similar findings as the previous study (Kornetsky et al., 2010). The simultaneous stimulation of the MRF and PLH significantly lowered MRF escape thresholds and eliminated the analgesic effects of morphine. A very low, subthreshold intensity of stimulation to the PLH yielded significantly increased sensitivity to MRF stimulation. Furthermore, the results show that morphine did not lower BSE threshold, when the MRF was simultaneously stimulated with the PLH. An examination of the rewarding electrode placements found in the simultaneous MRF and MFB stimulation experiment by Kornetsky and colleagues (2010) also show rewarding electrode in the PLH, which corroborates with the results in this experiment.
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