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. Author manuscript; available in PMC: 2015 Aug 25.

Published in final edited form as: Adv Psychosom Med. 2011 Apr 19;30:22–60. doi: 10.1159/000324065

Fig. 4 — Brain reward and anti-reward mechanisms recruited by systemic opiate administration. Enhancement or inhibition of brain-reward is measured using electrical brain-stimulation reward in laboratory rats. The stimulating electrode in Panel A is located in the medial portion of the mesotelencephalic dopaminergic reward fiber tract; the stimulating electrode in Panel B is located in the lateral portion of the mesotelencephalic dopaminergic reward fiber tract. Panel A: Acute systemic opiate administration enhances brain reward, which diminishes as opiate effects wear off during each test day, and which shows development of tolerance with successive opiate administrations. Panel B: Acute systemic opiate administration inhibits brain reward, which diminishes as opiate effects wear off during each test day, and which shows development of sensitization (enhancement, “reverse tolerance”) with successive opiate administrations. Overall hedonic tone is a combination of effects depicted in Panels A and B. Thus, with chronic opiate administration, the reward-enhancing effects diminish and the anti-reward effects intensify, producing and overall reward deficiency state. After [42,58].

Fig. 4 — Brain reward and anti-reward mechanisms recruited by systemic opiate administration. Enhancement or inhibition of brain-reward is measured using electrical brain-stimulation reward in laboratory rats. The stimulating electrode in Panel A is located in the medial portion of the mesotelencephalic dopaminergic reward fiber tract; the stimulating electrode in Panel B is located in the lateral portion of the mesotelencephalic dopaminergic reward fiber tract. Panel A: Acute systemic opiate administration enhances brain reward, which diminishes as opiate effects wear off during each test day, and which shows development of tolerance with successive opiate administrations. Panel B: Acute systemic opiate administration inhibits brain reward, which diminishes as opiate effects wear off during each test day, and which shows development of sensitization (enhancement, “reverse tolerance”) with successive opiate administrations. Overall hedonic tone is a combination of effects depicted in Panels A and B. Thus, with chronic opiate administration, the reward-enhancing effects diminish and the anti-reward effects intensify, producing and overall reward deficiency state. After [42,58].