The differential expression of the electron transport system in the six brain regions is consistent with the concept that these regions have different cellular and physiological functions. Because these regions are divergent in their cellular compositions and behaviors (e.g., neurotransmitter release, receptor expression, intracellular signaling cascades) in order to manage specific physiological activities, and because they have different energy consumption and reaction mechanisms in response to external disturbances, a region-specific transcriptional response of the electron transport system to chronic nicotine treatment would be expected. The different responses of the electron transport system in these regions to nicotine may be associated with the specific role of each region in the development of nicotine dependence. For example, the upregulation of the expression of this system in the amygdala, hippocampus, PFC, and VTA may represent the neuron’s effort to increase its energy-generating capacity or an acceleration of protein turnover. On the other hand, the suppression of the electron transport system in the NA and striatum may reflect a reduction in energy requirements in these regions or other slowdown in metabolism.
