transport) and two others (namely, regulation of transcription from RNA polymerase II promoter and signal transduction), all of which were positively related to nicotine treatment. On the other hand, the GO categories related to protein biosynthesis and modification and nervous system development were negatively related to nicotine exposure. For the NA, eight processes were overrepresented; two of them (i.e., proteolysis and protein biosynthesis) were upregulated, and six (i.e., calcium ion binding, electron transport, mitochondrion, mRNA processing, organ morphogenesis, and RNA splicing) were downregulated. For the PFC, eight GO categories (i.e., ATP synthesis-coupled proton transport, electron transport, mitochondrion, mitochondrial respiratory chain complex I, ion transport, neuron migration, protein folding, and response to stress) were positively associated with nicotine treatment, whereas only protein biosynthesis was negatively regulated by nicotine. For the striatum, five GO categories (i.e., axon guidance, cell proliferation, mitochondrial respiratory chain complex I, mitochondrion, and protein biosynthesis) were suppressed, and three (i.e., microtubule-based process, protein polymerization, and protein amino acid phosphorylation) were induced. For the VTA, eight GO categories were upregulated, including those related to mitochondrial function (i.e., electron transport, mitochondrial respiratory chain complex I, mitochondrion, and proton-transporting two-sector ATPase complex), ion transport, small GTPase-mediated signal transduction, and two others
