Nonspecific binding was blocked by preincubating the membrane for 1 h in TBST (0.5 M NaCl, 20 mM Tris-HCl pH 7.5, 0.1% Tween-20) containing 3% BSA. FosB/FosB immunoreactivity in all hippocampal regions measured (i.e., in the DG, CA1, and CA3 subfields of both the dorsal and ventral hippocampus). Results confirmed that wheel running induced region-specific expression of FosB/FosB immunoreactivity in the cortex, suggesting that the uniform increase in FosB/FosB within the hippocampus is not a nonspecific result of running. Western blot data indicated that this increased hippocampal FosB/FosB immunoreactivity was primarily due to increased FosB. These results suggest that long-term physical exercise is usually a potent trigger for FosB induction throughout the entire hippocampus, which would explain why exercise can improve both dorsal and ventral hippocampus-dependent functions. Interestingly, we found that FosB/FosB expression in the DG was positively correlated with the number of doublecortin-immunoreactive (i.e., immature) neurons. Even though mechanisms by which FosB mediates exercise-induced neurogenesis are still uncertain, these data imply that exercise-induced neurogenesis is at least activity dependent. Taken together, our current results suggest that FosB is usually a new molecular target involved in regulating exercise-induced hippocampal plasticity. == Introduction == Exercise confers diverse benefits on molecular, structural, and functional aspects of the hippocampus in rodents [1,2], some of which were supported by human studies [3,4]. However, the mechanisms underlying the exercise-induced changes in hippocampal plasticity are not sufficiently understood. Previous literature has consistently exhibited that exercise evokes hippocampal neuronal activation in rodents. Immunohistochemical studies using c-Fos, a marker of transient neuronal activation, have exhibited that both forced and voluntary running increased c-Fos expression Butoconazole in the dentate gyrus (DG), CA1, and CA3 subfields of the rodent hippocampus [5-7]. In addition, a previous study using laser-Doppler flowmetry (LDF) has demonstrated that moderate treadmill running increased regional cerebral blood flow (rCBF), an alternative marker of neuronal activation, in the CA1 subfield in rat [8]. Immunohistochemical studies enable detailed region-specific analyses after exercise has ceased, while LDF enables real-time monitoring of Butoconazole rCBF in a localized area during exercise. Despite the advantages and limitations of each study, these studies similarly exhibited an effect of acute bouts of exercise on hippocampal neuronal activity. These results suggest a mechanism whereby long-term regular exercise promotes hippocampal plasticity by repeatedly triggering neuronal activation [9]. The transcription factor FosB, a truncated splice isoform of full-length FosB, Itga9 is usually induced by various types of repeated stimuli in specific brain regions, where it gradually accumulates because of its unique stability (a half-life of weeks) [10-12]. A growing body of evidence demonstrates that increased levels of FosB mediate long-lasting neural and behavioral plasticity associated with particular stimuli [11,13]. For example, chronic administration of drugs of abuse such as cocaine and morphine generally increases FosB expression in the nucleus accumbens, representing one of the molecular mechanisms underlying increased sensitivity to these drugs Butoconazole [11,14,15]. Similarly to other incentive stimuli, including high-fat diet and sexual experience [16,17], long-term voluntary wheel running also increased FosB/FosB immunoreactivity in rat nucleus accumbens, suggesting that voluntary running is usually a natural incentive for rodents [18,19]. However, to the best of our knowledge, no literature has examined whether repeated exposure to physical exercise induces FosB expression in the hippocampus. Because exercise triggers neuronal activation in the hippocampus, we hypothesized that long-term voluntary wheel running would also induce FosB expression in the hippocampus. While the exact mechanisms by which FosB regulates hippocampal plasticity remain uncertain, studies have exhibited that mice lacking thefosBgene show impaired hippocampal neurogenesis and increased depression-like behavior [20,21]. Indeed, exercise is known to enhance neurogenesis and have antidepressant properties [22-25]. If our hypothesis is usually correct, FosB would be a new potential molecular target mediating exercise-induced hippocampal plasticity. The hippocampus has anatomical and functional Butoconazole gradient along its longitudinal (dorsoventral) axis [26]. The dorsal hippocampus plays a key role in spatial learning and memory [27,28], whereas the ventral hippocampus is usually preferentially involved in regulating emotional behaviors.