Hippocampal Brain-Derived Neurotrophic Factor Expression Following Treatment with Reboxetine, Citalopram, and Physical Exercise

The antidepressants, reboxetine and citalopram, were used in conjunction with voluntary physical exercise (wheel running) in order to assess the contribution of noradrenergic and serotonergic activation to enhancements in hippocampal brain-derived neurotrophic factor (BDNF) expression resulting from antidepressant treatment and exercise. Reboxetine (40 mg/kg/day), citalopram (10 mg/kg/day), voluntary physical activity, and the combination of antidepressants with exercise were applied to rats for a range of treatment intervals (2 to 14 days). Hippocampal BDNF transcription levels (full-length BDNF, as well as exons I-IV) were then assessed via in situ hybridization. Reboxetine treatment led to a rapid (evident at 2 days) enhancement in BDNF transcription in several hippocampal regions. This increase was also observed when reboxetine treatment was combined with voluntary physical activity for 2 weeks. Treatment with citalopram led to an increase in BDNF mRNA in only one hippocampal region (CA2) after short-term (2 days) treatment, and when combined with exercise, increased BDNF mRNA in the CA4 and dentate gyrus after 2 weeks. As reported in previous studies, voluntary physical activity enhanced BDNF transcription in several hippocampal areas, both on its own and in combination with antidepressant treatments. Examination of the levels of individual BDNF transcript variants influenced by each of these antidepressants revealed distinct patterns of expression in response to the various treatments, and showed that exercise-plus-antidepressant produced significant changes where antidepressant alone failed. Overall, treatment with the norephinephrine-selective antidepressant, reboxetine, in combination with exercise, led to both rapid and sustained increases in hippocampal BDNF mRNA expression. The serotonergic agent, citalopram, appeared to require longer treatment intervals in order to influence BDNF expression positively.