Repeated co-treatment with imipramine and amantadine induces hippocampal brain-derived neurotrophic factor gene expression in rats

The problem of drug-resistant depression indicates a strong need for alternative antidepressant therapies. In our earlier papers we described synergistic, antidepressant-like effects of a combination of imipramine (IMI) and amantadine (AMA) in the forced swimming test in rats, an animal model of depression. Moreover, preliminary clinical data showed that the above-mentioned combination had beneficial effects in treatment-resistant patients. In addition, a number of studies predicted a role of the brain-derived neurotrophic factor (BDNF) in the mechanism of action of antidepressant drugs (ADs). Since the most potent effect of ADs on BDNF gene expression was found after prolonged treatment, in the present study we investigated the influence of repeated treatment with IMI (5 or 10 mg/kg) and AMA (10 mg/kg), given separately or jointly (twice daily for 14 day), on mRNA level (the Northern blot) in the hippocampus and cerebral cortex. The experiment was carried out on male Wistar rats. The tissue for biochemical assays was dissected 24 h after the last dose of IMI and AMA. We also studied the effect of repeated treatment with IMI and AMA on the action of 5-HT1A- and 5-HT2A receptor agonists (8-OH-DPAT and (±)DOI, respectively) in behavioral tests. The obtained results showed that in the hippocampus IMI (10 mg/kg), and in the cerebral cortex IMI (5 and 10 mg/kg) and AMA (10 mg/kg) significantly elevated BDNF mRNA level. Joint administration of IMI (5 or 10 mg/kg) and AMA (10 mg/kg) induced a more potent increase BDNF gene expression in the hippocampus (but not in cerebral cortex) and either inhibited the behavioral syndrome induced by (±)DOI or did not change the action of 8-OH-DPAT (compared to treatment with either drug alone). The obtained results suggest that the enhancement of BDNF gene expression may be essential for the therapeutic effect of co-administration of IMI and AMA to drug-resistant depressed patients, and that among other mechanisms, 5-HT2A receptors possibly play some role in this effect.