Effects of age on susceptibility to the induction of depressive behavior and imipramine in rats

Intra-nucleus-accumbens SKF38393 improved the impaired acquisition of morphine-conditioned place preference in depression-like rats

Dopaminergic activity in the nucleus accumbens (NAc) and the globus pallidus (GP) is important for the interaction between depression and addiction, with D1- and D2-like receptors playing different roles. Here, we address the effect of depression on morphine reward and its underlying D1- and D2-like effects in the NAc and/or the GP. Novelty-seeking behaviors and the forced open-space swimming test were used to assess a depression-like state in rats that had undergone chronic mild restraint. Depression-like rats were then trained with morphine-induced conditioned place preference (CPP, 3 mg/kg, 4 days), and showed impaired acquisition of the CPP compared with controls. To examine the receptor-specific dopaminergic mechanism underlying this phenomenon, we microinjected the D1-like agonist SKF38393 (1 μg/side) or the D2-like agonist quinpirole (1 μg/side) into the NAc or the GP. The impairment in acquisition of CPP was reversed only by injecting the D1- but not the D2-like agonist in the NAc. These results suggest that enhancement of dopaminergic transmission in the NAc (via D1-like receptors) may be effective in recovering impaired reward learning during a depression-like state.

Cerebral ischemia-induced difference in sensitivity to depression and potential therapeutics in rats

The 'vascular depression' hypothesis has recently attracted significant research attention, although the causal relationship between vascular-related injuries and depression has not been established. Here, we show that one episode of cerebral ischemia was sufficient to greatly increase the sensitivity of rats to potentially depressogenic events, evaluated at below-threshold intensities in the open space swim test. The induced 'ischemic depression' was lasting and sensitive to an acute administration of brain-derived neurotrophic factor or bryostatin-1, a relatively selective activator of protein kinase Cε, during the induction phase. Chronic treatment with bryostatin-1 (5 weeks) after the induction of depressive behavior reversed the depressive immobility and produced a lasting therapeutic effect, which remained effective 3 weeks after discontinuation of the treatment. Similar treatment with alaproclate, a selective serotonin reuptake inhibitor, in contrast, produced temporary relief from the depressive symptoms, with the therapeutic effect disappearing soon after the end of the treatment. The results strongly suggest that cerebral ischemia has a direct role in shaping the sensitivity of an individual to depressogenic events and that bryostatin-1-like agents may be developed as therapeutics for treating ischemic depression in humans.