Effects of fluoxetine on hippocampal-dependent and hippocampal-independent learning tasks

It is generally assumed that fluoxetine does not produce cognitive impairments, based on observations that fluoxetine-treated animals do not show impairment in learning the spatial water-maze task. As fluoxetine has different effects on different brain regions and as learning is not a unitary phenomenon, it may be the case that fluoxetine has different effects on different types of learning and memory paradigms. In this study, 15 male Sprague-Dawley rats were given chronic injections of either fluoxetine or saline and received training in two hippocampal-independent tasks in addition to a spatial water-maze task. The two hippocampal-independent tasks were a short-delay appetitive Pavlovian-conditioning task and an object-recognition task. The results showed that the fluoxetine-injected rats did not show any impairment relative to the saline controls in either the acquisition or the retention phases of the water-maze task, but were significantly impaired in both of the hippocampal-independent tasks. Fluoxetine-injected rats spent significantly less time exploring the novel object in the object-recognition task and took longer to learn the association between the conditional stimulus and the appetitive unconditional stimulus in the appetitive Pavlovian-conditioning task.