New neurons are produced in the brains of adult animals, including humans, throughout the lifespan. Since one of the site of adult brain neurogenesis is the hippocampal formation, a brain structure involved in learning and memory, new neurons were expected to be involved in these phenomena. However, the very evidence supporting this hypothesis remains limited, inconsistent and in most cases indirect. Also, the experiments in which adult neurogenesis is blocked use irradiation and drugs known for their side effects. We used a novel approach, cyclin D2 knock-out mice (D2 KO mice), specifi cally lacking adult brain neurogenesis (which was verifi ed using DCX and NeuN staining) to verify its importance in learning and memory. D2 KO mice and their wild type siblings were tested in several behavioral paradigms including those in which the role of adult neurogenesis has been postulated. D2 KO mice showed no impairment in sensorimotor tests with only sensory impairment in an olfaction-dependent task. However, D2 KO mice showed proper procedural learning as well as learning in context (including remote memory), cue and trace fear-conditioning, Morris water maze, novel object recognition test, and in a multifunctional behavioral system – Intellicages. Our results suggest that adult brain neurogenesis is not obligatory in learning, including the kinds of learning where the role of adult neurogenesis has previously been strongly suggested. Support – MNiSW grant no N303 051 31/1624.
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