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Impairment of protein synthesis in the brain during learning prevents memory consolidation and results in amnesia, which until recently has been regarded irreversible. However, in some cases impaired memory could be restored by various "reminder" stimuli. The present study is based on the hypothesis that even in behaviorally profound amnesia, some disintegrated fragments of the engram are preserved in the brain and could be re-integrated into the whole system by specific types of stimuli. The aim of the present study was to test this hypothesis in an experimental model of pharmacologically induced memory impairment in young chicks and to reveal the brain areas involved in this process by mapping of reminder-induced expression of transcriptional factors c-Fos and Egr-1. We show that reminder treatment results in the recovery of memory impaired by protein synthesis inhibition during learning and induces c-Fos and Egr-1 expression in the brain regions involved in learning in this behavioral model. The patterns of c-Fos and Egr-1 induced expression in animals with impaired memory differed from the patterns of animals with unimpaired memory and as well as naïve animals with no memory. Thus, analysis of activity-induced c-Fos and Egr-1 expression revealed the brain regions that were specifically activated by the reminder treatment. At the behavioral level, this treatment led to memory recovery. Altogether, these results suggest that the reminder-induced transcriptional activity in the brain of amnestic animals occurs in regions maintaining the engram fragments that reintegrate to recover the impaired memory.

We developed a method to detect and superimpose neuronal populations involved in two different episodes of activity in the brain of single animal. This method is based on usage of two transcriptional factors with different accumulation curves, c-Fos and pCREB, as the markers. The overlap of neuronal populations involved in performance of spatial and nonspatial tasks in Morris water maze has been shown to occur at "chance" level.

We studied the effects of training on DNA synthesis intensity in mouse brain. Brain cells where DNA synthesis-associated processes took place under the influence of training were detected by immunohistochemical labeling of DNA molecules with synthetic thymine analogue 5-bromo-2’-deoxyuridine. The number of 5-bromo-2’-deoxyuridine-positive cell increased in various structures of the brain under the influence of training.

We studied the effects of training on DNA synthesis intensity in mouse brain. Brain cells where DNA synthesis-associated processes took place under the influence of training were detected by immunohistochemical labeling of DNA molecules with synthetic thymine analogue 5-bromo-2'-deoxyuridine. The number of 5-bromo-2'-deoxyuridine-positive cell increased in various structures of the brain under the influence of training.