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Zebrafish are a genetically tractable vertebrate that hold considerable promise for elucidating the molecular basis of behavior. Although numerous recent advances have been made in the ability to precisely manipulate the zebrafish genome, much less is known about many aspects of learning and memory in adult fish. Here, we describe the development of a contextual fear conditioning paradigm using an electric shock as the aversive stimulus. We find that contextual fear conditioning is modulated by shock intensity, prevented by an established amnestic agent (MK-801), lasts at least 14 d, and exhibits extinction. Furthermore, fish of various background strains (AB, Tu, and TL) are able to acquire fear conditioning, but differ in fear extinction rates. Taken together, we find that contextual fear conditioning in zebrafish shares many similarities with the widely used contextual fear conditioning paradigm in rodents. Combined with the amenability of genetic manipulation in zebrafish, we anticipate that our paradigm will prove to be a useful complementary system in which to examine the molecular basis of vertebrate learning and memory.

Trisomy 21 (Down syndrome, DS) is the most common genetic cause of developmental cognitive deficits, and the so-called Down syndrome critical region (DSCR) has been proposed as a major determinant of this phenotype. The regions on human chromosome 21 (Hsa21) are syntenically conserved on mouse chromosome 10 (Mmu10), Mmu16 and Mmu17. DSCR is conserved between the Cbr1 and Fam3b genes on Mmu16. Ts65Dn mice carry three copies of ∼100 Hsa21 gene orthologs on Mmu16 and exhibited impairments in the Morris water maze and hippocampal long-term potentiation (LTP). Converting the Cbr1-Fam3b region back to two copies in Ts65Dn mice rescued these phenotypes. In this study, we performed similar conversion of the Cbr1-Fam3b region in Dp(16)1Yey/+ mice that is triplicated for all ∼115 Hsa21 gene orthologs on Mmu16, which also resulted in the restoration of the wild-type phenotypes in the Morris water maze and hippocampal LTP. However, converting the Cbr1-Fam3b region back to two copies in a complete model, Dp(10)1Yey/+;Dp(16)1Yey/+;Dp(17)1Yey/+, failed to yield the similar phenotypic restorations. But, surprisingly, converting both the Cbr1-Fam3b region and the Hsa21 orthologous region on Mmu17 back to two copies in the complete model did completely restore these phenotypes to the wild-type levels. Our results demonstrated that the Hsa21 orthologous region on Mmu17 is a major determinant of DS-related developmental cognitive deficits. Therefore, the inclusion of the three copies of this Hsa21 orthologous region in mouse models is necessary for unraveling the mechanism underlying DS-associated developmental cognitive deficits and for developing effective interventions for this clinical manifestation.

Frankland et al. provide a history of research on engrams and their relationship to memory processes, highlighting new technologies that have allowed careful dissection of engrams and their function. [ABSTRACT FROM AUTHOR]

The FoxO family of transcription factors is known to slow aging downstream from the insulin/IGF (insulin-like growth factor) signaling pathway. The most recently discovered FoxO isoform in mammals, FoxO6, is highly enriched in the adult hippocampus. However, the importance of FoxO factors in cognition is largely unknown. Here we generated mice lacking FoxO6 and found that these mice display normal learning but impaired memory consolidation in contextual fear conditioning and novel object recognition. Using stereotactic injection of viruses into the hippocampus of adult wild-type mice, we found that FoxO6 activity in the adult hippocampus is required for memory consolidation. Genome-wide approaches revealed that FoxO6 regulates a program of genes involved in synaptic function upon learning in the hippocampus. Consistently, FoxO6 deficiency results in decreased dendritic spine density in hippocampal neurons in vitro and in vivo. Thus, FoxO6 may promote memory consolidation by regulating a program coordinating neuronal connectivity in the hippocampus, which could have important implications for physiological and pathological age-dependent decline in memory.

Pinpointing the precise age when young animals begin to form memories of aversive events is valuable for understanding the onset of anxiety and mood disorders and for detecting early cognitive impairment in models of childhood-onset disorders. Although these disorders are most commonly modeled in mice, we know little regarding the development of learning and memory in this species because most previous studies have been restricted to rats. Therefore, in the present study, we constructed an ontogenetic timeline of contextual fear memory ranging from infancy to adulthood in mice. We found that the ability of mice to form long-term context-shock associations emerged [approximately]13-14 d of age, which is several days earlier than previously reported for rats. Although the ability to form contextual fear memories remained stable from infancy into adulthood, infant mice had shorter-lasting memories than adolescent and adult mice. Furthermore, we found that mice subjected to fetal alcohol exposure showed a delay in the developmental emergence of contextual fear memory, illustrating the utility of this ontogenetic approach in detecting developmental delays in cognitive function stemming from maladaptive early life experience.

The first gene-targeting studies that examined learning and memory in mice were performed in 1992 (Grant et al. 1992; Silva et al. 1992). The ultimate goal of this new field was to understand the molecular and cellular process underlying normal cognition and how they may be altered in disease states. In the years since these pioneering studies, well over 100 different molecules have been identified that are essential to or modulate learning and memory. Despite this rapid progress, the translation of these basic findings to human cognitive disorders has been slow. However, this may be changing. In this article, the author presents a study by Wood et al. (2005) that use a combination of approaches to examine the molecular, cellular, and systems basis of a learning and memory disorder. Overall, the results of the study provide compelling evidence that CREB-binding protein (CBP) is a key molecule in mouse memory and offer important insights into the molecular and cellular basis of human cognition. These findings also highlight the power of mouse models to illuminate novel therapeutic targets for the treatment of cognitive disorders. (Contains 1 table.)