Deficits in memory tasks of mice with CREB mutations depend on gene dosage

Studies in Aplysia, Drosophila, and mice have shown that the transcription factor CREB is involved in formation and retention of long- term memory. To analyze the impact of differential CREB levels on learning and memory, we varied the gene dosage of CREB in two strains of mutant mice: (1) CREBαΔ mice, in which the α and Δ isoforms are disrupted, but a third isoform β is strongly up-regulated; (2) CREBcomp, a compound strain with one αΔ allele and one CREBnull allele in which all CREB isoforms are disrupted. To minimize genetic background effects, CREB mutations were backcrossed into a C57BL/6 and a FVB/N strain, respectively, and studies were performed in F₁ hybrids from these lines. CREBcomp but not CREBαΔ F₁ hybrids were impaired in water maze learning and fear conditioning, demonstrating a CREB gene dosage effect. However, analysis of the platform searching strategies in the water maze task suggested that CREBcomp mutants are impaired in behavioral flexibility rather than in spatial memory. In contrast to previous experiments using CREBαΔ mice with different genetic background, the F₁ hybrid CREBαΔ and CREBcomp mice did not show deficits in a social transmission of food preference task nor in dentate gyrus and CA1 LTP as recorded from slice preparations. These data indicate that the hybrid vigor typical for F₁ hybrids may compensate for a reduction in CREB levels in some tests. On the other hand, the persistence of clear behavioral deficits as shown by the F₁ hybrid CREBcomp mice in water maze and fear conditioning indicates a robust and repeatable phenomenon that will permit further functional analysis of CREB.