D1 receptor modulation of memory retrieval performance is associated with changes in pCREB and pDARPP-32 in rat prefrontal cortex.

We have recently shown a significant role of dopamine D(1) receptors in recognition and temporal order memory retrieval for objects in rodents [Hotte M, Naudon L, Jay TM. Modulation of recognition and temporal order memory retrieval by dopamine D(1) receptor in rats. Neurobiol Learn Mem 2005;84:85-92]. The present study investigates the signal transduction pathways underlying dopamine D(1) receptor modulation of retrieval performance in these memory tasks at different delays. We analyzed the level of phosphorylation of both CREB (cAMP response element binding protein) and DARPP-32 (dopamine and cAMP-regulated phosphoprotein, 32 kDa) in (1) the prefrontal cortex of rats that had performed the object recognition task, (2) the prefrontal and perirhinal cortices of rats that had performed the temporal order memory task for objects. For comparison, we explored the phosphorylation state of CREB and DARPP-32 in the prefrontal cortex, nucleus accumbens and hippocampus of rats having performed badly on the delayed spatial win-shift task after D(1) blockade. The improvement in recognition and temporal order memory performance at a 4h-delay was associated with an increased phosphorylation of both CREB and DARPP-32 in the prefrontal cortex of rats treated with the D(1) agonist SKF 81297. By contrast, the significant impairment of delayed spatial memory retrieval after administration of the selective D(1) antagonist SCH 23390 was associated with decreased phosphorylation of CREB and DARPP-32 in the prefrontal cortex. These results provide insight into molecular mechanisms involved in D(1) receptor-dependent modulation of short- versus long-term memory in prefrontal cortex where DARPP-32 in synergy with CREB may represent a pivotal role.

Characterization and tissue-specific expression of the Drosophila transaldolase gene.

Transaldolase (TAL) is an enzyme of the non-oxidative part of the pentose phosphate pathway which produces reductive potential in the form of NADPH as well as ribose 5-phosphate for incorporation into nucleotides. Developmental analysis via reverse transcriptase-polymerase chain reaction, immunoblots, enzymatic activity, in situ hybridization and immunocytochemistry demonstrate that TAL is expressed during all developmental stages in Drosophila. The tal locus is unique and contains two small introns. The first two introns in the human gene are situated at the same locations in the coding sequence as in Drosophila. Analysis of TAL protein levels and expression patterns reveals that it is also expressed in all larval tissues examined with particularly high levels in the fat body. Interestingly, we describe specific TAL expression only in non-neuronal cells in the larval brain.