The IκB kinase inhibitor sulfasalazine impairs long-term memory in the crab Chasmagnathus

Abstract

Evidence for the participation of Rel/NF-κB transcription factors in long-term memory has recently been reported in the context-signal learning paradigm of the crab Chasmagnathus, in which a high correlation between long-term memory formation and NF-κB activation was observed. Two components of the NF-κB pathway in the crab brain have now been identified by cross-immunoreactivity using mammalian antibodies for IκB-α and IκB kinase α. Furthermore, IκB kinase-like phosphotransferase activity, which was inhibited by the IκB kinase inhibitor sulfasalazine, was detected in brain extracts. We have evaluated the effect of sulfasalazine administration on long-term memory tested at 48 h. Amnesia was found when sulfasalazine was administered pre-training and 5 h after training but not at 0 or 24 h after training. Thus, two periods for sulfasalazine-induced amnesia were found in coincidence with the two phases of NF-κB activation previously described (immediately and 6 h after training). The cyclooxygenase inhibitor indomethacin did not induce amnesia when administered pre-training. Thus, the possibility that sulfasalazine induces amnesia by means of cyclooxygenase inhibition is unlikely to be tenable. In vivo sulfasalazine inhibition of basal NF-κB activity was found between 30 and 45 min after injection, as assessed by electrophoretic mobility shift assay. On the other hand, in vivo sulfasalazine administration 6 h after training inhibited the second phase of training-induced NF-κB activation, providing evidence that the sulfasalazine effect on memory is due to a direct effect of the drug on the NF-κB pathway. These results provide the first evidence that IκB kinase and NF-κB activation are necessary for memory formation.