 Role of neuromodulators in long-term memory storage vs long-term memory expression.

A. DELORENZI

Jena

Conferencia; lectures: Max Planck Institute Chemische Ökologie; 2011

Max Planck Institute Chemische Ökologie

Memory reconsolidation is a dynamic process in which a previously consolidated memory becomes labilefollowing reactivation by a reminder. In a previous study in the crab Chasmagnathus memory model, weshowed that a water-shortage episode, via angiotensin modulation during reconsolidation, could reveal amemory that otherwise remains unexpressed: weakly trained animals cannot reveal long-term memory(LTM) except when an episode of noticeable ethological meaning, water deprivation, is contingent uponreconsolidation. However, these results are at variance with two of our previous interpretations: weaktraining protocols do not build LTM and angiotensin II modulates the strength of the information storingprocess. A parsimonious hypothesis is that in Chasmagnathus angiotensins regulate LTM expression, butnot LTM storage. Here, we tested three predictions of this hypothesis. First, the well-known retrogradeamnesic effect of the angiotensin II antagonist saralasin is not due to interference on memory storage,but to modulation of memory expression. Second, the recovery of the LTM memory expression of theapparently amnesic retrograde effect produced by saralasin, through the water-shortage episode contingentupon reconsolidation, must be reconsolidation specific. Consequently, summation-like effects andretrieval deficits cannot explain these results because of the parametric conditions of reconsolidation.Third, weak training protocols build an unexpressed LTM that requires mRNA transcription and translation,a diagnostic characteristic of LTM. Results show that angiotensin modulates LTM expression but notLTM memory storage in the crab Chasmagnathus. The results lead us to suggest that, in Chasmagnathus,LTM expression ? the process of gaining appreciable control over behavior of the reactivated trace inthe retrieval session ? may be considered a distinct attribute of its long-term storage. This strategy, apositive modulation during reconsolidation, is proposed to distinguish between memories that can bereactivated, labilized and are not expressed, and memories that are not stored long term, obliteratedor altered in other retrieval mechanisms.