Role of ERK and JNK signaling pathways on the context-signal memory formation in the crab Chasmagnathus.

FELD M; DIMANT B; COSO O; ROMANO A

Los Cocos, Córdoba

Congreso; XVII Reunion Anual de la SAN; 2002

The role of ERK/MAPK (extracellular signal regulated kinase / mitogen-activated protein kinase) has been demonstrated on different models of synaptic plasticity and memory in vertebrates as well as in invertebrates. A previous report associated JNK (c-Jun amino terminal kinase) with conditioning in rodents. The present work was aimed at investigating whether MAPKs (ERK and JNK) are involved in the process of long-term associative memory (context-signal memory, CSM) consolidation in the crab Chasmagnathus. In this model, a spaced training induces formation of a long-term memory, dependent on gene expression and translation, while continuous training induces no retention. These protocols allow us the specific assessment of the processes involved in memory consolidation. Four training protocols were compared: spaced training (SP), inducing CSM; continuous training (active control, AC), inducing no retention; non-stimulated context-exposed animals (passive control, PC); and naïve animals (NV). ERK and JNK activation was determined on nuclear and citosolic protein extracts by Western blot analysis with phospho-specific antibodies (pERK and pJNK). Immunohystochemistry studies were also carried out on the central brain of Chasmagnathus (only for naïve animals). Both techniques showed high immunoreactivity. The putative amnesic effect of ERK inhibition was assayed by administration of 20 mg of PD098059, compared to DMSO (vehicle) injected animals, tested 24 hours after training. ERK activity increased about 2.5 times over NV activity in the citosolic fractions of PC and AC (PCc and ACc) immediately post-training. One hour post-training, ERK activity of the PCc and ACc groups decreased, while in the SPc group increased nearly 2.5 times. 3 hs. post-training, an inhibition of ERK activity was observed in SPc, which was restored to basal levels at 6 hs. Nuclear fractions showed no changes of activity at the times and groups studied. JNK1 and JNK2 reach two peaks of activity for the SPc group at 1 and 6 hs post-training, while the PCc group showed one at 3 hs post-training. Administration of ERK inhibitor, PD98059, 45 minutes after training (according to the pattern of ERK activation) induced amnesia during the testing session, 24 hs. after training. In conclusion, MAPK signaling pathways might be involved in neuronal circuitry underlying contextual information processing, being the context a common factor for all the protocols used. Consequently, inhibition of ERK by PD098059 during the period of activation of ERK has an amnesic effect. This body of evidence suggests a differential, time-dependent, ERK and JNK1/2 activation for the CSM consolidation in Chasmagnathus. This is the first report that specifically associates JNK1/2 with long-term memory formation in an invertebrate model.