Surface expression of NMDA receptor changes during memory consolidation in the crab Neohelice granulata.

YANIL HEPP; ANGELES SALLES; MARTIN CARBO-TANO; MARIA EUGENIA PEDREIRA; RAMIRO FREUDENTHAL

LEARNING & MEMORY (COLD SPRING HARBOR, N.Y.)

COLD SPRING HARBOR LAB PRESS

Año: 2016

1072-0502

The aim of the present study was to analyze the surface expression of the NMDA-like receptors during the consolidation of contextual learning in the crab Neohelice granulata. Memory storage is based on alterations in the strength of synaptic connections between neurons. The glutamatergic synapses undergo various forms of N-Methyl-D aspartate receptor (NMDAR)-dependent changes in strength, a process that affects the abundance of other receptors at the synapse and underlies some forms of learning and memory. Here we propose a direct regulation of the NMDAR. Changes in NMDAR?s functionality might be induced by the modification of the subunit?s expression or cellular trafficking. This trafficking does not only include NMDAR?s movement between synaptic and extra-synaptic localizations but also the cycling between intracellular compartments and the plasma membrane, a process called surface expression. Consolidation of contextual learning affects the surface expression of the receptor without affecting its general expression. The surface expression of the GluN1 subunit of the NMDAR is down-regulated immediately after training, up-regulated 3 hours after training and returns to naïve and control levels 24 hours after training. The changes in NMDAR surface expression observed in the central brain are not seen in the thoracic ganglion. A similar increment in surface expression of GluN1 in the central brain is observed 3 hours after administration of the competitive GABAA receptor antagonist, bicuculline. These consolidation changes are part of a plasticity event that first, during the down-regulation, stabilises the trace and later, at 3 hours post training, changes the threshold for synapse activation.