Molecular Characterization of NMDA-Like Receptors inAplysiaandLymnaea:Relevance to Memory Mechanisms

Abstract

Abstract. The N-methyl-D-aspartate (NMDA) receptor belongs to the group of ionotropic glutamate receptors and has been implicated in synaptic plasticity, memory acquisition, and learning in both vertebrates and invertebrates, including molluscs. However, the molecular identity of NMDA-type receptors in molluscs remains unknown. Here, we cloned two NMDA-type receptors from the sea slug Aplysia californica, AcNR1-1 and AcNR1-2, as well as their homologs from the freshwater pulmonate snail Lymnaea stagnalis, LsNR1-1 and LsNR1-2. The cloned receptors contain a signal peptide, two extracellular segments with predicted binding sites for glycine and glutamate, three recognized transmembrane regions, and a fourth hydrophobic domain that makes a hairpin turn to form a pore-like structure. Phylogenetic analysis suggests that both the AcNR1s and LsNR1s belong to the NR1 subgroup of ionotrophic glutamate receptors. Our in situ hybridization data indicate highly abundant, but predominantly neuron-specific expression of molluscan NR1-type receptors in all central ganglia, including identified motor neurons in the buccal and abdominal ganglia as well as groups of mechanosensory cells. AcNR1 transcripts were detected extrasynaptically in the neurites of metacerebral cells of Aplysia. The widespread distribution of AcNR1 and LsNR1 transcripts also implies diverse functions, including their involvement in the organization of feeding, locomotory, and defensive behaviors.

Delayed Intrinsic Activation of an NMDA-Independent CaM-kinase II in a Critical Time Window Is Necessary for Late Consolidation of an Associative Memory

“…This finding is consistent with the vertebrate learning literature (Silva et al, 1992;Davis et al, 1992;Giese et al, 1998;Shimizu et al, 2000;Rodrigues et al, 2004;Irvine et al, 2005;Bevilaqua et al, 2005), implying that the role of CaMKII and its close correlation with the activation of NMDA receptors in learning is conserved between invertebrates and vertebrates. NMDA-like receptors are present in both Aplysia and Lymnaea (Ha et al, 2006), providing a molecular foundation for functional conservation.…”

“…CaMKII-dependent acquisition, but not late consolidation, of associative memory Previous work in other systems has demonstrated a direct link between NMDA receptors and activation of CaMKII (Bayer et al, 2001), and recently, NMDA-like receptors have been characterized at the molecular level in both Aplysia and Lymnaea (Ha et al, 2006). Moreover, glutamate has been shown to be an important transmitter in the Lymnaea feeding system (Brierley et al, 1997;Hatakeyama et al, 2007).…”

Nitric oxide-coupled signaling in odor elicited molecular events in the olfactory center of the terrestrial snail, Helix pomatia

“…Santa Clara, CA) was used as control. CNS extract of Lymnaea stagnalis was used as a positive control testing the anti-NMDA receptor antibody, since the Lymnaea stagnalis NMDA receptor was sequenced [46].…”

“…2B). In Lymnaea stagnalis extract, used as a positive control, for the NMDA-receptor sequence [46], anti-NMDARζ1 detected a strongly labeled double band at the same mw. Probing Helix pomatia CNS protein extracts with NGS revealed that the other immunoreactive bands arose due to non-specific binding…”

“…Similarly to Glu release, Ca 2 + transients also showed rhythmic activity in the PC [45], implying the possibility of integration of an NMDA-type Ca 2 + ionophore in the membrane of PC neurons. NMDA-like receptors were sequenced and cloned from two non-stylommatophoran, heterobranch mollusks: the sea hare, Aplysia californica (AcGluR1, accession number: AAO62106) and the pond snail, Lymnaea stagnalis (LsGluR1, accession number: AY571900, [46]). Predicted transcripts of these putative NMDA-receptor sequences showed similarities (glycine and Glu binding sites, postsynaptic density protein [PDZ]-domain) to the mammalian GluN1 subunit.…”