Teleost fish are among the most ancient vertebrates possessing an adaptive immune system with B and T lymphocytes that produce memory responses to pathogens. Most bony fish, however, have only 2 types of B lymphocytes, in contrast to the 4 types available to mammals. To better understand the evolution of adaptive immunity, we generated transgenic zebrafish in which the major immunoglobulin M (IgM(+)) B-cell subset expresses green fluorescence protein (GFP) (IgM1:eGFP). We discovered that the earliest IgM(+) B cells appear between the dorsal aorta and posterior cardinal vein and also in the kidney around 20 days postfertilization. We also examined B-cell ontogeny in adult IgM1:eGFP;rag2:DsRed animals, where we defined pro-B, pre-B, and immature/mature B cells in the adult kidney. Sites of B-cell development that shift between the embryo and adult have previously been described in birds and mammals. Our results suggest that this developmental shift occurs in all jawed vertebrates. Finally, we used IgM1:eGFP and cd45DsRed;blimp1:eGFP zebrafish to characterize plasma B cells and investigate B-cell function. The IgM1:eGFP reporter fish are the first nonmammalian B-cell reporter animals to be described. They will be important for further investigation of immune cell evolution and development and host-pathogen interactions in zebrafish

Amyloid-β (Aβ) is a prime suspect for causing cognitive deficits during the early phases of Alzheimer’s disease (AD). Experiments in AD mouse models have shown that soluble oligomeric clusters of Aβ degrade synapses and impair memory formation. We show that all Aβ-driven effects measured in these mice depend on AMPA receptor (AMPAR) subunit GluA3. Hippocampal neurons that lack GluA3 were resistant against Aβ-mediated synaptic depression and spine loss. In addition, Aβ oligomers blocked long-term synaptic potentiation only in neurons that expressed GluA3. Furthermore, although Aβ-overproducing mice showed significant memory impairment, memories in GluA3-deficient congenics remained unaffected. These experiments indicate that the presence of GluA3-containing AMPARs is critical for Aβ-mediated synaptic and cognitive deficits.

Which neural circuits undergo synaptic changes when an animal learns? Although it is widely accepted that changes in synaptic strength underlie many forms of learning and memory, it remains challenging to connect changes in synaptic strength at specific neural pathways to specific behaviors and memories. Here we introduce SYNPLA (synaptic proximity ligation assay), a synapse-specific, high-throughput, and potentially brain-wide method capable of detecting circuit-specific learning-induced synaptic plasticity.