ABSTRACT
NMDA receptor-dependent long-term potentiation (LTP) at hippocampal synapses has been considered a crucial component of the cellular basis for learning and memory. This form of LTP occurs in excitatory synapses in both the CA1 area and the dentate gyrus in the hippocampus. However, differential roles of LTP in these areas have not yet been identified. To address this issue, we enhanced the degree of LTP by expressing Ca2+-permeable AMPA receptors at either hippocampal CA1 or dentate gyrus synapses using Sindbis viral vectors (SINs) encoding both green fluorescent proteins and unedited GluR2 (GluR2Q) subunits, and examined their effects on rat spatial learning. The viral vectors were locally injected into the 8-week-old-rat brain in vivo bilaterally. The postsynaptic expression of Ca2+-permeable AMPA receptors enhanced the degree of LTP, and induced NMDA receptor-independent LTP in the presence of the NMDA receptor antagonist in SIN-infected regions in both CA1 and dentate gyrus in hippocampal slice preparations. However, the regional expression of Ca2+-permeable AMPA receptors caused opposite behavioural consequences on the Morris water maze task: rats with SIN-infected CA1 pyramidal cells showed shorter escape latency and better probe test performance, whereas those with SIN-infected dentate gyrus granule cells showed impaired performance. Thus, it was demonstrated that CA1 and dentate gyrus synapses play different functional roles in spatial learning despite their similar mechanism for LTP induction.
Subject(s)
Hippocampus/physiology , Learning/physiology , Long-Term Potentiation/physiology , Receptors, AMPA/metabolism , Synapses/metabolism , Animals , Blotting, Western , Calcium/metabolism , Dentate Gyrus/physiology , Electric Stimulation , Excitatory Postsynaptic Potentials , Genetic Vectors/administration & dosage , Green Fluorescent Proteins , Injections, Intraventricular , Luminescent Proteins , Maze Learning/physiology , Organ Culture Techniques , Patch-Clamp Techniques , Plasmids , Rats , Rats, Wistar , Sindbis Virus/geneticsABSTRACT
Synaptophysin is one of the most abundant proteins of the synaptic vesicle membrane. Here, we selected the cytoplasmic carboxyterminal region of synaptophysin to search for interacting proteins by using the yeast two-hybrid system. This identified gamma-adaptin, a component of the AP-1 adaptor complex, as a synaptophysin binding protein. An anti-synaptophysin antibody coimmunoprecipitated gamma-adaptin from brain extracts, and immunocytochemistry disclosed a partial colocalization of synaptophysin and gamma-adaptin in the perinuclear region of cultured hippocampal neurons. Our results are consistent with synaptophysin serving as a docking site for AP-1 during clathrin-dependent vesicle budding and/or kinesin-based transport reactions.
