No description available.

No description available.

No description available.

Recent literature has shown that AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors lacking the GluR2 subunit (thus calcium permeable) are widely expressed in the CNS, especially in interneurons and glia, where they contribute to synaptic transmission and plasticity. Studies have also indicated that calcium permeable AMPARs (CP-AMPARs) are expressed and participate in synaptic regulation in principal neurons, including hippocampal pyramidal neurons. Furthermore, CP-AMPARs and their resultant calcium influx are implicated in various pathophysiological conditions such as ischemia and seizures. However, the synaptic events activated by calcium influx through CP-AMPARs remain unknown. I took advantage of genetically altered mice without (GluR2-/-) or with reduced GluR2 (GluR2+/-), thus allowing the expression and detailed analysis of synaptic CP-AMPARs in hippocampal pyramidal neurons. Utilizing electrophysiological techniques, I demonstrated that these receptors were capable of inducing numerous forms of long-term potentiation (referred to as CP-AMPAR-dependent LTP) through a number of different induction protocols, including high-frequency stimulation (HFS) and theta-burst stimulation (TBS). This included a previously undemonstrated form of protein-synthesis dependent late-LTP (L-LTP) at CA1 synapses that is NMDA-receptor (NMDAR) independent. This form of plasticity was completely blocked by the selective CP-AMPAR inhibitor IEM-1460. Surprisingly, calcium/calmodulin-dependent kinase II (CaMKII), the key protein kinase that is indispensable for NMDAR-dependent LTP at CA1 synapses appeared to be not required for the induction of CP-AMPAR-dependent LTP due to the lack of effect of two separate pharmacological inhibitors (KN-62 and staurosporine) on this form of potentiation. Both KN-62 and staurosporine strongly inhibited NMDAR dependent LTP in control studies. In contrast, inhibitors for the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) cascade (PD98059 and U0126) significantly attenuated this CP-AMPAR-dependent LTP. Additional studies with knockout mice revealed that the ERK/MAPK signalling cascade is likely acting through p-21 activated kinase 1 (or PAK1, a Rho-GTPase associated kinase) dependent mechanisms. These results suggest that distinct synaptic signalling underlies GluR2-lacking CP-AMPAR-dependent LTP, and reinforces the recent notions that CP-AMPARs are important facilitators of synaptic plasticity in the brain.

Recent literature has shown that AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptors lacking the GluR2 subunit (thus calcium permeable) are widely expressed in the CNS, especially in interneurons and glia, where they contribute to synaptic transmission and plasticity. Studies have also indicated that calcium permeable AMPARs (CP-AMPARs) are expressed and participate in synaptic regulation in principal neurons, including hippocampal pyramidal neurons. Furthermore, CP-AMPARs and their resultant calcium influx are implicated in various pathophysiological conditions such as ischemia and seizures. However, the synaptic events activated by calcium influx through CP-AMPARs remain unknown. I took advantage of genetically altered mice without (GluR2-/-) or with reduced GluR2 (GluR2+/-), thus allowing the expression and detailed analysis of synaptic CP-AMPARs in hippocampal pyramidal neurons. Utilizing electrophysiological techniques, I demonstrated that these receptors were capable of inducing numerous forms of long-term potentiation (referred to as CP-AMPAR-dependent LTP) through a number of different induction protocols, including high-frequency stimulation (HFS) and theta-burst stimulation (TBS). This included a previously undemonstrated form of protein-synthesis dependent late-LTP (L-LTP) at CA1 synapses that is NMDA-receptor (NMDAR) independent. This form of plasticity was completely blocked by the selective CP-AMPAR inhibitor IEM-1460. Surprisingly, calcium/calmodulin-dependent kinase II (CaMKII), the key protein kinase that is indispensable for NMDAR-dependent LTP at CA1 synapses appeared to be not required for the induction of CP-AMPAR-dependent LTP due to the lack of effect of two separate pharmacological inhibitors (KN-62 and staurosporine) on this form of potentiation. Both KN-62 and staurosporine strongly inhibited NMDAR dependent LTP in control studies. In contrast, inhibitors for the extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK) cascade (PD98059 and U0126) significantly attenuated this CP-AMPAR-dependent LTP. Additional studies with knockout mice revealed that the ERK/MAPK signalling cascade is likely acting through p-21 activated kinase 1 (or PAK1, a Rho-GTPase associated kinase) dependent mechanisms. These results suggest that distinct synaptic signalling underlies GluR2-lacking CP-AMPAR-dependent LTP, and reinforces the recent notions that CP-AMPARs are important facilitators of synaptic plasticity in the brain.

Lors des processus développementaux d'élongation axonale et de synaptogenèse, les protéines d'adhésion telles les cadhérines ou les Ig-CAM jouent des rôles fondamentaux en permettant la formation de contacts entre neurones. Pour étudier la dynamique de ces contacts et leurs rôles dans ces processus, nous avons mis en œuvre des techniques d'imagerie sur des neurones primaires d'hippocampe (clivage thrombine, FRAP, pinces optiques, quantum-dots), ceux-ci étant associés à un système semi-artificiel de microsphères recouvertes de protéines d'adhésion purifiées (N-cadhérine et L1). En utilisant une construction L1 portant une étiquette GFP extracellulaire clivable à la thrombine, j'ai pu précisé l'implication des processus de diffusion membranaire et d'exo- endocytose dans la dynamique des contacts L1-dépendants et obtenir des données quantitatives relatives à l'interaction homophile L1. J'ai également contribué à caractériser la liaison extracellulaire entre N-cadhérine et GluR2, sous-unité des récepteurs AMPA, et l'influence de l'expression de la N-cadhérine sur la mobilité de GluR2. L'interaction entre ces deux protéines pourrait être impliquée dans la formation et/ou la maturation des synapses.