fitIV: Current-Voltage data analysis software DESCRIPTION: A model independent function that fits... more fitIV: Current-Voltage data analysis software DESCRIPTION: A model independent function that fits nth degree polynomials to current-voltage (I-V) data using linear least-squares methods. The residuals of the fits are evaluated using F ratios and the first derivative of the user selected fit is used to determine the slope conductance as a function of the holding potential. The output of the script includes the reversal potential (Erev), and a rectification index (RI) determined from the ratio of slope conductances at user-defined voltages +/- Erev. Chord conductance (G) is calculated at each holding potential using the fitted current values in the equation G = I /(V - Erev) SYSTEM REQUIREMENTS: The script was written and tested on an Apple Mac (Processor: 2.4 GHz Intel Core 2 Duo; Memory: 4 GB 1067 MHz DDR3) running OS X (v10.5.8), GNU Octave (v3.2.2.) and GNU Plot (v4.2). Note that the syntax in this particular script is only suitable for Octave (and not for Matlab). This software a...
Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellu... more Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellular correlate for learning and memory. Early LTP (less than 1 h) had initially been explained either by presynaptic increases in glutamate release or by direct modification of postsynaptic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor function. Compelling models have more recently proposed that synaptic potentiation can occur by the recruitment of additional postsynaptic AMPA receptors (AMPARs), sourced either from an intracellular reserve pool by exocytosis or from nearby extra-synaptic receptors pre-existing on the neuronal surface. However, the exact mechanism through which synapses can rapidly recruit new AMPARs during early LTP remains unknown. In particular, direct evidence for a pivotal role of AMPAR surface diffusion as a trafficking mechanism in synaptic plasticity is still lacking. Here, using AMPAR immobilization approaches, we show that interfering with AMPAR surface diffusion markedly impairs synaptic potentiation of Schaffer collaterals and commissural inputs to the CA1 area of the mouse hippocampus in cultured slices, acute slices and in vivo. Our data also identify distinct contributions of various AMPAR trafficking routes to the temporal profile of synaptic potentiation. In addition, AMPAR immobilization in vivo in the dorsal hippocampus inhibited fear conditioning, indicating that AMPAR diffusion is important for the early phase of contextual learning. Therefore, our results provide a direct demonstration that the recruitment of new receptors to synapses by surface diffusion is a critical mechanism for the expression of LTP and hippocampal learning. Since AMPAR surface diffusion is dictated by weak Brownian forces that are readily perturbed by protein-protein interactions, we anticipate that this fundamental trafficking mechanism will be a key target for modulating synaptic potentiation and learning.
We investigated whether microRNAs could regulate AMPA receptor expression during activity blockad... more We investigated whether microRNAs could regulate AMPA receptor expression during activity blockade. miR-92a strongly repressed the translation of GluA1 receptors by binding the 3' untranslated region of rat GluA1 (also known as Gria1) mRNA and was downregulated in rat hippocampal neurons after treatment with tetrodotoxin and AP5. Deleting the seed region in GluA1 or overexpressing miR-92a blocked homeostatic scaling, indicating that miR-92a regulates the translation and synaptic incorporation of new GluA1-containing AMPA receptors.
Short-term plasticity of AMPAR currents during high-frequency stimulation depends not only on pre... more Short-term plasticity of AMPAR currents during high-frequency stimulation depends not only on presynaptic transmitter release and postsynaptic AMPAR recovery from desensitization, but also on fast AMPAR diffusion. How AMPAR diffusion within the synapse regulates synaptic transmission on the millisecond scale remains mysterious. Using single-molecule tracking, we found that, upon glutamate binding, synaptic AMPAR diffuse faster. Using AMPAR stabilized in different conformational states by point mutations and pharmacology, we show that desensitized receptors bind less stargazin and are less stabilized at the synapse than receptors in opened or closed-resting states. AMPAR mobility-mediated regulation of short-term plasticity is abrogated when the glutamate-dependent loss in AMPAR-stargazin interaction is prevented. We propose that transition from the activated to the desensitized state leads to partial loss in AMPAR-stargazin interaction that increases AMPAR mobility and allows faster recovery from desensitization-mediated synaptic depression, without affecting the overall nano-organization of AMPAR in synapses.
PSD-95 is a prominent organizer of the postsynaptic density (PSD) that can present a filamentous ... more PSD-95 is a prominent organizer of the postsynaptic density (PSD) that can present a filamentous orientation perpendicular to the plasma membrane. Interactions between PSD-95 and transmembrane proteins might be particularly sensitive to this orientation, as "long" cytoplasmic tails might be required to reach deeper PSD-95 domains. Extension/retraction of transmembrane protein C-tails offer a new way of regulating binding to PSD-95. Using stargazin as a model, we found that enhancing the apparent length of stargazin C-tail through phosphorylation or by an artificial linker was sufficient to potentiate binding to PSD-95, AMPAR anchoring, and synaptic transmission. A linear extension of stargazin C-tail facilitates binding to PSD-95 by preferentially engaging interaction with the farthest located PDZ domains regarding to the plasma membrane, which present a greater affinity for the stargazin PDZ-domain-binding motif. Our study reveals that the concerted orientation of the stargazin C-tail and PSD-95 is a major determinant of synaptic strength.
We investigated whether microRNAs could regulate AMPA receptor expression during activity blockad... more We investigated whether microRNAs could regulate AMPA receptor expression during activity blockade. miR-92a strongly repressed the translation of GluA1 receptors by binding the 3' untranslated region of rat GluA1 (also known as Gria1) mRNA and was downregulated in rat hippocampal neurons after treatment with tetrodotoxin and AP5. Deleting the seed region in GluA1 or overexpressing miR-92a blocked homeostatic scaling, indicating that miR-92a regulates the translation and synaptic incorporation of new GluA1-containing AMPA receptors.
fitIV: Current-Voltage data analysis software DESCRIPTION: A model independent function that fits... more fitIV: Current-Voltage data analysis software DESCRIPTION: A model independent function that fits nth degree polynomials to current-voltage (I-V) data using linear least-squares methods. The residuals of the fits are evaluated using F ratios and the first derivative of the user selected fit is used to determine the slope conductance as a function of the holding potential. The output of the script includes the reversal potential (Erev), and a rectification index (RI) determined from the ratio of slope conductances at user-defined voltages +/- Erev. Chord conductance (G) is calculated at each holding potential using the fitted current values in the equation G = I /(V - Erev) SYSTEM REQUIREMENTS: The script was written and tested on an Apple Mac (Processor: 2.4 GHz Intel Core 2 Duo; Memory: 4 GB 1067 MHz DDR3) running OS X (v10.5.8), GNU Octave (v3.2.2.) and GNU Plot (v4.2). Note that the syntax in this particular script is only suitable for Octave (and not for Matlab). This software a...
Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellu... more Long-term potentiation (LTP) of excitatory synaptic transmission has long been considered a cellular correlate for learning and memory. Early LTP (less than 1 h) had initially been explained either by presynaptic increases in glutamate release or by direct modification of postsynaptic AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor function. Compelling models have more recently proposed that synaptic potentiation can occur by the recruitment of additional postsynaptic AMPA receptors (AMPARs), sourced either from an intracellular reserve pool by exocytosis or from nearby extra-synaptic receptors pre-existing on the neuronal surface. However, the exact mechanism through which synapses can rapidly recruit new AMPARs during early LTP remains unknown. In particular, direct evidence for a pivotal role of AMPAR surface diffusion as a trafficking mechanism in synaptic plasticity is still lacking. Here, using AMPAR immobilization approaches, we show that interfering with AMPAR surface diffusion markedly impairs synaptic potentiation of Schaffer collaterals and commissural inputs to the CA1 area of the mouse hippocampus in cultured slices, acute slices and in vivo. Our data also identify distinct contributions of various AMPAR trafficking routes to the temporal profile of synaptic potentiation. In addition, AMPAR immobilization in vivo in the dorsal hippocampus inhibited fear conditioning, indicating that AMPAR diffusion is important for the early phase of contextual learning. Therefore, our results provide a direct demonstration that the recruitment of new receptors to synapses by surface diffusion is a critical mechanism for the expression of LTP and hippocampal learning. Since AMPAR surface diffusion is dictated by weak Brownian forces that are readily perturbed by protein-protein interactions, we anticipate that this fundamental trafficking mechanism will be a key target for modulating synaptic potentiation and learning.
We investigated whether microRNAs could regulate AMPA receptor expression during activity blockad... more We investigated whether microRNAs could regulate AMPA receptor expression during activity blockade. miR-92a strongly repressed the translation of GluA1 receptors by binding the 3' untranslated region of rat GluA1 (also known as Gria1) mRNA and was downregulated in rat hippocampal neurons after treatment with tetrodotoxin and AP5. Deleting the seed region in GluA1 or overexpressing miR-92a blocked homeostatic scaling, indicating that miR-92a regulates the translation and synaptic incorporation of new GluA1-containing AMPA receptors.
Short-term plasticity of AMPAR currents during high-frequency stimulation depends not only on pre... more Short-term plasticity of AMPAR currents during high-frequency stimulation depends not only on presynaptic transmitter release and postsynaptic AMPAR recovery from desensitization, but also on fast AMPAR diffusion. How AMPAR diffusion within the synapse regulates synaptic transmission on the millisecond scale remains mysterious. Using single-molecule tracking, we found that, upon glutamate binding, synaptic AMPAR diffuse faster. Using AMPAR stabilized in different conformational states by point mutations and pharmacology, we show that desensitized receptors bind less stargazin and are less stabilized at the synapse than receptors in opened or closed-resting states. AMPAR mobility-mediated regulation of short-term plasticity is abrogated when the glutamate-dependent loss in AMPAR-stargazin interaction is prevented. We propose that transition from the activated to the desensitized state leads to partial loss in AMPAR-stargazin interaction that increases AMPAR mobility and allows faster recovery from desensitization-mediated synaptic depression, without affecting the overall nano-organization of AMPAR in synapses.
PSD-95 is a prominent organizer of the postsynaptic density (PSD) that can present a filamentous ... more PSD-95 is a prominent organizer of the postsynaptic density (PSD) that can present a filamentous orientation perpendicular to the plasma membrane. Interactions between PSD-95 and transmembrane proteins might be particularly sensitive to this orientation, as "long" cytoplasmic tails might be required to reach deeper PSD-95 domains. Extension/retraction of transmembrane protein C-tails offer a new way of regulating binding to PSD-95. Using stargazin as a model, we found that enhancing the apparent length of stargazin C-tail through phosphorylation or by an artificial linker was sufficient to potentiate binding to PSD-95, AMPAR anchoring, and synaptic transmission. A linear extension of stargazin C-tail facilitates binding to PSD-95 by preferentially engaging interaction with the farthest located PDZ domains regarding to the plasma membrane, which present a greater affinity for the stargazin PDZ-domain-binding motif. Our study reveals that the concerted orientation of the stargazin C-tail and PSD-95 is a major determinant of synaptic strength.
We investigated whether microRNAs could regulate AMPA receptor expression during activity blockad... more We investigated whether microRNAs could regulate AMPA receptor expression during activity blockade. miR-92a strongly repressed the translation of GluA1 receptors by binding the 3' untranslated region of rat GluA1 (also known as Gria1) mRNA and was downregulated in rat hippocampal neurons after treatment with tetrodotoxin and AP5. Deleting the seed region in GluA1 or overexpressing miR-92a blocked homeostatic scaling, indicating that miR-92a regulates the translation and synaptic incorporation of new GluA1-containing AMPA receptors.
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