Thus, we verified a healthy resting membrane potential and then recorded the current responses to a series of hyperpolarizing and depolarizing actions, including intended for analysis only cells with firing patterns characteristic of excitatory pyramidal neurons. shape, dendritic filtering index, mEPSC slope == 1 == Synapses undergo activity-dependent strengthening or weakening, via processes known as synaptic plasticity. Associative synaptic plasticity produces patterns of synaptic strength (1, 2) which are thought to underlie learning and memory (3). A complementary adaptation, homeostatic synaptic plasticity (HSP), constrains synapses via negative feedback (4, 5) to stabilize Choline bitartrate neural networks (6). How can HSP occur without destroying synaptically encoded information (7, 8)? The synaptic scaling model (4) proposes that all synapses are homeostatically adjusted by the same proportion, thus preserving relative weights. Many studies support this theory, while others are inconsistent with the model (9). The question remains: does HSP scale globally along dendrites? It has been difficult to resolve this question due to technical limitations. Visualizing synaptic proteins permits analysis of the spatial distribution of synaptic change, but is an indirect read-out of synapse function. Conversely, patch-clamp recording AMPAR-mediated miniature excitatory postsynaptic currents (mEPSCs) is a direct readout of synaptic function, but the dendritic origin of each somatically Choline bitartrate recorded current is unknown. Here, we devised a novel electrophysiological parameter to determine the location of synaptic changes during homeostatic synaptic plasticity. == 2 . EXPERIMENTAL PROCEDURES == == Ethical approval == All animals were treated in accordance with the Georgetown University and Johns Hopkins University Choline bitartrate Institutional Animal Care and Use Committee guidelines. == Primary cultures and drug treatment == Hippocampal (10, 11) and cortical cultures (12) were prepared as described. Briefly, timed-pregnant Sprague Dawley rats or C57BL/6 mice were euthanized with CO2before cervical dislocation. Embryonic day 1819 Rabbit Polyclonal to MRPL20 rat or mouse embryos (both sexes) were decapitated into ice cold Hanks buffered saline solution (Gibco). Hippocampi were dissected, trypsinized, and dissociated intended for plating (75, 000 cells/well, 12-well tissue culture plates) on coverslips previously coated with poly-D-lysine (30 g/ml) and laminin (2 g/ml). Cortices were dissected, trypsinized, and dissociated for plating (250, 000 cells/well, 12-well tissue culture plates) on coverslips previously coated with poly-D-lysine (30 g/ml). Dissociated hippocampal neurons were grown in Neurobasal medium (Invitrogen) supplemented with SM1 (Stem Cell Technologies), 10U/mL penicillin/streptomycin, 0. 5 mM glutamine and 25 M glutamate. Neurons were fed once weekly with media lacking glutamate. Dissociated cortical neurons were grown in Neurobasal medium (Invitrogen) supplemented with B-27 (Invitrogen), 50U/mL penicillin/streptomycin, 2 mM Glutamax, and 1% horse serum. Activity was altered via drug application at > 21 DIV in hippocampal neurons and > DIV 11 in cortical neurons. TTX (Sigma), stock solution 1 mM in H2O, was diluted in Neurobasal to 1 M final concentration. == Antibodies and immunolabeling == Hippocampal or cortical neurons were fixed as described (11) in 1% paraformaldehyde/4% sucrose/PBS intended for 7 min at RT and methanol at 20C for 7 min. Neurons were permeabilized with 0. 01% Triton X-100 in PBS intended for 30 min at RT and then immunostained with antibodies in GDB buffer (0. 1% gelatin, 0. 3% Triton X-100, 16 mM sodium phosphate pH 7. 4, 450 mM NaCl) at the following concentrations: rabbit GluA1 N-terminal antibody (EMD Millipore Cat# PC246-100UG RRID: AB_564636, 1: 100); mouse GluA2 N-terminal antibody (Millipore); mouse monoclonal PSD-95 K28/43 (NeuroMab Cat# 75-028 RRID: AB_2307331, 1: 200-400), or rabbit polyclonal PSD-95 D27E11 (Cell Signaling Technology Cat# 3450S RRID: AB_2292883, 1: 200). Intended for surface staining (11, 13), neurons were incubated intended for 10 min at 37C with N-terminal specific anti-GluA1 antibody diluted in conditioned Neurobasal press. Neurons were then fixed, washed and treated with saturating concentrations of fluorescence-tagged secondary antibody all under non-permeabilizing conditions. Cells were then permeabilized and stained for other proteins as needed. == Quantification of immunostaining == Images were acquired using an Axiovert 200M (Zeiss) for conventional epifluorescence and analyzed using MetaMorph software (Molecular Devices). The 3 strongest dendrites of each neuron were traced and divided into 20 m segments, starting from the soma. Puncta were defined by thresholding images to exclude staining within the dendritic shaft. Integrated intensity was measured for each 20 m segment and averaged per neuron; neuronal means were then averaged to obtain population means. == Electrophysiology == DIV 1112 cortical neurons and DIV 2127 hippocampal neurons were incubated intended for 24 hr in normal growth media in the absence or presence of TTX (1 M). Intended for recording, neurons were transferred into room temperature (2225C) extracellular solution containing (in mM, all from Fisher Scientific): 145 NaCl, 2 . 5 KCl, 2 MgCl2, 1 CaCl2, 5 HEPES, 5 glucose, and 25 sucrose (330 mOsm, pH 7. 4). Whole-cell patch-clamp recordings were made with 36 M (Narishige) borosilicate pipettes containing (in mM, all from Fisher): 145 KGluconate, 5 EGTA, 5 MgCl2, 10 HEPES, 5 NaATP,.