Hello to everyone, 

I am trying to record NMDAR currents from beads injected auditory principal neurons in voltage clamp configuration. I use the following cutting solution (in mM):2.5 KCl, 1.25 NaH2PO4, 0.5 CaCl2, 7 MgCl2, 25 NaHCO3, 7 Glucose, 205 Sucrose, 1.3 Ascorbic acid, 3 Sodium pyruvate and pH=7.4, Osm=300. After i remove the brain into the continuously oxygenized cutting solution, slices of 300μm are been made with a vibratome LEICAVT1200S. I incubate the slices for 30min in 34oC in a chamber with aCSF of (in mM): 125NaCl, 2.5 KCl, 1MgCl2, 2 CaCl2, 26.25 NaHCO3, 10 Glucose,  1.3 Ascorbic acid, 3 Sodium Pyruvate and pH=7.4, Osm=300. After that I leave the slices at room temperature for another 30 min. Then I try to stimulate in two different locations of the cortex and to record the beads injected principal cells in 35oC.

I add DNQX and gabazine on the slices. I patch with pipettes of Re=2.5-4 MΩ and an internal solution of (in mM):126Cs(CH3O3S), 4 KCl, 10 HEPES, 4 Na2ATP, 0.3 tris-GTP, 4 MgCl26H2O, 10 Tris-phospocreatine, 1 CsEGTA, 1 QX-314 and 3 Sodium ascorbate and pH=7.4, Osm=300. 

I am able to patch, seal (1GΩ) and break in easily. I get good AMPA responses (over 200pA) at -70mV. After that I turn into +40mV, I am still getting good responses (over 200pA) for the next 10 min. Then for some reason, Rs or Rinput changes (increase or decrease) and I cannot keep doing my experiments. 

I must mention that I am able to record AMPAR currents for more than 30 min at -70mV in these beads-injected neurons. Also, in normal neurons (without beads) I can get good and steady AMPA or NMDA responses for a long period of time. 

Do you have any suggestions for improving the quality of my cells in these beads injected mice?