I think both are used mainly for blocking GABAA receptors. Since gabazine is more selelctive for GABAA receptors, is it better to use for studying EPSC? Is it enough to block IPSC by only blocking GABAA receptors? Thanks.
Hello,
Although they both block the GABAa receptor, they have different pharmacology. Picrotoxin is a non-competitive blocker while gabazine is an allosteric inhibitor.
Addressing the "is it enough to block GABAA", that totally depends on the brain area you are in. In the brainstem, there is often a significant glycinergic component, so 1 µM strychnine is necessary. You can determine this very simply, by applying NBQX and CPP to block your EPSC. If there is anything left over when you stimulate, then gabazine wasn't sufficient. That is probably a worthwhile thing to verify in a new prep. Good luck!
-Matthew
SR95531 (for antagonizing GABA-A) + CGP55845 (for antagonizing GABA-B) - 1 micromolar each worked well for 400 micrometer thick hippocampal slices. Complete blockade of IPSCs happened approximately 4-5 min (time for exchange of regular bath solution with the one containing the antagonists) after starting the bath solution with the antagonists. Prolonged bathing in this solution leads to hyperexcitability and action potentials at regular holding levels.
I guess you can always use GABA blockers to record IPSCs but in practice, I don't think it is required. From my experience with L2/3 and L5 somatosensory cortex, we (and others) have published recorded IPSCs (VC mode @ -70 mV Vholding) without the need for added GABA blockers. Now, If you intend to record EPSPs in Current-Clamp mode, then adding GABA blockers is advisable (you can avoid some shunting).
Hello Lingdi!
Of these two drugs, gabazine is more convenient to use, as it is water soluble and requires a smaller concentration to block the evoked IPSC (in rat cortical slices we use 5-10 uM of gabazine or 50-100 uM of PTX). However, gabazine is more expensive than PTX.
Bicuculline methiodide also blocks the GABAaR-mediated IPSC (it is water soluble and is cheaper than gabazine). Note that it affects the SK-channels.
If the IPSC in your preparation is mediated by both GABAaRs and GABAbRs you should also apply CGP-55845 or use the pipette solution with cesium salts.
Good luck with your experiments!
We also prefer gabazine despite the fact that it is more expensive. Best, Jakob
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