Dear Wei,

Some may consider that the presence of neurotransmitters in the extracellular environment of the neuron obscures the intrinsic excitability.

APV (https://www.tocris.com/search?keywords=APV), CNQX (https://www.tocris.com/search?keywords=CNQX) and bicuculline (https://www.tocris.com/search?keywords=bicuculline) are ionotropic receptor blockers. For instance, if you investigate the firing frequency during constant current injection, you may recruit network activity or autaptic activity that affects the excitability of the neuron during the constant current injection. To eliminate these effects, you can include these blockers (and others).

In some cases it may be inconvenient to include these blocking agents as the researcher may be interested in more than the intrinsic excitability. That may be one argument to decide against these blockers.

On the other hand, if you want to investigate the intrinsic excitability as entirely separated from the network, why would you only block ionotropic receptors? You may need to consider metabotropic receptors and gap junctions as well.

It is upto the judgment of the researcher what to do. And depending on the question you ask and/or the conclusions you want to draw, you will decide what is best suited to your situation.

And, if you clearly write in your methods section how you performed your experiments, everyone can judge for themselves how well the experiment supports the conclusions that are made in the publication.

I hope this helps a bit.

Martijn

It will depend a lot on the preparation. If there is a lot of spontaneous activity in the preparation then the EPSPs/IPSPs will make it harder to measure the resulting traces. The spontaneous activity might also already cause the neurons you are recording from to spike, which will obviously make it harder to separate out intrinsic from synaptically-driven excitability. Possibly if synaptic transmission is not blocked you will even change the amount of synaptic input during your current steps (when your cell spikes it will spike or silence other neurons that connect back). So if the preparation is pretty silent then no need for the inhibitors but if you have a powerful network then you have to add inhibitors.

Hello！

Whether adding these synaptic blockers depends on your goal of the experiments. Many papers performed both experiments (with or without blockers) to see the intrinsic excitability with or without the effect of synaptic transmission. See the figure 1 of following article:

Jin X, Chen Q, Song Y, Zheng J, Xiao K, Shao S, Fu Z, Yi M, Yang Y, Huang Z. Dopamine D2 receptors regulate the action potential threshold by modulating T-type calcium channels in stellate cells of the medial entorhinal cortex. J Physiol. 2019 Jul;597(13):3363-3387.

Good luck!