When you cut a slice, you sever many axons. So when you use your stimulating electrode (or a light in optogenetics) to evoke currents in the cell you've patched, can you evoke a response if the afferents are severed proximal to your stimulation?
What I'm hung up about really is, if you express channelrhodopsin in some nucleus, then cut a brain slice which does NOT include the cell bodies of that structure but does have the afferents, will the light evoke a response from those severed axons?
Dear Casey,
Usually distal end of cut axons live for sometime and therefore respond to electrical stimulation and release neurotransmitter, although their capacity may be reduced.
Best wishes,
Refik
Most definitely. For example, we and others express ChR2 (or derivative like chronic) in prefrontal cortex and after letting the neurons express for 4-6 weeks, make slices and can optically evoke TTX sensitive monosynaptic EPSCs in brainstem targets (e.g. dorsal raphe). These EPSCs can also be reinstated following TTX blockage by adding 4-AP which, by blocking K channels in the cut axons, allows the Opto depolarization to be large enough to open voltage-gated Ca2_ channels and drive synaptic release. Thus, the cut axons as sufficiently hyperpolarized to sustain Na-channel dependent action potentials.
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