I've been trying to acquire thalamocortical slices (in rats, described in Article Somatotopic organization of rat thalamocortical slices
) and then measure LFPs (stimulating in VB and recording in cortex). However, there seems to be something wrong:1. I place my recording and stimulating electrodes in the cortex, and then try to move the stim. electrode further and further away, "tracing" back the connections. But I can rarely get the stim. electrode even as far away as the striatum. The slices seem to be cut at the correct angle (visually, at least).
2. A second issue can be seen in the attached image: The cortex on the "side" and "top" of the brain often seems darker than that lower down, and this "darkness" often corresponds to difficulty in finding any response, even if both electrodes are within the cortex. I've tried to be very careful removing the brain to ensure I'm not squishing it, but nothing seems to help.
Any ideas what might be going on???
Did you try to increase the intensity of stimulation when you move further away ?
For the second point, your slices are maybe not "flat", what slicer are you using ? Also, maybe your microscope if not very well adjust, the field diaphragm could be incorrectly centered, you can play with it using the condenser focus knob.
Yanis Inglebert , thanks for your reply!
1. Yes, I do increase the stimulation as I move the stimulating electrode away.
2. It's an older slicer (Leica VT1000S) but I'm not sure that's the problem: The "darkness" occurs in roughly the same area, even if I slice from a different direction (i.e., glue down the brain so that the blade first contacts the lateral cortex instead of the superior cortex). Also, I've just recently noticed it appear (or at least get worse) as I'm recording from the slice. I'm also not sure whether it's caused by the microscope, for those reasons and also because the darkness seems somewhat correlated with being able to get responses in that region.
It seems like something is happening to my slice while it's in the recording chamber. It's not a contamination problem, because it doesn't affect the whole slice. I've got something to try, and we'll see if it improves things.... But I'm open to other suggestions!
Catherine Swytink-Binnema Ok thanks for the update. You should at least try to play with the condenser focus knob on the microscope.
Also, maybe do not use the first slices, wait 2 or 3 slices before recover them. Perhaps the first one are not flat enough.
Did you try to record in another region to see if it's working ? Like hippocampus between CA3-CA1.
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