Hi All,
I have been running into a technical issue when I try to cannulate the prelimbic cortex of mice. I find that I am about .1-.2 off from being even (see the attached pictures). I am using bilateral cannula with .8 mm between the tubing. I found coordinates (AP: 1.78, ML: ± 0.4, DV: -1.5) that get me to the right place A/P-wise but my problem is M/L. I am careful with how I place the mouse in the stereotaxic frame and I check bregma and lambda prior to drilling my screw and cannula holes to make sure the brain is level. I suspect I am setting my reference (i.e. bregma) incorrectly but I don't see how. Has anyone experienced this and if so, how did it you fix it?
I have a few questions. Is your correct placement always on the same side or does it vary? I assume you are using one side of the bilateral cannula to make your measurements? IS it 0.8mm between the center point of each guide cannula or 0.8mm from the start of one to the start of the other?
What are you using to hold you r bilateral cannula during placement? It appears to me that your cannula is not level when it is placed. One way to check this would be to make sure the Dorsal/Ventral(DV) coordinates are exactly the same on both sides when the cannula touches the skull before drilling holes. If they are off of level by even tenths of a millimeter it can make a HUGE difference in placement. I would also caution you to wait a significant amount of time after dental glue placement, before removing said cannula from the holder as any slight movements before the glue is completely set will cause change in placement.
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