I am interested in scaling my coordinates for stereotaxic injections by measuring the distance from bregma to lamda in each of my mice and then scaling this to the "typical" value used in mouse brain atlases. This scaling factor should reduce some error that results from differences in mouse brain sizes. I would be most interested in knowing the bregma-lamda distance in the "average" or "typical" mouse used to map brain coordinates in the Paxinos Mouse Brain Atlas. Does anyone know this value? I see other people have used this method successfully in rats, where the Bregma-Lamda distance is 9mm.
Is that information not in the mouse brain atlas? I know the scaling works reasonably in rats. However, if you are trying to hit a very small deep structure I would take a different approach. (1) Make a best estimate of the coordinates based on the atlas. (2) Take animals of the same age within a very narrow weight range. (3) Do a few injections with ink or just make a track with a needle to mark where you end up. (4) Perfuse and analyze the brains. If you are consistently too superficial, lateral or anterior, adjust your coordinates and repeat the cycle untill you get the correct ones.
Finally, mouse brains are so small in comparison to the inherent errors in our hands, eyes, stereotactic equipment etc. that it is to be expected to miss a small structure more often than you would in rats. Just doing more injections and keeping the ones that worked is the solution. This only becomes a problem if the injection is just a small step in a long line of experiments, e.g. extended behavioral training, electrophysiological recordings etc., as the investment in animals that you will not be able to use once you post-mortem check if you injection was successful.
good luck
Nils
From the atlas: "The mean (±SD) position of bregma was 3.8 (±0.25) mm rostral and 5.8 (±OA8) mm dorsal to the interaural line (IA). Lambda was located 0.41 (±0.26) mm caudal and 5.8mm dorsal to the interaural line."
So, the distance between lambda and bregma is 4.21 mm, but with quite a bit of variation.
Thanks Nils, I was getting my definition of Lambda confused but the numbers you shared should be enough to go on.
I see some references where they define lambda as being the midpoint of the interaural line and "true lamda" being the intersection of the sagittal and occipital suture (rostral to the interaural line). Do you know which definition of lambda Paxinos is referring to? It's not obvious from the the arrow drawn in the atlas.
Other sources (below) show the interaural line connecting the occipital sutures but I suppose this doesn't always line up with the ears, which is how Paxinos seems to have measured interaural.
Chapter Intraparenchymal Stereotaxic Delivery of rAAV and Special Co...
Chapter Stereotaxic Neurosurgery in Laboratory Rodent
(see fig 5.25)
Hi Steve,
now I am learning form you. I did not know the about 'true lambda'. I was taught that was the 'wrong lambda'. As far as I know Paxinos uses the 'lambda' as drawn in fig.1 of your reference. You estimate the where the saggital midline would cross the lamboid suture if it would not curve.
The interaural line I have never used, nor do I know anyone who uses it. In mice this would probably be harder to use than in rats, as most people use jaw/cheek bars instead of ear bars in mice.
cheers
Nils
I'll go with lambda as being "where the saggital midline would cross the lamboid suture if it would not curve" and not "true lambda", i.e., the wrong lambda!
I attached images to my previous comment to make it clearer to others what we've discussed.
Cheers
Interesting discussion that I just found!
When I was performing stereotaxic surgeries on my rats either for cannulation or for finding the exact coordination to insert my recording and stimulation electrodes, I came across the intricate difference of lambda and so called true lambda.
As I had been told that no significant difference would it make to choose either, I was dubious enough to do my own trial and error. I removed the brains of those that I performed surgery with experimental lambda, dissected 50 um coronal sections through the region of cannulae and electrode insertion, and compared them with those that I did surgery with true lambda under a microscope. Even though the difference was insignificant for large areas like hippocampal formation, it was remarkable for small nuclei like the VTA or NAc (core).
Unsurprisingly, the anatomical distance of lambda and true lambda that is something around 0.7 mm-1 mm on the skull surface (typically depends on age and weight of rats), is considered significant in terms of brain size and scale ratio of rat brain.
I think that considering lambda or true lambda is the matter of the ratio or scale of the target region size to the whole brain. But to be meticulous the middle point of the interaural line or the imaginary point on the midline of the lamdoid suture right below the sagital suture (that is the midpoint of the base of the imaginary equilateral triangle of three touching skull bones) is a safe and sure point to estimate the distance to bregma and lay your calculations for the rest of the procedure.