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Rate of diffusion in brain

Stephan Anagnostaras stephan at psych.ucla.edu
Tue Dec 10 00:59:34 EST 1996

> On 4 Dec 1996, William Barnes wrote:
> > Hello,
> >       I have been infusing solid drugs into the brain and have been having a
> > hard time controlling the rate of diffusion of the drug through brain
> > tissue.  Does anyone have any comments to offer in this regard?  Thanks.
> >                       William Barnes

I'm not sure what you mean by contorlling the rate of diffusion. Do you mean
that you want to know where it diffused to? There are several procedures
for doing this. Some are simple (e.g., after you're done, infuse
black ink using the same parameters; or infuse NMDA and see where
there is a lesion) while others are more complex (use radiolabelled
ligand, and then do autoradiographs).  The latter is necessary if you
are talking about an implant of some sort (or minipump), but the earlier
work fine if you are just infusing down a cannula for a few minutes
(also the radiographic estimate is just as flawed, if not more,
since it depends on the amount of time you leave it on the film how far
it appears to diffuse).  Now there are some good review papers on infusion
parameters, one of which is with lidocaine, but I can't remember the
reference (but it's a damn good one).  

Probably the best method, but the most difficult, is to do some pilot
electrophysiology work. If you know the physiological effect of the
drug infused, you can place recording electrodes at various distances
from your infusion site and do electrophysiological recording. This
can be nice, say, if you are working in the BL amygdala, and say you infuse
lidocaine, you can record in the central nucleus (right next to it) and show
your infusion parameters don't do anything to central but mess up
BL physiology.  Nice, but a pain in the ass.

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