Re: Paraform/fluoro

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If he's using DiI, he might want to look at J Neurosci Meth 88 (1999) 27-31.  This 
article suggests that adding a little EDTA to the paraformaldehyde sharpens the 
signal and reduces crosstalk. -Karen

Date:          Mon, 06 Mar 2000 15:46:35 -0800 (PST)
From:          "P. Emry" <>
Subject:       Re: Paraform/fluoro
To:            Karen Larison <>

Thanks, really.  I told him I reluctantly was going to show this to him.
It is good to know why.

On Fri, 3 Mar 2000, Karen Larison wrote:

> Trisha,
> What fluorescent retrograde tracers is he using?  If he's using DiI, I would 
> absolutely recommend sticking with aqueous-based fixatives, preferably 
> paraformaldehyde.  Don't use Prefer if it contains alcohols or organic solvents!  
> Other fluorescent tracers may be less picky, but I would still advise caution, 
> because most neurotracers work because they can't breach the membrane once they are 
> in the axon, so you don't want to use anything that can possibly perturb the 
> membrane.  That's why people use paraformaldehyde rather than formaldehyde in these 
> applications.  The methanol in formalin has the potential to perturb the membrane 
> you can get cross-talk between in axons in the nerve.  In otherwords, the dye 
> too easily from axon to axon instead of staying within the axon of interest.
> Paraformaldehyde is no different than formaldehyde once it's in solution.  However, 
> it will tend to polymerize over time, and precipitate.  Thus, you have to make it 
> fresh.  The purpose of the methanol in formalin is to keep the formaldehyde in 
> solution.  But it can and does mess up cell membranes.
> Personally, I wouldn't ask him to venture into places unknown with unknown 
> in the commercial fix.  It's just too likely to mess up his experiments.  And some 
> these tracer experiments are quite long and involved.  He should stick with the 
> paraformaldehyde.
> Karen Larison
> Institute of Neuroscience
> University of Oregon
> Date:          Thu, 02 Mar 2000 18:46:52 -0800 (PST)
> From:          "P. Emry" <>
> Subject:       Paraform/fluoro
> To:  
> Hi all,
> I am working with a post doc who wants to inject some "fluorescent
> retrograde neurotracers" in to pigs and use paraformaldehyde to fix the
> specimens. (Forgive me if I have muddled that up.)
> He is being very kind in considering my formaldehyde aversions and 
> said he would work after I go home.  He is reluctant to use my
> substitute Prefer thinking it may effect the fluorescent signal.
> Have any of you worked with Prefer or any other
> formaldehyde-paraformaldehyde substitute for that use?  (I have never used
> paraform. and have no idea how it differs from formaldehyde.)
> I am sure he will want some references if possible.
> Thanks,
> Trisha  


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