Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

[Commercial disclaimer - we make silver enhancement reagents]

Hello Andrew:

Interesting question! - transition metal ions are thought to be one cause 
of background deposition in the silver enhancement reaction when silver 
enhancing gold particles for blots and light microscopy, and we sometimes 
wash with a chelating agent - such as an EDTA (ethylene diamine tetraacetic 
acid) salt to remove or chelate them before silver enhancement.

For activity towards silver enhancement, what we look for is an active 
redox chemistry where it's likely that one of the redox couples of the 
target can couple with that of the silver/hydroquinone reduction. Manganese 
is an excellent candidate for this (as is iron) because of its extensive 
redox chemistry; compounds are known for every oxidation state from +2 to 
+7, so there's a good chance that it has some reactivity towards silver 
enhancement. It's certainly worth trying.

I couldn't find any references to silver enhancement of manganese (Gorm 
Danscher is a good name to search, since he has used silver enhancement - 
or variations of the method - to localize many other metals, and may have 
some observations about the reactivity or interference of maganese in these 
processes). There is, however, a reference to manganese dioxide absorbing 
silver in water, which suggests that it could react with silver enhancement:

Anderson, J. B.; Jenne, E. A., and Chao, T. T.: The sorption of silver by 
poorly crystallized manganese oxides. Geochimica et Cosmochimica Acta, 37, 
611-622 (1973).

Callahan et al find that

Callahan, M. A.; Slimak, M. W.; Gabel, N. W., et al. Water-related 
environmental fate of 129 priority pollutants. EPA-440/4-79-029a,b (1979).

Speaking from experience making manganese compounds in a previous 
life...Manganese (II) likes to form manganese dioxide, which is an 
insoluble black precipitate, upon oxidation (in fact, manganese in almost 
any oxidation state likes to form manganese dioxide), so treatment of your 
sections with an oxidizing agent could generate manganese dioxide; dilute 
hydrogen peroxide would probably work, although never having looked at this 
from a histological perspective, I'm not sure how compatible that would be 
with your fixation / perfusion (note that once formed, manganese dioxide 
decomposes hydrogen peroxide into water and oxygen). It's even possible 
that manganese (II) will react directly with silver enhancement.

Hope this helps,

Rick Powell

*****************************************************************************************
Richard D. Powell   *   [log in to unmask]   *   www.nanoprobes.com
NANOPROBES, Incorporated
95 Horse Block Road, Yaphank, NY 11980-9710, USA

US Toll-free: (877) 447-6266   *   Tel: (919) 845-6324   *   Fax: (631) 
980-3608
*****************************************************************************************


At 04:26 PM 9/21/2005, you wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Posted for a colleague..
>
>Hi all,
>
>I've been looking into using Manganese as a neuronal tracer lately.
>Radioactive Mn ions are transported actively and can be visualized
>autoradiographically, but I would like to find a way to do this without using
>radionuclides.  The goal would be to inject a MnCl2 solution, let the neurons
>take it up and transport it, then deposit the Mn as an insoluble precipitate
>within the neurons during perfusion/fixation of the brain.  I would like to
>find a Mn precipitate that could be visualized through silver intensification
>(deposition of reduced silver by reaction with hydroquinone) but one which
>wouldn't co-precipitate other ions like iron.  Does anyone know if Mn itself
>can be silver intensified, and if not, can you suggest a Mn compound which
>could be?
>
>Thanks in advance,
>Andrew
>
>Andrew Ray, PhD
>Research Associate
>The Scripps Research Institute
>[log in to unmask]