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Dyes and tracers

Sitemarking and tracktracing by microiontophoresis

A dye or tracer substance can be ejected by iontophoresis into the cytoplasm of a cell (intracellular iontophoresis) or into the intercellular space (extracellular iontophoresis). Intracellular deposition of a dye or tracer by microiontophoresis is made to mark the cell for subsequent histological examination. In extracellular studies, iontophoresis is used to mark brain sites where recordings have been made. Neuronal projections are also studied by microiontophoretic application of tracers into specific brain areas. In such experiments, tracer compounds iontophoresed into the intercellular space are taken up by axonterminals (retrograde tracing) or by dendrites and somata (anterograde tracing) and are then intracellularly transported across the whole cell.

A list of popular dye and tracer substances used in neuroscience research for track-tracing or site marking. Many of these compounds can be iontophoresed by our precision BAB-350 iontophoresis pump designed to deliver iontophoretic currents between 1 and 20 µA. See references for application examples.

Compound	Pipette Concentration	Ejection polarity/current/time	References
Alcian Blue	3-8%	(+) 1 µA; 1-2 min
Cobalt	1-50 mM	(+) 50 nA; 1 hour
Fast Green	Saturated	(-) 2-10 µA; 5-10 min	2, 15, 22, 24, 39, 48
Fluoro-Gold	1-4 %	(+) 1-5 µA; 15-30 min	3-7, 10, 12, 26, 34, 38, 43, 46
Fluoro-Ruby	10%	(+) 5 µA	35, 46
Horseradish peroxidase	2.5%	(-) 10 nA; 10-20 sec	18, 20, 21, 24, 25, 37, 40, 47
Lucifer Yellow (Lithium)	5%	(-) 1-2 nA; 5-10 min
Methyl Blue	Saturated	(-) 1-3 µA; 1-3 min
Neutral Red	14 mg/l	(+) 100-150 nA
Phaseolus Leucoagglutinin	2.5%	(+) 2-7 µA; 15 min	1, 8, 9, 11, 14, 19, 24, 27-31, 33, 41-45
Pontamine Sky Blue	2%	(-) 1-20 µA; 3-10 min	13, 16, 17, 23, 32, 36
Potassium ferrocyanide	0.5 M	(-) 3-10 µA; 10-15 min
Procion Brilliant Red	4%	(-) 40 nA; 1 min
Procion Yellow	5%	(-) 10 nA; 5-10 min
SITS	4%	(-) 8 µA	35

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References:

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46	Varoqueaux F and Poulain P (1994) Lateral septal projections onto tubero-infundibular neurons in the hypothalamus of the guinea pig. Cell and Tissue Research 278(2): p. 217-225.
47	Veenman CL, Reiner A, and Honig MG (1992) Biotinylated dextran amine as an anterograde tracer for single- and double-labeling studies. Journal of Neuroscience Methods 41(3): p. 239-254.
48	White TD, Tan AM, and Finch DM (1991) Functional connections of the rat medial cortex and basal forebrain: an in vivo intracellular study. Neuroscience 44(3): p. 571-583.