Carrie,
 
PLP stands for Periodate-Lysine-Paraformaldehyde.
 
See:  McLean IW and Nakane PK  J Histochem Cytochem 22:1077-1083, 1974.
 
PLP Working Solution
 
 50 ml      3% (w/v) Paraformaldehyde
100ml      0.1 M Disodium hydrogen othophosphate
 0.9g       Lysine
0.15g      Sodium periodate
 
Adjust to pH 7.4
 
Joan
RTI