Greg,

Check out the publications by E.J. Speel, for example this one:

J Histochem Cytochem 1999 Mar;47(3):281-8
Amplification methods to increase the sensitivity of in situ hybridization:
play card(s).

Speel EJ, Hopman AH, Komminoth P

Department of Pathology, University of Zurich, Zurich, Switzerland.

In situ hybridization (ISH) has proved to be an invaluable molecular tool in
research and diagnosis to visualize nucleic acids in their cellular
environment. However, its applicability can be limited by its restricted
detection sensitivity. During the past 10 years, several strategies have
been developed to improve the threshold levels of nucleic acid detection in
situ by amplification of either target nucleic acid sequences before ISH
(e.g., in situ PCR) or the detection signals after the hybridization
procedures. Here we outline the principles of tyramide signal amplification
using the catalyzed reporter deposition (CARD) technique, present practical
suggestions to efficiently enhance the sensitivity of ISH with CARD, and
discuss some applications and possible future directions of in situ nucleic
acid detection using such an amplification strategy.

Good luck,
Jacques