Is there a difference between ISH and ISHH? (In Situ Hybridization, In Situ Hybridization Histochemistry)

Question

I came across the term ISHH in my document and discovered that it stands for In Situ Hybridization Histochemistry. I's translating to Russian a document that uses this abbreviation.

Example from the PubMed:

We then validated these findings by using a combination of tools, including the analysis of an additional brain region in an independent subject cohort, cross-validation with an alternate custom microarray platform, and follow-up with in situ hybridization histochemistry (ISHH).

Is there any difference between ISH and ISHH, or are these just synonyms for the same method, in situ hybridization?

Answer 1

The term appears to be in use as a synonym. PLOS ONE is a good journal, and in it Okubo, 2016 write "The protocol for ISHH was described in detail previously [22]." Where [22] is Yamanaka, 2007, describing a classic ISH protocol.

Note that both papers use good old fashioned nuclear tract emulsion for S-35 labelled probes. The ISHH protocol is in its own section separate from IHC. It seems a bit odd because no literal "chemistry" is involved in recognizing the target - the RNA probe binds non-covalently and emits radiation. However, as noted in the question discussion, IHC is formally defined (OED) as "the branch of science concerned with the identification and distribution of the chemical constituents of tissues by means of stains, indicators, and microscopy". For example, though I have seen immunofluorescence and immunohistochemistry used to describe mutually exclusive visualization options, noncovalent binding of fluorophore-labelled antibodies is described as "fluorescent IHC".