Can I have 2 styles in one paragraph in order to populate a TOC with the first words only?

[mlkmnsgrl]

Formatting a dissertation. There are only a handful of places in the document where it goes into a 3rd subheading, but the requisite style for that subheading is to have it in line with the paragraph. For example:



This is my subheading. This is the body of my paragraph, in the normal style. The subheading's only difference from normal is italics.

I have the TOC set to pull each heading and subheading automatically, however I can't figure out how to set only the subheading segment of the paragraph so that the entire paragraph doesn't go into the TOC.

I tried style separators before and after the subheading, but it still won't let me have the subheading in a different style than the text body.

Help! I'm far from an expert, just trying to do the ETD for my husband.