Abbreviations (abbrv.) in journal (jrn) articles (artcs)
In my opinion the general rule is that abbreviations should be used exactly when they make reading easier; in particular, in some circumstances it will be easier to understand a sentence when a long term is abbreviated (provided the abbreviation has been defined of course). The same rule should apply in abstract and captions, except that the cost (in term of reading comfort) of having to look for the meaning of the abbreviation is usually greater.

The problem comes from the fact that we tend to use abbreviations when they make writing easier (or quicker), and this does not coincide with reading easiness.