MD80: to clarify; what is the main point is if the thrust lies above or below, and in front of or behind, the centre of gravity. You know that objects tend to rotate around their centre of gravity. A line of thrust directed through (or equally around, for aircraft, probably) will not tend to influence pitch, while a thrust line below (say for underslung engines) will tend to make the aircraft pitch up when power is applied. Conversely an engine mounted above and behind the CG, directed straight backwards, will tend to pitch the aircraft nose down, with increasing power.
This is of course not taking aerodynamics into effect, such as an increased airflow over the horizontal stabilizer or trim speed stability.