"Relativistic Electrons in Flaring Loops: What We Get From Microwave Observations and Simulations?" Summary: "We will review recent studies of Nobeyama observations concerning 1) spatial distribution of microwave brightness and spectral slope along flaring loops; 2) peculiarities of their temporal dynamics in different parts of a loop; 3) consequences of the obtained findings on spatial, spectral and pitch-angle distributions of high energy electrons."