  A compact expression has been obtained for the superexchange coupling of
magnetic ions via intermediate anions with regard to polaron effects at both
magnetic ions and intermediate anions. This expression is used to analyze the
main features of the behavior of isotope shifts for temperatures of three types
in layered cuprates: the Neel temperatures ($T_N$), critical temperatures of
transitions to a superconducting state ($T_C$), and characteristic temperatures
of the pseudogap in the normal state ($T^*$).
