HETEROSYNAPTIC SHORT-TERM DEPRESSION OF POPULATION SPIKE AMPLITUDE INTHE PYRAMIDAL LAYER OF THE CA1 HIPPOCAMPAL REGION EVOKED BY A THETA-LIKE TETANIZATION

Heterosynaptic short-term depression (STD) of the stratum radiatum and stratum oriens inputs to the CA1 region was studied in rat hippocampa l slices. STD was evoked by trains of 1050 impulses with interstimulus interval (ISI) variable from 10 to 700 ms. The STD was found to be ve ry pronounced for tetanizations with ISI around 200 ms, and almost abs ent for ISI less than 50 ms or more than 500 ms. These data show that thetalike tetanization is an effective pattern not only for induction of the long-term potentiation (LTP), as has been shown previously,but for production of the heterosynaptic STD as well. This implies that he terosynaptic STD can effectively modulate induction of LTP by theta-li ke tetanization, and plays an important role in differentiation of pot entiated pathways. It is discussed that the theta-like tetanization-in duced release of ACh is a possible mechanism of the STD.