[Excitability of septo-hippocampal axon terminals: changes as a function of the level of neuronal activity]

The septo-hippocampal terminals were electrically stimulated at the level of the gyrus dentatus in urethane anesthetized rats and antidromic responses were recorded in the medial septum. The excitability of the terminals was assessed by the threshold of terminal antidromic activation. An increase in the discharge frequency of the septal neurons following a microiontophoretic application of glutamate to their soma induced an increase in the antidromic activation threshold, i.e. a decrease in excitability of the terminals. An application of GABA which inhibited septal neuronal activity, induced a decrease in the antidromic activation threshold, i.e. an increase in the terminal excitability of septo-hippocampal neurons. These results are discussed in the light of the presynaptic autoreceptor hypothesis.