Studies on homosynaptic (posttetanic) potentiation: a cholinergic modulator of presynaptic origin

Effects of soluble proteins (peptides, glycopeptides) extracted from presynaptic cholinergic vesicles of both rat brain and electric organ of Torpedo marmorata on postsynaptic spike generation were studied. The extracts potentiated postsynaptic effects of both endogenous and exogenous acetylcholine and had properties that fulfilled the minimum necessary requirements by Zetler of a modulator of a specific putative neurotransmitter effect. This modulator seems responsible for homosynaptic (posttetanic) potentiation. Therefore when cholinergic vesicle walls fuse with presynaptic terminal membrane during presynaptic stimulation, they verse into the synaptic cleft "modulator" substance(s) together with acetylcholine.