Figure 2. Tests of the presynaptic function of synapsin.

A, measurements of presynaptic (V_pre) and postsynaptic (V_post) responses before (control), during (pepE) and after (recovery) microinjection of a peptide from domain E of squid synapsin. B, injection of peptide from domain E of rat synapsin I enhances synaptic depression, measured as the decline in the rate of rise of postsynaptic responses (EPSP) evoked by a 50 Hz train of presynaptic action potentials. EPSP slope was normalized to values measured for the first response in each train. C, electron micrographs of presynaptic terminals injected with an inert control peptide (left) or a peptide from domain E of rat synapsin I (pepE; right). D, spatial distribution of synaptic vesicles measured in 50 nm shells surrounding active zones of terminals following injection of peptide from domain E of rat synapsin I or a control peptide. E, relative spatial distribution of synaptic vesicles in terminals injected with peptide from domain E of rat synapsin I, determined from the data shown in D by dividing values for domain E-injected terminals by values measured in control terminals. Modified from Hilfiker et al. (1998).