“…Second, the efficacy of CA1 synapses is reported to be high [release probability (P r ) close to unity] in very young (P4 -P6) hippocampi but diminishes to a lower level (P r Ͻ0.5) with maturation (Bolshakov and Siegelbaum, 1995). A purely presynaptic role for N-V DCC s is probably unlikely, however, because N-VDCCs also are found on hippocampal dendrites (Jones et al, 1989;Westenbroek et al, 1992;Mills et al, 1994;Christie et al, 1995) and their spines (Mills et al, 1994). Although the functional contribution such postsynaptic N-VDCCs make is unclear (Mills et al, 1994;Elliott et al, 1995), one plausible role is to direct afferent axons to discrete synapses.…”