Maturation of Schaffer collateral synapses generates a phenotype of unreliable basal evoked release and very reliable facilitated release.

Short-term synaptic plasticity undergoes important age-dependent changes that have crucial implications during the development of the nervous system. Paired-pulse facilitation is a form of short-term synaptic plasticity by which the response to the second of two temporally-paired stimuli is larger and more reliable than the response to the first stimulus. In this study, a paired-pulse minimal stimulation technique was used to measure the probability and quantal amplitude of synaptic release at hippocampal synapses from 12-16-day-old (young) and 7-9-week-old (adult) rats. In order to assess the contribution of temperature-dependent processes, we carried out experiments at both room temperature and at near physiological temperature. We report here that neither temperature nor maturation affected the low basal evoked release probability and quantal amplitude of release. However, the warmer temperature revealed a unique developmental increase in facilitated evoked release probability and quantal amplitude of release. As a result, although both basal evoked release and facilitated release are rather unreliable in synapses from young animals, the maturation process at near physiological temperature generates a phenotype with unreliable basal evoked release and highly reliable facilitated release.