抄録
At the brainstem auditory synapse in rodents, high fidelity (HI-FI) transmission is acquired through postnatal development, and plays crucial roles in sound source localization. At the calyx of Held synapse in auditory brainstem, a variety of molecules undergo developmental changes during the first postnatal month. Among them the endogenous Ca2+ buffer calretinin was immunocytochemically detectable in the calyceal presynaptic terminal only after postnatal day 10 (P10) in mice. To address the role of calretinin in synaptic development, we compared the properties of synaptic transmission between calretinin-knockout homogygous (CRKO) mice and wild type (WT) mice. During the postnatal period from P7 to P21, paired-pulse ratio (PPR) of EPSCs increased in WT mice, whereas this increase was much smaller in CRKO mice. We estimated release probability (p) and pool size of readily releasable synaptic vesicles (N) using the high frequency stimulation protocol. In WT mice p decreases and N increases with development as reported in rats. In CRKO mice, however, the developmental increase in p was largely impaired, whereas the developmental increase in N was similar to WT mice. Furthermore, in CRKO mice, the developmental acquisition of HI-FI transmission in response to high frequency synaptic inputs was markedly impaired. We conclude that a developmental increase in the expression of calretinin in the nerve terminal increases synaptic efficacy to high frequency inputs via decreasing p, thereby contributing to the developmental acquisition of HI-FI synaptic transmission. [Jpn J Physiol 54 Suppl:S155 (2004)]
