Abstract
Synapses undergo activity-dependent changes not only during development but also in adulthood. Mechanisms underlying these dynamic changes have been studied intensively. However, it is largely unknown how the strength of once matured synapse is maintained stably in the brain. We show that significant weakening in the strength of excitatory climbing fiber (CF) to Purkinje cell (PC) synapse followed chronic inhibition of neuronal activity by tetrodotoxin or persistent blockade of postsynaptic AMPA receptors by their selective antagonist, NBQX. These treatments reduced glutamate concentration transients at synaptic clefts and decreased the frequency of quantal excitatory postsynaptic current (EPSC). In contrast, neither the amplitude of quantal EPSC nor the release probability was changed. Our morphological examination demonstrates selective reduction of CF innervation at PC shaft dendrites after NBQX-treatment. We thus conclude that in the mature cerebellum, AMPA receptor-mediated neuronal activity in PCs maintains CF's functional release sites and its innervation of PC shaft dendrites. [J Physiol Sci. 2006;56 Suppl:S59]
