Abstract
Synapses show dynamic changes during development and adulthood, and mechanisms underlying these dynamic changes have been studied intensively. By contrast, it is largely unknown how synaptic strength is maintained stably in mature brain, which must be important for stable information transfer and storage. In the present study, we examined this issue using climbing fiber (CF) - Purkinje cell synapse in the mouse cerebellum as a model. Most Purkinje cells are innervated by single CFs in the adult. CF activation yields large and constant excitatory postsynaptic currents (EPSCs) in an all-or-none fashion, which makes a reliable electrophysiological examination possible. To block neuronal activity locally and chronically within the cerebellum, we implanted a small piece of ethylene-vinyl acetate copolymer (Elvax) containing TTX on the surface of the mouse cerebellum at P24. Three to seven days after the implantation, acute cerebellar slices were prepared and CF synapses were examined electrophysiologically. The amplitude of CF-mediated EPSC was significantly smaller, and glutamate concentration transient at the CF synaptic clefts was lower in the TTX-treated mice than those in control mice. The frequency but not the amplitude of quantal EPSC was reduced in the TTX-treated mice. Similar presynaptic changes were induced by chronic blockade of postsynaptic AMPA receptors by means of Elvax containing NBQX, a selective antagonist of AMPA receptors. These results suggest that presynaptic functions of mature CF synapses are maintained by postsynaptic activity through some retrograde signaling. [Jpn J Physiol 54 Suppl:S33 (2004)]
