Short-term synaptic plasticity during development of rat mossy fibre to granule cell synapses.

Changes occur during the postnatal development of the rat glutamatergic mossy fibre to granule cell synapse: to the morphology of synapses, glutamate transporter expression, AMPA receptor expression and the kinetics of AMPA receptor-mediated synaptic transmission. For example, both the rise and decay times of AMPA receptor-mediated excitatory postsynaptic currents significantly shorten. To further define the development of mossy fibre to granule cell synaptic transmission, the properties and mechanisms of short-term plasticity have been described. The characterization of short-term plasticity will aid our understanding of the mechanisms that define the parameters of synaptic transmission during development and furthermore short-term plasticity may play an important role in determining information transfer between mossy fibres and granule cells. In response to pairs of stimuli (2-100-ms interval), depression (second excitatory postsynaptic current amplitude smaller than the first) was observed at both mature (older than 40 postnatal days) and immature (between 8 and 12 postnatal days) synapses. The degree of depression was similar at both stages of development, although recovery from depression was slower at mature synapses (tau 22 vs 12.5 ms). Several experimental approaches (coefficient of variation, low-affinity antagonists and cyclothiazide) suggest that depression at immature synapses results from multiple mechanisms. At mature synapses, postsynaptic receptor desensitization appears to be the major cause of depression.