Short-term synaptic plasticity in the rat geniculo-cortical pathway during development in vivo.

The critical period for visual system development in rats normally peaks at postnatal three weeks and ends at postnatal five weeks. However, the change of short-term synaptic plasticity during this period has rarely been investigated. In the present study, we compared the short-term plasticity of visual cortical responses to lateral geniculate nucleus stimulation in rats at different development stages (P20, P30 and adult) in vivo. The results show that paired-pulse depression (PPD) and frequency-dependent depression of evoked field potentials (FP) are present in P20 rats and increase in magnitude with development. The time course of this maturation of synaptic depression parallels that of the visual critical period. The weak synaptic depression observed in juvenile rats may be important in enhancing excitatory neurotransmission at a time when synapses are immature; this could endow immature synapses with wide integrative capabilities. In contrast, suppressive temporal interactions could provide an important substrate for neuronal processing of visual information in the mature cortex.