The influences of dark rearing on the transmission characteristics of layer II/III pyramidal cells during the critical period

The characteristics of synaptic plasticity on layer II/III pyramidal cells in different ages of rats have been studied extensively, and dark rearing is one of the important impact factors. To systematically analyze the influence of dark rearing on synaptic plasticity during the critical period of visual development, we studied the characteristics of short-term and long-term synaptic plasticities of layer II/III pyramidal cells of rats in three rearing conditions during P14 to P37. The paired-pulse ratio (PPR) of inhibitory postsynaptic currents (IPSCs) of layer II/III pyramidal cells was effected by both ages and rearing conditions, but the PPR of excitatory postsynaptic currents (EPSCs) did not change obviously. Moreover, long-term synaptic plasticity of rats in the dark rearing condition did not significantly change with age, while it was elevated during P16 and P21 for rats in the normal rearing condition. These results suggest that visual experience can affect the characteristics of short-term and long-term synaptic plasticities. The IPSC/EPSC ratio increased gradually with aging for NR rats, but the ratio slightly decreased for DR rats, which indicates the relative increase of inhibitory components during the critical period of visual development. The characteristics during P35 and P37 of the 30-day dark-reared (30 D × N) group had similar trends with the normal-reared rats during P16 and P21, which emphasizes that dark rearing can postpone the timing of the critical period.

► The PPR of EPSCs and IPSCs changed mainly during P16 and P21 for NR rats.
► Inhibitory afferents increased relatively during the critical period.
► Dark rearing can postpone the timing of the critical period of visual development.