Time-dependent changes in rat hippocampal synapsin I mRNA expression during long-term potentiation

We studied the time-dependent changes in synapsin I mRNA levels after hippocampal long-term potentiation (LTP) in rats in vivo. Following LTP induction by stimulating the perforant path, synapsin I mRNA expression in the granule cell layer of the denture gyms ipsilateral to stimulation increased significantly in a time-dependent manner. From 2 to 8 h after stimulation, the synapsin I mRNA levels in the ipsilateral dentate gyms were significantly higher than those of controls subjected to a sham procedure. The synapsin I mRNA level (157.4 ± 7.1% of the control level, mean ± SEM) was at a maximum 8 h after stimulation. The synapsin I mRNA level of animals that received only test pulses did not increase significantly, compared with the control level. These results suggest that the increased level of synapsin I mRNA is related to persistent enhancement of synaptic activity within the neural networks in which dentate granule cells participate in LTP.