LTP of mossy fiber-stimulated potentials in CA3 during learning in rats.

The study was done to determine whether long-term potentiation (LTP) of the potentials occurs at mossy fiber (MF)-CA3 synapses with the advance of learning in unrestrained and unanesthetized rats. The rats were divided into two groups, the test and control groups. The test group was given daily learning tasks in the radial arm maze, whereas the control group was similarly handled without learning tasks. Complete acquisition of learning was observed in the test group on day 5, and the learning was maintained over 3 days. Under freely moving conditions, a significant increase in population spikes (PS) elicited by MF stimulation with the progress in learning was observed in the test group, and the PS potentiation remained stable after day 4. Furthermore, on day 7, when MF stimulation-induced PS in the test group were compared with that in the control group in pentobarbital-anesthetized rats, the responses were comparatively higher in the former. As the training-induced PS potentiation in CA3 occurred with the advance of learning, these findings suggest that LTP in CA3 induced by learning may be related to memory storage.