Abstract
Long-term potentiation (LTP) and long-term depression (LTD) are both forms of synaptic plasticity, which have been studied extensively in rodents. However, information about LTP and LTD in the primate brain is limited, especially when using in vivo models. This limitation is primarily due to difficulties in the precise implantation of electrodes within deep telencephalic structures of the primate brain. Using MRI and local field potentials to guide the implantation procedure, we inserted a stimulation electrode in the perforant pathway and a recording electrode in the dentate gyrus of the monkey. Correct implantation was confirmed by the appearance of evoked potentials in the dentate gyrus following stimulation of the perforant pathway. Evoked potentials changed systematically according to the depth of the electrodes. The effects of high-frequency stimulation (HFS; 100, 200 or 400 Hz) or low-frequency stimulation (LFS; 1, 2 or 5 Hz) on evoked potentials were tested in an awake condition. We used HFS or LFS parameters that have been demonstrated to produce LTP or LTD in rodents. In the monkey, however, we found that only the HFS with the highest frequency induced LTP, while all LFS levels failed to induce LTD. These data suggest that 1) the present animal model is suitable for testing long-term synaptic plasticity in the primate brain, and 2) the primate hippocampus is more resistant to the induction of long-term synaptic plasticity than the rodent hippocampus. [J Physiol Sci. 2006;56 Suppl:S193]
