The properties of the long-term potentiation (LTP) in the superior colliculus.

(1) Postsynaptic potential (PSP) was recorded in the SGL of guinea pig SC slices after stimulation to the OL. (2) Tetanic stimulation (optimum parameter: 50 Hz in frequency, 20 sec in duration) to the OL induced LTP in the PSP of SGL. (3) NMDA-receptor antagonist MK801 inhibited the LTP occurrence but D-APV and gamma-DGG masked the appearance of LTP, suggesting that the mode of involvement of the NMDA receptor for LTP formation in the SC may be different from that reported in the hippocampus. (4) Protein kinase C inhibitors such as H-7, polymixin B and K-252a inhibited the maintenance of LTP. (5) Application of GABA prevented the occurrence of LTP and bicuculline facilitated the formation of LTP. (6) In in vivo preparations of the rat, the LTP in the SC was only elicited by tetanic stimulation to the optic nerve either when the visual cortical are ipsilateral to the SC tested was ablated or when picrotoxin was administered to the animal before tetanic stimulation.