Glycine induces a novel form of long‐term potentiation in the superficial layers of the superior colliculus

1 The mammalian superior colliculus (SC) is a midbrain nucleus containing space maps of different sensory modalities which show various forms of age‐ and activity‐dependent plasticity in vivo and in vitro . In the present study, we aimed to characterize the role of glycine (Gly) receptors in the SC, and we observed that application of glycine (Gly; 500 μ M and 3 m M ) for 7 min to SC slices of adult guinea‐pigs caused a novel form of long‐term potentiation (termed LTP gly ) of evoked excitatory postsynaptic potentials recorded in the superficial layers. 2 The strength of potentiation was found to be concentration‐dependent and partially independent from synaptic stimulation. 3 LTP gly did not involve NMDA receptor activation as proven by the lack of inhibition by 100 μ M D,L‐2‐amino‐5‐phosphonovaleric acid (APV) and 10 μ M MK‐801. 4 LTP gly could only be masked but not prevented by strychnine (100 μ M ) and remained undisturbed in the presence of picrotoxin (100 μ M ). 5 Inhibition of carbonic anhydrase by acetazolamide (20 μ M ) had no effect on LTP gly suggesting that the excitatory action of Gly is not due to a differential breakdown of the Cl − /HCO 3 − gradients. 6 As indicated by the inhibition of LTP gly of the fEPSP slope by the L‐type calcium channel blocker nifedipine (20 μ M ), voltage‐dependent calcium channels are the source for Ca 2+ elevation as the intracellular trigger. 7 Our data provide the first evidence for a role of Gly in SC synaptic transmission. They illustrate a so far unknown action of Gly which can lead to long‐lasting changes of synaptic efficacy and which is not mediated via NMDA‐related or strychnine‐sensitive binding sites.British Journal of Pharmacology (1998) 125 , 293–300; doi: 10.1038/sj.bjp.0702062