Long-term potentiation of glutamatergic synaptic transmission induced by activation of presynaptic P2Y receptors in the rat medial habenula nucleus

A novel form of long-term potentiation of glutamatergic synaptic transmission is described in the rat medial habenula nucleus. It occurs when uridine 5'-triphosphate is bath applied at low micromolar concentrations and is prevented by Reactive Blue 2, suggesting that it is mediated by P2Y(4) receptors. Uridine 5'-diphosphate can also cause such a Reactive Blue 2-sensitive potentiation, but at higher concentrations (200 mum), suggesting that this might also be an effect on the relatively uridine 5'-diphosphate-insensitive P2Y(4) receptor. The potentiation is due to an increase in presynaptic release probability. It requires neither depolarization nor calcium influx postsynaptically and is thus probably non-Hebbian. When potentiation due to low concentrations of uridine 5'-triphosphate is inhibited in the presence of Reactive Blue 2, uridine 5'-triphosphate causes instead a significant inhibition of glutamate release. We suggest that this inhibition may be mediated by a Reactive Blue 2-insensitive P2Y(2) -like receptor. At higher concentrations of uridine 5'-triphosphate (200 mum), the inhibitory effect dominates such that even in the absence of Reactive Blue 2 no potentiation is seen.