Abstract

ATP-gated cation channels (P2X receptors) exist on the soma of proprioceptive neurons in the trigeminal mesencephalic nucleus (MNV) in the brain stem. However, these pseudomonopolar neurons seem to receive no synaptic input to their soma; we therefore hypothesized that in MNV neurons, the P2X receptors of importance may be those located on their central terminal projections. Here, we show in trigeminal mesencephalic motor nucleus neurons, which receive their major input from the MNV, that both exogenous ATP (1 mm) and high frequency focal stimulation to evoke endogenous ATP release enhanced the frequency of spontaneous fast excitatory postsynaptic currents (EPSCs) with no change in their amplitude. The enhancement was reduced by the antagonists suramin (300 μm) and pyridoxal-phosphate-6-azophenyl-2′,4′-disulfonic acid (30 μm) and persisted when action potential conduction was blocked with tetrodotoxin (1 μm). Thus, functional P2X receptors are expressed on nerve terminals in the brain stem, where they increase the spontaneous release of glutamate onto trigeminal mesencephalic motor nucleus neurons.