J Physiol. 2026 May 24.
Presynaptic receptors are important regulators of CNS activity. We have examined presynaptic receptor populations using a vibrodissociated rat cerebellar Purkinje cell preparation. In this preparation, NMDA receptor immunoreactivity co-localized with antibody staining for the presynaptic marker synaptophysin. The application of NMDA increased the frequency of both inhibitory and excitatory synaptic currents, an effect that was blocked by the addition of 1 mM Mg2+. Similar stimulation of excitatory inputs occurred when applying a high concentration of glycine (100 µM) alone, a response that was blocked by 500 nM strychnine, but not by 1 mM Mg2+. Both glycine and NMDA stimulation produced many large amplitude excitatory postsynaptic currents of ∼200-600 pA. The size of these events suggests that they arise from climbing fibre, rather than parallel fibre, connections. In keeping with this idea, the largest events were consistently eliminated by tetrodotoxin (TTX) and isolated Purkinje neurons stained positively for the climbing fibre marker peripherin. Finally, we examined the effect of 100 µM glycine in a brain slice preparation. As was seen when using dissociated cells, a 100 µM concentration of glycine stimulated large postsynaptic currents and this effect was blocked by low concentrations of strychnine. Taken together, our findings indicate the presynaptic presence of NMDA and glycine receptors that can both operate as regulators of climbing fibre excitatory transmitter release. KEY POINTS: Functional presynaptic NMDA receptors are present on the cerebellar climbing fibre. Functional presynaptic glycine receptors are also present on the cerebellar climbing fibre. Both presynaptic NMDA and presynaptic glycine receptors can regulate the release of glutamate from the climbing fibre. In vibrodissociated neurons action potentials are generated locally to drive the largest climbing fibre events.
Keywords: NMDA; climbing fibre; glycine; presynaptic