Figure 1. Presynaptic NMDA receptors regulate synapse-typespecific neurotransmission.

(A) In the textbook view of central neurotransmission, the presynaptic spike (lightning symbol) elicits the release of a neurotransmitter (e.g., glutamate; green), which binds to postsynaptic glutamate receptors such as NMDARs (blue). (B) However, Lituma et al. found that presynaptic NMDARs (red) in hippocampal mossy fibers facilitate the release of glutamate (green) and a growth factor called BDNF (purple), possibly through an influx of calcium ions (Ca²⁺; question marks). The released glutamate may further activate presynaptic NMDARs (red) in a form of loop.