The principle route for recycling glutamate at central excitatory synapses is thought to be via the glutamate-glutamine cycle. This involves the uptake of glutamate into glial cells, conversion to glutamine by the enzyme glutamine synthase and subsequent transport out of the glial cells by the system N transport. The cycle is completed by the transport of glutamine into the presynaptic terminal via the system A transporters and conversion into glutamate by phosphate-activated glutaminase (Chaudhry et al. 2002a). Although currents generated by the electrogenic system A transporters have been demonstrated in expression systems and some postsynaptic cells (Chaudhry et al. 2002b), direct electrical recording of this transporter’s activity from presynaptic terminals has not been shown. Using patch-clamp recordings from rat brainstem slices I have been able to demonstrate the presence of electrogenic system A transporter currents in both postsynaptic cells and presynaptic terminals at the calyx of Held synapse. Brainstem slices were prepared from Lister Hooded rats (P9 to 12). Postsynaptic medial nucleus of the trapezoid body (MNTB) cells or presynaptic calyx of Held terminals were whole-cell voltage-clamped and all recordings performed at 35-37°C. All data are represented as mean ± SEM. Puff application of glutamine (10 mM for 1 s) elicited an inward current in postsynaptic MNTB neurones held at –70mV. This current was not blocked by inhibitors of ionotropic glutamate, GABA or glycine receptors (22.1 ± 1.7 pA in control, 21.0 ± 2.3 pA in blockers, n=6, P=0.71, 2-tailed t test), but was inhibited by the system A-specific analogue 2-(methylamino)isobutyrate (10 mM MeAIB; 3.3 ± 0.8 pA, n=6, P<0.01, 2-tailed t test). Moreover, the current did not reverse at depolarized membrane potentials, consistent with properties of system A transport (Chaudhry et al. 2002b). Similar currents were also recorded from the calyx of Held presynaptic terminal, where puff application of glutamine evoked a current of 12.1 ± 2.6 pA (n=5). This current was inhibited by 54 ± 6% upon application of 10 mM MeAIB (n=5, P=0.01, 2-tailed paired t test), indicating a significant system A transporter component. These data show for the first time the presence of system A transporter currents in presynaptic terminals in situ, demonstrating their potential importance in glutamate recycling. It will also allow the regulation of this transporter to be studied in a synaptic preparation and permit investigations into the role it plays in supplying the glutamate needed to sustain neurotransmission.