L-aspartate effects on single neurons and interactions with glutamate in striatal slice preparation from chicken...

There is an accumulating evidence for a transmitter role of l-aspartate (l-Asp) in various brain regions. Recent studies from our laboratory have indicated that l-Asp is present in excitatory synapses of the striatum/nucl. accumbens of domestic chicks where it is co-released with l-glutamate (l-Glu) from axon terminals. Here we provide data on the postsynaptic effects of l-Asp alongside with l-Glu in striatal slices from chicken (1- to 10-day-old) using visually guided patch-clamp technique. l-Asp and l-Glu produced similar dose-dependent inward currents and an increase in spontaneous synaptic activity in all of the recorded striatal neurons. In the presence of TTX both the NMDA receptor antagonist D-AP5 and the AMPA/kainate receptor antagonist CNQX reduced and the co-application of these two antagonists almost abolished the postsynaptic effects of l-Asp and l-Glu in a reversible manner. Testing the interactions of l-Asp and l-Glu in these striatal neurons we found that co-application of l-Asp and l-Glut produced significantly larger inward currents than l-Asp or l-Glut alone. Our data are the first to demonstrate that l-Asp can induce postsynaptic effects on the chicken striatal neurons. These effects are mediated by both NMDA and non-NMDA type ionotropic glutamate receptors and are similar to those evoked by l-Glu. In addition our results show that co-application of l-Asp and l-Glut facilitates each other's effect, which is at least in part an excitatory amino acid (EAA) transporter dependent process. This phenomenon may explain the biological importance of the two EAAs with apparently similar postsynaptic activities in the same brain region.