Figure 5.

Glutamate released by GC mediates both reciprocal and lateral excitation. (A) The reciprocal excitation elicited by depolarization of the recorded MC (Left) is recorded in control conditions (1.3 mM Mg²⁺ with 10 μM BMI and 100 μM PTX). 4-AP (5 mM) increased significantly the amplitude response (middle traces) in five tested cells. (Right) Summary graph of the 4-AP effect. (B) EPL stimulation triggered lateral excitation recorded in control conditions containing Mg²⁺ (1.3 mM) with BMI (10 μM), PTX (100 μM), and QX-314 (10 mM) in the recording pipette. 4-AP (5 mM) also increased significantly the amplitude response (middle traces) in five tested cells. (Right) Summary graph of the 4-AP effect. (C) Model representing the two reciprocal synapses mediated by the same or different subtypes of GC. The term reciprocal implies that MC releases glutamate, activating both non-NMDA and APV-sensitive NMDA receptors, which trigger neurotransmitter release by GC spines at the same synapse (arrows). Glutamate from GC activates both non-NMDA and APV-resistant NMDA receptors on the MC dendrites. It is possible that glutamate released by MC could activate directly the MC glutamate receptors (dotted arrow) although our data indicate a moderate contribution (supplemental Fig. 8).