Inhibition of transmitter release and long-term depression in the avian hippocampus

Long-term depression has recently been shown to occur at glutamatergic syna pses in the avian hippocampus and requires activation of calcium/calmodulin -dependent protein kinase II in the nerve terminal. Here using whole cell a nd intracellular recordings from brain slices, we show that the N-type calc ium channel contributes significantly to glutamate release in the avian hip pocampus. Activation of the metabotrobic gamma-aminobutyric acid (GABA)(B) receptor by the specific agonist baclofen blocks synaptic transmission. The action of baclofen was associated with a change in paired pulse facilitati on indicating that it resulted from a reduction in the probability of trans mitter release, In contrast, no change in paired pulse facilitation was obs erved following the induction of long-term depression. These results show t hat activation of GABA(B) receptors and long-term depression reduce transmi tter release by distinct mechanisms. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.