IMPAIRMENT OF HIPPOCAMPAL MOSSY FIBER LTD IN MICE LACKING MGLUR2

Subtype 2 of the metabotropic glutamate receptor (mGluR2) is expressed in the presynaptic elements of hippocampal messy fiber-GAS synapses. Knockout mice deficient in mGluR2 showed no histological changes and n o alterations in basal synaptic transmission, paired-pulse facilitatio n, or tetanus-induced long-term potentiation (LTP) al the messy fiber- CA3 synapses. Long-term depression (LTD) induced by low-frequency stim ulation, however, was almost fully abolished. The mutant mice performe d normally in water maze learning tasks. Thus, the presynaptic mGluR2 is essential for inducing LTD at the mossy fiber-CA3 synapses, but thi s hippocampal LTD does not seem to be required for spatial learning.