Induction mechanisms for L-LTP at thalamic input synapses to the lateral amygdala: requirement of mGluR5 activation

L-LTP (late-phase long-term potentiation) at thalamo-amygdala synapses is thought to be critical for auditory fear conditioning, but it has not been clear what kinds of surface receptors and channels are involved in the induction phase of the L-LTP. Here we report that the NMDA receptor antagonist D-AP5 (50 microM), the L-type calcium channel antagonist nifedipine (30 microM) and the metabotropic glutamate receptor 5 antagonist MPEP (10 microM) prevented L-LTP induction when each antagonist was separately applied at saturating concentrations before and during repeated tetanus. By contrast, the mGluR1 antagonist CPCCOEt (80 microM) failed to show any effects on L-LTP induction. Neither D-AP5 nor MPEP produced any significant effects on potentiated synaptic responses when applied after L-LTP had been established. Thus, our data suggest that NMDA receptors, L-type calcium channels and mGluR5 are involved in L-LTP induction in the thalamo-amygdala pathway.