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Neuron. 2008 Dec 26;60(6):980-7. doi: 10.1016/j.neuron.2008.11.018.

State-dependent cAMP sensitivity of presynaptic function underlies metaplasticity in a hippocampal feedforward inhibitory circuit.

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Laboratory of Cellular and Synaptic Neurophysiology, National Institute of Child Health and Human Development, NIH, Bethesda, MD 20892, USA.


At hippocampal mossy fiber (MF)-st. lucidum interneuron (SLIN) synapses, mGluR7 serves as a metaplastic switch controlling bidirectional plasticity. mGluR7 activation during high-frequency stimulation (HFS) triggers presynaptic LTD due to persistent P/Q-type Ca(2+) channel inhibition. However, following mGluR7 internalization HFS produces presynaptic LTP. Surprisingly, LTP is not a simple molecular reversal of Ca(2+) channel depression. Rather, mGluR7 activation/internalization controls plasticity polarity by gating cAMP sensitivity of release. While naive surface mGluR7 expressing MF-SLIN synapses are insensitive to cAMP elevation, synapses that have internalized mGluR7 robustly potentiate following cAMP increases. Moreover, MF-SLIN LTP requires adenylate cyclase (AC) and protein kinase A (PKA) activities. We also discovered an association between mGluR7 and RIM1alpha, an active zone molecule required for AC/PKA-dependent presynaptic LTP. Importantly, the mGluR7-RIM1alpha interaction is regulated by mGluR7 activation, and mice lacking RIM1alpha are deficient in MF-SLIN LTP. We conclude that state-dependent cAMP sensitivity controlled by mGluR7-RIM1alpha interactions underlies MF-SLIN metaplasticity.

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