title: Bidirectional Hebbian plasticity at hippocampal mossy fiber synapses on CA3 interneurons.
abstract: Hippocampal area CA3 is critically involved in the formation of nonoverlapping neuronal subpopulations ("pattern separation") to store memory representations as distinct events. Efficient pattern separation relies on the strong and sparse excitatory input from the mossy fibers (MFs) to pyramidal cells and feedforward inhibitory interneurons. However, MF synapses on CA3 pyramidal cells undergo long-term potentiation (LTP), which, if unopposed, will degrade pattern separation because MF activation will now recruit additional CA3 pyramidal cells. Here, we demonstrate MF LTP in stratum lacunosum-moleculare (L-M) interneurons induced by the same stimulation protocol that induces MF LTP in pyramidal cells. This LTP was NMDA receptor (NMDAR) independent and occurred at MF Ca(2+)-impermeable AMPA receptor synapses. LTP was prevented by with voltage clamping the postsynaptic cell soma during high-frequency stimulation (HFS), intracellular injections of the Ca(2+) chelator BAPTA (20 mm), or bath applications of the L-type Ca(2+) channel blocker nimodipine (10 microm). We propose that MF LTP in L-M interneurons preserves the sparsity of pyramidal cell activation, thus allowing CA3 to maintain its role in pattern separation. In the presence of the mGluR1alpha antagonist LY367385 [(S)-(+)-a-amino-4-carboxy-2-methylbenzeneacetic acid] (100 microm), the same HFS that induces MF LTP in naive slices triggered NMDAR-independent MF LTD. This LTD, like LTP, required activation of the L-type Ca(2+) channel and also was induced after blockade of IP(3) receptors with heparin (4 mg/ml) or the selective depletion of receptor-gated Ca(2+) stores with ryanodine (10 or 100 microm). We conclude that L-M interneurons are endowed with Ca(2+) signaling cascades suitable for controlling the polarity of MF long-term plasticity induced by joint presynaptic and postsynaptic activities.
authors.affiliation: Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Emilio J
authors.initials: EJ
authors.lastname: Galván
authors.forename: Eduardo
authors.initials: E
authors.lastname: Calixto
authors.forename: Germán
authors.initials: G
authors.lastname: Barrionuevo
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D001703:Biophysics / Q000379:methods; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002614:Chelating Agents / Q000494:pharmacology; D003521:Cyclopropanes / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004558:Electric Stimulation / Q000379:methods; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology*; D066298:In Vitro Techniques; D007395:Interneurons / Q000187:drug effects / Q000502:physiology*; D017774:Long-Term Potentiation / Q000187:drug effects / Q000502:physiology; D008239:Lysine / Q000031:analogs & derivatives / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D019599:Mossy Fibers, Hippocampal / Q000187:drug effects / Q000502:physiology*; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D018733:Nicotinic Antagonists / Q000494:pharmacology; D009553:Nimodipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques / Q000379:methods; D011073:Polyamines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D002121:Calcium Channel Blockers; D002614:Chelating Agents; D003521:Cyclopropanes; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D018733:Nicotinic Antagonists; D011073:Polyamines; C082313:2-(2,3-dicarboxycyclopropyl)glycine; D004533:Egtazic Acid; D009553:Nimodipine; C034092:delta-philanthotoxin; C013411:biocytin; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D008239:Lysine; D002118:Calcium; D005998:Glycine; D001640:Bicuculline