Distinct Transmitter Release Properties Determine Differences in Short-Term Plasticity at Functional and Silent Synapses

• Published in: Journal of neurophysiology Vol. 95; no. 5; pp. 3024 - 3034
• Main Authors: Cabezas, Carolina, Buno, Washington
• Format: Journal Article
• Language: English
• Published: United States Am Phys Soc 01.05.2006
• Subjects: alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid - pharmacology; Animals; Caffeine - pharmacology; Dose-Response Relationship, Radiation; Drug Interactions; Electric Stimulation - methods; Excitatory Amino Acid Agonists - pharmacology; Excitatory Postsynaptic Potentials - physiology; Excitatory Postsynaptic Potentials - radiation effects; Hippocampus - cytology; In Vitro Techniques; N-Methylaspartate - pharmacology; Neuronal Plasticity - drug effects; Neuronal Plasticity - physiology; Neuronal Plasticity - radiation effects; Neurons - drug effects; Neurons - physiology; Neurons - radiation effects; Neurotransmitter Agents - metabolism; Patch-Clamp Techniques - methods; Rats; Rats, Wistar; Ryanodine - pharmacology; Synapses - classification; Synapses - drug effects; Synapses - physiology; Synapses - radiation effects
• ISSN: 0022-3077; 1522-1598
• DOI: 10.1152/jn.00739.2005

Instituto Cajal, Consejo Superior de Investigaciones Científicas, Madrid, Spain Submitted 13 July 2005; accepted in final form 21 January 2006 Recent evidence suggests that functional and silent synapses are not only postsynaptically different but also presynaptically distinct. The presynaptic differences may be of functional importance in memory formation because a proposed mechanism for long-term potentiation is the conversion of silent synapses into functional ones. However, there is little direct experimentally evidence of these differences. We have investigated the transmitter release properties of functional and silent Schaffer collateral synapses and show that on the average functional synapses displayed a lower percentage of failures and higher excitatory postsynaptic current (EPSC) amplitudes than silent synapses at +60 mV. Moreover, functional but not silent synapses show paired-pulse facilitation (PPF) at +60 mV and thus presynaptic short-term plasticity will be distinct in the two types of synapse. We examined whether intraterminal endoplasmic reticulum Ca 2+ stores influenced the release properties of these synapses. Ryanodine (100 µM) and thapsigargin (1 µM) increased the percentage of failures and decreased both the EPSC amplitude and PPF in functional synapses. Caffeine (10 mM) had the opposite effects. In contrast, silent synapses were insensitive to both ryanodine and caffeine. Hence we have identified differences in the release properties of functional and silent synapses, suggesting that synaptic terminals of functional synapses express regulatory molecular mechanisms that are absent in silent synapses. Address for reprint requests and other correspondence: W. Buño. Instituto Cajal, CSIC, Av. Dr Arce 37, 28002, Madrid (E-mail: wbuno{at}cajal.csic.es )