PT  - JOURNAL ARTICLE
AU  - Debanne, Dominique
AU  - Gähwiler, Beat H.
AU  - Thompson, Scott M.
TI  - Heterogeneity of Synaptic Plasticity at Unitary CA3–CA1 and CA3–CA3 Connections in Rat Hippocampal Slice Cultures
AID  - 10.1523/JNEUROSCI.19-24-10664.1999
DP  - 1999 Dec 15
TA  - The Journal of Neuroscience
PG  - 10664--10671
VI  - 19
IP  - 24
4099  - http://www.jneurosci.org/content/19/24/10664.short
4100  - http://www.jneurosci.org/content/19/24/10664.full
SO  - J. Neurosci.1999 Dec 15; 19
AB  - Long-term potentiation (LTP) of unitary EPSPs, generated by pairs of monosynaptically connected CA3 and CA1 pyramidal cells, was compared with LTP of extracellularly evoked, multi-unitary EPSPs in rat hippocampal slice cultures. LTP was induced by repeated, synchronous pairing of low-frequency presynaptic and postsynaptic activity. Three differences were observed. First, LTP of multi-unitary EPSPs displayed two phases: transient (<5 min) and sustained. Potentiation of unitary EPSPs displayed both phases in 42% of experiments; the remainder showed sustained potentiation only. Unitary EPSPs displaying transient-sustained and only sustained potentiation could be recorded from single postsynaptic cells, indicating that excitatory synapses on a given cell are heterogeneous with respect to short-term plasticity. Second, whereas LTP of multi-unitary EPSPs never resulted in greater than twofold increases in amplitude (mean potentiation of 175% of control), maximal LTP of unitary EPSPs was as great as 13-fold (mean potentiation of 250%). Third, LTP could not be induced in 24% of unitary EPSPs. We provide here the first evidence for the coexistence of potentiatable and nonpotentiatable synapses on individual postsynaptic neurons. Thirty-seven percent of connections not displaying LTP exhibited long-term depression (LTD), suggesting that the connections were already maximally potentiated. In the remaining 63% of these pairs, neither LTP nor LTD could be induced, despite the existence of a pharmacologically identified, NMDA receptor-mediated EPSP component. In conclusion, there is considerable heterogeneity in the amplitude and time course of LTP expression at different synaptic connections. A substantial proportion of apparently nonplastic synapses probably accounts for the weaker potentiation displayed by compound EPSPs.