Analysis of NMDA-independent long-term potentiation induced at CA3-CA1 synapses in rat hippocampus in vitro

1. Excitatory postsynaptic currents (EPSCs) were evoked at synapses formed by Schaffer collaterals/commissural (CA3) axons with CA1 pyramidal cells us ing the rat hippocampal slice preparation. Long-term potentiation (LTP) was induced at these synapses using a pairing protocol, with 50 mu M D,L-APV p resent in the artificial cerebrospinal fluid (ACSF). 2. Quantal analysis of the amplitudes of the control and conditioned EPSCs showed that the enhancement of synaptic strength was due entirely to an inc rease in quantal content of the EPSC. No change occurred in the quantal cur rent. 3. These results were compared with those obtained front a previous quantal analysis of LTP induced in normal ACSF, where both quantal current and qua ntal content increased. The results suggest that calcium entering via NMDA receptors initiates the signalling cascade that results in enhanced AMPA cu rrents because it is adding to cytoplasmic calcium from other sources to re ach a threshold for this signalling pathway, or because calcium entering vi a NMDA receptors specifically activates this signalling pathway.