Whole cell recording from neurons in slices of reptilian and mammalian cerebral cortex

Presynaptic enhancement shown by whole-cell recordings of long-term potentiation in hippocampal slices

Long-term potentiation (LTP) of synaptic transmission in the hippocampus is a widely studied model system for understanding the cellular mechanisms of memory. In region CA1, LTP is triggered postsynaptically by Ca2(+)-dependent activation of protein kinases, but the locus of persistent modification remains controversial. Statistical analysis of synaptic variability has been proposed as a means of settling this debate, although a major obstacle has been the poor signal-to-noise ratio of conventional intracellular recordings. We have applied the whole-cell voltage clamp technique to study synaptic transmission in conventional hippocampal slices (compare refs 28-30). Here we report that robust LTP can be recorded with much improved signal resolution and biochemical access to the postsynaptic cell. Prolonged dialysis of the postsynaptic cell blocks the triggering of LTP, with no effect on expression of LTP. The improved signal resolution unmasks a large trial-to-trial variability, reflecting the probabilistic nature of transmitter release. Changes in the synaptic variability, and a decrease in the proportion of synaptic failures during LTP, suggest that transmitter release is significantly enhanced.

Whole-cell patch-clamp recordings of an NMDA receptor-mediated synaptic current in rat hippocampal slices

Whole-cell patch-clamp recordings and pharmacological techniques have been used to obtain low noise recordings of 2 excitatory postsynaptic synaptic currents (termed EPSCA and EPSCB) evoked by stimulation of the Schaffer collateral-commissural pathway in rat hippocampal slices. EPSCA was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and EPSCB was blocked by D-2-amino-5-phosphonovalerate (APV), indicating their mediation by non-N-methyl-D-aspartate (non-NMDA) and NMDA receptors, respectively. EPSCB has a slower time-course than EPSCA and its current-voltage relationship was highly non-linear with a region of negative slope conductance from -35 to -100 mV. These properties of EPSCA and EPSCB can explain their differing participation in synaptic transmission in this pathway.

Comparison of two forms of long-term potentiation in single hippocampal neurons

In invertebrate nervous systems, some long-lasting increases in synaptic efficacy result from changes in the presynaptic cell. In the vertebrate nervous system, the best understood long-lasting change in synaptic strength is long-term potentiation (LTP) in the CA1 region of the hippocampus. Here the process is initiated postsynaptically, but the site of the persistent change is unresolved. Single CA3 hippocampal pyramidal cells receive excitatory inputs from associational-commissural fibers and from the mossy fibers of dentate granule cells and both pathways exhibit LTP. Although the induction of associational-commissural LTP requires in the postsynaptic cell N-methyl-D-aspartate (NMDA) receptor activation, membrane depolarization, and a rise in calcium, mossy fiber LTP does not. Paired-pulse facilitation, which is an index of increased transmitter release, is unaltered during associational-commissural LTP but is reduced during mossy fiber LTP. Thus, both the induction and the persistent change may be presynaptic in mossy fiber LTP but not in associational-commissural LTP.