Ka. Clark et al., A COMPARISON OF PAIRED-PULSE FACILITATION OF AMPA AND NMDA RECEPTOR-MEDIATED EXCITATORY POSTSYNAPTIC CURRENTS IN THE HIPPOCAMPUS, Experimental Brain Research, 101(2), 1994, pp. 272-278
Paired-pulse facilitation of excitatory synaptic transmission was inve
stigated in the CA1 region of rat hippocampal slices using whole-cell
patch-clamp recording. To optimise the measurement of excitatory synap
tic transmission, gamma-amino-butyric acid (GABA)mediated synaptic inh
ibition was eliminated using both GABA(A) and GABA(B) antagonists. Pur
e lpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or N-
methyl-D-aspartate (NMDA) receptor-mediated excitatory postsynaptic cu
rrents (EPSCs) were then isolated pharmacologically. Paired-pulse faci
litation of either AMPA or NMDA receptor-mediated EPSCs (EPSC(A) and E
PSC(N), respectively) was investigated using two stimuli of identical
strength delivered at intervals of between 25 and 1000 ms. The paired-
pulse facilitation profiles of both EPSC(A) and EPSC(N) were similar.
Paired-pulse facilitation of EPSC(A) was independent of holding potent
ial. In contrast paired-pulse facilitation of EPSC(N) was markedly vol
tage-dependent; maximum facilitation was recorded at hyperpolarised me
mbrane potentials. At positive membrane potentials there was little or
no paired-pulse facilitation and, in most neurones, paired-pulse depr
ession was observed. Voltage-dependence of paired-pulse facilitation o
f EPSC(N) was similar in the presence or nominal absence of Mg2+ in th
e bathing medium, and was unaffected by extensive dialysis of neurones
with ,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA).
These data are consistent with a presynaptic locus for paired-pulse f
acilitation of EPSC(A). However, paired-pulse facilitation of EPSC(N)
involves postsynaptic factors.