Paired‐pulse and frequency facilitation in the CA1 region of the in vitro rat hippocampus

Abstract

SUMMARY1. Several types of facilitation of evoked synaptic responses were investigated in the CAI region of the in vitro rat hippocampus. Homosynaptic paired-pulse facilitation and heterosynaptic frequency facilitation were characterized and found to be differentiable processes on the basis of several characteristics.2. Paired-pulse facilitation, which occurs when the same input is stimulated twice in rapid succession, is manifested as an increase in both the extracellularly recorded population spike and the field e.p.s.p., and is specific to the set of afferents excited by the first impulse. Responses to other excitatory afferents show no facilitation by a heterosynaptic conditioning pulse.3. At intervals less than 200 msec, the degree of facilitation produced by a preceding impulse appears to decline as a first order exponential function of time. Facilitation is increased by lowering calcium or raising magnesium concentrations in the bathing medium, with no apparent change in the time constant of the decay process.4. The phenomenon that has sometimes been termed frequency facilitation, and which occurs during the early phase of repetitive stimulation, appears to be an extension of paired-pulse facilitation. It is seen as an increase in amplitude of both the e.p.s.p. and population spike in response to stimulation of homosynaptic inputs, can be predicted with fair accuracy by assuming that the residual paired-pulse facilitation produced by each impulse adds linearly with that from previous impulses, and is affected by calcium and magnesium ions in the same manner as is paired-pulse facilitation. These two types of facilitation, which apparently share a common mechanism, are termed synaptic or primary facilitation.5. Another type of facilitation, which we suggest might more properly be called frequency facilitation, develops slowly during the course of repetitive stimulation. It is the result of an increase in cell firing in response to any excitatory input, either homo-or heterosynaptic, at time points at which the field e.p.s.p. is typically depressed.6. Increases in the potassium concentration of the perfusion medium produce effects similar to those observed with frequency facilitation; stimulation-evoked increases in the extracellular concentration of this ion are hypothesized to underlie this type of generalized facilitation.t Address for correspondence.

Involvement of neurogranin in the modulation of calcium/calmodulin-dependent protein kinase II, synaptic plasticity, and spatial learning: A study with knockout mice

“…At IPIs Ն 40 ms, both strains displayed EPSP facilitation (PPF), which agreed with other studies (23). The PPD obtained at an IPI of 10 ms is most likely because the second pulse arrives during the period of recurrent GABA A -mediated inhibition generated by the conditioning stimulus (23).…”

Modeling the Nonlinear Dynamic Interactions of Afferent Pathways in the Dentate Gyrus of the Hippocampus

“…Note that the positive values exhibited in the early lags (up to 100 ms) of the secondorder kernels may be attributed to NMDA-mediated synaptic events. Similar facilitation characteristics are observed at intermediate lags of the third-order LPP kernel and may be attributed to augmentation of excitatory transmitter release 4,19 or presynaptic inhibition of GABA release. 12,29 This is consistent with the reported facilitation in the region of intermediate lags (100-200 ms).…”

Caffeine‐mediated BDNF release regulates long‐term synaptic plasticity through activation of IRS2 signaling

“…To determine whether the effects of caffeine on synaptic transmission were exerted pre or postsynaptically, we estimated changes in PPF (see Methods), which are considered of presynaptic origin (Creager et al 1980; Martín & Buño 2003). CAF LTP was paralleled by a significant concentration‐dependent reduction of PPF during caffeine perfusion (100 μM: 0.72 ± 0.10; P  < 0.05; n  = 12; N  = 6; 500 μM: 0.49 ± 0.03; P  < 0.001; n  = 14; N  = 6; 5 mM: 0.34 ± 0.04; P  < 0.001; n  = 7; N  = 3; Fig.…”

“…The time course of the fEPSP response was then normalized to this baseline. The pre‐ or postsynaptic origin of the observed modification of fEPSP slopes by caffeine was tested by estimating changes in the paired pulse facilitation (PPF), which are considered of presynaptic origin (Creager et al 1980; Martín & Buño 2003, 2005). PPF was studied by the application of pairs of stimuli at different interpulse intervals (15 to 400 ms) every 30 s. The stimulus intensity was adjusted to elicit 30–50 percent of the maximum response signal (mean stimulation strength of 3.5 ± 1.5 V).…”