Very short-term plasticity in hippocampal synapses

Abstract

Hippocampal pyramidal neurons often fire in bursts of action potentials with short interspike intervals (2-10 msec). These high-frequency bursts may play a critical role in the functional behavior of hippocampal neurons, but synaptic plasticity at such short times has not been carefully studied. To study synaptic modulation at very short time intervals, we applied pairs of stimuli with interpulse intervals ranging from 7 to 50 msec to CA1 synapses isolated by the method of minimal stimulation in hippocampal slices. We have identified three components of short-term paired-pulse modulation, including (i) a form of synaptic depression manifested after a prior exocytotic event, (ii) a form of synaptic depression that does not depend on a prior exocytotic event and that we postulate is based on inactivation of presynaptic N-type Ca 2؉ channels, and (iii) a dependence of paired-pulse facilitation on the exocytotic history of the synapse.

Paired-pulse depression of unitary quantal amplitude at single hippocampal synapses

“…Paired-pulse facilitation (PPF) is generally explained as an increase of release probability (P r ) during the second stimulus, arising from prior accumulation of residual Ca 2ϩ near active zones or a lingering effect of Ca 2ϩ on a Ca 2ϩ sensor (1,2). In contrast, paired-pulse depression (PPD) comes in multiple forms (3) and is open to a much wider range of possible explanations: receptor desensitization can be important in some cases (4) but is in general excluded. Instead, PPD is thought to originate presynaptically in most systems, as reflected by decreased transmitter output (5,6).…”

Quantifying impacts of short-term plasticity on neuronal information transfer

“…APs have successfully evoked neurotransmitter release or not [1,3,[8][9][10]. Although it has been argued that RID is a selection effect caused by stochastic state-changes of the release machinery [11], previous work suggests that RID indeed has a distinct physiological basis [3].…”

“…Synapses show a broad range of activity-dependent adaptive behaviours [1][2][3][4]. Those that occur on the shortest time scales are known as short-term plasticity.…”

“…This AP propagates along the neuronal membrane until it reaches a nerve terminal, where it may evoke the release of one or more synaptic vesicles containing neurotransmitter. The neurotransmitter diffuses through the extracellular space, and may bind to the membranes of other neurons.Synapses show a broad range of activity-dependent adaptive behaviours [1][2][3][4]. Those that occur on the shortest time scales are known as short-term plasticity.…”

“…We evoked stimulus sequences of APs in presynaptic cells under current clamp using short DC current pulses (5 ms, 1 nA), and recorded excitatory postsynaptic currents (EPSCs) from postsynaptic cells under voltage clamp. 1 We used constant rate and Poisson stimulus sequences, with characteristic frequencies of 5,10,20,30,35,40 or 50 Hz. Constant-rate stimuli consisted of either 6 or 20 pulses, and all sequences were followed by a recovery pulse after a delay of 400 or 500 ms.…”