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- O. Beck, M. Chistiakova,
K. Obermayer, and M. Volgushev. Adaptation of Synaptic Connections to
Layer 2/3 Pyramidal Cells in Rat Visual Cortex.
.
In Soc. Neurosci. Abstr. 30, 2004.
CD-ROM.
Neocortical synapses express differential dynamic properties. When
activated at high frequencies, the amplitudes of the subsequent postsynaptic
responses may increase or decrease, depending on the stimulation frequency
and on the properties of that particular synapse. These changes in the
synaptic dynamics can dramatically affect the communication between nerve
cells. Motivated by the question whether changes of dynamic properties of
synapses may contribute to mechanisms of neural adaptation [1], we made
intracellular recordings from layer 2/3 pyramidal cells in slices of rat
visual cortex. Synaptic responses were evoked by application of trains of
electric pulses through the stimulation electrodes positioned below and aside
the recorded cell. Trains of stimuli of different frequencies (5-40 Hz) were
applied either in isolation or after a potentially adaptation inducing
stimulus. The data were fitted with a three-parameter model of synaptic
dynamics [2]. Our estimates of the synaptic parameters without adaptation are
broadly consistent with previous studies. After applying an adaptation
protocol, we found a statistically significant reduction in release
probability after weak adaptation (low frequency stimulus for 4s) as well as
a decrease in the recovery time constant after strong adaptation (high
frequency stimulus for 4s). Finally, we found a significant drop in the
amplitude of the first response after adaptation that correlated well with
the drop in release probability for weak but not for strong adaptation. To
account for this latter finding we introduce an extended model, which
includes an interaction between a ready to release and serve pool of synaptic
vesicles.<br><br>[1] Adorjan et al., Rev. Neurosci. 1999, pp.
181-200<br>[2] Tsodyks et al., PNAS 1997, pp. 719-723
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