Properties of the proximally and distally evoked synaptic responses in hippocampal CA1 pyramidal cells
Properties of the proximally and distally evoked synaptic responses in hippocampal CA1 pyramidal cells
Hippocampal CA1 pyramidal cells can be excited via stimulation of afferent fibres to the proximal and distal apical dendritic regions. Intracellular techniques were used on the in vitro transverse hippocampal slice preparation to monitor the evoked responses from these two spatially distinct regions, typically at stimulation intensities giving a 50% action potential failure rate. Control data showed significant differences between the proximally and distally evoked excitatory postsynaptic potentials (EPSPs) and fast synaptic prepotentials (FPPs), the distal events having smaller signal peaks and longer 10-90% rise times and times to peaks. Furthermore, the distal action potential was shown to have an apparently lower threshold than the equivalent proximal action potential. The possible involvement of the early inhibitory postsynaptic potential (IPSP) in shaping the proximal and distal EPSPs was investigated by use of the GABAA antagonist, bicuculline (0.6μM). Blockade of the early IPSP resulted in the proximal and distal EPSPs and spike firing thresholds appearing very similar, accounted for mainly by changes in the proximal events. It is therefore likely that a GABA_A-mediated IPSP is responsible for providing a tonic inhibition of the proximal and, to a lesser extent, the distally evoked excitatory events under control conditions, thereby controlling the level of excitation within these neurones. Intracellular injection of the local anaesthetic QX314 (35mM) caused a block of the proximal, followed by the distal, action potentials under conditions of threshold and suprathreshold stimulation, coinciding with block of the FPPs. However, QX314 had no effect on the proximal and distal EPSPs. This provides convincing evidence that action potentials/FPPs can be generated within the apical dendrites of these CA1 pyramidal cells, even at the more distal locations, and this would account for the apparent difference in proximal and distal spike firing thresholds.
University of Southampton
1992
Colling, Simon Brodie
(1992)
Properties of the proximally and distally evoked synaptic responses in hippocampal CA1 pyramidal cells.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Hippocampal CA1 pyramidal cells can be excited via stimulation of afferent fibres to the proximal and distal apical dendritic regions. Intracellular techniques were used on the in vitro transverse hippocampal slice preparation to monitor the evoked responses from these two spatially distinct regions, typically at stimulation intensities giving a 50% action potential failure rate. Control data showed significant differences between the proximally and distally evoked excitatory postsynaptic potentials (EPSPs) and fast synaptic prepotentials (FPPs), the distal events having smaller signal peaks and longer 10-90% rise times and times to peaks. Furthermore, the distal action potential was shown to have an apparently lower threshold than the equivalent proximal action potential. The possible involvement of the early inhibitory postsynaptic potential (IPSP) in shaping the proximal and distal EPSPs was investigated by use of the GABAA antagonist, bicuculline (0.6μM). Blockade of the early IPSP resulted in the proximal and distal EPSPs and spike firing thresholds appearing very similar, accounted for mainly by changes in the proximal events. It is therefore likely that a GABA_A-mediated IPSP is responsible for providing a tonic inhibition of the proximal and, to a lesser extent, the distally evoked excitatory events under control conditions, thereby controlling the level of excitation within these neurones. Intracellular injection of the local anaesthetic QX314 (35mM) caused a block of the proximal, followed by the distal, action potentials under conditions of threshold and suprathreshold stimulation, coinciding with block of the FPPs. However, QX314 had no effect on the proximal and distal EPSPs. This provides convincing evidence that action potentials/FPPs can be generated within the apical dendrites of these CA1 pyramidal cells, even at the more distal locations, and this would account for the apparent difference in proximal and distal spike firing thresholds.
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Published date: 1992
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Local EPrints ID: 461875
URI: http://eprints.soton.ac.uk/id/eprint/461875
PURE UUID: ed7cfa4b-543e-47f4-9ee7-cdd8f3bc3923
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Date deposited: 04 Jul 2022 18:57
Last modified: 04 Jul 2022 18:57
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Author:
Simon Brodie Colling
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