| Abstract No.: | C-B3043 |
| Country: | Canada |
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| Title: | INHIBITION DOMINATES IN SHAPING IN VITRO SPONTANEOUS HIPPOCAMPAL NETWORK RHYTHMS |
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| Authors/Affiliations: | 1 Ernest Ho*; 2 Liang Zhang; 3 Frances Skinner;
1 Dept of Physiology, U of Toronto; TWRI/UHN; 2 TWRI/UHN; Dept of Medicine (Neurology), U of Toronto; 3 TWRI/UHN; Depts of Medicine(Neurology), IBBME, U of Toronto, ON, Canada
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| Content: | Objective: To quantify the balance of excitatory and inhibitory conductances (ge0 and gi0) underlying a robust in vitro rodent hippocampal rhythm with frequencies from 0.5 to 4.5Hz. We term these rhythms as spontaneous rhythmic field potentials (SRFPs) [1,2].
Materials and Methods: We use simultaneous field and single cell recordings to record the effect of SRFPs on the hippocampal network at both the intra/extracellular levels. A network “rhythmic” state is defined as the state where the variations in local field activities due to SRFPs are concurrent with well-defined summated postsynaptic potentials (PSPs) at the intracellular level. A network quiescent state is defined as the state in which the local field potentials are not associated with any well-defined change in intracellular activity. Our data set consists of five CA3 pyramidal cells and one CA2 putative interneuron.
From the intracellular data of both the “quiescent” and “rhythmic” states, we can extract the relevant synaptic quantities (such as g{e,i}0 and their variances sigma{e,i}0) each neuron in the network experiences by mathematically modelling the effects these synaptic quantities have on the membrane potential readings of the neuron in question.
Results:
1. Inhibitory dominance for quiescent state
2. Increase in inhibition during the transition to the rhythmic state
3. This transition from the quiescent to the rhythmic state is associated with an inhibitory variance of at least 10%
Conclusions:
1. We have been able to quantify the variance of the inhibition associated with SRFPs. Since SRFPs co-exist with other population activities (such as sharp waves) the level of variance may act as a control of these other population activities.
2. Since the CA3 network is likely inhibitory dominant in the quiescent state, this may mean emergence of SRFPs requires a minimal level of inhibition.
References
1. Papatheodoropoulos C and Kostopoulos G, Neurosci Lett 319: 17–20. 2002.
2. Wu C, Luk WP, Gillis J, Skinner F, Zhang L, J Neurophysiol 93:2302-2317. 2005.
Acknowledgements
This research is supported by NSERC and CIHR, and by a NSERC scholarship awarded to ECYH.
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