| Abstract No.: | B-B2054 |
| Country: | Canada |
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| Title: | LAYER 5 CELLS ARE THE FIRST TO FIRE DURING DEVELOPMENT OF ACTIVE STATE OF THE SLOW OSCILLATION. |
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| Authors/Affiliations: | 1 Sylvain Chauvette*; 1 Igor Timofeev;
1 Laval University - CRULRG, Québec, QC, Canada
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| Content: | Objectives: During slow-wave sleep, activity in thalamocortical system alternates between active and silent states. The active states start when the whole thalamocortical network is silent. We previously suggested that summation of spike independent minis leads to the depolarization of some neurons to firing threshold. From this observation a hypothesis arise that larger cortical neurons, layer 5 pyramidal neurons, will be the first to fire action potential at the onset of active network state. Previous in vivo and in vitro studies demonstrated that indeed deeply laying pyramidal neurons would trigger active cortical states with a higher likelihood. Unclear points to answer: What is the latency between active state onset and first action potential onset in different cortical neurons and what kind of neurons fire more action potentials during an active state. Materials and methods: In order to answer these questions, we performed multisite local field potential (LFP) and multi-unit recordings in neocortex via a Michigan probe on cats either under ketamine/xylazine anaesthesia or during natural sleep. We also performed multisite intracellular recordings in neocortex of cats in the same conditions. Results: We found that cells located at a depth of about -800 µm to -1200 µm (cortical layer 5) on most occasions were the first to be depolarized. The results were very similar under anaesthesia and during natural sleep. The firing rates of the same neurons estimated from multiunit activities were much higher than that of more superficial or deep neurons. Next, we investigated what type of cells fired the earliest action potential in a cycle. Using recordings with a Michigan probe inserted perpendicularly to the cortical surface, we found that cells located at a depth of about -800 µm to -1200 µm were the first to fire spike and had a higher firing rate. From intracellular data, we found that cells located deeper than 1000 µm from the surface fired a first spike after the onset of depolarisation with an average delay of 118 ms (n=7), but the earliest spikes in some cycles occurred within initial 6-10 ms. The cells located between surface and 1000 µm had an average delay for their first spike of 205 ms (n=7). Conclusion: These results demonstrate that layer 5 cells play a leading role in the onset and maintenance of spontaneous active states during slow-wave sleep.
Supported by CIHR and NSERC |
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