Thalamic Mechanisms Mediating the Sedating Effects of General Anesthesia
Bibliographic record
Abstract
Alterations in thalamic activity are associated with electrocortical patterns that characterize non-rapid eye movement (non-REM) sleep and general anesthetic-induced sedation and loss-of-consciousness. Both non-REM sleep and general anesthesia are states that are characterized by increased inhibitory Îł aminobutyric acid (GABA)-ergic signaling in the thalamus. There are three forms of GABA type A (GABAA) receptor-mediated inhibition that have been identified in thalamocortical neurons: (1) phasic inhibition mediated by the transient activation of synaptic GABAA receptors, (2) tonic inhibition mediated by the prolonged activation of extrasynaptic GABAA receptors, and (3) spillover inhibition mediated by the transient activation of extrasynaptic GABAA receptors. The separate impact of each of these forms of thalamic GABAergic inhibition on electrocortical activity is unclear and such an understanding would assist in elucidating the thalamic mechanisms mediating the changes in electrocortical activity that signal sedation and loss-of-consciousness. The experiments presented in this thesis identify the electrocortical effects of enhanced thalamic GABAA receptor-mediated tonic and spillover inhibition in vivo. The electrocortical changes elicited by a prototypic GABAA receptor-targeting general anesthetic agent when it is administered directly into the thalamus are characterized and compared to the effects identified with separate manipulations of GABAA receptor-mediated inhibition. These studies show that enhanced thalamic tonic inhibition in mice promotes electrocortical patterns associated with deep non-REM sleep. Specifically, enhanced GABAA receptor-mediated tonic inhibition in the thalamus elicits a state-independent increase in 1-4 Hz electrocortical activity and a decrease in sleep spindle-like oscillations. These effects were altered by blockade of thalamic T-type Ca2+ channels. Importantly, microperfusion of the general anesthetic etomidate into the thalamus elicits changes in electrocortical activity that are distinct form those associated with enhanced thalamic tonic inhibition. Moreover, the action of etomidate at the thalamus is sufficient to elicit an electrocortical signature associated with anesthetic-induced loss-of-consciousness, but only during non-REM sleep. Finally, enhanced GABAA receptor-mediated spillover inhibition in the thalamus fully recapitulates the electrocortical effects identified with etomidate at the thalamus. Together, the findings of this thesis indicate that alterations in thalamic spillover inhibition could underlie the changes in electrocortical activity that signal anesthetic-induced loss-of-consciousness.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".