Lack of endogenous opioid release during sustained visceral pain: A [11C]carfentanil PET study
Bibliographic record
Abstract
Opioidergic neurotransmission in the central nervous system is involved in somatic pain, but its role in visceral pain remains unknown. We aimed to quantify endogenous opioid release in the brain during sustained painful gastric distension. Therefore, 2 dynamic [11C]carfentanil positron emission tomography scans were performed in 20 healthy subjects during 2 conditions: sustained (20 minutes) painful proximal gastric balloon distension at predetermined individual discomfort threshold (PAIN) and no distension (NO PAIN), in counterbalanced order. Pain levels were assessed during scanning using visual analogue scales and after scanning using the McGill Pain Questionnaire. Emotional state was rated after scanning using the Positive and Negative Affect Schedule. Distribution volume ratios in 21 volumes of interest in the pain matrix were used to quantify endogenous opioid release. During the PAIN compared to the NO PAIN condition, volunteers reported a significantly higher increase in negative affect (5.50±1.29 versus 0.10±1.08, P=.0147) as well as higher pain ratings (sensory: 74.05±9.23 versus 1.50±0.95, P<.0001; affective: 91.42±8.13 versus 4.33±6.56, P<.0001). No difference in endogenous opioid release was demonstrated in any of the volumes of interest. Thus, contrary to its somatic counterpart, no opioid release is detected in the brain during sustained visceral pain, despite similar pain intensities. Endogenous opioids may play a less important role in visceral compared to somatic pain.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.014 | 0.009 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".