Different neural systems mediate morphine reward and its spontaneous withdrawal aversion
Bibliographic record
Abstract
The opponent-process theory posits that the aversive state of acute opiate withdrawal is a consequence of, and depends on, the previous rewarding state evoked by acute morphine reward. Although the brainstem tegmental pedunculopontine nucleus (TPP) is crucial for the rewarding component of morphine, the source of the later aversive component is not known. It is possible that (i) the second aversive process takes place within the TPP itself or (ii) morphine reward in the TPP activates an unconditioned opponent motivational process in another region of the brain. The effects of reversible inactivation of the TPP on the motivational properties of acute morphine and its spontaneous withdrawal effects in non-drug-dependent rats were examined using a place-conditioning paradigm. Reversible inactivation of the TPP with lidocaine or bupivacaine immediately before the morphine injection blocked the rewarding properties of morphine in non-dependent rats. Blocking the rewarding effects of morphine also blocked the opponent aversive effects of acute morphine withdrawal. In contrast, reversible inactivation of the TPP during the acute morphine withdrawal did not block this opponent aversive process. Our results confirm that the TPP is a critical neural substrate underlying the acute rewarding effects of morphine in non-dependent rats. Furthermore, the opponent aversive process of acute morphine withdrawal is induced by the acute rewarding effects of morphine. However, the TPP does not directly mediate the spontaneous withdrawal aversion (the opponent process), suggesting that a different system, triggered by the changes in the TPP after the primary drug response, produces the aversion itself.
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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 | 0.001 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 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".