The Role of Serotonin Availability in the Rat Insular Cortex on Conditioned Disgust and Conditioned Taste Avoidance
Bibliographic record
Abstract
Although the neural mechanisms regulating vomiting are well understood, the neurobiology of nausea is not. Unlike conditioned taste avoidance (CTA), conditioned disgust (indicated by orofacial gaping reactions) is a model of nausea-induced behaviour in rats because it is selectively produced by emetic drugs and anti-emetics attenuate it. Treatments that reduce serotonin (5-HT) availability selectively interfere with conditioned gaping (Limebeer and Parker, 2000; 2003) and forebrain serotonin is critical for the production of disgust reactions (Grill and Norgren, 1978b; Limebeer et al., 2004). The insular cortex (IC) is a site of taste-illness associations and is involved in the sensation of nausea and vomiting in humans (Penfield and Faulk, 1955; Fiol et al., 1988; Catenoix et al., 2008) and other animals (Kaada, 1951; Contreras et al., 2007). Therefore, we investigated the relationship between serotonin, conditioned gaping and CTA in the insular cortex. \nSystemic pretreatment with the classic anti-emetic ondansetron (OND) reduced both LiCl-induced unconditioned malaise (assessed by lying on belly) and conditioned gaping reactions, without modifying CTA. These experiments demonstrate that decreases in serotonin availability interfere with conditioned gaping and unconditioned malaise as well as provide further evidence of the validity of the conditioned gaping model.\nRats with bilateral NMDA lesions of the agranular IC showed attenuated CTA learning but conditioned gaping reactions were unaffected. This finding suggests that the agranular IC, a site of gustatory input, may be required for CTA learning.\nPartial serotonergic depletion of the IC attenuated conditioned gaping reactions, suggesting that serotonin in the IC is required to establish conditioned gaping. A double dissociation in the regulation of disgust and taste avoidance, by selective 5-HT3 receptor antagonism/agonism in the visceral (granular) IC and the gustatory (agranular) IC was observed. Infusion of OND into the visceral IC attenuated conditioned gaping but spared CTA. Additionally, administration of the 5-HT3 receptor agonist m-chlorophenylbiguanide (mCPBG) enhanced LiCl-induced conditioned gaping reactions (which was prevented by intracranial administration of OND), but spared CTA. In contrast, intracranial OND pretreatment in the gustatory IC attenuated CTA and mCPBG infusions produced CTA, but neither affected the nausea-induced behaviour of conditioned gaping.\nTogether, these studies shed light on the neurobiology of nausea. These results suggest that 5-HT activity (at the 5-HT3 receptor) in the visceral IC may selectively produce the nausea-induced reactions of conditioned disgust, while activity in the gustatory IC may be involved in the production of CTA learning.
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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) | 0.000 | 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 | 0.001 |
| 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".