Pharmacological manipulation of immune-induced food aversion in rats.
BACKGROUND
Mice allergic to ovalbumin (OVA) avoid drinking a solution containing this antigen. This was interpreted as related to IgE-dependent mast cell degranulation and sensory C fiber activation.


METHODS
We employed pharmacological manipulation to further investigate the mediators involved in immune-induced food aversion.


RESULTS
While nonimmunized rats preferred a sweetened OVA solution, immunized rats avoided it. We also employed a paradigm in which rats are conditioned to drink water for two 10-min sessions a day. Tolerant rats presented lower IgE titers, and this manipulation abrogated food aversion. Dexamethasone (1.0 mg/kg) prevented the aversion of OVA-immunized rats to the antigen-containing solution. Combined blockade of H(1) and 5-hydroxytryptamine (5-HT)(2) receptors by promethazine (3.0 mg/kg) plus methysergide (5.0 mg/kg) was unable to alter food aversion. Blockade of 5-HT(3) receptors by ondansetron (1.0 mg/kg) caused a twofold increase in the ingestion of the sweetened OVA solution by immunized rats, suggesting the involvement of 5-HT(3) receptors in food aversion. Finally, we showed that dexamethasone or promethazine plus methysergide, but not ondansetron, effectively prevented the IgE-dependent mast-cell-degranulation-induced increase in vascular permeability in rats.


CONCLUSIONS
We suggest that regardless of whether or not they cause edema, IgE-mediated mast cell degranulation and consequent 5-HT(3) signaling are involved in the process that triggers avoidance to the source of the allergen in allergic rats.
Zarzana
Eduardo C
EC
Laboratory of Pharmacology and Toxicology, Department of Pathology, School of Veterinary Medicine, University of São Paulo, São Paulo, Brazil.
Basso
Alexandre S
AS
Costa-Pinto
Frederico A
FA
Palermo-Neto
João
J
D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects / Q000502:physiology; D002199:Capillary Permeability / Q000187:drug effects / Q000276:immunology; D015550:Cell Degranulation / Q000187:drug effects / Q000276:immunology; D003213:Conditioning, Psychological / Q000502:physiology; D003907:Dexamethasone / Q000494:pharmacology; D004195:Disease Models, Animal; D005247:Feeding Behavior; D005512:Food Hypersensitivity / Q000276:immunology* / Q000503:physiopathology; D007073:Immunoglobulin E / Q000097:blood / Q000276:immunology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008297:Male; D008407:Mast Cells / Q000187:drug effects / Q000276:immunology; D008784:Methysergide / Q000494:pharmacology; D017294:Ondansetron / Q000494:pharmacology; D010047:Ovalbumin / Q000276:immunology; D051381:Rats; D017208:Rats, Wistar; D012701:Serotonin / Q000378:metabolism; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists / Q000494:pharmacology
D007166:Immunosuppressive Agents; D058831:Serotonin 5-HT3 Receptor Antagonists; D012702:Serotonin Antagonists; D012701:Serotonin; D007073:Immunoglobulin E; D017294:Ondansetron; D003907:Dexamethasone; D010047:Ovalbumin; D008784:Methysergide