Odor cues released by Ehrlich tumor-bearing mice are aversive and induce psychological stress.
OBJECTIVE
This study aimed to verify if odor cues released by Ehrlich tumor-bearing mice are aversive and stressful.


METHODS
Female mice were divided into a control group and an experimental group. One animal of each experimental pair of mice was inoculated with 5 × 10(6) Ehrlich tumor cells intraperitoneally; the other animal was kept undisturbed and was referred to as a CSP (companion of sick partner). One mouse of each control pair was treated intraperitoneally with 0.9% NaCl (1 mg/kg); the other animal (CHP, companion of healthy partner) was kept undisturbed.


RESULTS
It was shown that, in relation to CHP, CSP mice (1) spent less time within the companion zone in a T-maze place preference test, (2) had increased levels of social interaction, (3) had increased levels of plasmatic adrenaline and noradrenaline and (4) displayed no changes in serum corticosterone levels before and after an immobilization stress challenge. It was also shown that (5) cohabitation with 2 tumor-bearing mice was more effective in decreasing neutrophil oxidative burst than cohabitation with 1 sick partner and (6) the presence of a healthy conspecific within the cage of the tumor-injected/CSP pair abrogated the effects of cohabitation on neutrophil activity. These results show that odor cues released by Ehrlich tumor-injected mice are aversive and induce psychological stress.


CONCLUSIONS
We postulate that the aversive response induced by the chemosignals released by Ehrlich tumor-injected animals activates the sympathetic nervous system and causes the neuroimmunal changes that occur in the mice cohabiting with the sick mice.
Laboratory of Applied Pharmacology and Toxicology, School of Veterinary Medicine, University of São Paulo, São Paulo, Brazil.
Glaucie Jussilane
GJ
Alves
João
J
Palermo-Neto
D000704:Analysis of Variance; D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000503:physiopathology / Q000523:psychology*; D002395:Catecholamines / Q000378:metabolism; D003345:Corticosterone / Q000097:blood; D003463:Cues; D004195:Disease Models, Animal; D004924:Escape Reaction / Q000502:physiology*; D005260:Female; D007398:Interpersonal Relations; D018782:Maze Learning / Q000502:physiology; D051379:Mice; D009504:Neutrophils / Q000473:pathology; D009812:Odorants; D018384:Oxidative Stress / Q000502:physiology; D010587:Phagocytosis; D011863:Radioimmunoassay; D013315:Stress, Psychological / Q000503:physiopathology*; D013997:Time Factors
D002395:Catecholamines; D003345:Corticosterone