Cohabitation with a sick cage mate: Effects on noradrenaline turnover and neutrophil activity

The present study was designed to evaluate the effects of cohabitation for 11 days with a sick conspecific on hypothalamic levels and turnover of noradrenaline NA (experiment 1) and on neutrophil oxidative burst and phagocytosis in mice (experiment 2). Female mice were divided into two groups: control and experimental. One mouse of each control pair was kept undisturbed and called “companion of health partner” (CHP). One animal of each experimental pair of mice was inoculated with 5 × 10 6 Ehrlich tumor cells i.p., and the other, the subject of this study, was called “companion of sick partner” (CSP). In experiment 3, CHP and CSP mice were treated with diazepam (1.0 mg/kg) or with control solution (vehicle of diazepam, 1.0 mL/kg) 1 h before evaluation of neutrophil activity. The CSP mice presented (1) decreased levels and increased turnover of hypothalamic NA; (2) decreased neutrophil oxidative burst after PMA or Staphylococcus aureus induction; (3) decreased percentage and intensity of neutrophil phagocytosis. In CSP mice, diazepam induced no changes in neutrophil oxidative burst or intensity of phagocytosis, but abolished almost completely the percentage of neutrophils performing phagocytosis. These data were discussed in the light of possible neuroimmune interactions.