Mortality of septic old and adult male mice correlates with individual differences in premorbid behavioral phenotype and acute-phase sickness behavior.

Individual differences in premorbid behaviors and in those exhibited in the course of an infection disease may be useful to explain the individual susceptibility to infections, the underlying neuroimmunological mechanisms and be helpful to design patient oriented treatments with better prediction of pharmacological reactivity/outcome. Age (old) and gender (male) are also considered vulnerability factors. In the present study, the motor, emotional, anxious-like and social phenotypes of adult (6-month-old) and old (18-month-old) male C57BL/6 × 129Sv mice were determined using both a transversal and longitudinal designs prior to the analysis of LPS (150 mg/kg, i.p.)-induced sickness behavior and mortality. The results show: i) Individual premorbid behavioral phenotype had short- and long-term predictive value of hours of survival; ii) Persistence of behavioral traits from adulthood to old age and predictive value on hours of survival; iii) First signs of sickness behavior were also predicting mortality, mostly in old animals; iv) LPS-sickness behavior was the same at both ages but adult animals were able to show attempts of motor recovery; v) The mortality rate over 96 h was 100% in both ages, but old animals showed shorter survival times. In summary, these results confirm the relevance of age/aging but also individual behavioral differences in the premorbid phenotype and the morbidity response to the LPS-induced-sepsis that correlate with the individual's mortality. Thus, this work supports the translational scenarios to study personalized evaluation of risks factors and psycho-neuro-immunological mechanisms relevant for better interventions and prognosis in the critically ill young but specially aged patient population.