Presence of mother prompts dissociation of sickness behavior, fever, and hypothalamic gene expression in lipopolysaccharide-injected guinea pig pups

Abstract

During infection, sickness behaviors, such as a hunched stance with piloerection, can facilitate host resistance by supporting the generation and maintenance of fever. Fever, in turn, is mediated by hypothalamic neuroimmune signaling. Sickness behaviors, however, can also be influenced by social stimuli. In this study, guinea pig pups were injected with lipopolysaccharide to simulate a bacterial infection and then exposed to a novel, threatening environment while either with their mother or alone. We found that the presence of the mother suppressed sickness behavior, but enhanced fever, and had no measureable effect on gene expression of hypothalamic mediators of fever. This 3-way dissociation induced by the mother's presence is interpreted in terms of the differential adaptive consequences of behavioral and febrile responses for pups in this situation. The results contribute to a growing literature linking immunological and social processes.

Keywords: fever; infection; maternal influence; maternal separation; mother-infant; sickness behavior; stress.

Figure 1.

Mean core temperature of pups tested with the mother or alone in Experiment 1. Temperature is averaged across 15-min time blocks during a 3-hr exposure to a novel environment. Vertical lines indicate standard errors of the means. There was a significant With Mother/Alone x Time Block interaction, p = 0.001.

Figure 2.

Mean movement counts of pups tested with the mother or alone in Experiment 1. Activity is averaged across 15-min time blocks during a 3-hr exposure to a novel environment. Vertical lines indicate standard errors of the means. There was a significant Mother/Alone x Time Block interaction, p < 0.001, however the pattern seen differed greatly from the pattern for core temperature.

Figure 3.

Mean expression relative to control of IL-1β, TNF-α, IL-6, COX-2, and MCP-1 in hypothalamus of pups injected with saline and returned to the home cage or injected with 100 μg/kg LPS and placed into a novel environment either with the mother or alone for 30 or 90 min prior to harvesting brain tissue. Vertical lines indicate standard errors of the means. * indicates a significant difference (p < 0.05) from saline or as indicated by overlying lines.