Neonatal programming by neuroimmune challenge: effects on responses and tolerance to septic doses of lipopolysaccharide in adult male and female rats

Abstract

A mild immune challenge experienced during the neonatal period leads to attenuated febrile responses to a similar challenge experienced later in life. However, the immune response to an endotoxin differs depending upon the severity of the challenge and it is not clear whether a neonatal immune challenge will also affect responses to a severe, potentially life-threatening stimulus, such as sepsis. In the present study, we examined the effects of a neonatal immune challenge with lipopolysaccharide (LPS) on adult sickness responses, as well as the development of endotoxin tolerance, to a septic dose (1 or 3 mg/kg) of the same LPS in male and female rats. We demonstrate significant differences, particularly in males, in the fever profiles of neonatally LPS-treated rats compared to neonatally saline-treated controls. Specifically, male rats treated neonatally with LPS have reduced hypothermic and enhanced hyperthermic responses to both septic doses of LPS in adulthood. A somewhat different profile is seen in females, with neonatally LPS-treated females having reduced hypothermia and enhanced hyperthermia compared to controls with 1 mg/kg but no differences with 3 mg/kg LPS. The results obtained demonstrate that alterations in innate immune responses previously reported for low doses of LPS can, for the most part, also be observed after severe immune challenge in later life.

Fig. 1

Basal measurements: (A, B) Body weight; percentage of baseline (percentage of first day of measurement). (C, D) Food consumption during day- and night-time. Values are averaged over 3 days. (E, F) Temperature indices for stress (injection)-induced hyperthermia, 0–1 h after injection with 1 or 3 mg/kg lipopolysaccharide (LPS). nSal, neonatally saline-treated, nLPS, neonatally LPS-treated.

Fig. 2

One milligram per kilogram lipopolysaccharide (LPS) measurements: (A, B) Body weight; percentage of the morning of injection with 1 mg/kg LPS. (C, D) Temperature changes in the hours after injection. Injection = 08.00 h, arrow. (E, F) Temperature indices for the hypothermic (1–2 h) and hyperthermic (3–9 h) phases of the response to 1 mg/kg LPS. nSal, neonatally saline-treated; nLPS, neonatally LPS-treated. ***P < 0.0005.

Fig. 3

Three milligram per kilogram lipopolysaccharide (LPS) measurements: (A, B) Body weight; percentage of the morning of injection with 3 mg/kg LPS. (C, D) Temperature changes in the hours after injection. Injection = 08.00 h, arrow. (E, F) Temperature indices for the hypothermic (1–2 h) and hyperthermic (3– 9 h) phases of the response to 3 mg/kg LPS. nSal, neonatally saline-treated; nLPS, neonatally LPS-treated. *P < 0.05, ***P < 0.0005.

Fig. 4

Tolerance measurements; 3 mg/kg lipopolysaccharide (LPS) 1 week after 1 mg/kg LPS: (A, B): Body weight; percentage of the morning of injection with 3 mg/kg LPS. (C, D) Temperature changes in the hours after injection. Injection = 08.00 h, arrow. (E, F) Temperature indices for stress (injection)-induced hyperthermia, 0–1 h after injection. (G, H) Temperature indices for the hypothermic (1–2 h) and hyperthermic (3–9 h) phases of the response to 3 mg/kg LPS. nSal, neonatally saline-treated; nLPS, neonatally LPS-treated. **P < 0.005, ***P < 0.0005.

Fig. 5

Tolerance measurements; 3 mg/kg lipopolysaccharide (LPS) 1 week after 1 mg/kg LPS: (A, B) Plasma corticosterone 1 h after injection. (C, D) Locomotor activity in the open field 1 and 3 h after injection i.e. number of lines crossed in the 10-min period. (E, F) Vertical exploration (i.e. rearing in the open field). (G, H) Middle exploration in the open field (i.e. number of crosses through the middle). nSal, neonatally saline-treated; nLPS, neonatally LPS-treated. *P < 0.05, ***P < 0.0005.