Cannabinoid (CB) 1 receptors are involved in the induction of lipopolysaccharide (LPS)-evoked fever

Marnie Duncan1, Winnie Ho2, Beat Lutz3, Keith Sharkey2, Quentin Pittman2

1Robert Gordon University, Aberdeen, Aberdeenshire, UK, 2University of Calgary, Calgary, Alberta, Canada, 3Johannes Gutenberg University Mainz, Mainz, Germany

The anti-inflammatory actions of cannabinoids have been well documented. There is uncertainty, however, as to the role of CB1 receptors in the neuroimmune response to lipopolysaccharide (LPS), in that both the cannabinoid agonist WIN55,212, and the CB1 receptor antagonist SR141716A attenuate the LPS-evoked fever in rats (Benamar et al, 2006). The aim of the present study was to clarify the role of cannabinoid receptors in the febrile response to LPS. This is important, as fever comprises part of the body’s defence against infection.

Male C57BL6N and CB1 knockout mice (C57BL6N background) (26-36g) were implanted with temperature data loggers under anaesthesia (SubCue Dataloggers, Calgary.). Animals were then left for 7 days to recover, then were acclimatized to 27° C for 18 hours prior to experiment. Animals were then given an injection of either saline or LPS (100 μg/kg, i.p.)/Poly IC (1 mg/kg, i.p.), and temperature was monitored for a further 7 hours. In the antagonist studies, wild type mice were treated with either vehicle (5% EtOH in saline) or the CB1 receptor antagonist AM251 (1 mg/kg; i.p.) 4 hrs prior to LPS injection. Statistical significance was determined by calculating the fever index (FI; change in temperature from baseline x 15 min) from 60 min - 240 min post-injection for the control and treatment groups. Statistical comparison was carried out using unpaired Student’s t test.

Wildtype mice treated with LPS displayed a typical biphasic fever response, with an initial peak in core body temperature at around 120 minutes post-injection at 1.9 ± 0.2 °C above baseline, compared the saline treated control (FI: P < 0.05). In contrast, CB1-/- mice had no febrile response to LPS in that their temperature responses were not significantly different to the saline controls or to their own baseline temperatures (FI: P > 0.05). To determine if the lack of LPS fever was a developmental change in the CB1-/- mice, AM251 was administered to wildtypes and the LPS-evoked fever was significantly attenuated in these animals compared to vehicle controls (FI: P < 0.05). The viral mimetic Poly IC was used to establish if CB1-/- mice were capable of mounting a febrile response to a different inflammatory mediator. In wildtype animals, Poly IC produced a robust fever response peaking at around 75 minutes post-injection with temperature increase of 1.7 ± 0.3 °C which remained elevated for 6 hours (FI: P < 0.001). In CB1-/- mice, the onset of febrile response to Poly IC was delayed when compared to wild type mice where the fever began 60 mins post-injection and peaked around 150 min where the temperature increase was 1.3 ± 0.4 °C above baseline (FI: P < 0.05).

Our findings that CB1-/- mice are unable to mount a fever to an LPS challenge suggest that CB1 receptors play an important role in the induction of the febrile response. This action appears to be specific to toll like receptor (TLR) 4 signalling pathways as the CB1-/- mice were able to respond to Poly IC which signals via TLR3.

Benamar et al, (2006). J. Pharmacol. Exp. Ther. 320:1127-1133.