Effects of lipopolysaccharide and interleukin-6 on cataleptic immobility and locomotor activity in mice.

Catalepsy (animal hypnosis, tonic immobility) is a type of passive defensive behavior. Its exaggerated form is a syndrome of some psychopathological disorders. Numerous neurotransmitters have impact on the regulation of catalepsy. In this paper we demonstrated the involvement of interleukin-6 (IL-6) in the mechanism of cataleptic immobility. Effects of exogenous IL-6 treatment (7.5 and 10μg/kg, i.p) or stimulation of endogenous IL-6 secretion with lipopolysaccharide (LPS) administration (50, 100 and 200μg/kg, i.p.) on catalepsy and locomotor activity were studied in adult C57BL/6 male mice. IL-6 induced catalepsy in 70% (7.5μg/kg) or 72.7% (10μg/kg) of animals with no effect on locomotor activity. LPS administration reduced distance travelled and number of rears in the open field at any dose used, however, only high doses (100 or 200μg/kg) of the toxin induced catalepsy in 50% of mice. This result indicates that IL-6 is involved in the regulation of catalepsy, this effect is specific and does not arise from inhibition of locomotor activity. The study provides a new evidence on participation of IL-6 in mechanisms of abnormal behavior.