L-arginine aggravates lipopolysaccharide induced anxiety-like behaviors and interleukin 6 levels in male albino rats

Abstract EN

In rodents, lipopolysaccharide (LPS, a product of Gram-negative bacteria) induces septic shock and depression.

Animal studies based on the relationship of nitrergic system and the pathogenesis of such neuropsychiatric disorders is still unclear.

This study was designed to find out whether the L-arginine (L-Arg)/nitric oxide (NO) pathway and the proinflammatory cytokine interleukin-6 (IL-6) have a role in anxiety and behavioral responses to systemic LPS administration in rats.

The open field test (OFT) was chosen for assessment of anxiety-like behaviors and L-Arg, a NO precursor, was used to evaluate the role of nitrergic system in LPS-induced anxiogenesis.

The animals were identified, weighed and randomly divided into four groups (five in each): Control group (saline, 1ml/kg b.wt), LPS group (LPS alone, 1 mg/kg b.wt), L-Arg group (L-Arg alone, 10 mg/kg b.wt for 7 consecutive days), and LPS+L-Arg group (L-Arg, 10 mg/kg b.wt for 7 consecutive days then once injected with LPS, 1mg/kg).

All drugs were administered intraperitoneally (i.p.).

Behavioral tests were performed 3 h after saline/ LPS injection using LE8811 Actimeter Pan LAB device.

Serum IL-6 levels were measured 6 h after saline/LPS injection with test kits by enzyme-linked immunosorbent assay (ELISA) method.

The results showed that acute systemic administration of LPS induced a significant increase anxiety-like behaviors as indicated by reduced frequency of central square entries and less time spent in the central region of the open field.

Additionally, LPS increased serum IL-6 levels in rats.

Pretreatment of rats with L-Arg aggravated the anxiogenic effects of LPS, as well as induced an increment in serum IL-6 levels.

Interestingly, systemic administration of L-Arg alone caused mild anxiety-like behaviors in rats with significantly increase in serum IL-6 levels.

These findings lead to the conclusion that L-Arg increases the severity of LPS-induced anxiogenesis, most likely by inducing IL-6 production in the present experimental model.