In 1975 Besedovsky’s team as a first reported that hypothalamopituitary-adrenal axis (HPA) can be activated by immune stimuli. In his seminal experiment he noted that plasma corticosterone was elevated after peripheral immune challenges, such as horse and sheep red blood cells. Subsequently very many experimental data has been collected and confirmed his idea. Also many investigators have noted that immune challenges increased plasma concentrations of ACTH and glucocorticosteroides, although the effects appear almost immediately – within a few hours after injections. Up to now, the mechanisms by which HPA is activated by cytokines or LPS have not been fully established. In many previous experiments, endotoxin (from E. coli) administration to animals induces many physiological and behavioral effects, as shivering, fever, reduced locomotion and other behavioral changes, along with activation of the HPA-axis and brain noradrenergic (NE) and adrenergic (A) systems. During the present study we decided to use LPS from Proteus mirabilis (O17 32/57), a Gramnegative bacterium, which is responsible mainly for urinary tract inflammation and for meningitis to check it influences on the brain NE and A systems activity after stressful stimuli in the open field arena. LPS administration increased plasma concentrations of corticosterone. These increased concentrations were somewhat different than those observed after E. coli endotoxin treatment. Also, LPS administration increased hypothalamus concentrations of norepinephrine, epinephrine, their main metabolites; MHPG and MT as well as MHPG/NE and A/MT ratios, which reflects the neurotransmitter system activity, in all brain regions analyzed. Each of these responses was marked 90 minutes after injections with peak concentration at 240 minutes. These results indicate that i.p. injected LPS from P. mirabilis (O17 32/57) influenced the brain noradrenergic and adrenergic systems activity and HPAaxis too.
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