Peripheral catecholamines are involved in the neuroendocrine and immune effects of LPS

There is evidence for bidirectional communication between the brain and the immune system. The immune system is subjected to neuroendocrine influences and reciprocally the hypothalamopituitary-adrenal axis is modulated by immune signals. Lipopolysaccharides (LPS), used to mimic infectious/inflammatory diseases, induce a series of stress markers, including modifications of monoaminergic transmission, enhancement of HPA axis activity, and decreased immune activity. In the present work we investigated the participation of peripheral catecholamines in the immune and endocrine responses to LPS in vivo. We studied the effects of LPS after chemical sympathectomy using 6-hydroxydopamine (6-OHDA), which does not cross the brain-blood barrier (BBB) in adults when peripherally injected. 6-OHDA administration was able to interfere with the effects of LPS on immune cells; however, the effects depended on the lymphoid tissue tested. In fact, the depression of mitogenesis induced by LPS was reversed by 6-OHDA in the spleen but not in the thymus. Moreover, 6-OHDA also interfered with the endocrine modifications induced by LPS. This neurotoxin completely or partially inhibited the effect of LPS on ACTH and corticosterone secretion, respectively. Taken together, these results clearly demonstrate that in vivo, the peripheral sympathetic nervous system participates in the immune and endocrine effects of LPS.