Hypothalamic noradrenergic pathways exert an influence on neuroendocrine and clinical status in experimental autoimmune encephalomyelitis

Abstract

The immunomodulatory action of corticosteroids and the ability of central noradrenergic systems to activate the hypothalamic-pituitary-adrenal (HPA) axis led us to investigate the relationship between neuroendocrine status and the clinical course of encephalomyelitis (EAE) following adrenalectomy and depletion of noradrenaline (NA) centrally or peripherally. A significant inverse correlation was found between hypothalamic NA and serum corticosterone (CS) at peak clinical signs of EAE in all the sham groups or when NA was depleted only in the peripheral nervous system. A positive correlation was found between serum CS and disease severity, and in all experimental groups with intact peripheral and/or central noradrenergic pathways a uniformly increased splenic NA content was also observed at peak disease. Administration of 6-OHDA i.p. to neonatal or adult Lewis rats produced a significant depletion of splenic NA alone which resulted in increased disease severity, despite the fact that circulating CS was elevated. Thus the rise in the NA content of lymphoid tissue at peak clinical signs contributes to recovery. A single i.c.v. injection of 6-OHDA into the hypothalamic region resulted in an 80% reduction in NA content, which subsequently modified the clinical severity of EAE. Serum CS levels rose preclinically in the treated group and remained high despite milder clinical disease than that seen in the sham group. The overriding immunoregulatory influence of glucocorticoids is demonstrated by the rapid onset of clinical EAE and morbidity in adrenalectomized animals. However, the strong inverse correlation found between hypothalamic NA and circulating CS indicates that regulation of the HPA axis may ultimately be controlled by central sympathetic pathways.