CIRCUMSCRIBED LESION OF THE MEDIAL FOREBRAIN-BUNDLE AREA CAUSES STRUCTURAL IMPAIRMENT OF LYMPHOID ORGANS AND SEVERE DEPRESSION OF IMMUNE FUNCTION IN RATS

Interactions between the immune system and the brain are a key element in the pathophysiology of diseases such as multiple sclerosis, neuroA IDS, and Alzheimer's, which affect large numbers of individuals and ar e associated with a high social cost. However, the neuroanatomical bas is of brain-immune interactions has not been elucidated. We report tha t in Wistar rats of either sex bilateral electrolytic lesion of the me dial forebrain bundle reduces body weight by 28% 7 days after lesionin g, and causes widespread infections, aphagia, adypsia, structural dama ge to the lymphoid organs and heavy depression of T lymphocytes cytoto xicity. The following alterations occur in the immune system after tho se lesions: the weight of the thymus, spleen and lymphonodes is reduce d by 77.9%, 49.1% and 48.4%, respectively. The thymus is atrophied and contains fewer lymphoid cells in the cortex than in the medulla. In t he spleen the white pulp is reduced and lymphoid cells from periarteri olar zones and at the chords are almost absent. In lymph nodes cortica l small lymphocytes are depleted and primary and secondary nodules and germinal centers ail but disappear. Cytotoxicity of lymphocytes is re duced by 86.2% in the thymus, 77.6% in the spleen and 70.2% in lymph n odes. The critical area of lesion is at the medialmost portion of the medial forebrain bundle, at the preoptic area and rostral part of the anterior hypothalamus. We suggest that this area contains neural circu its that are crucial for keeping the structure of lymphoid organs and the functional integrity of the immune system.