Neuronal constitutive and inducible nitric oxide synthase expression in the brains of Listeria monocytogenes - Infected cattle

Nitric oxide (NO) is important for intracellular signaling and neurotransmi ssion. Nitric oxide synthase (NOS) is involved in central nervous system (C NS) disorders through excess generation of NO. In this study. we examined t he expression of both constitutive and inducible nitric oxide synthase (NOS ) in Listeria monocytogenes-infected brains of cattle by immunohistochemist ry. Microabscesses, focal gliosis, and perivascular cuffing characterized the h istopathological changes in the brain in listeriosis. L. monocytogenes anti gen was present in the microabscesses and perivascular cuffs. Mononuclear p hagocytes and neutrophils were the most numerous inflammatory cells in the affected areas of the brainstem. In natural listeriosis, brain cells. inclu ding neurons and some neuroglial cells, expressed both nNOS and iNOS. The i mmunoreactivity of iNOS was more intense than that of the control. In some lesions, inflammatory cells (mainly macrophages) expressed nNOS and iNOS in the microabscesses and perivascular cuffs, while inflammatory neutrophils in the same lesion were not stained with iNOS. These findings suggest that normal bovine brain cells, including neurons an d neuroglia, constitutively express iNOS and nNOS, and that there is increa sed expression of these molecules in L. monocytogenes infections. Furthermo re, inflammatory cells, including macrophages, expressing both nNOS and iNO S may play an important role in the pathogenesis of bacterial meningoenceph alitis in cattle.