Neurons and glial cells of the rat organum vasculosum laminae terminalis directly respond to lipopolysaccharide and pyrogenic cytokines

During systemic immune challenge, the organum vasculosum laminae terminalis (OVLT) with its dense vascularization by fenestrated capillaries lacking blood-brain barrier function allows direct access of circulating pyrogens to brain tissue located in close vicinity to the preoptic area We aimed to analyze direct responses of OVLT cells to exposure to lipopolysaccharide (LPS) and fibroblast stimulating lipopeptide 1 (FSL 1) or the cytokines tumor necrosis factor alpha (TNF alpha), interleulan 1 beta (IL 1 beta) and IL 6 A primary microculture of the OVLT was established from topographically excised rat pup brain tissue, with cellular identification by marker protein specific immunocytochemistry Employing the ratio calcium imaging technique, pyrogen induced calcium signaling in single OVLT cells could be characterized LPS - as opposed to FSL 1 - stimulation caused fast transient rises in intracellular calcium concentration in 17% of neurons 9% of astrocytes, and <5% of microglial cells investigated LPS additionally led to enhanced expression of TNF a and IL 113 exclusively in microglial cells as well as a time dependent release of TNF a and IL 6 from OVLT microcultures TNF a evoked calcium signals in 11% of neurons 22% of astrocytes and 5% of microglial cells tested A considerable population of neurons (11%) but only few astrocytes and microglial cells responded to IL 6, whereas 8% of microglial cells and 3% of astrocytes or neurons were activated by IL 113 The demonstration of direct cellular responses of OVLT intrinsic cells to stimulations with LPS or cytokines reinforces the suggested role of this brain structure as a responsive brain site to circulating pyrogens (C) 2010. Elsevier B V All rights reserved