The viral mimetic polyinosinic:polycytidylic acid (poly I:C) induces cellular responses in primary cultures from rat brain sites with an incomplete blood-brain barrier.

Primary microcultures of the organum vasculosum laminae terminalis (OVLT) and the area postrema (AP), brain sites with an incomplete blood-brain barrier, were established from topographically excised rat pup tissue, with cellular identification by marker protein-specific immunocytochemistry. Employing the ratio calcium imaging technique, we showed for the first time that polyinosinic:polycytidylic acid (poly I:C) can induce calcium signalling in single OVLT and AP cells. Poly I:C stimulation caused fast, transient rises in intracellular calcium in about 5% of neurons and astrocytes and some microglial cells. Frequently, the responses of astrocytes and microglial cells showed a shorter onset-latency compared to neurons. In addition, exposure to poly I:C led to a time dependent release of bioactive tumour necrosis factor (TNF) and interleukin-6 (IL-6) into the supernatants of OVLT and AP cultures. The demonstration of direct cellular responses of OVLT- and AP-intrinsic cells to stimulations with poly I:C is in agreement with the discovered existence of Toll-like receptor 3 (TLR3), the cognate receptor for poly I:C, in the brain.