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.

► The TLR3-agonist poly I:C induces Ca2+-transients in cultured astrocytes and neurons from OVLT and AP.
► The increase in intracellular Ca2+ in activated astrocytes occurs with shorter onset latency compared to neurons.
► Poly I:C-stimulated microcultures from OVLT and AP release bioactive TNF and IL-6 into the supernatant.