Intravenous human interleukin-1alpha impairs memory processing in mice: dependence on blood-brain barrier transport into posterior division of the septum

Peripherally administered cytokines profoundly affect the central nervous system (CNS). One mechanism by which they could affect the CNS is by crossing the blood-brain barrier (BBB) to interact directly with brain receptors. Human and murine IL-1alpha (hIL-1alpha; mIL-1alpha) are transported across the murine BBB with a high rate of transport into the posterior division of the septum (PDS), but it is unknown whether BBB transport is relevant to their actions. Here, we injected species-specific blocking antibodies into the PDS to determine whether transport across the BBB is required for blood-borne hIL-1alpha to affect memory. Retention was impaired in a dose-dependent manner when hIL-1alpha was injected either by tail vein (i.v.) or into the PDS, with the PDS route being 1000 times more potent. About 70% of the memory impairment induced by i.v. hIL-1alpha was reversed by injecting a blocking antibody (Ab) specific for hIL-1alpha into the PDS. This shows that much of the memory impairment induced by hIL-1alpha depends on its ability to cross the BBB. Ab specific for mIL-1alpha was also effective in reversing memory impairment, showing that hIL-1alpha releases mIL-1alpha from endogenous stores. Whether the mIL-1alpha was released from peripheral stores, which would require it to cross the BBB, or from brain stores is unknown. In conclusion, these results show that exogenous, blood-borne hIL-1alpha affects memory by releasing mIL-1alpha from endogenous stores and by crossing the BBB to act at sites within the PDS.