Neuroinflammation is a major driver of secondary brain cell death after ischaemic stroke, seizure activity and traumatic brain injury. In a model of excitotoxic neuroinflammation, striatal injection of a toxic dose of AMPA causes cell death in the striatum after 24 hours. Co-injection of AMPA with the pro-inflammatory cytokine interleukin-1β (IL-1β) leads to additional cortical cell death. Injected alone, IL-1β leads to little or no cell death. It is hypothesised that IL-1β may exacerbate cell death by interfering with blood flow coupling. In the first study, two-dimensional optical imaging spectroscopy was used to measure early changes in the haemodynamic response in the anaesthetised rat barrel cortex before and for 6 hours after injection of vehicle, AMPA, IL-1β, or AMPA+IL-1β. After injection of IL-1β, with or without AMPA, the oxygenated blood flow response to mechanical whisker stimulation approximately halved over the course of 6h. In the second study, to determine whether the IL-1β-dependent changes in blood flow response are reflected by altered cellular activity, local field potentials, multi-unit activity and local tissue oxygenation responses to whisker stimulation were recorded simultaneously from the active barrel before and up to 6h after injection. A similar reduction in the size of the oxygenation response was seen again in the IL-1β- and AMPA+IL-1β-treated groups. Importantly, the level of gamma frequency oscillations at stimulus onset decreased within the first hours after injection of AMPA+IL-1β or IL-1β, suggesting a disruption of the fast-spiking interneuron network in the barrel cortex. These findings, along with histological observations of IL-1β-dependent markers of neuroinflammation, suggest that IL-1β may exacerbate AMPA-induced excitotoxicity by potentiating seizure activity and decoupling the neurovascular response in the cortex.
- haemodynamic response
- optical imaging spectroscopy