Impairment of the blood-brain barrier accelerates a negative ultraslow potential in the locust CNS.

Insects provide useful models for investigating evolutionarily conserved mechanisms underlying electrical events associated with brain injury and death. Spreading depolarizations (SD) are transient events that propagate through neuropil whereas the negative ultraslow potential (NUP) is sustained and reflects accumulating damage in the tissue. We used the locust, Locusta migratoria, to investigate ion homeostasis at the blood-brain barrier (BBB) during SD and NUP induced by treatment with the Na+/K+-ATPase inhibitor, ouabain. We found that sustained SD caused by the metabolic inhibitor, sodium azide, was associated with a large reduction of K+ efflux from the BBB at ganglia (= gray matter) but not at connectives (= white matter). This was accompanied by a large increase in tissue resistivity but no conductance changes of identified motoneuron dendrites in the neuropil. Males recovered more slowly from ouabain-induced SD, as previously described for anoxic SD. Impairment of barrier functions of the BBB pharmacologically with cyclosporin A or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS), or by cutting nerve roots, accelerated the NUP, thus promoting earlier and more frequent SD, but had no effect on the temporal parameters of SD. We conclude that the mechanisms underlying onset and recovery of SD are minimally affected by the damage associated with the NUP. We suggest that future research using tissue-specific genetic approaches in Drosophila to target identified molecular structures of the BBB are likely to be fruitful.NEW & NOTEWORTHY Inhibition of the sodium pump in the locust central nervous system (CNS) causes repetitive spreading depolarization (SD) and a negative ultraslow potential (NUP) providing a model for investigation of phenomena relevant to human health. We show that impairment of the blood-brain barrier accelerates the NUP but has no impact on the trajectory of SD events. Hence, rapid mechanisms of onset and recovery of ion homeostasis occur against a background of slowly increasing neural damage.