Spreading depression reversibly impairs autoregulation of cortical blood flow.

The experiment examines whether the mechanisms responsible for the autoregulation of cerebral blood flow (CBF) in response to hypotension were affected during the initial phase of cortical spreading depression (CSD). CSD was induced by a cortical pinprick in anesthetized rabbits, and CBF was measured by laser-Doppler flowmetry through a chronically implanted Plexiglas window. The reactivity to CO2 and papaverine was also studied before and after CSD. Fifteen minutes after CSD, autoregulatory vasodilation was reduced (P < 0.01). This impairment was reversible, since the autoregulatory response was restored 35 min after CSD. The time course of the reactivity to papaverine after CSD paralleled the autoregulatory response, with a significant correlation between the two reactivities (r = 0.47; P < 0.01). Conversely, the reactivity to CO2 was significantly reduced after CSD (P < 0.001) and remained affected for at least 95 min. We conclude that the mechanisms underlying autoregulation are transiently disturbed by CSD and that these mechanisms are not mediated by an accumulation of CO2 but seem instead to be related to an increase in adenosine 3',5'-cyclic monophosphate concentration.