3 research outputs found
Neuroelectric Mechanisms of Delayed Cerebral Ischemia after Aneurysmal Subarachnoid Hemorrhage
Delayed cerebral ischemia (DCI) remains a challenging but very important condition, because DCI is preventable and treatable for improving functional outcomes after aneurysmal subarachnoid hemorrhage (SAH). The pathologies underlying DCI are multifactorial. Classical approaches to DCI focus exclusively on preventing and treating the reduction of blood flow supply. However, recently, glutamate-mediated neuroelectric disruptions, such as excitotoxicity, cortical spreading depolarization and seizures, and epileptiform discharges, have been reported to occur in high frequencies in association with DCI development after SAH. Each of the neuroelectric disruptions can trigger the other, which augments metabolic demand. If increased metabolic demand exceeds the impaired blood supply, the mismatch leads to relative ischemia, resulting in DCI. The neuroelectric disruption also induces inverted vasoconstrictive neurovascular coupling in compromised brain tissues after SAH, causing DCI. Although glutamates and the receptors may play central roles in the development of excitotoxicity, cortical spreading ischemia and epileptic activity-related events, more studies are needed to clarify the pathophysiology and to develop novel therapeutic strategies for preventing or treating neuroelectric disruption-related DCI after SAH. This article reviews the recent advancement in research on neuroelectric disruption after SAH
Cerebrovascular pathophysiology of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage
Aneurysmal subarachnoid hemorrhage
(SAH) remains a serious cerebrovascular disease. Even
if SAH patients survive the initial insults, delayed
cerebral ischemia (DCI) may occur at 4 days or later
post-SAH. DCI is characteristics of SAH, and is
considered to develop by blood breakdown products and
inflammatory reactions, or secondary to early brain
injury, acute pathophysiological events that occur in the
brain within the first 72 hours of aneurysmal SAH. The
pathology underlying DCI may involve large artery
vasospasm and/or microcirculatory disturbances by
microvasospasm, microthrombosis, dysfunction of
venous outflow and compression of microvasculature by
vasogenic or cytotoxic tissue edema. Recent clinical
evidence has shown that large artery vasospasm is not
the only cause of DCI, and that both large artery
vasospasm-dependent and -independent cerebral
infarction causes poor outcome. Animal studies suggest
that mechanisms of vasospasm may differ between large
artery and arterioles or capillaries, and that many kinds
of cells in the vascular wall and brain parenchyma may
be involved in the pathogenesis of microcirculatory
disturbances. The impairment of the paravascular and
glymphatic systems also may play important roles in the
development of DCI. As pathological mediators for DCI,
glutamate and several matricellular proteins have been
investigated in addition to inflammatory molecules.
Glutamate is involved in excitotoxicity contributing to
cortical spreading ischemia and epileptic activity-related
events. Microvascular dysfunction is an attractive
mechanism to explain the cause of poor outcomes
independently of large cerebral artery vasospasm, but
needs more studies to clarify the pathophysiologies or
mechanisms and to develop a novel therapeutic strategy
Roles of glutamate in brain injuries after subarachnoid hemorrhage
Aneurysmal subarachnoid hemorrhage
(SAH) is a stroke type with a high rate of mortality and
morbidity. Post-SAH brain injury as a determinant
of poor outcome is classified into the following two
types: early brain injury (EBI) and delayed cerebral
ischemia (DCI). EBI consists of various acute brain
pathophysiologies that occur within the first 72 hours of
SAH in a clinical setting. The underlying mechanisms of
DCI are considered to be cerebral vasospasm or
microcirculatory disturbance, which develops mostly 4
to 14 days after clinical SAH. Glutamate is the principal
neurotransmitter in the central nervous system, but
excessive glutamate is known to induce neurotoxicity.
Experimental and clinical studies have revealed that
excessive glutamates are released after SAH. In addition,
many studies have reported the relationships between
excessive glutamate release or overactivation of
glutamate receptors and excitotoxicity, cortical spreading
depolarization, seizure, increased blood-brain barrier
permeability, neuroinflammation, microthrombosis
formation, microvasospasm, cerebral vasospasm,
impairments of brain metabolic supply and demand,
impaired neurovascular coupling, and so on, all of which
potentially contribute to the development of EBI or DCI.
As glutamates always exert their functions through one
or more of 4 major receptors of glutamates, it would be
valuable to know the mechanisms as to how glutamates
cause these pathologies, and the possibility that a
glutamate receptor antagonist may block the pathologies.
To prevent the mechanistic steps leading to glutamatemediated neurotoxicity may ameliorate SAH-induced
brain injuries and improve the outcomes. This review
addresses the current knowledge of glutamate-mediated
neurotoxicity, focusing on EBI and DCI after SAH