Evidence for in vivo cerebrovascular neurogenic vasodilatation in the rat

Promising Cerebral Blood Flow Enhancers in Acute Ischemic Stroke

Ischemic stroke presents a major global economic and public health burden. Although recent advances in available endovascular therapies show improved functional outcome, a good number of stroke patients are either ineligible or do not have access to these treatments. Also, robust collateral flow during acute ischemic stroke independently predicts the success of endovascular therapies and the outcome of stroke. Hence, adjunctive therapies for cerebral blood flow (CBF) enhancement are urgently needed. A very clear overview of the pial collaterals and the role of genetics are presented in this review. We review available evidence and advancement for potential therapies aimed at improving CBF during acute ischemic stroke. We identified heme-free soluble guanylate cyclase activators; Sanguinate, remote ischemic perconditioning; Fasudil, S1P agonists; and stimulation of the sphenopalatine ganglion as promising potential CBF-enhancing therapeutics requiring further investigation. Additionally, we outline and discuss the critical steps required to advance research strategies for clinically translatable CBF-enhancing agents in the context of acute ischemic stroke models.

Facial nerve stimulation as a future treatment for ischemic stroke

Stimulation of the autonomic parasympathetic fibers of the facial nerve system (hereafter simply “facial nerve”) rapidly dilates the cerebral arteries and increases cerebral blood flow whether that stimulation is delivered at the facial nerve trunk or at distal points such as the sphenopalatine ganglion. Facial nerve stimulation thus could be used as an emergency treatment of conditions of brain ischemia such as ischemic stroke. A rich history of scientific research has examined this property of the facial nerve, and various means of activating the facial nerve can be employed including noninvasive means. Herein, we review the anatomical and physiological research behind facial nerve stimulation and the facial nerve stimulation devices that are in development for the treatment of ischemic stroke.

Vascular remodeling after ischemic stroke: mechanisms and therapeutic potentials

The brain vasculature has been increasingly recognized as a key player that directs brain development, regulates homeostasis, and contributes to pathological processes. Following ischemic stroke, the reduction of blood flow elicits a cascade of changes and leads to vascular remodeling. However, the temporal profile of vascular changes after stroke is not well understood. Growing evidence suggests that the early phase of cerebral blood volume (CBV) increase is likely due to the improvement in collateral flow, also known as arteriogenesis, whereas the late phase of CBV increase is attributed to the surge of angiogenesis. Arteriogenesis is triggered by shear fluid stress followed by activation of endothelium and inflammatory processes, while angiogenesis induces a number of pro-angiogenic factors and circulating endothelial progenitor cells (EPCs). The status of collaterals in acute stroke has been shown to have several prognostic implications, while the causal relationship between angiogenesis and improved functional recovery has yet to be established in patients. A number of interventions aimed at enhancing cerebral blood flow including increasing collateral recruitment are under clinical investigation. Transplantation of EPCs to improve angiogenesis is also underway. Knowledge in the underlying physiological mechanisms for improved arteriogenesis and angiogenesis shall lead to more effective therapies for ischemic stroke.

Experimental activation of the sphenopalatine ganglion provokes cluster-like attacks in humans

Background

High frequency (HF) stimulation of the sphenopalatine ganglion (SPG) is an emerging abortive treatment for cluster headache (CH) attacks. HF SPG stimulation is thought to exert its effect by physiologically blocking parasympathetic outflow. We hypothesized that low frequency (LF) SPG stimulation may activate the SPG, causing increased parasympathetic outflow and thereby provoking cluster attacks in CH patients.

Methods

In a double-blind randomized cross-over study, seven CH patients implanted with an SPG neurostimulator were randomly allocated to receive HF or LF stimulation for 3 min on 2 separate days. We recorded headache characteristics and autonomic symptoms during and after stimulation.

Results

Six patients completed the study. Three out of six patients (50%) reported ipsilateral cluster-like attacks during or within 30 min of LF SPG stimulation. These cluster-like attacks were all successfully treated with the therapeutic HF SPG stimulation. One out of six reported a cluster-like attack with 3 min HF SPG stimulation, which was also successfully treated with continued HF therapeutic SPG stimulation.

Discussion

LF SPG stimulation may induce cluster-like attacks with autonomic features, which can subsequently be treated by HF SPG stimulation. Efferent parasympathetic outflow from the SPG may initiate autonomic symptoms and activate trigeminovascular sensory afferents, which may initiate the onset of pain associated with CH.

Stimulation of the nucleus basalis of Meynert increases diameter of the parenchymal blood vessels in the rat cerebral cortex

To verify the hypothesis that stimulation of the nucleus basalis of Meynert (NBM) induces vasodilation in the cerebral cortical parenchyma, we investigated whether the diameter of parenchymal blood vessels of rat parietal cortex is increased during stimulation of NBM using histological techniques. The parietal cortex was fixed by immersion fixation in situ during focal electrical stimulation of the NBM, which increased cortical blood flow. Cortical tissues were sectioned horizontally to the cortical surface, and the parenchymal blood vessels were morphometrically analyzed using electron microscopy. Mean inner diameter of the parenchymal blood vessels in NBM stimulated rats (5.51+/-0.33 microm) was significantly larger than that in non-stimulated control rats (4.93+/-0.23 microm). The result suggests that functional vasodilation in the cortical parenchyma during NBM stimulation correlates with histologically observed vasodilation in the cortical parenchyma.

Control of cerebral and ocular blood flow autoregulation in neonates

Several factors have been implicated in the regulation of cerebral and ocular vasomotor tone in the newborn: the interrelationship between prostanoids, NO, and other vasoactive mediators remains a subject of interest and active investigation. Pharmacologic modulation may provide new treatment modalities for diseases of the newborn that are mostly hemodynamic and vascular in nature.

Influence of cerebrovascular sympathetic, parasympathetic, and sensory nerves on autoregulation and spontaneous vasomotion

The effect of removal of cerebrovascular sympathetic, parasympathetic or sensory nerve on brain cortical blood flow and spontaneous vasomotion during changes in systemic blood pressure was studied by laser-Doppler flowmetry in anaesthetized rats. Selective section of sympathetic fibres along the internal carotid artery markedly affected the ability to autoregulate, as measured in microvessels of the middle cerebral arterial territory. Removal of the parasympathetic nerves tended to reduce the ability to autoregulate, whereas no significant influence was found after sensory denervation. Following the denervations, spontaneous vasomotion was not significantly affected in frequency or amplitude.

Distribution and pathway of the cerebrovascular nerve fibers from the otic ganglion in the rat: anterograde tracing study

The distribution and pathway of cerebrovascular nerve fibers from the otic ganglion were studied by an anterograde tracing technique in the rat. Wheat germ agglutinin-horseradish peroxidase was injected as an anterograde axonal tracer into the otic ganglion on one side. Forty-eight hours later, the animals were killed and specimens were reacted with tetramethylbenzidine. Wheat germ agglutinin-horseradish peroxidase positive fine nerve fibers were observed in the circle of Willis and its branches, i.e., anterior cerebral artery, middle cerebral artery, internal ethmoidal artery and posterior cerebral artery, while no positive fiber could be detected in the vertebrobasilar artery. A positive reaction with tetramethylbenzidine was also observed in the lesser superficial petrosal nerve, the greater superficial petrosal nerve, the vidian nerve, the greater deep petrosal nerve, the internal carotid ganglion and the trigeminal ganglion. The sphenopalatine ganglion, however, failed to reveal any positive neurons or nerve fibers. It is concluded that the cerebrovascular nerve fibers originating from the otic ganglion run along the lesser superficial petrosal nerve to join the greater superficial petrosal nerve. They then reach the greater deep petrosal nerve and ascend along the internal carotid artery to distribute themselves to the cerebral blood vessels. This study demonstrated, for the first time, that the otic ganglion innervates the cerebral vessels and elucidated the pathway from the otic ganglion to the cerebral vessels directly by means of an anterograde axonal tracing technique.