Essay: Stroke

Stroke is one of the leading causes of death and long-term adult disability with a worldwide prevalence of 15 million people per year according to the World Health Organization. A number that is likely to increase in the near future due to aging of the population. There are two main types of stroke, namely, hemorrhagic stroke which occurs when a blood vessel ruptures, and ischemic stroke meaning a blood vessel becomes blocked, both leading to a disruption of blood flow and a contralateral loss of function. Approximately 80% of the stroke patients suffer ischemic stroke, whereas the remainder experiences hemorrhagic stroke.1 Unfortunately, current approved stroke treatments have a very small time frame in which they can be performed, leaving the majority of stroke patients untreated.2,3
Functional recovery over time is a common finding in patients suffering stroke. It has been noted that intact peri-infarct as well as contralateral brain areas are capable of adopting the lost functions, resulting in the observed functional recovery in stroke patients.4’6
There is now much evidence to support the hypothesis that stimulation of the vagus nerve has beneficial effects, not only in people suffering epilepsy and depression, but also patients suffering stroke. The effects of vagus nerve stimulation (VNS) on the brain have been studied extensively, resulting in evidence for VNS affecting the cerebral blood flow, inhibiting inflammatory processes and supporting neurogenesis.7’9 In recent years, researchers reported an infarct size reduction up to 50% and anti-inflammatory effects when rats received stimulation of the vagus nerve 30 minutes after stroke induction.10’14 Most of these studies have only focused on the effect of VNS on infarct size; the present study will also focus on brain plasticity and functional connectivity during and directly following VNS. Furthermore, studies so far have typically stimulated the vagus nerve as soon as 30 to 60 minutes after stroke induction, a time frame that is not realistic when translated to clinic. For this reason, our present study will use a 24 hour stimulation time point following stroke.
Brain plasticity and functional connectivity in the mouse brain can be observed using a novel technique called intrinsic optical signal imaging (IOSI). Furthermore, this technique allows for fast and high resolution imaging of blood volume, vasculature and oxygen levels.15,16
The aim of the present study is to evaluate the effect of VNS 24 hours after mice received photothrombotic stroke. Besides studying infarct size after VNS in stroke models, we additionally look at brain plasticity and functional connectivity. Results of this study may contribute to improve current stroke treatment and support the development of potential new therapies to treat patients suffering stroke.