A stroke is commonly referred to as an attack of the brain that is characterized by a sudden loss in brain function. It can be caused either by the interruption of blood flow to the brain (referred to as an ischemic stroke) or the rupture of blood vessels in the brain (referred to as a hemmoragic stroke). Post-stroke patients are susceptible to neurological dysfunction that is often irreversible, depending on the area of the brain where the stroke occurred as well as how much of the brain was damaged. Hyperglycemia is one specific complication that is often associated with the acute post-stroke phase, which is a brief period following a stroke leading up to the onset of chronic complications. Hyperglycemia refers to a condition in which a person has abnormally high levels of glucose (sugar) in their blood. Excess glucose is normally controlled by a hormone known as insulin, which is secreted by beta cells present in the pancreas. Previous studies have found that these beta cell areas in the pancreas were reduced in number following an ischemic stroke, which could explain the unusual rise in blood glucose levels often seen in post-stroke patients. This study also showed a 62% decrease in the number of active neurons present in the CA1 region of the hippocampus. The hippocampus is a brain structure known to be largely responsible for forming memories. Neurons present in the CA1 region of the hippocampus are specialized brain cells that play an important role in long-term memory as well as spatially related tasks.
Recently, researchers at Hoseo University in South Korea examined the effects of pre-stroke exercise and whether or not this would prevent neuronal injury and improve glucose homeostasis (the maintenance of internal levels of glucose) in gerbils subjected to cerebral ischemia. Cerebral ischemia is an ischemic stroke that occurs in the cerebrum, the upper-most region of the central nervous system which is responsible for all voluntary movement with the help of other brain structures. All gerbils were randomly divided into four groups: Sham operation only, Sham operation + exercise, Artery occlusion operation only, or artery occlusion + exercise. Artery occlusion was used to induced an ischemic stroke by isolating the carotid arteries and occluding (blocking) them using aneurysm clips. Sham operations used the same surgical technique, however, did not induce a stroke as done in the artery occlusion operation. Following this experiment, they performed various techniques to evaluate glucose homeostasis as well as hippocampal injuries caused by an ischemic stroke.
Pre-stroke exercise resulted in a 48% reduction in neuronal cell death in the CA1 region of the hippocampus in gerbils subjected to cerebral ischemia. What was interesting was that exercise also caused an increase in the number of CA1 neurons present in the hippocampus of gerbils that underwent the sham operation despite not actually experiencing a stroke. Blood glucose levels were higher in the artery occlusion group gerbils compared to the sham group gerbils. However, these readings were lower in the groups of gerbils who underwent pre-stroke exercise. This highlights the effects that pre-stroke exercise had on the gerbils.
In addition to these findings, neurological severity scores were determined. These scores were assessed by evaluating some of the many side-effects typically observed following cases of ischemia. Overall, these neurological severity scores were the highest in the group of artery-occlusion gerbils, therefore showing how a stroke can cause complications to the health of its victims. However, exercise significantly decreased these scores in gerbils who experienced an ischemic stroke.
Other studies of this nature revealed that an ischemic stroke can lead to hyperglycemia by causing an increased amount of beta cell death in the pancreas. This particular study, however, is the first to report that exercise protects against beta cell loss during cerebral ischemia. These findings suggest, once again, the multitude of effects that exercise can have on brain health.
Source: Park, S., Sol Kim, D., Kang, S. (2013). Exercise Training attenuates cerebral ischemic hyperglycemia by improving hepatic insulin signalling and B-cell survival. Life Sciences, 93, 153-160.
