Each and every second we are experiencing the world around us. Our sensory systems are constantly bombarded by the variety of environmental stimuli that surround us wherever we go — sounds, sights, smells, itches, thoughts —our brains are constantly processing this information, drawing our attention to the things that matter and filtering out the things that don’t. If any these experiences are significant enough, our brain makes sure to tag the experience, storing these instances as memories. In this way, we can recall them and use them later when we need to. Scientists have already shown that experience can shape neural networks. It has been well documented that different experiences and different patterns of activity in the brain can cause networks of brain cells and their connections to reorganize, strengthen or weaken, or completely disappear. A new paper published in the most recent issue of Neuron shows that experience can also shape the network of brain vasculature, potentially providing the brain with a way to control the amount of nutrients and oxygen that is delivered to various networks of cells.
In this study, researchers out of Harvard Medical School, University of Sao Paulo, and Brigham and Women’s Hospital, show that changing sensory experience in mice can alter the blood vessels of the brain, changing their branching and density. Specifically, reducing or eliminating sensory experience can reduce the density and branching of blood vessels and eliciting sensory experiences via whisker stimulation can increase these vascular properties.
To carry out this investigation, Lacoste et al. used a transgenic mouse that selectively labeled both neuronal processes (in this case axons) and the blood vessels themselves. In this transgenic mouse, the axons were labeled with a red marker and blood vessels were labeled with a green marker. This method allowed the team to visualize and analyze the distribution and morphology of the vascular networks in these mice. Since visual quantification/qualification of these features is very difficult when the vascular complexity has matured, Lacoste et al. approached the problem with a 3D computational analysis.
After monitoring initial vascular formation and development during the early postnatal stage, the authors next tested what would happen if the sensory inputs from the whiskers were completely eliminated. The point of this procedure is to reduce the sensory information/activity that could be processed by the sensory area of the brain. As mentioned, it is known that increases in brain activity can drive changes in the connections between cells. The authors reasoned that blocking whisker stimulation, which would reduce neural activity, might change the properties of the blood vessels near the affected area. When they performed this procedure, this was in fact the case. The authors also tested how the lack of neurotransmitter release affects brain vasculature. To do this, they disrupted the protein RIM, a molecule important for proper neurotransmitter release. Disruption of RIM prevents proper neurotransmitter signaling and in this study the manipulation also caused similar disruptions in vascular formation. To complement these results, the authors also increased neural activity by stimulating whiskers for 1 week. This experiment showed that increased sensory experience via whisker stimulation led to a significant increase in both vascular branching and density.
As our brains are constantly dealing with the processing of sensory stimuli and other neural activity, it is important to understand how these ongoing processes change the structure and strength of neural networks. This paper adds an additional layer of complexity to this picture, showing that increased or decreased levels of sensory stimulation can change the density and complexity of vascular networks related to the affected brain areas. This study presents interesting new research opportunities for the future, such as determining the mechanisms that underlie this vascular rearrangement, identifying what molecules or drugs can mimic or block this process, and investigating whether or not this rearrangement can be harnessed and used as a potential therapy for treating neurodegenerative or related disease.
Lacoste, B. et al. Sensory-Related Neural Activity Regulates the Structure of Vascular Networks in the Cerebral Cortex. Neuron 1–14 (2014)