Mishra Lab

This image shows glial cells and blood vessels of the retina, which is the nervous tissue in the back of the eye. Tiny blood vessels called capillaries are shown in blue, vascular cells called pericytes are in red, and glial cells called astrocytes are in green. Astrocytes relay messages from active neurons to pericytes on capillaries to co-ordinate blood flow.

Astrocytes in neurovascular coupling

Side-by-side images contrasting  brain sections of the healthy rat and the post-stroke rat.
GFAP immunolabeled astrocyte endfeet (magenta) terminating on a cortical vessel in a healthy adult rat brain section (left) and in the peri-infarct region of the stroke hemisphere in a rat exposed to middle cerebral artery occlusion (model of stroke). Blue = DAPI; green = rat endothelial cell marker 1 (RECA-1).

Glial cells called astrocytes are abundant in the central nervous system. Increasingly, scientists are recognizing important contributions of astrocytes to many aspects of CNS function, one of them being neurovascular coupling – the process by which active neurons signal to blood vessels to increase the local blood flow and hence the supply of energy substrates. This process underlies several non-invasive neuroimaging techniques applied to human cognitive research and clinical diagnosis, such as functional magnetic resonance imaging. Under healthy mature conditions, neurovascular coupling is very robust, thus allowing this proxy measure to reliably report neuronal activity. However, the neurovascular coupling relationship is altered in pathological/disease contexts, which not only results in a mismatch of energy supply and demand in the brain, but also complicates the interpretation of neuroimaging data. Work in the Mishra lab is aimed at understanding the mechanisms of neurovascular coupling impairment in disease, particularly at the microvascular capillary level, with a focus on the role of astrocytes.

Neurovascular coupling impairment following stroke

A significant attenuation of neurovascular coupling is observed clinically in stroke patients for many years after the stroke. In the Mishra lab, we have revealed a similar suppression of neurovascular coupling at capillaries after experimental stroke models. This impairment occurs in peri-infarct tissue that otherwise looks healthy but displays changes in astrocyte morphology and expression patterns suggesting reactive astrogliosis. The functional outcomes manifested by these astrocytic changes are not understood. Current work in Dr. Mishra’s lab investigates the possibility that the constriction of capillaries and loss of neurovascular coupling observed after stroke may be due to pathophysiological signaling from reactive astrocytes. Some of the characteristics of these reactive astrocytes are reminiscent of developing astrocytes; thus, we are also studying how the neurovascular coupling response matures with the hope that this may help us understand how it is dysregulated after stroke.

Chronic effects of stroke-induced neurovascular impairment – role in dementia

Astrogliosis and neurovascular impairment are common features of many diseases of the central nervous system (including Alzheimer's disease, traumatic brain injury, vascular dementia, and chronic hypertension). Especially noteworthy are the epidemiological observations that patients harboring ischemic injuries develop dementia at a higher rate, and conversely, patients with dementia show evidence of ischemic damage in their brains. Thus, we are also investigating the long-lasting effects of mild strokes on neurovascular coupling and their contributions to cognitive loss.

Functions of astrocytic gap junctions

In a more basic research direction, we are also interested in how gap junctions help astrocytes do what they do. Although it has been known for many decades that astrocytes are coupled by gap junctions, the role of this coupling in neurovascular coupling, a prominent function of astrocytes, remains unknown. Thus, we are investigating whether gap junctional coupling of astrocytes contributes to their functions in K+ buffering and neurovascular coupling.